Biomechanical Basis of Human Movement

CHAPTER 6 Functional Anatomy of the Lower Extremity OBJECTIVES After reading this chapter, the student will be able to: 1. Describe the structure, support, and movements of the hip, knee, ankle, and subtalar joints. 2. Identify the muscular actions contributing to movements at the hip, knee and ankle joints. 3. List and describe some of the common injuries to the hip, knee, ankle, and foot. 4. Discuss strength differences between muscle groups acting at the hip, knee, and ankle. 5. Develop a set of strength and flexibility exercises for the hip, knee, and ankle joints. 6. Describe how alterations in the alignment in the lower extremity influences function at the knee, hip, ankle, and foot. 7. Discuss the structure and function of the arches of the foot. 8. Identify the lower extremity muscular contributions to walking, running, stair climbing, and cycling. 9. Discuss various loads on the hip, knee, ankle, and foot in daily activities. The Pelvis and Hip Complex Strength of the Knee Joint Muscles Pelvic Girdle Conditioning of the Knee Joint Muscles Hip Joint Injury Potential of the Knee Joint Combined Movements of the Pelvis and Thigh The Ankle and Foot Muscular Actions Talocrural Joint Strength of the Hip Joint Muscles Subtalar Joint Conditioning of the Hip Joint Muscles Midtarsal Joint Injury Potential of the Pelvic and Hip Other Articulations of the Foot Complex Arches of the Foot Movement Characteristics The Knee Joint Combined Movements of the Knee Tibiofemoral Joint and Ankle/Subtalar Patellofemoral Joint Alignment and Foot Function Tibiofibular Joint Muscle Actions Movement Characteristics Strength of the Ankle and Foot Muscles Muscular Actions Conditioning of the Foot and Ankle Combined Movements of the Hip Muscles and Knee Injury Potential of the Ankle and Foot 187

188 SECTION II Functional Anatomy Contribution of Lower Extremity Hip Joint Musculature to Sports Skills or Knee Joint Movements Ankle and Foot Stair Ascent and Descent Summary Locomotion Review Questions Cycling Forces Acting on Joints in the Lower Extremity The lower extremities are subject to forces that are movement. Therefore, concomitant movement of the generated via repetitive contacts between the foot pelvic girdle and the thigh at the hip joint is necessary for and the ground. At the same time, the lower extremities efficient joint actions. are responsible for supporting the mass of the trunk and the upper extremities. The lower limbs are connected to The pelvic girdle and hip joints are part of a closed kinetic each other and to the trunk by the pelvic girdle. This chain system whereby forces travel up from the lower establishes a link between the extremities and the trunk extremity through the hip and the pelvis into the trunk or that must always be considered when examining move- down from the trunk through the pelvis and the hip to the ments and the muscular contributions to movements in lower extremity. Finally, pelvic girdle and hip joint position- the lower extremity. ing contribute significantly to the maintenance of balance and standing posture by using continuous muscular action Movement in any part of the lower extremity, pelvis, or to fine-tune and ensure equilibrium. trunk influences actions elsewhere in the lower limbs. Thus, a foot position or movement can influence the posi- The pelvic region is one area of the body where there tion or movement at the knee or hip of either limb, and a are noticeable differences between the sexes in the general pelvic position can influence actions throughout the lower population. As illustrated in Figure 6-1, women generally extremity (23). It is important to evaluate movement and have pelvic girdles that are lighter, thinner, and wider than actions in both limbs, the pelvis, and the trunk rather than their counterparts in men (66). The female pelvis flares focus on a single joint to understand lower extremity func- out more laterally in the front. The female sacrum is also tion for the purpose of rehabilitation, sport performance, wider in the back, creating a broader pelvic cavity than in or exercise prescription. men. This skeletal difference is discussed later in this chap- ter because it has a direct influence on muscular function For example, in a simple kicking action, it is not just the in and around the hip joint. kicking limb that is critical to the success of the skill. The contralateral limb plays a very important role in stabiliza- tion and support of body weight. The pelvis establishes the correct positioning for the lower extremity, and trunk positioning determines the efficiency of the lower extrem- ity musculature. Likewise, in evaluating a limp in walking, attention should not be focused exclusively on the limb in which the limp occurs because something happening in the other extremity may cause the limp. The Pelvis and Hip Complex FIGURE 6-1 The pelvis of a female is lighter, thinner, and wider than that of a male. The female pelvis also flares out in the front and has a wider PELVIC GIRDLE sacrum in the back. The pelvic girdle, including the hip joint, plays an integral role in supporting the weight of the body while offering mobility by increasing the range of motion in the lower extremity. The pelvic girdle is a site of muscular attach- ment for 28 trunk and thigh muscles, none of which are positioned to act solely on the pelvic girdle (130). Similar to the shoulder girdle, the pelvis must be oriented to place the hip joint in a favorable position for lower extremity

CHAPTER 6 Functional Anatomy of the Lower Extremity 189 Sacroiliac Sacrum Sacral Pelvic inlet Sacroiliac articulation articulation promontary Anterior superior Iliac crest iliac spine Iliac fossa Anterior inferior iliac spine Arcuate line Ilium Outline of pelvic brim Pubis Coxa Acetabulum Ischium Pelvic brim Pubic crest Superior and inferior Coccyx pubic ramus Obturator Pubic symphysis A foramen Pubic tubercle Sacral foramina Median Iliac crest sacral crest FIGURE 6-2 The pelvic girdle supports the Posterior superior Pubic Greater sciatic weight of the body, serves as an attachment site iliac spine angle notch for numerous muscles, contributes to the effi- cient movements of the lower extremity, and Posterior inferior Sacrum helps maintain balance and equilibrium. The gir- iliac spine dle consists of two coxal bones, each created Ischial spine through the fibrous union of the ilium, ischium, Pelvic outlet and pubic bones. The right and left coxal bones Ischial are joined anteriorly at the pubic symphysis (A), B Coccyx tuberosity and connect posteriorly (B) via the sacrum and the two sacroiliac joints. The bony attachment of the lower extremity to the of the joint. Movement at this joint is limited, maintain- trunk occurs via the pelvic girdle (Fig. 6-2). The pelvic ing a firm connection between right and left sides of the girdle consists of a fibrous union of three bones: the supe- pelvic girdle. rior ilium, the posteroinferior ischium, and the anteroin- ferior pubis. These are separate bones connected by The pelvis is connected to the trunk at the sacroiliac hyaline cartilage at birth but are fully fused, or ossified, by joint, a strong synovial joint containing fibrocartilage and age 20 to 25 years. powerful ligamentous support (Fig. 6-2). The articulating surface on the sacrum faces posteriorly and laterally and The right and left sides of the pelvis connect anteriorly articulates with the ilium, which faces anteriorly and medi- at the pubic symphysis, a cartilaginous joint that has a ally (165). fibrocartilage disc connecting the two pubic bones. The ends of each pubic bone are also covered with hyaline car- The sacroiliac joint transmits the weight of the body to tilage. This joint is firmly supported by a pubic ligament the hip and is subject to loads from the lumbar region and that runs along the anterior, posterior, and superior sides from the ground. It is also an energy absorber of shear forces during gait (130). Three sets of ligaments support

190 SECTION II Functional Anatomy Anterior sacroiliac Iliolumbar ligament Iliolumbar ligament ligament Sacrolumbar ligament Sacrotuberous Sacrospinous Sacrospinous Posterior ligament ligament ligament sacroiliac ligament A Anterior B sacrococcygeal Sacrotuberus ligament ligament Anterior pubic ligament Iliofemoral Iliofemoral ligament ligament Pubofemoral ligament C Ligament Insertion Action Anterior pubic Transverse fiber from body of pubis Maintain relationship between right and TO body of pubis left pubic bones Anterior sacrococcygeal Anterior surface of sacrum TO front Maintain relationship between sacrum and Anterior sacroiliac of coccyx coccyx Iliofemoral Thin; pelvic surface of sacrum TO pelvic Maintains relationship between sacrum and Iliolumbar surface of ilium ilium Interosseous (SI) Anterior, inferior iliac spine TO Supports anterior hip; resists in movements intertrochanteric line of femur of extension, internal rotation, external rotation Ischiofemoral Ligament of head Transverse process of L5 TO iliac crest Limits lumbar motion in flexion, rotation Posterior sacroiliac Tuberosity of ilium TO tuberosity of sacrum Prevents downward displacement of sacrum caused by body weight Pubofemoral Posterior acetabulum TO iliofemoral ligament Resists adduction and internal rotation Sacrospinous Acetabular notch and transverse liagment TO pit of head of femur Transmits vessel to head of femur; no mechanical function Posterior, inferior spine of ilium TO pelvic surface of sacrum Maintains relationship between sacrum and ilium Pubic part of acetabulum; superior rami TO intertrochanteric line Resists abduction and external rotation Spine of ischium TO lateral margins of the Prevent posterior rotation of ilia respect to sacrum and coccyx the sacrum Sacrotuberous Posterior ischium TO sacral tubercles, inferior Prevents the lower part of the sacrum from titling margin of sacrum, & upper coccyx upward and backward under the weight of the rest of the vertebral column FIGURE 6-3 Ligaments of the pelvis and hip region shown for the anterior (A) and posterior (B) perspective and for the hip joint (C).

CHAPTER 6 Functional Anatomy of the Lower Extremity 191 the left and right sacroiliac joints, and these ligaments are placed on the sacroiliac joint, which in turn creates a the strongest in the body (Fig. 6-3). tighter and more stable joint (165). Even though the sacroiliac joint is well reinforced by Motion at the sacroiliac joint can best be described by very strong ligaments, movement occurs at the joint. The sacral movements. The movements of the sacrum that amount of movement allowed at the joint varies consider- accompany each specific trunk movement are presented in ably between individuals and sexes. Males have thicker and Figure 6-4. The triangular sacrum is actually five fused stronger sacroiliac ligaments and consequently do not vertebrae that move with the pelvis and trunk. The top of have mobile sacroiliac joints. In fact, three in 10 men have the sacrum, the widest part, is the base of the sacrum, and fused sacroiliac joints (165). when this base moves anteriorly, it is termed sacral flex- ion (130). Clinically, this is also referred to as nutation. In females, the sacroiliac joint is more mobile because This movement occurs with flexion of the trunk and with there is greater laxity in the ligaments supporting the bilateral flexion of the thigh. joint. This laxity may increase during the menstrual cycle, and the joint is extremely lax and mobile during Sacrum extension, or counternutation, occurs as the pregnancy (60). base moves posteriorly with trunk extension or bilateral thigh extension. The sacrum also rotates along an axis run- Another reason the sacroiliac joint is more stable in ning diagonally across the bone. Right rotation is desig- males is related to positioning differences in the center of nated if the anterior surface of the sacrum faces to the right gravity. In the standing position, body weight forces the and left rotation if the anterior surface faces to the left. This sacrum down, tightening the posterior ligaments and forc- sacral torsion is produced by the piriformis muscle in a ing the sacrum and ilium together. This provides stability side-bending exercise of the trunk (130). Additionally, in to the joint and is the close-packed position for the the case of asymmetrical movement such as standing on sacroiliac joint (130). In females, the center of gravity is in one leg, there can be asymmetrical movement at the the same plane as the sacrum, but in males, the center of sacroiliac joint, which results in torsion of the pelvis. gravity is more anterior. Thus, in males, a greater load is A Neutral position B Trunk extension; C Trunk flexion: Sacral flexion Sacral extension FIGURE 6-4 A. In the neutral position, the sacrum is placed in the close-packed position by the force of gravity. The sacrum responds to movements of both the thigh and the trunk. B. When the trunk extends or the thigh flexes, the sacrum flexes. Flexion of the sacrum occurs when the wide base of the sacrum moves anteriorly. C. During trunk flexion or thigh extension, the sacrum extends as the base moves posteriorly. The sacrum also rotates to the right or left with lateral flexion of the trunk (not shown).

192 SECTION II Functional Anatomy Anterior tilt Posterior tilt Left Left FIGURE 6-6 The pelvis can assist with movements of the thigh by tilting anteriorly to add to hip extension (left) or tilt posteriorly to add to hip flexion (right). Right Right tilt and posterior tilt in an open-chain movement can substitute for hip extension and hip flexion, respectively FIGURE 6-5 The pelvis moves in six directions in response to a trunk or (Fig. 6-6). In a closed-chain movement, posterior tilt is thigh movement. Anterior tilt of the pelvis accompanies trunk flexion or created through trunk extension or flattening of the low thigh extension (A). Posterior tilt accompanies trunk extension or thigh back and hip extension. In the open chain, posterior tilt flexion (B). Left (C) and right (D) lateral tilt accompany weight bearing occurs with flexion of the thigh. on the right and left limbs, respectively, or lateral movements of the thigh or trunk. Left (E) and right (F) rotation accompany left and right The pelvis can also tilt laterally and naturally tries to rotation of the trunk, respectively, or unilateral leg movement. move through a right lateral tilt when weight is supported by the left limb. In the closed-chain weight-bearing posi- In addition to the movement between the sacrum and tion, if the right pelvis elevates, adduction of the hip is the ilium, there is movement of the pelvic girdle as a produced on the weight-bearing limb and abduction of whole. These movements, shown in Figure 6-5, accom- the hip is produced on the opposite side to which the pany trunk and thigh movements to facilitate positioning pelvis drops. This movement is controlled by muscles, par- of the hip joint and the lumbar vertebrae. Although mus- ticularly the gluteus medius, so that it is not pronounced cles facilitate the movements of the pelvis, no one set of unless the controlling muscles are weak. Thus, right and muscles acts on the pelvis specifically; thus, pelvic move- left lateral tilt occur with weight bearing and any lateral ments occur as a consequence of movements of the thigh movement of the thigh or trunk (Fig. 6-7). or the lumbar vertebrae. Finally, the pelvic girdle rotates to the left and right as Movements of the pelvis are described by monitoring unilateral leg movements take place. As the right limb swings the ilium, specifically, the anterior-superior, and anterior- forward in a walk, run, or kick, the pelvis rotates to the left. inferior iliac spines on the front of the ilium. In a closed- Hip external rotation accompanies the forward pelvis, and chain weight-bearing movement, the pelvis moves about a hip internal rotation accompanies the backward pelvic side. fixed femur, and anterior tilt of the pelvis occurs when the trunk flexes and the hip flexes. In an open-chain position HIP JOINT such as hanging, the femur moves on the pelvis, and ante- rior tilt occurs with extension of the thighs. This anterior The final joint in the pelvic girdle complex is the hip joint, tilt can be created by protruding the abdomen and cre- which can be generally characterized as stable yet mobile. ating a swayback position in the low back. Both anterior The hip, which has 3 degrees of freedom (df), is a ball- and-socket joint consisting of the articulation between the acetabulum on the pelvis and the head of the femur. The structure of the hip joint and femur is illustrated in Figure 6-8.

CHAPTER 6 Functional Anatomy of the Lower Extremity 193 FIGURE 6-7 In the lower extremity, seg- ments interact differently depending on whether an open- or closed-chain move- ment is occurring. As shown on the left, the hip abduction movement in the open chain occurs as the thigh moves up toward the pelvis. In the closed-chain movement shown on the right, abduction occurs as the pelvis lowers on the weight- bearing side. The acetabulum is the concave surface of the ball and the hip joint (119). The head is also lined with articular car- socket, facing anteriorly, laterally, and inferiorly (119,133). tilage that is thicker in the middle central portions of the Interestingly, the three bones forming the pelvis—the head, where most of the load is supported. The cartilage on ilium, ischium, and pubis—make their fibrous connections the head thins out at the edges, where the acetabular carti- with each other in the acetabular cavity. The cavity is lined lage is thick (119). Approximately 70% of the head of the with articular cartilage that is thicker at the edge and thick- femur articulates with the acetabulum compared with 20% est on the top part of the cavity (77,119). There is no car- to 25% for the head of the humerus with the glenoid cavity. tilage on the underside of the acetabulum. As with the shoulder, a rim of fibrocartilage called the acetabular Surrounding the whole hip joint is a loose but strong labrum encircles the acetabulum. This structure serves to capsule that is reinforced by ligaments and the tendon of deepen the socket and increase stability (152). the psoas muscle and encapsulates the entire femoral head and a good portion of the femoral neck. The capsule is The spherical head of the femur fits snugly into the densest in the front and top of the joint, where the stresses acetabular cavity, giving the joint both congruency and a are the greatest, and it is quite thin on the back side and large surface contact area. Both the femoral head and the bottom of the joint (143). acetabulum have large amounts of spongy trabecular bone that facilitates the distribution of the forces absorbed by Three ligaments blend with the capsule and receive nourishment from the joint (Fig. 6-3). The iliofemoral

194 SECTION II Functional Anatomy Anterior View Fovea for ligament Head Posterior View of head Fovea for ligament Greater Greater trochanter of head trochanter Shaft (body) Head Trochanteric fossa Gluteal tuberosity Neck Neck Intertrochanteric line Intertrochanteric crest Lesser trochanter Lesser trochanter Linea aspera Medial lip Lateral lip Nutrient foramen Shaft (body) Adductor Adductor Popliteal surface tubercle tubercle Lateral epicondyle Medial Lateral epicondyle epicondyle Lateral condyle FIGURE 6-8 The hip is a stable joint with Medial Intercondylar fossa considerable mobility in three directions. epicondyle It is formed by the concave surface of the acetabulum on the pelvis and the large Patellar surface Medial Medial head of the femur. The femur is one of condyle condyle the strongest bones in the body.

CHAPTER 6 Functional Anatomy of the Lower Extremity 195 ligament, or Y-ligament, is strong and supports the ante- 20° to 25°, and it gets smaller as the person matures and rior hip joint in the standing posture, resisting extension, assumes weight-bearing positions. It is also believed that external rotation, and some adduction (152). This liga- the angle continues to reduce by approximately 5° in later ment is capable of supporting most of the body weight adult years. and plays an important role in standing posture (123). Also, hyperextension may be so limited by this ligament The range of the angle of inclination is usually within that it may not actually occur in the hip joint itself but 90 °to 135° (119). The angle of inclination is important rather as a consequence of anterior pelvic tilt. because it determines the effectiveness of the hip abduc- tors, the length of the limb, and the forces imposed on the The second ligament on the front of the hip joint, the hip joint (Fig. 6-10). An angle of inclination greater than pubofemoral ligament, primarily resists abduction, with 125° is termed coxa valga. This increase in the angle of some resistance to external rotation and extension. The inclination lengthens the limb, reduces the effectiveness of final ligament on the outside of the joint is the the hip abductors, increases the load on the femoral head, ischiofemoral ligament, on the posterior capsule, where and decreases the stress on the femoral neck (152). Coxa it resists extension, adduction, and internal rotation vara, in which the angle of inclination is less than 125°, (152). None of the ligaments surrounding the hip joint shortens the limb, increases the effectiveness of the hip resist during flexion movements, and all are loose during abductors, decreases the load on the femoral head, and flexion. This makes flexion the movement with the great- increases stress on the femoral neck. This varus position est range of motion. gives the hip abductors a mechanical advantage needed to counteract the forces produced by body weight. The result The femur is held away from the hip joint and the pelvis is reductions in the load imposed on the hip joint and in by the femoral neck. The neck is formed by cancellous tra- the amount of muscular force needed to counteract the becular bone with a thin cortical layer for strength. The force of body weight (143). There is a higher prevalence of cortical layer is reinforced on the lower surface of the coax vara in athletic females than males (122). neck, where greater strength is required in response to greater tension forces. Also, the medial femoral neck is the The angle of the femoral neck in the transverse plane is portion responsible for withstanding ground reaction termed the angle of anteversion (Fig. 6-11). Normally the forces. The lateral portion of the neck resists compression femoral neck is rotated anteriorly 12° to 14° with respect forces created by the muscles (119). to the femur (152). Anteversion in the hip increases the mechanical advantage of the gluteus maximus, making it The femoral neck joins up with the shaft of the femur, more effective as an external rotator (133). Conversely, which slants medially down to the knee. The shaft is very there is reduced efficiency of the gluteus medius and vas- narrow in the middle, where it is reinforced with the tus medialis, resulting in a loss of control of motion in the thickest layer of cortical bone. Also, the shaft bows anteri- frontal and transverse plan (122). If there is excessive orly to offer the optimal structure for sustaining and sup- anteversion in the hip joint, in which it rotates beyond 14° porting high forces (143). to the anterior side, the head of the femur is uncovered, and a person must assume an internally rotated posture or The femoral neck is positioned at a specific angle in gait to keep the femoral head in the joint socket. The toe- both the frontal and transverse planes to facilitate congru- ing-in accompanying excessive femoral anteversion is illus- ent articulation within the hip joint and to hold the femur trated in Figure 6-12. Other accompanying lower away from the body. The angle of inclination is the angle extremity adjustments to excessive anteversion include an of the femoral neck with respect to the shaft of the femur increase in the Q-angle, patellar problems, long legs, more in the frontal plane. This angle is approximately 125° (143) (Fig. 6-9). This angle is larger at birth by almost FIGURE 6-9 The angle of inclination of the neck of the femur is approximately 125°. If the angle is less than 125°, it is termed coxa vara. When the neck angle is greater than 125°, it is termed coxa valga.

196 SECTION II Functional Anatomy Abductor muscles Moment arm “Normal” Varus Valgus FIGURE 6-10 The femoral neck inclination angle influences both load on the femoral neck and the effectiveness of the hip abduc- tors. When the angle is reduced in coxa vara, the limb is shortened and the abductors are more effective because of a longer moment arm resulting in less load on the femoral head but more load on the femoral neck. The coxa valgus position lengthens the limb, reduces the effectiveness of the abductors because of a shorter moment arm, increases the load on the femoral head, and decreases the load on the neck. pronation at the subtalar joint, and an increase in lumbar hip is a stable joint even though the acetabulum is not curvature (119,143). Excessive anteversion has also been deep enough to cover all of the femoral head. The acetab- associated with increased hip joint contact forces and ular labrum deepens the socket to increase stability, and higher bending moments (63) as well as higher the joint is in a close-packed position in full extension patellofemoral joint contact pressures (122). when the lower body is stabilized on the pelvis. The joint is stabilized by gravity during stance, when body weight If the angle of anteversion is reversed so that it moves presses the femoral head against the acetabulum (143). posteriorly, it is termed retroversion (Fig. 6-11). There is also a difference in atmospheric pressure in the Retroversion creates an externally rotated gait, a supinated hip joint, creating a vacuum and suction of the femur up foot, and a decrease in the Q-angle (143). into the joint. Even if all of the ligaments and muscles were removed from around the hip joint, the femur would The hip is one of the most stable joints in the body still remain in the socket (75). because of powerful muscles, the shape of the bones, the labrum, and the strong capsule and ligaments (123). The FIGURE 6-11 The angle of the femoral neck in the frontal plane is called the angle of anteversion. The normal angle is approximately 12° to 14° to the anterior side. If this angle increases, a toe-in position is created in the extremity. If the angle of anteversion is reversed so the femoral neck moves posteriorly, it is termed retroversion. Retroversion causes toeing out.

CHAPTER 6 Functional Anatomy of the Lower Extremity 197 FIGURE 6-12 Individuals who have excessive femoral anteversion com- 120°–125° pensate by rotating the hip medially so that the knees face medially in stance. There is also usually an adaptation in the tibia that develops 10°–15° external tibial torsion to reorient the foot straight ahead. FIGURE 6-13 The thigh can move through a wide range of motion in Strong ligaments and muscular support in all directions three directions. The thigh moves through approximately 120° to 125° support and maintain stability in the hip joint. At 90° of flex- of flexion, 10 to 15° of hyperextension, 30° to 45° of abduction, 15° to ion with a small amount of rotation and abduction, there is 30° of adduction, 30° to 50° of external rotation, and 30 to 50° of inter- maximum congruence between the femoral head and the nal rotation. socket. This is a stable and comfortable position and is com- mon in sitting. A position of instability for the hip joint is in Finally, the thigh can internally rotate through 30° to flexion and adduction, as when the legs are crossed (75). 50° and externally rotate through 30° to 50° from the anatomical position (75,131). The range of motion for Movement Characteristics rotation at the hip can be enhanced by the position of the The hip joint allows the thigh to move through a wide thigh. Both internal and external rotation ranges of range of motion in three directions (Fig. 6-13). The thigh motion can be increased by flexing the thigh (75). Both can move through 120° to 125° of flexion and 10° to 15° internal and external rotation are limited by their antago- of hyperextension in the sagittal plane (57,119). These nistic muscle group and the ligaments of the hip joint. measurements are made with respect to a fixed axis and Range of motion in the hip joint is usually lower in older vary considerably if measured with respect to the pelvis age groups, but the difference is not that substantial and (7). Also, if thigh extension is limited or impaired, com- is usually in the range of 3° to 5° (137). pensatory joint actions at the knee or in the lumbar verte- brae accommodate the lack of hip extension. COMBINED MOVEMENTS OF THE PELVIS AND THIGH Hip flexion range of motion is limited primarily by the soft tissue and can be increased at the end of the range of The pelvis and the thigh commonly move together unless motion if the pelvis tilts posteriorly. Hip flexion occurs the trunk restrains pelvic activity. The coordinated move- freely with the knees flexed but is severely limited by the ment between the pelvis and the hip joint is termed the hamstrings if the flexion occurs with knee extension (75). Extension is limited by the anterior capsule, the strong hip flexors, and the iliofemoral ligament. Anterior tilt of the pelvis contributes to the range of motion in hip extension. The thigh can abduct through approximately 30° to 45° and can adduct 15° to 30° beyond the anatomical position (75). Most activities require 20° of abduction and adduc- tion (75). Abduction is limited by the adductor muscles, and adduction is limited by the tensor fascia latae muscle.

Range of motion at the hip, knee, and ankle in common activities Activity Hip Range of Motion Knee Range of Motion Ankle/Foot Range of Motion Walking • 35°–40° of flexion during • 5°–8° of knee flexion at heel • 20°–40° of total ankle Running late swing (119) strike (157) movement Lowering into • Full extension at heel lift • 60°–88° of knee flexion during • 10° of plantarflexion at or raising out of a chair • 12° of abduction and swing phase (78,157) heel strike (128) Climbing stairs adduction (max abduc- • 17°–20° of flexion during • 5°–10° of dorsiflexion in Bending down and picking up tion after toe-off; max support (78,157) midstance (128) an object Tying a shoe adduction in stance) • 12°–17° of rotation during • 20° of plantarflexion at while seated (75,143) swing phase (78,157) toe-off (128) • 8°–10° of external rota- • 8°–11° of valgus during swing • Dorsiflexion back to the tion in swing phase of phase (78,157) neutral position in the gait (75) • 5°–8° of knee flexion at heel swing phase (168) • 4°–6° of internal rotation strike (157) • 4° of calcaneal inversion before heel strike and • 17°–20° of flexion during at toe-off (89) through the support support (78,83,157) • 6°–7° of calcaneal ever- phase • 5°–7° of internal rotation sion in midstance (89) during support (78,83,157) • 2°–3° of supination at • 7°–14° of external rotation heel strike (39) during support (78,83,157) • 3°–10° of pronation at • 3°–7° of varus during support midstance (8,31,157) (78,83,157) • 3°–10° of supination up until heel-off (62) • 80° of knee flexion during • 10° of dorsiflexion prior swing phase (55) to contact (157) • 36° of flexion during support (55) • As much as 50° of dorsi- • 8° of valgus during swing flexion in midstance (157) phase(55) • 25° of plantarflexion at • 19° of varus during support (55) toe-off (157) • 8° of internal rotation during • 8°–15° of pronation in support (55) midstance (8,31,157) • 11° of external rotation during support (55) • 80°–100° of flexion (65) • 93° of flexion, 15° of abduction/ adduction and 14° of rotation (85) • 63° of flexion for ascent; • 83° of flexion, 17° of abduction, 24°–30° for descent and 16° of rotation for ascent (65,143) (85) • 83° of flexion, 14°of abduction/ adduction and 15° of rotation for descent (85) • 18°–20° of abduction (143) • 10°–15° of external rotation (143) • 106° of flexion, 20° of abduction/ adduction, 18° of rotation 198

CHAPTER 6 Functional Anatomy of the Lower Extremity 199 pelvifemoral rhythm. In hip flexion movements in an iliopsoas produces hyperextension of the lumbar verte- open chain (leg raise), the pelvis rotates posteriorly in the brae and flexion of the trunk. first degrees of motion. In a leg raise with the knees flexed or extended, 26% to 39% of the hip flexion motion is The iliopsoas is highly activated in hip flexion exercises attributed to pelvic rotation, respectively (36). At the end where the whole upper body is lifted or the legs are lifted of the range of motion in hip flexion, additional posterior (6). In sit-ups with the hips flexed and the feet held in pelvic rotation can contribute to more hip flexion. place, the hip flexors are more active. Also, double leg lifts Anterior pelvic tilt accompanies hip extension when the result in much higher activity in the iliopsoas than single limb is off the ground. In running, the average anterior leg lifts (6). tilt of the swing limb has been shown to be approximately 22°, which increases if there is limited hip extension flexi- The rectus femoris is another hip flexor whose contri- bility (145). There is more pelvic motion in non–weight- bution depends on knee joint positioning. This is also a bearing motions. two-joint muscle because it acts as an extensor of the knee joint as well. It is called the kicking muscle because it is in In a closed-chain, weight-bearing, standing position, maximal position for output at the hip during the prepara- the pelvis moves anteriorly on the femur, and pelvic motion tory phase of the kick, when the thigh is drawn back into during hip flexion has been shown to contribute only 18% hyperextension and the leg is flexed at the knee. This posi- to the change in hip motion (110). Posterior pelvic motion tion puts the rectus femoris on stretch and into an optimal in weight bearing contributes to hip extension. length–tension relationship for the succeeding joint action, in which the rectus femoris makes a powerful contribution In the frontal plane, pelvic orientation is maintained or to both hip flexion and knee extension. During the kicking adjusted in response to single-limb weight bearing seen in action, the rectus femoris is very susceptible to injury and walking or running. When weight is taken onto one limb, avulsion at its insertion site, the anterior inferior spine on there is a mediolateral shift toward the nonsupport limb the ilium. Loss of function of the rectus femoris diminishes that requires abduction and adduction muscle torque to thigh flexion strength as much as 17% (96). shift the pelvis toward the stance foot (73). This elevation of the nonsupport side pelvis creates hip adduction on the The three other secondary flexors of the thigh are the support side and abduction on the nonsupport side. sartorius, pectineus, and tensor fascia latae (see Fig. 6-14). The sartorius is a two-joint muscle originating at the ante- In the transverse plane during weight bearing, a rota- rior superior iliac spine and crossing the knee joint to the tion forward of the pelvis on one side creates lateral rota- medial side of the proximal tibia. It is a weak fusiform tion on the front hip and medial rotation on the back hip. muscle producing abduction and external rotation in addition to the flexion action of the hip. MUSCULAR ACTIONS The pectineus is one of the upper groin muscles. It is The insertion, action, and nerve supply for each individual primarily an adductor of the thigh except in walking, muscle in the lower extremity are outlined in Figure 6-14. actively contributing to thigh flexion. It is accompanied by Thigh flexion is used in walking and running to bring the the tensor fascia latae, which is generally an internal rota- leg forward. It is also an important movement in climbing tor. During walking, however, the tensor fascia latae aids stairs and walking uphill and is forcefully used in kicking. thigh flexion. The tensor fascia latae is considered a two- Little emphasis is placed on training the hip joint for flex- joint muscle because it attaches to the fibrous band of fas- ion movements because most consider flexion at the hip cia, the iliotibial band, running down the lateral thigh to play a minor role in activities. However, hip flexion is and attaching across the knee joint on the lateral aspect of very important for sprinters, hurdlers, high jumpers, and the proximal tibia. Thus, this muscle is stretched in knee others who must develop quick leg action. Elite athletes in extension. these activities usually have proportionally stronger hip flexors and abdominal muscles than do less skilled ath- During thigh flexion, the pelvis is pulled anteriorly by letes. Recently, more attention has been given to training these muscles unless stabilized and counteracted by the of the hip flexors in long distance runners as well because trunk. The iliopsoas muscle and tensor fascia latae pull the it has been shown that fatigue in the hip flexors during pelvis anteriorly. If either of these muscles is tight, pelvic running may alter gait mechanics and lead to injuries that torsion, pelvic instability, or a functional short leg may may be avoidable with better conditioning of this muscle occur. group. Extension of the thigh is important in the support of The strongest hip flexor is the iliopsoas muscle, which the body weight in stance because it maintains and con- consists of the psoas major, psoas minor, and iliacus trols the hip joint actions in response to gravitational pull. (143). The iliopsoas is a two-joint muscle that acts on Thigh extension also assists in propelling the body up and both the lumbar spine of the trunk and the thigh. If the forward in walking, running, or jumping by producing hip trunk is stabilized, the iliopsoas produces flexion at the joint actions that counteract gravity. The extensors attach hip joint that is slightly facilitated with the thigh to the pelvis and consequently play a major role in stabi- abducted and externally rotated. If the thigh is fixed, the lizing the pelvis in the anterior and posterior directions. The muscles contributing in all conditions of exten- sion at the hip joint are the hamstrings. The two medial

200 SECTION II Functional Anatomy Psoas Gluteus maximus minor Iliacus Gluteus Psoas medius A major Piriformis Pectineus B Maximus Medius Minimus Adductor brevis Superior Adductor longus gemellus C Adductor magnus Obturator Gracilis internus Inferior gemellus Quadratus femoris Ischial Psoas major tuberosity Iliacus Semi- Inguinal tendinosus ligament Biceps Iliopsoas femoris Sartorius Semi- Tensor muscle membranosus of fascia lata Pectineus Adductor longus Vastus lateralis Iliotibial tract (band) Gracilis Rectus femoris Vastus medialis D EF Muscle Group Insertion Nerve Supply Flexion Extension Abduction Adduction Medial Lateral Rotation Rotation Adductor brevis Inferior rami of pubis TO Anterior obturator Adductor longus PM Asst upper half of posterior femur nerve; L3, L4 PM Asst Asst Asst PM Asst Asst Inferior rami of pubis TO Anterior obturator PM PM middle third of posterior femur nerve; L3, L4 PM Adductor magnus Anterior pubis, ischial Posterior obturator, PM PM tuberosity TO linea aspera on sciatic; L3, L4 PM PM posterior femur, adductor PM Asst tubercle Biceps femoris Ischial tuberosity TO lateral Tibial, peroneal Gemellus inferior condyle of tibia, head of fibula portion of sciatic nerve; L5, S1–S3 Ischial tuberosity TO greater Sacral plexus; L4, trochanter on femur L5, S1 sacral nerve Gemellus superior Ischial spine TO greater Sacral plexus; L5, Gluteus maximus trochanter S1, S2 sacral nerve Gluteus medius Posterior ilium, sacrum, Inferior gluteal nerve; coccyx TO gluteal tuberosity; L5, S1, S2 iliotibial band Superior gluteal Anterior, lateral ilium TO nerve; L4, L5, S1 lateral surface of greater trochanter Gluteus minimus Outer, lower ilium TO front of Superior gluteal greater trochanter nerve; L4, L5, S1 Gracilis Inferior rami of pubis TO Anterior obturator medial tibis (pes anserinus) nerve; L3, L4 FIGURE 6-14 Muscles acting on the hip joint, including the adductors and flexors (A), the external rotators (B), abductors (C), and extensors (D). A combination of knee and hip joint muscles comprise the anterior thigh region (E, F).

CHAPTER 6 Functional Anatomy of the Lower Extremity 201 Muscle Group Insertion Nerve Supply Flexion Extension Abduction Adduction Medial Lateral Rotation Rotation Asst Iliacus Inner surface of ilium, sacrum Femoral nerve; L2, L3 PM PM Obturator externus TO lesser trochanter PM Obturator internus Pectineus Sciatic notch, margin of Sacral plexus; L5, S1, PM Asst obturator foramen TO greater S2 PM trochanter PM Pubis, ischium, margin of Obturator nerve; obturator formamen TO L3, L4 upper posterior femur Pectineal line on pubis TO Femoral nerve; L2–L4 PM PM below lesser trochanter Asst Piriformis Anterior lateral sacrum TO S1, S2, L5 superior greater trochanter Psoas Transverse processes, body Femoral nerve; L1–L3 PM Quadratus femoris of L1–L5, T12 TO lesser trochanter Sacral plexus; L4, L5, S1 Ischial tuberosity TO greater trochanter Rectus femoris Anterior inferior iliac spine TO Femoral nerve; L2, PM Asst Asst patella, tibial tuberosity L3, L4 PM Sartorius Anterior superior iliac spine Femoral nerve; L2, L3 PM PM Asst Semimembranosus TO medial tibia (pes Asst anserinus) Tibial portion of sciatic Asst PM nerve: L5, S1, S2 Ischial tuberosity TO medial condyle of tibia Semitendinosus Ischial tuberosity TO medial Tibial portion of sciatic tibia (pes anserinus) nerve: L5, S1, S2 Tensor fasica latae Anterior superior iliac spine Superior gluteal Asst TO ilitibial tract nerve: L4, L5, S1 FIGURE 6-14 (CONTINUED) hamstrings—the semimembranosus and the semitendi- running up hills, climbing stairs, rising out of a deep nosus—are not as active as the lateral hamstring, the squat, sprinting, and rising from a chair. It also occurs in biceps femoris, which is considered the workhorse of an optimal length–tension position with thigh hyperex- extension at the hip. tension and external rotation (152). Because all of the hamstrings cross the knee joint, pro- The gluteus maximus appears to dominate the pelvis ducing both flexion and rotation of the lower tibia, their during gait rather than contribute significantly to the gen- effectiveness as hip extensors depends on positioning at the eration of extension forces. Because the thigh is almost knee joint. With the knee joint extended, the hamstrings extended during the walking cycle, the function of the are put on stretch for optimal action at the hip. The ham- gluteus maximus is more trunk extension and posterior tilt string output also increases with increasing amounts of of the pelvis. At foot strike when the trunk flexes, the glu- thigh flexion; however, the hamstrings can be lengthened teus maximus prevents the trunk from pitching forward. to a position of muscle strain if the leg is extended with the Because the gluteus maximus also externally rotates the thigh in maximal flexion. thigh, internal rotation places the muscle on stretch. Loss of function of the gluteus maximus muscle does not sig- The hamstrings also control the pelvis by pulling down nificantly impair the extension strength of the thigh on the ischial tuberosity, creating a posterior tilt of the because the hamstrings dominate production of extension pelvis. In this manner, the hamstrings are responsible for strength (96). maintaining an upright posture. Tightness in the ham- strings can create significant postural problems by flatten- Finally because the flexors and extensors control the ing the low back and producing a continuous posterior tilt pelvis anteroposteriorly, it is important that they are bal- of the pelvis. anced in both strength and flexibility so that the pelvis is not drawn forward or backward as a result of one group In level walking or in low-output hip extension activi- being stronger or less flexible. ties, the hamstrings are the predominant muscles that con- tributed to the extension movement in the weight-bearing Abduction of the thigh is an important movement in positions. Loss of function in the hamstrings produces sig- many dance and gymnastics skills. During gait, the abduc- nificant impairment in hip extension. tion and the abduction muscles are more important in their role as stabilizers of the pelvis and thigh. The If the resistance in extension is increased or if a more abductors can raise the thigh laterally in the frontal vigorous hip extension is needed, the gluteus maximus is plane, or if the foot is on the ground, they can move the recruited as a major contributor (152). This occurs in

202 SECTION II Functional Anatomy pelvis on the femur in the frontal plane. When abduction the adductors on the opposite side to maintain pelvic posi- occurs, such as in doing splits on the ground, both hip tioning and prevent tilting. As shown earlier, the abduc- joints displace the same number of degrees in abduction, tors and adductors must be balanced in strength and even though only one limb may have moved. The relative flexibility so that the pelvis can be balanced side to side. angle between the thigh and the trunk is the same in both Figure 6-15 illustrates how imbalances in abduction and hip joints in abduction because of the pelvic shift in adduction can tilt the pelvis. If the abductors overpower response to abduction initiated in one hip joint. the adductors through contracture or a strength imbal- ance, the pelvis will tilt to the side of the strong, con- The main abductor of the thigh at the hip joint is the tracted abductor. Adductor contracture or strength gluteus medius. This multipennate muscle contracts during imbalances produce a similar effect in the opposite direc- the stance in a walk, run, or jump to stabilize the pelvis so tion. The adductors also work with the hip flexors and that it does not drop to the nonstance limb. This is impor- extensors to maintain limb position and to counteract the tant for all the joints and segments in the lower extremity rotation of the pelvis when the front limb is flexed and the because a weak gluteus medius can lead to changes such as back limb is extended in the double-support phase of contralateral pelvis drop and increased femoral adduction walking (123). and internal rotation, which can lead to increased knee val- gus, excessive lateral tracking of the patella, and increased External rotation of the thigh is important in prepara- tibial rotation and pronation in the foot (44). The effec- tion for power production in the lower extremity because tiveness of the gluteus medius muscle is determined by its it follows the trunk during rotation. The muscles prima- mechanical advantage. It is more effective if the angle of rily responsible for external rotation are the gluteus max- inclination of the femoral neck is less than 125°, taking the imus, obturator externus, and quadratus femoris. The insertion further away from the hip joint, and it is also obturator internus, inferior and superior gemellus, and more effective for the same reason in the wider pelvis piriformis contribute to external rotation when the thigh (133). As the mechanical advantage of the gluteus medius is extended. The piriformis also abducts the hip when the increases, the stability of the pelvis in gait will also improve. hip is flexed and creates the movement on lifting the leg into abduction with the toes pointing upward in external The gluteus minimus, tensor fascia latae, and piriformis rotation. Because most of these muscles attach to the also contribute to abduction of the thigh, with the gluteus anterior face of the pelvis, they also exert considerable minimus being the most active of the three. A 50% reduc- control over the pelvis and sacrum. tion in the function of the abductors results in a slight to moderate impairment in abduction function (96). If the Internal rotation of the thigh is basically a weak move- abductors are weak, there will be an excessive tilt in the ment. It is a secondary movement for all of the muscles frontal plane, with a higher pelvis on the weaker side (88). contracting to produce this joint action. The two muscles The abductors on the support side work to keep the pelvis most involved in internal rotation are the gluteus medius level and to avoid any tilting. Additionally, the shear forces and the gluteus minimus. Internal rotation is also aided by across the sacroiliac joint will greatly increase, and the contractions of the gracilis, adductor longus, adductor individual will walk with greater side-to-side sway. magnus, tensor fascia latae, semimembranosus, and semi- tendinosus. The adductor muscle group works to bring the thigh across the body, as seen commonly in dance, soccer, gym- The muscles of the trunk, pelvis, and hip also work nastics, and swimming. The adductors, similar to the together to control the pelvic posture. The pelvis serves as abductors, also work to maintain the pelvic position dur- a link between the lumbar vertebrae and the hip and must ing gait. The adductors as a group constitute a large mus- be stabilized by the trunk or thigh musculature to main- cle mass, with all of the muscles originating on the pubic tain its position (135). For example, at the beginning of bone and running down the inner thigh. Although the lifting, the gluteus maximus contracts to stabilize pelvis so adductors are important in specific activities, it has been that the spinal extensors can extend the trunk in the lift. shown that a 70% reduction in the function of the thigh The gluteus maximus also stabilizes the pelvis in trunk adductors results in only a slight or moderate impairment rotation (112). In upright standing, the pelvis is main- in hip function (96). tained in a vertical position but can also assume a variety of tilt postures. The rectus femoris and the erector spinae The adductor muscles include the gracilis, on the medial muscles can pull the pelvis anteriorly, and the gluteals and side of the thigh; the adductor longus, on the anterior side abdominals can pull the pelvis posteriorly if the pelvis is in of the thigh; the adductor brevis, in the middle of the a position out the neutral vertical position (43,135). thigh; and the adductor magnus, on the posterior side of the inner thigh. High in the groin is the pectineus, previ- STRENGTH OF THE HIP JOINT MUSCLES ously discussed briefly in its role as hip flexor. The adduc- tors are active during the swing phase of gait as they work The hip muscles generate the greatest strength output in to swing the limb through (152), and if they are tight, a extension. The most massive muscle in the body, the glu- scissors gait can result, leading to a crossover plant. teus maximus, combines with the hamstrings to produce hip extension. Extension strength is maximum with the The adductors work with the abductors to balance the pelvis. The abductors on one side of the pelvis work with

CHAPTER 6 Functional Anatomy of the Lower Extremity 203 FIGURE 6-15 The abductors and adductors work in pairs to maintain pelvic height and levelness. For example, the left abductors work with the right adductors and lateral trunk flexors to create a left lateral tilt. If an abductor or adductor mus- cle group is stronger than the contralateral group, the pelvis will tilt to the strong side. This also happens with contracture of the muscle group. hip flexed to 90° and diminishes by about half as the hip develop more force output than the abductors (97). flexion angle approaches the 0° or neutral position (152). Adduction, however, is not the primary contributor to Extension strength also depends on knee position because many movements or sport activities, so it is minimally the hamstrings cross the knee joint. The hamstrings’ con- loaded or strengthened through activity. Adduction tribution to hip extension strength is enhanced with the strength values are greater from a position of slight abduc- knees extended (75). tion as a stretch is placed on the muscle group. Many muscles contribute to hip flexion strength, but The strength of the external rotators is 60% greater many of the muscles do so secondarily to other main than that of the internal rotators except in hip flexion, roles. Hip flexion strength is primarily generated with when the internal rotators are slightly stronger (152). The the powerful iliopsoas muscle, although its strength strength output of both the internal and external rotators diminishes with trunk flexion. Additionally, the flexion is greater in a seated position than in a supine one. strength of the thigh can be enhanced if flexion at the knee joint increases the contribution of the rectus CONDITIONING OF THE HIP JOINT femoris to flexion strength. Abduction strength is maxi- MUSCLES mal from the neutral position and diminishes more than half at 25° of abduction (152). This reduction is associ- The muscles surrounding the hip joint receive some form ated with decreases in muscle length even though the of conditioning during walking, rising from or lowering ability of the gluteus medius to abduct the leg improves into a chair, and performing other common daily activi- as a consequence of improving the direction of the pull ties, such as climbing stairs. The hip musculature should of the muscle. The strength output of the abduction be balanced so that the extensors do not overpower the movement can also be increased if it is performed with flexors and the abductors are equivalent to the adductors. the thigh flexed (152). Abduction strength has also been This ensures sufficient control over the pelvis. Sample shown to be greater in the dominant limb than in the stretching and strengthening exercises for the hip joint nondominant limb (71,115). muscles are provided in Figure 6-16. The potential for the development of adduction Because the hip muscles are used in all support activi- strength is substantial because the muscles contributing to ties, it is best to design exercises using a closed kinetic the movement are massive as a group and adductors can chain. In this type of activity, the foot or feet are in contact

204 SECTION II Functional Anatomy Muscle Group Sample Stretching Exercise Sample Strengthening Exercise Other Exercises Hip flexors Hanging leg lifts Manual resistance Band or tube hip flexion Hip flexor machine Hip extensors Glutal leg lift Leg curl squat FIGURE 6-16 Sample stretching and strengthening exercises for selected muscle groups.

CHAPTER 6 Functional Anatomy of the Lower Extremity 205 Muscle Group Sample Stretching Exercise Sample Strengthening Exercise Other Exercises Hip abductors Abductor machine Leg swings (tubing) Hip adductors Adductor machine Leg swings (tubing) Hip rotators Ball sqeeze FIGURE 6-16 (CONTINUED)

206 SECTION II Functional Anatomy with a surface (i.e., the ground), and forces are applied to The abductors and adductors can be exercised from the the system at the foot or feet. An example of a closed- sidelying position so that they can work against gravity. chain exercise is a squat lift in weight training. An exam- This position requires stabilization of the pelvis and low ple of an open kinetic chain exercise is one using a back. It is hard to exercise the abductors or adductors on machine, in which the muscle group moves the limb one side without working the other side as well; both sides through a prescribed arc of motion. Finally, many two- are affected equally because of the action of the pelvis. For joint muscles act at the hip joint, so careful attention example, 20° of abduction at the right hip joint results in should be paid to adjacent joint positioning to maximize 20° of abduction at the left hip joint because of the pelvic a stretch or strengthening exercise. tilt accompanying the movement. The flexors are best exercised in the supine or hanging The rotators of the thigh are the most challenging in position so that the thigh can be raised against gravity or terms of conditioning because it is so difficult to apply in lifting the whole upper body. The hip flexors are mini- resistance to the rotation. The seated position is recom- mally used in a lowering activity, such as a squat, when mended for strengthening the rotators because the rotators there is flexion of the thigh, because the extensors control are strong in this position and resistance to the rotation can the movement eccentrically. Because the hip flexors attach easily be applied to the leg either with surgical tubing or on the trunk and across the knee joint, their contribution manually. Because the internal rotators lose effectiveness in to flexion can be enhanced with the trunk extended. the extended supine position, they should definitely be Flexion at the knee also enhances thigh flexion. It is easy exercised with the person seated. Both muscle groups can to stretch the flexors with both the trunk and thigh placed be stretched in the same way they are strengthened, using in hyperextension. The rectus femoris can be placed in a the opposite joint action for the stretch. These exercises very strenuous stretch with thigh hyperextension and may be contraindicated, however, for individuals with knee maximal knee flexion. pain, particularly patellofemoral pain. The success of conditioning the extensors depends on INJURY POTENTIAL OF THE PELVIC trunk and knee joint positioning. The greater the knee AND HIP COMPLEX flexion, the less the hamstrings contribute to extension, requiring a greater contribution from the gluteus max- Injuries to the pelvis and hip joint are a small percentage imus. For example, in a quarter-squat activity with the of injuries in the lower extremity. In fact, overuse injuries extensors used eccentrically to lower the body and con- to this area account for only 5% of the total for the whole centrically to raise the body, the hamstrings are the most body (129). This may be attributable to the strong liga- active contributors. In a deep squat, with the amount of mentous support, significant muscular support, and solid knee flexion increased to 90° and beyond, the gluteus structural characteristics of the region. maximus is used more because the hamstrings are inca- pacitated by their reduced length. Injuries to the pelvis primarily occur in response to abnormal function that excessively loads areas of the Trunk positioning is also important, and the activity of pelvis. This can result in an irritation at the site of muscu- the hamstrings is enhanced with trunk flexion because lar attachment, and in adolescents, a more common type trunk flexion increases the length of both the hamstrings of injury might be an avulsion fracture at the apophysis, or and the gluteus maximus. The extensors are best exercised bony outgrowth. Iliac apophysitis is an example of such in a standing, weight-supported position because they are an injury, in which excessive arm swing in gait causes used in this position in most cases and are one of the excessive rotation of the pelvis, creating stress on the propulsive muscle groups in the lower extremity. attachment site of the gluteus medius and tensor fascia latae on the iliac crest (129). This can also occur at the The extensors can be stretched to maximum levels with iliac crest as a result of direct blow or as a result of a sud- hip flexion accompanied by full extension at the knee. The den, violent contraction of the abdominals (3,104). A hip stretch on the gluteus maximus can be increased with pointer results when the anterior iliac crest is bruised as a thigh internal rotation and adduction. result of a direct blow. Apophysitis, an inflammation of an apophysis, can also develop into a stress fracture. The abductors and adductors are difficult to condition because they influence balance and pelvic position so sig- Another site in the pelvis subjected to apophysitis or nificantly. In a standing position, the thigh can be stress fracture is the anterior superior iliac spine where the abducted against gravity, but it will shift the pelvis dra- sartorius attaches (104) and high tensions develop in matically so that the person loses balance. The adductors activities such as sprinting where there is vigorous hip present an even greater problem. It is very difficult to extension and knee flexion. At the anterior inferior iliac place the adductors so that they work against gravity spine, the rectus femoris can produce the same type of because the abductors are responsible for lowering the injury in an activity such as kicking.. limb to the side after abducting it. Consequently, the supine position is best for strengthening and stretching A stress fracture in the pubic rami can be produced by the abductors and adductors. Resistance can be offered strong contractions from the adductors, often associated manually or through an exercise machine with external with overstriding in a run (159). Finally, the hamstrings resistance to the movement.

CHAPTER 6 Functional Anatomy of the Lower Extremity 207 can exert enough force to create an avulsion fracture on caused by some traumatic event that forces the femoral the ischial tuberosity. Commonly called the hurdler’s frac- neck into external rotation, or it can be caused by failure of ture, this ischial tuberosity injury is also common to the cartilaginous growth plates (2). This tilts the femoral waterskiing (5). All of these injuries are most common in head back and medially and tilts the growth plate forward activities such as sprinting, jumping, soccer, football, bas- and vertically, producing a nagging pain on the front of the ketball, and figure skating, in which sudden bursts of thigh. An individual with this disorder walks with an exter- motion are required (104). nally rotated gait and has limited internal rotation with the thigh flexed and abducted (143). Such slippage may occur The sacrum and sacroiliac joint can dysfunction as a in a baseball player who rounds a base with the left foot result of injury or poor posture. If one assumes a round- fixed in internal rotation while the trunk and pelvis rotate shouldered, forward-head posture, the center of gravity of in the opposite direction. the body moves forward. This increase in the curvature of the lumbar spine produces a ligamentous laxity in the dor- The final major childhood disorder to the hip joint is sal sacroiliac ligaments and stress on the anterior ligaments congenital hip dislocation, a disorder that affects girls (40). Also, any skeletal asymmetry, such as a short leg, more often than boys (143). This condition is usually produces a ligament laxity in the sacroiliac joint (130). diagnosed early as the infant assumes weight on the lower extremity. The hip joint subluxates or dislocates for no With excessive mobility, large forces are transferred to apparent reason. The thigh cannot abduct, the limb short- the sacroiliac joint, producing an inflammation of the joint ens, and a limp is usually present. Fortunately, this condi- known as sacroiliitis. Inflammation of the joint may occur tion is easily corrected with an abduction orthotic. in an activity such as long jumping, in which the landing is absorbed with the leg extended at the knee. At the same An age-related disorder of the hip joint seen commonly time, the hip is flexed or there is extreme flexion of the in elderly individuals is osteoarthritis. This condition trunk combined with lateral flexion (130). The sacroiliac results in degeneration of the joint cartilage and the joint also becomes very mobile in pregnant women, mak- underlying subchondral bone, narrowing of the joint ing them more susceptible to sacroiliac sprain (60). space, and the growth of osteophytes in and around the joint. This affliction strikes millions of elderly people, cre- The functional positions of the sacrum and the pelvis ating a significant amount of pain and discomfort during are also important for maintaining an injury-free lower weight support and gait activities. To reduce the pain in extremity. A functional short leg can be created by poste- the joint, individuals often assume a position of flexion, rior rotation of the ipsilateral ilium, anterior ilium rotation adduction, and external rotation or whichever position of the opposite side, superior ilium movement on the results in the least tension for the hip. same side, forward or backward sacral torsion to the same side, or sacral flexion of the opposite side (130). A func- More than 60% of injuries to the hip occur in the soft tional short leg requires adjustments in the whole limb, tissue (88). Of these injuries, 62% occur in running, 62% creating stress at the sacroiliac joint, knee, and foot. are associated with a varum alignment in the lower extrem- ity, and 30% are associated with a leg length discrepancy The hip joint can withstand large loads, but when (88). These types of injuries are usually muscle strains, ten- muscle imbalance develops with high forces, injury can dinitis of the muscle insertions, or bursitis (25). result. For example, in a high-force situation involving flexion, adduction, and internal rotation, a dislocation The most common soft tissue injury to the hip region posteriorly can occur. Falling on an adducted limb with is gluteus medius tendinitis, which occurs more frequently the knee flexed or an abrupt stop over the weight-bear- in women as a result of excessive pull by the gluteus ing limb can push the femoral head to the posterior rim medius during running (21,88). A hamstring strain is also of the acetabulum, resulting in a hip subluxation (5). common and is seen in activities such as hurdling, in Activities more prone to a posterior dislocation of the hip which the lower limb is placed in a position of maximum are stooping activities, leg-crossing activities, or rising hip flexion and knee extension. It can also occur with from a low seat (113). Anterior dislocations or subluxa- speed or hill running and in individuals performing with tions are uncommon. poor flexibility or conditioning in this muscle group. Also, a number of age-related hip conditions must be Iliopsoas strain can occur in activities such as sprinting, considered when working with children or older adults. In in which a rapid forceful flexion taxes the muscle or the children 3 to 12 years old, the condition known as Legg- muscle is used eccentrically to slow a rapid extension at Calvé-Perthes disease may appear (143). In this condition, the hip. The adductors are often strained in an activity also called coxa plana, the femoral head degenerates, and such as soccer, in which the lower extremity is rapidly the proximal femoral epiphysis is damaged. This disorder abducted and externally rotated in preparation for contact strikes boys five times more frequently than girls and usually with the ball. Strain to the rectus femoris can occur in a occurs to only one limb (2). It is caused by trauma to the rapid forceful flexion of the thigh, such as is seen in sprint- joint, synovitis or inflammation to the capsule, or some vas- ing, and in a vigorous hyperextension of the thigh, such as cular condition that limits blood supply to the area. in the preparatory phase of a kick. Slipped capital femoral epiphysitis is another disorder A piriformis strain may be caused by excessive external that can affect children aged 10 to 17 years. It is usually rotation and abduction when the thigh is being flexed.

208 SECTION II Functional Anatomy This creates pain in adduction, flexion, and internal rota- femoral neck are seen more often on the superior side and tion of the thigh. A piriformis syndrome can develop. are caused by high tension forces (3). The abductors can This is an impingement of the sciatic nerve aggravated by create an avulsion fracture on the greater trochanter, and internal and external rotation movement of the thigh the iliopsoas can pull hard enough to produce an avulsion during walking (21,88). The syndrome can also be cre- fracture at the lesser trochanter (3,143). Stress fractures ated by a functional short leg that lengthens the piri- can also appear in the femoral neck. It is believed that formis and then stretches it as the pelvis drops to the these stress fractures may be related to some type of vas- shorter leg. The irritation of the sciatic nerve causes pain cular necrosis in which the blood supply is limited or to in the buttock area that can travel down the posterior sur- some hormonal deficiency that reduces the bone density face of the thigh and leg. in the neck (88). Stress fracture at this site produces pain in the groin area. Other soft tissue injuries to the hip region are seen in the bursae. The most common of these is greater The Knee Joint trochanteric bursitis, which is caused by hyperadduction of the thigh. This can be produced by running with too The knee joint supports the weight of the body and trans- much leg crossover in each stride, imbalance between the mits forces from the ground while allowing a great deal of abductors and adductors, running on banked surfaces, movement between the femur and the tibia. In the having a leg length difference, or remaining on the out- extended position, the knee joint is stable because of its side of the foot during the support phase of a walk or run vertical alignment, the congruency of the joint surfaces, (22,129). It is especially prevalent in runners with a wide and the effect of gravity. In any flexed position, the knee pelvis, a large Q-angle, and an imbalance between the joint is mobile and requires special stabilization from the abductors and adductors (22,129). powerful capsule, ligaments, and muscles surrounding the joint (148). The joint is vulnerable to injury because of Because the right hip adductors work with the left hip the mechanical demands on it and the reliance on soft tis- abductors and vice versa, any imbalance causes asymmet- sue for support. rical posture. For example, a weak right abductor creates a lateral pelvic tilt, with the right side high and the left side The ligaments surrounding the knee support the joint low. This places stress on the lateral hip, setting up the passively as they are loaded in tension only. The muscles conditions for bursitis. Pain on the outside of the hip is support the joint actively and are also loaded in tension, accentuated with trochanteric bursitis when the legs are and bone offers support and resistance to compressive crossed. loads (101). Functional stability of the joint is derived from the passive restraint of the ligaments, joint geometry, Ischial bursitis can develop with prolonged sitting and the active muscles, and the compressive forces pushing the is aggravated by walking, stair climbing, and flexion of bones together. the thigh. Finally, iliopectineal bursitis may develop in reaction to a tight iliopsoas muscle or osteoarthritis of the There are three articulations in the region known as the hip (143). knee joint: the tibiofemoral joint, the patellofemoral joint, and the superior tibiofibular joint (166). The Two remaining soft tissue injuries seen in dancers and bony landmarks of the knee joint and tibia and fibula are distance runners are lateral hip pain created by iliotibial illustrated in Figure 6-17. band syndrome and snapping hip syndrome. The strain to the iliotibial band is created because dancers warm up TIBIOFEMORAL JOINT with the hip abducted and externally rotated. They have very few flexion and extension routines in warmup and The tibiofemoral joint, commonly referred to as the actual dance routines. The stress to the iliotibial band occurs knee joint, is the articulation between the two longest and with thigh adduction and internal rotation, movements strongest bones in the body, the femur and the tibia (Fig. that are extremely limited in dancers by technique (136). 6-17). It has been referred to as a double condyloid joint Iliotibial band syndrome can also be caused by excess ten- or a modified hinge joint that combines a hinge and a sion in the tensor fascia latae in abducting the hip in single- pivot joint. In this joint, flexion and extension occur sim- stance weight bearing. The snapping hip also commonly ilar to flexion and extension at the elbow joint. In the knee produces a click as the hip capsule moves or the iliopsoas joint, however, flexion is accompanied by a small but sig- tendon snaps over a bony surface. nificant amount of rotation (148). The bony or osseous injuries to the hip are usually a At the distal end of the femur are two large convex result of a strong muscular contraction that creates an surfaces, the medial and lateral condyles, separated by avulsion fracture. Stress fractures can develop in the hip the intercondylar notch in the posterior and the patel- region and are common in endurance athletes, particularly lar, or trochlear, groove in the anterior (148) (Fig. 6-17). women (25). Stress fractures to the femoral neck account It is important to review the anatomical characteristics for 5% to 10% of all stress fractures (98). A stress fracture of these two condyles because their differences and the to the inferior medial aspect of the femoral neck is seen more often in younger patients and is caused by high com- pression forces. In older adults, stress fractures to the

CHAPTER 6 Functional Anatomy of the Lower Extremity 209 Distal end of Articular facet femur for tibia Lateral Medial condyle condyle Tuberosity Intercondylar of tibia eminence Head Apex (styloid process) Fibula Soleal line Tibia Medial LATERAL crest MEDIAL Medial Medial malleolus surface A Interosseous border MEDIAL Fibular notch Medial malleolus Lateral malleolus B C FIGURE 6-17 The structure of the knee joint is complex with asymmetrical condyles on the distal end of the femur articulat- ing with asymmetrical facets on the tibial plateau. The patella moves in the trochlea groove on the femur. The anterior (A) and posterior (B) views of the lower leg and a close-up view of the knee joint (C) illustrate the complexity of the joints.

210 SECTION II Functional Anatomy corresponding differences on the tibia account for the FIGURE 6-18 Two fibrocartilage menisci lie in the lateral and medial com- rotation in the knee joint. The lateral condyle is flatter, has partments of the knee. The medial meniscus is crescent shaped, and the a larger surface area, projects more posteriorly, is more lateral meniscus is oval to match the surfaces of the tibial plateau and prominent anteriorly to hold the patella in place, and is the differences in the shape of the femoral condyles. Both menisci serve basically aligned with the femur (166). The medial important roles in the knee joint by offering shock absorption, stability, condyle projects more distally and medially, is longer in and lubrication and by increasing the contact area between the tibia and the anteroposterior direction, angles away from the femur the femur. in the rear, and is aligned with the tibia (166). Above the condyles on both sides are the epicondyles, which are the in full extension and a significant portion of the load in sites of capsule, ligament, and muscular attachment. flexion (170). In flexion, the lateral meniscus carries the greater portion of the load. By absorbing some of the The condyles rest on the condyle facet or tibial plateau, load, the menisci protect the underlying articular cartilage a medial and lateral surface separated by a ridge of bone and subchondral bone. The menisci transmit the load termed the intercondylar eminence. This ridge of bone across the surface of the joint, reducing the load per unit serves as an attachment site for ligaments, centers the joint, of area on the tibiofemoral contact sites (53). The contact and stabilizes the bones in weight bearing (166). The area in the joint is reduced by two thirds when the menisci medial surface of the plateau is oval, larger, longer in the are absent. This increases the pressure on the contacting anteroposterior direction, and slightly concave to accept surfaces and increases the susceptibility to injury (116). the convex condyle of the femur. The lateral tibial During low-load situations, the contact is primarily on the plateau is circular and slightly convex (166). Consequently, menisci, but in high-load situations, the contact area the medial tibia and femur fit fairly snugly together, but increases, with 70% of the load still on the menisci (53). the lateral tibia and femur do not fit together well because The lateral meniscus carries a significantly greater percent- both surfaces are convex (148). This structural difference age of the load. is one of the determinants of rotation because the lateral condyle has a greater excursion with flexion and extension The menisci also enhance lubrication of the joint. By at the knee. acting as a space-filling mechanism, they allow dispersal of more synovial fluid to the surface of the tibia and the Two separate fibrocartilage menisci lie between the femur. It has been demonstrated that a 20% increase in tibia and the femur. As shown in Figure 6-18, the lateral friction within the joint occurs with the removal of the meniscus is oval, with attachments at the anterior and meniscus (170). posterior horns (53,166). It also receives attachments from the quadriceps femoris anteriorly and the popliteus Finally, the menisci limit motion between the tibia and muscle and posterior cruciate ligament (PCL) posteri- femur. In flexion and extension, the menisci move with orly. The lateral meniscus occupies a larger percentage of the femoral condyles. As the leg flexes, the menisci move the area in the lateral compartment than the medial meniscus in the medial compartment. Also, the lateral meniscus is more mobile, capable of moving more than twice the distance of the medial meniscus in the antero- posterior direction (166). The medial meniscus is larger and crescent shaped, with a wide base of attachment on both the anterior and pos- terior horns via the coronary ligaments (Fig. 6-18). It is connected to the quadriceps femoris and the anterior cru- ciate ligament (ACL) anteriorly, the tibial collateral liga- ment laterally, and the semimembranosus muscle posteriorly (166). Both menisci are wedge shaped because of greater thick- ness at the periphery. The menisci are connected to each other at the anterior horns by a transverse ligament. The menisci have blood supply to the horns at the anterior and posterior ends of the arcs of each meniscus but have no blood supply to the inner portion of the fibrocartilage. Thus, if a tear occurs in the periphery of the menisci, heal- ing can occur, unlike with tears to the thinner inner por- tion of the menisci. The menisci are important in the knee joint. The menisci enhance stability in the joint by deepening the contact surface on the tibia. They participate in shock absorption by transmitting half of the weight-bearing load

CHAPTER 6 Functional Anatomy of the Lower Extremity 211 posteriorly because of the rolling of the femur and mus- The PCL offers the primary restraint to posterior cular action of the popliteus and semimembranosus mus- movement of the tibia on the femur, accounting for 95% cles (170). At the end of the flexion movement, the of the total resistance to this movement (120). This liga- menisci fill up the posterior portion of the joint, acting as ment decreases in length and slackens by 10% at 30° of a space-filling buffer. The reverse occurs in extension. The knee flexion and then maintains that length throughout quadriceps femoris and the patella assist in moving the flexion (167). The PCL increases in length by about 5% menisci forward on the surface. Additionally, the menisci with internal rotation of the joint up to 60° of flexion and follow the tibia during rotation. then decreases in length by 5% to 10% as flexion contin- ues. The PCL is not affected by external rotation in the The tibiofemoral joint is supported by four main liga- joint, maintaining a fairly constant length. It is maximally ments, two collateral and two cruciate. These ligaments strained through 45° to 60° of flexion (167) (Fig. 6-20). assist in maintaining the relative position of the tibia and As with the ACL, the fibers of the PCL participate in dif- femur so that contact is appropriate and at the right time. ferent functions. The posterior fibers are taut in extension, See Figure 6-19 for insertions, actions, and illustration of the anterior fibers are taut in midflexion, and the posterior these ligaments. They are the passive load-carrying struc- fibers are taut in full flexion; however, as a whole, the PCL tures of the joint and serve as a backup to the muscles (101). is taut in maximum knee flexion. On the sides of the joint are the collateral ligaments. Both the cruciate ligaments stabilize, limit rotation, The medial collateral ligament (MCL) is a flat, triangu- and cause sliding of the condyles over the tibia in flex- lar ligament that covers a large portion of the medial side ion. They both also offer some stabilization against varus of the joint. The MCL supports the knee against any val- and valgus forces. In a standing posture, with the tibial gus force (a medially directed force acting on the lateral shaft vertical, the femur is aligned with the tibia and side of the knee) and offers some resistance to both inter- tends to slide posteriorly. A hyperextended position to 9° nal and external rotation (118). It is taut in extension and of flexion is unstable because the femur tilts posteriorly reduces in length by approximately 17% in full flexion and is minimally restricted (101). At a 9° tilt of the tibia, (167). The MCL offers 78% of the total valgus restraint at the femur slides anteriorly to a position where it is more 25° of knee flexion (120). stable and supported by the patella and the quadriceps femoris. The lateral collateral ligament (LCL) is thinner and rounder than the MCL. It offers the main resistance to Another important support structure surrounding the varus force (a lateral force acting on the medial side) at the knee is the joint capsule. One of the largest capsules in the knee. This ligament is also taut in extension and reduces body, it is reinforced by numerous ligaments and muscles, its length by approximately 25% in full flexion (167). The including the MCL, the cruciate ligaments, and the arcu- LCL offers 69% of the varus restraint at 25° of knee flex- ate complex (166). In the front, the capsule forms a sub- ion (120) and offers some support in lateral rotation. stantial pocket that offers a large patellar area and is filled with the infrapatellar fat pad and the infrapatellar bursa. In full extension, the collateral ligaments are assisted by The fat pad offers a stopgap in the anterior compartment tightening of the posteromedial and posterolateral capsules, of the knee. thus making the extended position the most stable (100). Both collaterals are taut in full extension even though the The capsule is lined with the largest synovial membrane anterior portion of the MCL is also stretched in flexion. in the body, which forms embryonically from three sepa- rate pouches (18). In 20% to 60% of the population, a per- The cruciate ligaments are intrinsic, lying inside the manent fold, called a plica, remains in the synovial joint in the intercondylar space. These ligaments control membrane (19). The common location of plica is medial both anteroposterior and rotational motion in the joint. and superior to the patella. It is soft and pliant and passes The anterior cruciate ligament (ACL) provides the pri- over the femoral condyle in flexion and extension. If mary restraint for anterior movement of the tibia relative injured, it can become fibrous and create both resistance to the femur. It accounts for 85% of the total restraint in and pain in motion (19). There are also more than 20 bur- this direction (120). The ACL is 40% longer than its sae in and around the knee, reducing friction between counterpart, the PCL. It elongates by about 7% as the muscle, tendon, and bone (166). knee moves from extension to 90° of flexion and main- tains the same length up through maximum flexion (167). PATELLOFEMORAL JOINT If the joint is internally rotated, the insertion of the ACL moves anteriorly, elongating the ligament slightly more. The second joint in the region of the knee is the With the joint externally rotated, the ACL does not elon- patellofemoral joint, consisting of the articulation of the gate up through 90° of knee flexion but elongates up to patella with the trochlear groove on the femur. The patella 10% from 90° to full flexion (167). Different parts of the is a triangular sesamoid bone encased by the tendons of ACL are taut in different knee positions. The anterior the quadriceps femoris. The primary role of the patella is fibers are taut in extension, the middle fibers are taut in to increase the mechanical advantage of the quadriceps internal rotation, and the posterior fibers are taut in flex- femoris (18). ion. The ACL as a whole is considered to be taut in the extended position (Fig. 6-20).

212 SECTION II Functional Anatomy Lateral Posterior meniscus cruciate ligament Coronary ligament Anterior cruciate (cut) ligament Fibular (lateral) Coronary collateral ligament (cut) ligament Medial B meniscus Tibial (medial) collateral ligament A C Ligament Insertion Action Anterior cruciate Anterior intercondylar area of tibia TO medial Prevents anterior tibial displacement; resists Arcuate surface of lateral condyle extension, internal rotation, flexion Lateral condyle of femur TO head of fibula Reinforces back of capsule Coronary Medial collateral Meniscus TO tibia Holds menisci to tibia Medial epicondyle of femur TO medial condyle Resists valgus forces; taunt in extension; resists Lateral collateral of tibia and medial meniscus internal, external rotation Patellar Lateral epicondyle of femur TO head of fibula Resists varus forces; taut in extension Posterior cruciate Inferior patela TO tibial tuberosity Transfers force from quariceps to tibia Posterior oblique Posterior spine of tibia TO inner condyle of Resists posterior tibial movement; resists flexion Transverse femur and rotation Expansion of semimembranosus muscle Supports posterior, medial capsule Medial meniscus TO lateral meniscus in front Connects menisci to each other FIGURE 6-19 Ligaments of the knee joint shown from the anterior (A), posterior (B), and medial (C) perspective.

CHAPTER 6 Functional Anatomy of the Lower Extremity 213 FIGURE 6-20 The anterior cruciate ligament provides anterior restraint of FIGURE 6-21 The patella increases the mechanical advantage of the the movement of the tibia relative to the femur. The posterior cruciate quadriceps femoris muscle group. The patella has five facets, or articu- ligament offers restraint to posterior movement of the tibia relative to lating surfaces: the superior, inferior, medial, lateral, and odd facets. the femur. The posterior articulating surface of the patella is cov- ered with the thickest cartilage found in any joint in the body (148). A vertical ridge of bone separates the under- side of the patella into medial and lateral facets, each of which can be further divided into superior, middle, and inferior facets. A seventh facet, the odd facet, lies on the far medial side of the patella (166). The structure of the patella and the location of these facets are presented in Figure 6-21. During normal flexion and extension, five of these facets typically make contact with the femur. The patella is connected to the tibial tuberosity via the strong patellar tendon. It is connected to the femur and tibia by small patellofemoral and patellotibial ligaments that are actually thickenings in the extensor retinaculum surrounding the joint (18). Positioning of the patella and alignment of the lower extremity in the frontal plane is determined by measuring the Q-angle (quadriceps angle). Illustrated in Figure 6-22, FIGURE 6-22 The Q-angle is meas- >17° ured between a line from the ante- rior superior iliac spine to the middle of the patella and the projection of a line from the middle of the patella to the tibial tuberosity. Q-angles range from 10° to 14° for males and 15° to 17° for females. Very small Q-angles create a condition known as genu varum, or bowleggedness. Large Q-angles create genu valgrum, or knock-kneed position.

214 SECTION II Functional Anatomy the Q-angle is formed by drawing one line from the ante- TIBIOFIBULAR JOINT rior superior spine of the ilium to the middle of the patella and a second line from the middle of the patella to the tib- The third and final articulation is the small, superior ial tuberosity. The Q-angle forms because the two condyles tibiofibular joint, shown in Figure 6-23. This joint con- sit horizontal on the tibial plateau and because the medial sists of the articulation between the head of the fibula and condyle projects more distally, the femur angles laterally. In the posterolateral and inferior aspect of the tibial condyle. a normal alignment, the hip joint should still be vertically It is a gliding joint moving anteroposteriorly, superiorly, centered over the knee joint even though the anatomical and inferiorly and rotating in response to rotation of the alignment of the femur angles out. The most efficient tibia and the foot (132). The fibula externally rotates and Q-angle for quadriceps femoris function is one close to 10° moves externally and superiorly with dorsiflexion of the of valgus (92). Whereas males typically have Q-angles aver- foot and accepts approximately 16% of the static load aging 10° to 14°, females average 15° to 17°, speculated to applied to the leg (132). be primarily because of their wider pelvic basins (92). However, a recent evaluation of the Q-angle in males and The primary functions of the superior tibiofibular joint females suggests that the positioning of the anterior supe- are to dissipate the torsional stresses applied by the move- rior iliac spine is not significantly positioned more laterally ments of the foot and to attenuate lateral tibial bending. in females, and the differences in values between males and Both the tibiofibular joint and the fibula absorb and con- females are attributable to height differences (59). trol tensile rather than compressive loads applied to the lower extremity. The middle part of the fibula has more The Q-angle represents the valgus stress acting on the ability to withstand tensile forces than any other part of knee, and if it is excessive, many patellofemoral problems the skeleton (132). can develop. Any Q-angle over 17° is considered to be excessive and is termed genu valgum, or knock-knees MOVEMENT CHARACTERISTICS (92). A very small Q-angle constitutes bowleggedness, or genu varum. The function of the knee is complex because of its asym- metrical medial and lateral articulations and the patellar Mediolaterally, the patella should be centered in the mechanics on the front. When flexion is initiated in the trochlear notch, and if the patella deviates medially or lat- closed-chain or weight-bearing position, the femur rolls erally, abnormal stresses can develop on the underside. backward on the tibia and laterally rotates and abducts The vertical position of the patella is determined primarily with respect to the tibia. In an open-chain movement such by the length of the patellar tendon measured from the as kicking, flexion is initiated with movement of the tibia distal end of the patella to the tibia. Patella alta is an align- on the femur, resulting in tibial forward motion, medial ment in which the patella is high and has been associated rotation, and adduction. The opposite occurs in extension with higher levels of patellar subluxations. Patella baja is with the femur rolling forward, medially rotating, and when the patella is lower than normal. adducting in a closed-chain movement and the tibia rolling backward, laterally rotating, and abducting in an FIGURE 6-23 The tibiofibular joint is a small joint between the head of open-chain activity. The femoral contact with the tibia the fibula and the tibial condyle. It moves anteroposteriorly, superiorly, and moves posteriorly during flexion and anteriorly during inferiorly and rotates in response to movements of the tibia or the foot. extension. Through 120° of extension, the anterior move- ment is 40% of the length of the tibial plateau (166). It has also been suggested that after the rolling is complete in the flexion movement that the femur finishes off in maxi- mal flexion by just sliding anteriorly. These movements are illustrated in Figure 6-24. Rotation at the knee is created partly by the greater movement of the lateral condyle on the tibia through almost twice the distance. Rotation can occur only with the joint in some amount of flexion. Thus, there is no rotation in the extended, locked position. Internal tibial rotation also occurs with dorsiflexion and pronation at the foot. Roughly 6° of subtalar motion results in roughly 10° of internal rotation (141). External rotation of the tibia also accompanies plantarflexion and supination of the foot. With 34° of supination, there is a corresponding 58° of external rotation (141). The rotation occurring in the last 20° of extension has been termed the screw-home mechanism. The screw- home mechanism is the point at which the medial and

CHAPTER 6 Functional Anatomy of the Lower Extremity 215 POSTERIOR MEDIAL LATERAL ANTERIOR FIGURE 6-24 A. The movements at the knee joint are flexion and extension and internal and external rotation. B. When the knee flexes, there is an accompanying internal rotation of the tibia on the femur (non–weight bear- ing). In extension, the tibia externally rotates on the femur. C. There are also translatory movements of the femur on the tibial plateau surface. In flexion, the femur rolls and slides posteriorly. lateral condyles are locked to form the close-packed posi- The movement of the patella is most affected by the tion for the knee joint. The screw-home mechanism joint surface and the length of the patellar tendon and moves the tibial tuberosity laterally and produces a minimally affected by the quadriceps femoris. In the first medial shift at the knee. Some of the speculative causes 20° of flexion, the tibia internally rotates and the patella is of the screw-home movement are that the lateral condyle drawn from its lateral position down into the groove, surface is covered first and a rotation occurs to accom- where first contact is made with the inferior facets (166). modate the larger surface of the medial condyle or that The stability offered by the lateral condyle is most impor- the ACL becomes taut just before rotation, forcing rota- tant because most subluxations and dislocations of the tion of the femur on the tibia (149). Finally, it is specu- patella occur in this early range of motion. lated that the cruciate ligaments become taut in early extension and pull the condyles in opposite directions, The patella follows the groove to 90° of flexion, at causing the rotation. The screw-home mechanism is dis- which point contact is made with the superior facets of rupted with injury to the ACL because the tibia moves the patella (Fig. 6-25). At that time, the patella again more anteriorly on the femur. It is not significantly dis- moves laterally over the condyle. If flexion continues to rupted with loss of the PCL, indicating that the ACL is 135°, contact is made with the odd facet (166). In flex- the main controller (149). ion, the linear and translatory movements of the patella The normal range of motion at the knee joint is Flexion >90° approximately 130° to 145° in flexion and 1° to 2° of hyperextension. It has been reported that there is 6° to FIGURE 6-25 When the knee flexes, the patella moves inferiorly and pos- 30° of internal rotation through 90° of flexion at the joint teriorly over two times its length. The patella sits in the groove and is around an axis passing through the medial intercondylar held in place by the lateral condyle of the femur. If the knee continues tubercle of the tibial plateau (78,119). External rotation into flexion past 90°, the patella moves laterally over the condyle until at of the tibia is possible through approximately 45° (75). approximately 135° of flexion, when contact is made with the odd facet. The range of motion in varus or abduction and valgus or adduction is small and in the range of 5°. When the knee flexes, the patella moves distally through a distance more than twice its length, entering the intercondylar notch on the femur (75) (Fig. 6-25). In extension, the patella returns to its resting position high and lateral on the femur, where it is above the trochlear groove and resting on the suprapatellar fat pad. The patella is free to move in the extended position and can be shifted in multiple directions. Patellar movement is restricted in the flexed position because of the increased contact with the femur.

216 SECTION II Functional Anatomy are posterior and inferior, but the patella also has some activation of the vastus medialis muscles occurs in the last angular movements that affect its position. During knee degrees of extension, and the quadriceps muscles contract flexion, the patella also flexes, abducts, and externally equally throughout the range of motion (86). rotates, and these movements reverse in extension (exten- sion, adduction, and internal rotation). Flexion and The only two-joint muscle of the quadriceps femoris extension of the patella occur about a mediolateral axis group, the rectus femoris, does not significantly contribute running through a fixed axis in the distal femur, with flex- to knee extension force unless the hip joint is in a favorable ion representing the upward tilt and extension represent- position. It is limited as an extensor of the knee if the hip ing the downward tilt about this axis. Likewise, patellar is flexed and is facilitated as a knee extensor if the hip joint abduction and adduction involve movement of the patella is extended, lengthening the rectus femoris. In walking and away from and toward from midline in the frontal plane, running, the rectus femoris contributes to the extension respectively. External and internal rotation is rotation of force in the toe-off phase when the thigh is extended. the patella outward and inward about a longitudinal axis, Likewise, in kicking, rectus femoris activity is maximized in respectively (82). the preparatory phase as the thigh is brought back into hyperextension with the leg in flexion. MUSCULAR ACTIONS Flexion of the leg at the knee joint occurs during sup- Knee extension is a very important contributor to the gen- port, when the body lowers toward the ground; however, eration of power in the lower extremity for any form of this downward movement is controlled by the extensors human projection or translation. The musculature produc- so that buckling does not occur. The flexor muscles are ing extension is also used frequently to contract eccentri- very active with the limb off the ground, working fre- cally and decelerate a rapidly flexing knee joint. Fortunately, quently to slow a rapidly extending leg. the quadriceps femoris muscle group, the producer of extension at the knee, is one of the strongest muscle groups The major muscle group that contributes to knee flex- in the body; it may be as much as three times stronger than ion is the hamstrings, consisting of the lateral biceps its antagonistic muscle group, the hamstrings, because of its femoris and the medial semimembranosus and semitendi- involvement in negatively accelerating the leg and continu- nosus (see Fig. 6-26). The action of the hamstrings can be ously contracting against gravity (75). quite complex because they are two-joint muscles that work to extend the hip. The hamstrings work with the The quadriceps femoris is a muscle group that consists ACL to resist anterior tibial displacement. They are also of the rectus femoris and vastus intermedius forming the rotators of the knee joint because of their insertions on the middle part of the muscle group, the vastus lateralis on the sides of the knee. As flexors, the hamstrings can generate lateral side, and the vastus medialis on the medial side (19). the greatest force from a flexion position of 90° (121). The specific insertions, actions, and nerve supply are pre- sented in Figure 6-26. Flexion strength diminishes with extension because of an acute tendon angle that reduces the mechanical advan- The quadriceps femoris connect to the tibial tuberosity tage. At full extension, flexion strength is reduced by 50% via the patellar tendon and contribute somewhat to the sta- compared with 90° of flexion (121). bility of the patella. As a muscle group, they also pull the menisci anteriorly in extension via the meniscopatellar lig- The lateral hamstring, the biceps femoris, has two ament. When they contract, they also reduce the strain in heads connecting on the lateral side of the knee and offer- the MCL and work with the PCL to prevent posterior dis- ing lateral support to the joint. The biceps femoris also placement of the tibia. They are antagonistic to the ACL. produces external rotation of the lower leg. The largest and strongest of the quadriceps femoris is The semimembranosus bolsters the posterior and the vastus lateralis, a muscle applying lateral force to the medial capsule. In flexion, it pulls the meniscus posteriorly patella. Pulling medially is the vastus medialis. The vastus (166). This medial hamstring also contributes to the pro- medialis has two portions referred to as the vastus medi- duction of internal rotation in the joint. The other medial alis longus and the vastus medialis oblique, and the hamstring, the semitendinosus, is part of the pes anseri- boundary of these two portions of the vastus medialis is nus muscular attachment on the medial surface of the located at the medial rim of the patella . The direction of tibia. It is the most effective flexor of the pes anserinus the muscle fibers in the more proximal vastus medialis muscle group, contributing 47% to the flexion force longus runs more vertical, and the fibers of the lower vas- (166). The semitendinosus works with both the ACL and tus medialis oblique run more horizontal (124). Although the MCL in supporting the knee joint. It also contributes the vastus medialis as a whole is an extensor of the knee, to the generation of internal rotation. the vastus medialis oblique is also a medial stabilizer of the patella (166). The hamstrings operate most effectively as knee flexors from a position of hip flexion by increasing the length and It has been noted in the literature that the vastus medi- tension in the muscle group. If the hamstrings become alis was selectively activated in the last few degrees of exten- tight, they offer greater resistance to extension of the knee sion. This has been proved not to be true. No selective joint by the quadriceps femoris. This imposes a greater workload on the quadriceps femoris muscle group. The two remaining pes anserinus muscles, the sarto- rius and the gracilis, also contribute 19% and 34% to the

CHAPTER 6 Functional Anatomy of the Lower Extremity 217 flexion strength, respectively (121). The popliteus is a weak Internal rotation of the tibia is produced by the medial flexor that supports the PCL in deep flexion and draws the muscles: sartorius, gracilis, semitendinosus, semimembra- meniscus posteriorly. Finally, the two-joint gastrocnemius nosus, and popliteus (see Fig. 6-26). Internal rotation contributes to knee flexion, especially when the foot is in force is greatest at 90° of knee flexion and decreases by the neutral or dorsiflexed position. 59% at full extension (125,126). The internal rotation Psoas major Iliacus Inguinal ligament Iliopsoas Sartorius Tensor muscle of fascia lata Pectineus Adductor longus Vastus lateralis Iliotibial tract (band) Gracilis Rectus femoris Vastus medialis AB Semi- tendinosus Biceps femoris Semi- membranosus C DE FIGURE 6-26 Muscles acting on the knee joint. Shown are the anterior thigh muscles (A) with corresponding surface anatomy (B), the posterior thigh muscles (C) and posterior (D) and lateral (E) surface anatomy, and other supporting anterior and posterior muscles (F) (next page).

218 SECTION II Functional Anatomy F Muscle Insertion Nerve Supply Flexion Extension Pronation Supination Biceps femoris Tibial, peroneal portion of PM PM Gastrocnemius Ischial tuberosity TO lateral sciatic nerve; L5, S1–S3 Gracilis condyle of tibia, head of fibula Tibial nerve; S1, S2 Asst Popliteus Rectus femoris Medial, lateral condyles of femur Anterior obturator nerve; Asst PM Sartorius TO calcaneus L3, L4 Semimembranous Asst PM Semitendinosus Inferior rami of pubis TO medial Tibial nerve Vastus intermedius tibial (pes anserinus) Vastus lateralis Vastus medialis Lateral condyle of femur TO proximal tibia Anterior inferior iliac spine TO Femoral nerve; L2–L4 PM patella, tibial tuberosity Anterior superior iliac spine TO Femoral nerve; L2, L3 Asst PM medial tibia (pes anserinus) Ischial tuberosity TO medial Tibial portion of sciatic PM PM condyle of tibia nerve: L5, S1, S2 PM PM Ischial tuberosity TO medial Tibial portion of sciatic PM tibia (pes anserinus) nerve: L4, S1, S2 Anterior lateral femur TO Femoral nerve; L2–L4 patella, tibial tuberosity Intertrochanteric line; linea aspera Femoral nerve; L2–L4 PM TO patella, tibial tuberosity PM Linea apsera; trochanteric line Femoral nerve; L2–L4 TO patella, tibial tuberosity FIGURE 6-26 (CONTINUED)

CHAPTER 6 Functional Anatomy of the Lower Extremity 219 force can be increased by 50% if it is preceded by 15° of to construct a hamstring-to-quadriceps ratio. A generally external rotation. Of the three pes anserinus muscles, the acceptable ratio is 0.5, with the hamstrings at least half as sartorius and the gracilis are the most effective rotators, strong as the quadriceps femoris. It has been suggested accounting for 34% and 40% of the pes anserinus force in that anything below this ratio indicates a strength imbal- rotation (121). The semitendinosus contributes 26% of ance between the quadriceps femoris and the hamstrings the pes anserinus rotation force. The pes anserinus muscle that predisposes one to injury. Caution must be observed group also contributes significantly to medial knee stabi- when using this ratio because it applies only to slow, iso- lization. Only one muscle, the biceps femoris, contributes kinetic testing speeds. significantly to the generation of external rotation of the tibia. Both internal and external rotation are necessary At faster testing speeds, when the limbs move through movements associated with function of the knee joint. 200° to 300°/sec, the ratio approaches 1 because the effi- ciency of the quadriceps femoris decreases at higher COMBINED MOVEMENTS OF THE HIP speeds. Even at the isometric testing level, the hamstring- AND KNEE to-quadriceps ratio is 0.7. Thus, a ratio of 0.5 between the hamstrings and the quadriceps femoris is not acceptable at Many lower extremity movements require coordinated fast speeds and indicates a strength imbalance between the actions at the hip and knee joint, and this is complicated two groups, but at a slower speed, it would not indicate by the number of two-joint muscles that span both joints. an imbalance (111). Coactivation of both monarticular and biarticular ago- nists and antagonists is required to produce motion with Internal and external rotation torques are both greatest appropriate direction and force. This coordination is with the knee flexed to 90° because a greater range of rota- required for uninterrupted transitions between extension tion motion can be achieved in that position. Internal rota- and flexion. For example, in walking, coactivation of the tion strength increases by 50% from 45° of knee flexion to gluteus maximus (monoarticular) and the rectus femoris 90° (126). The position of the hip joint also influences (knee extensor) is necessary to generate forces for the internal rotation torque, with the greatest strength devel- simultaneous extension of both the hip and the knee oped at 120° of hip flexion, at which point the gracilis and (144,163,172). Additionally, coactivation of the iliopsoas the hamstrings are most efficient (125). At low hip flexion and the hamstrings facilitate knee flexion by cancelling out angles and in the neutral position, the sartorius is the most the motion at the hip joint. effective lateral rotator. Peak rotation torques occur in the first 5° to 10° of rotation. The internal rotation torque is Positioning of the hip changes the effectiveness of the greater than the external rotation torque (126). muscles acting at the knee joint. For example, changing the hip joint angle has a large effect on increasing the CONDITIONING OF THE KNEE JOINT moment arm of the biceps femoris. It is the opposite for MUSCLES the rectus femoris, which is more influenced by a change in the knee angle (164). The range of motion at the knee The extensors of the leg are easy to exercise because they also changes with a change in hip positioning. For exam- are commonly used both to lower and to raise the body. ple, the knee flexes through approximately 145° with the Examples of stretching and strengthening exercises for the thigh flexed and 120° with the thigh hyperextended (75). extensors are presented in Figure 6-27. The squat is used This difference in range is attributable to the length–ten- to strengthen the quadriceps femoris. When one lowers sion relationship in the hamstring muscle group. into a squat, the force coming through the joint, directed vertically in the standing position, is partially directed STRENGTH OF THE KNEE JOINT MUSCLES across the joint, creating a shear force. This shear force increases as knee flexion increases. Thus, in a deep squat The extensors at the knee joint are usually stronger than position, most of the original compressive force is directed the flexors throughout the range of motion. Peak exten- posteriorly, creating a shear force. With the ligaments and sion strength is achieved at 50° to 70° of knee flexion muscles unable to offer much protection in the posterior (116). The position of maximum strength varies with the direction at the full squat position, this is considered a vul- speed of movement. For example, if the movement is slow, nerable position. This position of maximum knee flexion peak extension strength occurs in the first 20° of knee is contraindicated for beginner and unconditioned lifters. extension from the 90° flexed position. Flexion strength is greatest in the first 20° to 30° of flexion from the An experienced and conditioned lifter who has strong extended position (127). This position also fluctuates with musculature and uses good technique at the bottom of the speed of movement. Greater knee flexion torques can the lift will most likely avoid any injury when in this posi- be obtained if the hips are flexed because the hamstring tion. Good technique involves control over the speed of length–tension relationship is improved. descent and proper segmental positioning. For example, if the trunk is in too much flexion, the low back will be It is common in sports medicine to evaluate the isoki- excessively loaded and the hamstrings will perform more netic strength of the quadriceps femoris and the hamstrings of the work and the quadriceps femoris less, focusing con- trol on the posterior side.

220 SECTION II Functional Anatomy Muscle Group Sample Stretching Exercise Sample Strengthening Exercise Other Exercises Knee flexors Leg curl Stability ball curls Squats Knee extensors Leg extension Leg press Lunge Squat FIGURE 6-27 Sample stretching and strengthening exercises for selected muscle groups.

CHAPTER 6 Functional Anatomy of the Lower Extremity 221 The quadriceps femoris group may also be exercised in the rotators in a position of maximum effectiveness. an open-chain activity, as in a leg extension machine. Toeing in the foot contracts the internal rotators and Starting from 90° of flexion, one can exert considerable stretches the external rotators. Different levels of resist- force because the quadriceps femoris muscles are very effi- ance can be added to this exercise through the use of elas- cient throughout the early parts of the extension action. tic bands or cables. Near full extension, the quadriceps femoris muscles become inefficient and must exert greater force to move There continues to be debate over the use of closed- the same load. Thus, quadriceps activity in an open-chain chain versus open-chain exercises for the rehabilitation leg extension is higher near full extension in the squat, but after ACL repair at the knee joint. Some surgeons and there is more activity in the quadriceps near full flexion at physical therapists advocate using only closed-chain exer- the bottom of the squat (49). cises (28). The reason behind this is that closed-chain exercises have been shown to produce significantly less The terminal extension exercise is good for individuals posterior shear force at all angles and less anterior shear who have patellar pain because the quadriceps femoris force at most angles (91). This occurs because of higher work hard with minimal patellofemoral compression compressive loads and muscular coactivation. Recently, force. This kind of exercise should be avoided, however, there has been added support for the inclusion of open- in early rehabilitation of an ACL injury because the ante- chain exercises in an ACL rehabilitation protocol (15). rior shear force is so large in this position. To minimize Knee extension exercises at angles of 60° to 90° have been the stress on the ACLϭ, no knee extension exercise shown to be very effective for isolation of quadriceps and should be used at any angle less than 64° (169). do not negatively influence healing of the ACL graft (51). Coactivation from the hamstrings increases as the knee Studies have shown that anterior tibial translation is less in reaches full extension, and this also minimizes the stress a closed-chain exercise (81), giving support for their use. on the ACL by preventing anterior displacement (41). In other studies, however, maximum ACL strains have However, any knee extension exercise for individuals with been shown to be similar in both open- and closed-chain ACL injuries should be done from a position of consider- exercises (16), supporting the inclusion of both types of able knee flexion. Also, the terminal extension exercise exercise in the rehabilitation protocol. does not selectively exercise the medial quadriceps more than the lateral quadriceps (45). Extension exercises for individuals with patellofemoral pain also vary between closed- and open–chain exercises. The flexors of the knee are not actively recruited in the In the open-chain knee extension, the patellofemoral force performance of a flexion action with gravity because the increases with extension with the quadriceps force high quadriceps femoris muscles control the flexion action via from 90° to 25° of knee flexion (45). In a closed-chain eccentric muscle activity. Fortunately, the hamstrings are squat, it is opposite, with the patellofemoral force zero at extensors of the hip as well as flexors of the knee joint. full extension and increasing with increases in knee flexion Thus, they are active during a squat exercise by virtue of and with load (14). their influence at the hip because hip flexion in lowering is controlled eccentrically by the hip extensors. The squat INJURY POTENTIAL OF THE KNEE JOINT generates twice as much activity in the hamstrings as a leg press on a machine (49). If it were not for the hamstrings’ The knee joint is a frequently injured area of the body, role as extensors at the hip, the hamstrings group would depending on the sport, accounting for 25% to 70% of be considerably weaker than the quadriceps femoris. reported injuries. In a 10-year study of athletic knee injuries in which 7769 injuries related to the knee joint The knee flexors are best isolated and exercised in a were documented, the majority of the knee injuries seated position using a leg curl apparatus. The seated posi- occurred in males and in the age group of 20 to 29 years tion places the hip in flexion, thus optimizing their per- (94). Activities associated with most of the injuries were formance. The knee flexors, especially the hamstrings and soccer and skiing. the pes anserinus muscles, are important for knee stability because they control much of the rotation at the knee. As The cause of an injury to the knee can often be related presented earlier in this chapter, the hamstrings should be to poor conditioning or training or to an alignment prob- half as strong as the quadriceps femoris groups for slow lem in the lower extremity. Injuries in the knee have been speeds and should be as strong as the quadriceps femoris attributable to hindfoot and forefoot varus or valgus, tib- group at fast speeds. It is also important to maintain flex- ial or femoral varus or valgus, limb length differences, ibility in the hamstrings because if they are tight, the deficits in flexibility, strength imbalances between agonists quadriceps femoris muscles must work harder and the and antagonists, and improper technique or training. pelvis will develop an irregular posture and function. A number of knee injuries are associated with running The rotators of the knee, because they are all flexor or jogging because the knee and the lower extremity are muscles, are exercised along with the flexion movements. subjected to a force equivalent to approximately three If the rotators are to be selectively stretched or strength- times body weight at every foot contact. It is clear that if ened as they perform the rotation, it is best to do the exer- 1500 foot contacts are made per mile of running, the cise from a seated position with the knee flexed to 90° and potential for injury is high.

222 SECTION II Functional Anatomy Traumatic injuries to the knee usually involve the liga- The LCL is injured upon receipt of a lateral force that ments. Ligaments are injured as a result of application of is usually applied when the foot is fixed and the knee is in a force causing a twisting action of the knee. High-friction slight flexion (35). Injury to the MCL or LCL creates or uneven surfaces are usually associated with increased medial or lateral planar instabilities, respectively. A force- ligamentous injury. Any movement fixing the foot while ful varus or valgus force can also create a distal femoral the body continues to move forward, such as often occurs epiphysitis as the collateral ligaments forcefully pull on in skiing, will likely produce a ligament sprain or tear. their attachment site (84). Simply, any turn on a weight-bearing limb leaves the knee vulnerable to ligamentous injury. Damage to the menisci occurs much the same way as lig- ament damage. The menisci can be torn through compres- The ACL is the most common site of ligament injuries, sion associated with a twisting action in a weight-bearing which are usually caused by a twisting action while the position. They can also be torn in kicking and other violent knee is flexed, internally rotated, and in a valgus position extension actions. Tearing the meniscus by compression is a while supporting weight. It can also be damaged with a result of the femur grinding into the tibia and ripping the forced hyperextension of the knee. If the trunk and thigh menisci. A meniscal tear in rapid extension is a result of the rotate over a lower extremity while supporting the body’s meniscus getting caught and torn as the femur moves rap- weight, the ACL can be sprained or torn because the lat- idly forward on the tibia. eral femoral condyle moves posteriorly in external rotation (61). The quadriceps can also be responsible for ACL Tears to the medial meniscus are usually incurred dur- sprain by producing anterior displacement of the tibia ing moves incorporating valgus, knee flexion, and external when eccentrically controlling knee motion when there is rotation in the supported limb or when the knee is hyper- limited hamstring coactivation (32). If the hamstrings are flexed (148). Lateral meniscus tears have been associated co-contracting, they resist the anterior translation of the with a forced axial movement in the flexed position; a tibia. Examples from sport in which this ligament is often forced lateral movement with impact on the knee in exten- injured are skiers catching the edge of the ski; a football sion; a forceful rotational movement; a movement incor- player being blocked from the side; a basketball player porating varus, flexion, and internal rotation of the landing off balance from a jump, cutting, or rapid decel- support limb; and the hyperflexed position (148). eration; and a gymnast landing off balance from a dis- mount (125). Many injuries to the knee are a result of less traumatic noncontact forces. Muscle strains to the quadriceps femoris Loss of the ACL creates valgus laxity and single-plane or the hamstrings muscle groups occur frequently. Strain to or rotatory instability (30). Whereas planar instability is the quadriceps femoris usually involves the rectus femoris usually anterior, rotatory instabilities can occur in a variety because it can be placed in a very lengthened position with of directions, depending on the other structures injured hip hyperextension and knee flexion. It is commonly (22). Instability created by an inefficient or missing ACL injured in a kicking action, especially if the kick is mist- places added stress on the secondary stabilizers of the imed. A hamstring strain is usually associated with inflexi- knee, such as the capsule, collateral ligaments, and iliotib- bility in the hamstrings or a stronger quadriceps femoris ial band. There is an accompanying deficit in quadriceps that pulls the hamstrings into a lengthened position. femoris musculature. The “side effects” of an ACL injury Sprinting when the runner is not in condition to handle are often more debilitating in the long run. the stresses of sprinting can lead to a hamstring strain. Injury to the PCL is less common than to the ACL. On the lateral side of the knee is the iliotibial band, The PCL is injured by receiving an anterior blow to a which is frequently irritated as the band moves over the flexed or hyperextended knee or by forcing the knee into lateral epicondyle of the femur in flexion and extension. external rotation when it is flexed and supporting weight. Iliotibial band syndrome is seen in individuals who run on Hitting the tibia up against the dashboard in a car crash or cambered roads, specifically affecting the downhill limb. It falling on a bent knee in soccer or football can also dam- has also been identified in individuals who run more than age the PCL. Damage to the PCL results in anterior or 5 miles per session, in stair climbing and downhill run- posterior planar instability. ning, and in individuals who have a varum alignment in the lower extremity (58). Medial knee pain can be associ- The collateral ligaments on the side are injured upon ated with many structures, such as tendinitis of the pes receipt of a force applied to the side of the joint. The anserinus muscle attachment and irritation of the semi- MCL, torn in an application of force in the direction of membranosus, parapatellar, or pes bursae (58). the medial side of the joint, can also sprain or tear with a violent external rotation or tibial varus (35,151). The Posterior knee pain is likely associated with popliteus MCL is typically injured when the foot is fixed and slightly tendinitis, which causes posterior lateral pain. This is often flexed. A change in direction with the person moving brought on by hill running. Posterior pain can also be away from the support limb, as when running the bases in associated with strain or tendinitis of the gastrocnemius baseball, is a common event leading to an MCL injury. muscle insertion or by collection of fluid in the bursae, The MCL is usually injured at the proximal end, resulting called a Baker’s or popliteal cyst. in tenderness on the femoral side of the knee joint. Anterior knee pain accounts for most overuse injuries to the knee, especially in women. Patellofemoral pain

CHAPTER 6 Functional Anatomy of the Lower Extremity 223 syndrome is pain around the patella and is often seen in Most of the motion in the foot occurs at three of the syn- individuals who exhibit valgum alignments or femoral ovial joints: the talocrural, the subtalar, and the midtarsal anteversion in the extremity (34). Patellofemoral pain is joints (103). The foot moves in three planes, with most of aggravated by going down hills or stairs or squatting. the motion occurring in the rear foot. Stress on the patella is associated with a greater Q-angle The foot contributes significantly to the function of the because of increased stress on the patella. Patellar injury whole lower limb. The foot supports the weight of the may be caused by abnormal tracking, which in addition to body in both standing and locomotion. The foot must be an increased Q-angle, can be created by a functional short a loose adapter to uneven surfaces at contact. Also, upon leg, tight hamstrings, tight gastrocnemius, a long patellar contact with the ground, it serves as a shock absorber, tendon (termed patella alta), a short patellar tendon attenuating the large forces resulting from ground con- (termed patella baja), a tight lateral retinaculum or ili- tact. Late in the support phase, it must be a rigid lever for otibial band, or excessive pronation at the foot. effective propulsion. Finally, when the foot is fixed during stance, it must absorb the rotation of the lower extremity. Some patellofemoral pain syndromes are associated These functions of the foot all occur during a closed with cartilage destruction, in which the cartilage under- kinetic chain as it is receiving frictional and reaction forces neath the patella becomes soft and fibrillated. This condi- from the ground or another surface (103). tion is known as chondromalacia patellae. Patellar pain similar to that of patellar pain syndrome or chondromala- The foot can be divided into three regions. The rear- cia patellae is also seen with medial retinaculitis, in which foot, consisting of the talus and the calcaneus; the mid- the medial retinaculum is irritated in running (166). foot, including the navicular, cuneiforms, and the cuboid; and the forefoot, containing the metatarsals and the pha- A subluxated or dislocated patella is common in indi- langes. These structures are shown in Figure 6-28. viduals with predisposing factors. These are patella alta, ligamentous laxity, a small Q-angle with outfacing patella, TALOCRURAL JOINT external tibial torsion, and an enlarged fat pad with patella alta (166). Dislocation of the patella may be congenital. The proximal joint of the foot is the talocrural joint, or The dislocation occurs in flexion as a result of a faulty knee ankle joint (Fig. 6-28). It is a uniaxial hinge joint formed extension mechanism. by the tibia and fibula (tibiofibular joint) and the tibia and talus (tibiotalar joint). This joint is designed for sta- The attachment site of the quadriceps femoris to the bility rather than mobility. The ankle is stable when large tibia at the tibial tuberosity is another site for injury and forces are absorbed through the limb, when stopping and the development of anterior pain. The tensile force of the turning, and in many of the lower limb movements per- quadriceps femoris can create tendinitis at this insertion formed on a daily basis. If any of the anatomical support site. This is commonly seen in athletes who do vigorous structures around the ankle joint are injured, however, the jumping, such as in volleyball, basketball, and track and joint can become very unstable (61). field (106). In children age 8 to 15 years, a tibial tubercle epiphysitis can develop. This is referred to as Osgood- The tibia and fibula form a deep socket for the trochlea Schlatter disease. This disease is an avulsion fracture of of the talus, creating a mortise. The medial side of the mor- the growing tibial tuberosity that can also avulse the epi- tise is the inner side of the medial malleolus, a projection physis. Bony growths can develop on the site. The cause on the distal end of the tibia. On the lateral side is the inner of both of these conditions is overuse of the extensor surface of the lateral malleolus, a distal projection on the mechanism (106). fibula. The lateral malleolus projects more distally than the medial malleolus and protects the lateral ligaments of Overuse of the extensor mechanism can also cause irri- the ankle. It also acts as a bulwark against any lateral dis- tation of the plica. Plica injury can also result from a direct placement. Because the lateral malleolus projects more blow, a valgus rotary force applied to the knee, or weak- distally, it is also more susceptible to fracture with an ness in the vastus medialis oblique. The plica become inversion sprain to the lateral ankle. thick, inelastic, and fibrous with injury, making it difficult to sit for long periods and creating pain on the superior The tibia and fibula fit snugly over the trochlea of the knee (19). The medial patella may snap and catch during talus, a bone that is wider anteriorly than posteriorly (75). flexion and extension with injury to the plica. The difference in width of the talus allows for some abduction and adduction of the foot. The close-packed The Ankle and Foot position for the ankle is the dorsiflexed position when the talus is wedged in at its widest spot. The foot and ankle make up a complex anatomical struc- ture consisting of 26 irregularly shaped bones, 30 synovial The ankle has excellent ligamentous support on the joints, more than 100 ligaments, and 30 muscles acting on medial and lateral sides. The location and actions of the the segments. All of these joints must interact harmo- ligaments are presented in Figure 6-29. The ligaments niously and in combination to achieve a smooth motion. that surround the ankle limit plantarflexion and dorsiflex- ion, anterior and posterior movement of the foot, tilting of the talus, and inversion and eversion (156). Each of the

224 SECTION II Functional Anatomy Calcaneus Lateral tubercle of talus Medial tubercle Facet for Trochlear surface of talus lateral malleolus Facet of fibula Cuboid Neck of talus Head of talus Tuberosity Navicular Lateral cuneiform Base V IV Intermediate cuneiform III Medial cuneiform Metatarsals Body II I Head Proximal A Phalanges Middle Distal Site for attachment Talus LATERAL MEDIAL of Achilles tendon Navicular Cuneiforms Phalanges Calcaneus Cuboid Metatarsals BC FIGURE 6-28 Thirty joints in the foot work in combination to produce the movements of the rear foot, mid- foot, and forefoot. The subtalar and midtarsal joints contribute to pronation and supination. The intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal joints contribute to movements of the forefoot and the toes. Joints are shown from the superior (A), lateral (B), and posterior (C) view. lateral ligaments has a specific role in stabilizing the ankle The axis of rotation for the ankle joint is a line between depending on the position of the foot (64). the two malleoli, running oblique to the tibia and not in line with the body (33). Dorsiflexion occurs at the ankle The stability of the ankle depends on the orientation of joint as the foot moves toward the leg (e.g., when lifting the ligaments, the type of loading, and the position of the the toes and forefoot off the floor) or as the leg moves ankle at the time of stress. The lateral side of the ankle toward the foot (e.g., in lowering down with the foot flat joint is more susceptible to injury, accounting for 85% of on the floor). These actions are illustrated in Figure 6-30. ankle sprains (156).

CHAPTER 6 Functional Anatomy of the Lower Extremity 225 Ligament Insertion Action Anterior talofibular Lateral malleolus TO neck of talus Limits anterior displacement of foot or talar Anterior talotibial Anterior margin of tibia TO front margin on talus tilt; limits plantarflextion and inversion Calcaneocuboid Calcaneofibular Limits plantarflexion and abduction of foot Calcaneus TO cuboid on dorsal surface Limits inversion of foot Lateral malleolus TO tubercle on outer calcaneus Resists backward displacement of foot; resists inversion Deltoid Medial malleolus TO talus, navicular, calcaneus Resists valgus forces to ankle; limits plantarflexion, Dorsal (tarsometatarsal) dorsiflexion, eversion, abduction of foot Tarsals TO metatarsals Dorsal calcaneocuboid Supports arch; maintains relationship between Dorsal talonavicular Calcaneus TO cuboid on dorsal side tarsals and metatarsal Interosseous (intertarsal) Neck of talus TO superior surface of navicular Connects adjacent tarsals Limits inversion Supports talonavicular joint; limits inversion Supports arch of foot, intertarsal joints Interosseous (talocalcaneal) Undersurface of talus TO upper surface of Limits pronation, supination, abduction, Plantar calcaneocuboid calcaneus adduction, dorsiflextion, plantarflexion Plantar calcaneonavicular Supports arch Undersurface of calcaneus TO undersurface of cuboid Supports arch; limits abduction Anterior margin of calcaneus TO undersurface on navicular Posterior talofibular Inner, back lateral malleolus TO posterior Limits plantarflexion, dorsiflexion, inversion; surfacce of talus supports lateral ankle Posterior talotibial Tibial TO talus behind articulating facet Limits planatarflexion; supports medial ankle Talocalcaneal Connecting ant./posterior, medial, lateral talus Supports subtalar joint TO calcaneus FIGURE 6-29 Ligaments of the foot and ankle. SUBTALAR JOINT bearing bones in the foot and form the hindfoot. The talus links the tibia and fibula to the foot and is called the keystone Moving distally from the talocrural joint is the subtalar, or of the foot. No muscles attach to the talus. The calcaneus talocalcaneal, joint, which consists of the articulation provides a moment arm for the Achilles tendon and must between the talus and the calcaneus. All of the joints in the accommodate large impact loads at heel strike and high ten- foot, including the subtalar joint, are shown in Figure 6-28. sile forces from the gastrocnemius and soleus muscles. The talus and the calcaneus are the largest of the weight-

226 SECTION II Functional Anatomy FIGURE 6-30 Plantarflexion (PF) and dorsiflexion (DF) occur about a mediolateral axis running through the ankle joint. The range of motion for plantarflexion and dorsiflexion is approximately 50° and 20°, respectively. Plantarflexion and dorsiflexion can be produced with the foot moving on a fixed tibia or with the tibia moving on a fixed foot. The talus articulates with the calcaneus at three sites, The axis of rotation for the subtalar joint runs obliquely anteriorly, posteriorly, and medially, where the convex sur- from the posterior lateral plantar surface to the anterior face of the talus fits into a concave surface on the calcaneus. dorsal medial surface of the talus (Fig. 6-31). It is tilted The subtalar joint is supported by five short and powerful vertically 41° to 45° from the horizontal axis in the sagit- ligaments that resist severe stresses in lower extremity tal plane and is slanted 16° to 23° medially from the lon- movements. The location and action of these ligaments are gitudinal axis of the tibia in the frontal plane (152). presented in Figure 6-29. The ligaments that support the Because the axis of the subtalar joint is oblique through talus limit the motions of the subtalar joint. the sagittal, frontal, and transverse planes of the foot, tri- planar motion can occur. FIGURE 6-31 The axis of rotation for the subtalar joint runs diagonally from the posterolateral plantar surface to the anteromedial dorsal sur- The triplanar movements at the subtalar joint are face. The axis is approximately 42° in the sagittal plane (top) and 16° in termed pronation and supination. Pronation, occurring in the transverse plane. The solid line bisects the posterior surface of the an open-chain system with the foot off the ground, con- calcaneus and the distal anteromedial corner of the calcaneus; the sists of calcaneal eversion, abduction, and dorsiflexion dashed line bisects the talus. (146). Eversion is the movement in the frontal plane in which the lateral border of the foot moves toward the leg in non–weight bearing or the leg moves toward the foot in weight bearing (Fig. 6-32). The transverse plane move- ment is abduction, or pointing the toes out. It occurs with external rotation of the foot on the leg and lateral move- ment of the calcaneus in the non–weight-bearing position or internal rotation of the leg with respect to the calcaneus and medial movement of the talus in weight bearing. The sagittal plane movement of dorsiflexion occurs as the cal- caneus moves up on the talus in non–weight bearing or as the talus moves down on the calcaneus in weight bearing. An illustration of differences in subtalar movements between open- and closed-chain positioning is shown in Figure 6-32. Supination is just the opposite of pronation, with cal- caneal inversion, adduction, and plantarflexion in the non–weight-bearing position and calcaneal inversion and talar abduction and dorsiflexion in the weight-bearing position (102). The frontal plane movement of inversion occurs as the medial border of the foot moves toward the medial leg in non–weight bearing or as the medial aspect of the leg moves toward the medial foot in weight bearing,

CHAPTER 6 Functional Anatomy of the Lower Extremity 227 Right foot Pronation Neutral Supination Right foot FIGURE 6-32 Top. With the foot off Pronation Supination the ground, the foot moves on a fixed tibia, and the subtalar move- ment of pronation is produced by eversion, abduction, and dorsiflex- ion. Supination in the open chain is produced by inversion, adduction, and plantarflexion. Bottom. In a closed kinetic chain with the foot on the ground, much of the pronation and supination are produced by the weight of the body acting on the talus. In this weight-bearing posi- tion, the tibia moves on the talus to produce pronation and supination. as the calcaneus lies on the lateral surface. In the transverse A second function of the subtalar joint is shock absorp- plane, adduction, or toeing-in, occurs as the foot internally tion. This may also be accomplished by pronation. The sub- rotates on the leg in non–weight bearing, and the calcaneus talar movements also allow the tibia to rotate internally faster moves medially or the leg externally rotates on the foot in than the femur, facilitating unlocking at the knee joint. weight bearing and the talus moves laterally. The plan- tarflexion movements in the sagittal plane occur as the MIDTARSAL JOINT calcaneus moves distally while non–weight bearing or as the talus moves proximally while weight bearing. Of the remaining articulations in the foot, the midtarsal, or transverse tarsal, joint has the greatest functional signif- The prime function of the subtalar joint is to absorb the icance (Fig. 6-28). It actually consists of two joints, the rotation of the lower extremity during the support phase calcaneocuboid joint on the lateral side and the talonav- of gait. With the foot fixed on the surface and the femur icular joint on the medial side of the foot. In combina- and tibia rotating internally at the beginning of stance and tion, they form an S-shaped joint with two axes, oblique externally at the end of stance, the subtalar joint absorbs and longitudinal (152). Five ligaments support this region the rotation through the opposite actions of pronation of the foot (see Fig. 6-29). Motion at these two joints and supination (72). Pronation is a combination of dorsi- contributes to the inversion and eversion, abduction and flexion, abduction, and eversion, and supination is a com- adduction, and dorsiflexion and plantarflexion at the sub- bination of plantarflexion, adduction, and inversion. The talar and ankle joints. subtalar joint absorbs rotation by acting as a mitered hinge, allowing the tibia to rotate on a weight-bearing Movement at the midtarsal joint depends on the subta- foot (160). Inversion and eversion are also used as correc- lar joint position. When the subtalar joint is in pronation, tive motions in postural adjustments to keep the foot sta- the two axes of the midtarsal joint are parallel, which ble under the center of gravity (160). unlocks the joint, creating hypermobility in the foot (119).

228 SECTION II Functional Anatomy This allows the foot to be very mobile in absorbing the vertical axis of the heel in normal forefoot alignment. This shock of contact with the ground and also in adapting to is the neutral position for the forefoot (Fig. 6-34). If the uneven surfaces. When the axes are parallel, the forefoot is plane is tilted so that the medial side lifts, it is termed fore- also allowed to flex freely and extend with respect to the foot supination or varus (72). If the medial side drops rear foot. The motion at the midtarsal joint is unrestricted below the neutral plane, it is termed forefoot pronation or from heel strike to foot flat as the foot bends toward the valgus. Forefoot valgus is not as common as forefoot surface. varus (Fig. 6-34). Also, if the first metatarsal is below the plane of the adjacent metatarsal heads, it is considered to During supination of the subtalar joint, the two axes run be a plantarflexed first ray and is commonly associated through the midtarsal joint converge. This locks in the joint, with high-arched feet (72). creating rigidity in the foot necessary for efficient force appli- cation during the later stages of stance (119). The midtarsal The base of the metatarsals is wedge shaped, forming a joint becomes rigid and more stable from foot flat to toe-off mediolateral or transverse arch across the foot. The tar- in gait as the foot supinates. It is usually stabilized, creating sometatarsal articulations are gliding or planar joints a rigid lever, at 70% of the stance phase (102). At this time, allowing limited motion between the cuneiforms and the there is also a greater load on the midtarsal joint, making first, second, and third metatarsals and the cuboid and the the articulation between the talus and the navicular more fourth and fifth metatarsals (75). stable. Figure 6-33 depicts these actions. The tarsometatarsal joint movements change the OTHER ARTICULATIONS OF THE FOOT shape of the arch. When the first metatarsal flexes and abducts as the fifth metatarsal flexes and adducts, the arch The other articulations in the midfoot, the intertarsal artic- deepens, or increases in curvature. Likewise, if the first ulations, between the cuneiforms and the navicular and metatarsal extends and adducts and the fifth metatarsal cuboid and intercuneiform, are gliding joints (Fig. 6-28). extends and abducts, the arch flattens. At the articulation between the cuneiforms and the navicu- lar and cuboid, small amounts of gliding and rotation are Flexion and extension at the tarsometatarsal articula- allowed (75). tions also contribute to inversion and eversion of the foot. Greater movement is allowed between the first metatarsal At the intercuneiform articulations, a small vertical and the first cuneiform than between the second metatarsal movement takes place, thus altering the shape of the and the cuneiforms (102). Mobility is an important factor transverse arch in the foot (38). These joints are sup- in the first metatarsal because it is significantly involved in ported by strong interosseous ligaments. weight bearing and propulsion. The limited mobility at the second metatarsal is also significant because it is the peak of The forefoot consists of the metatarsals and the pha- the plantar arch and a continuation of the long axis of the langes and the joints between them. The function of the foot. The tarsometatarsal joints are supported by the forefoot is to maintain the transverse metatarsal arch, medial and lateral dorsal ligaments. maintain the medial longitudinal arch, and maintain the flexibility in the first metatarsal. The plane of the forefoot The metatarsophalangeal joints are biaxial, allowing at the metatarsal head is formed by the second, third, both flexion and extension and abduction and adduction and fourth metatarsals. This plane is perpendicular to the (Fig. 6-28). These joints are loaded during the propulsive phase of gait after heel-off and the initiation of plan- FIGURE 6-33 The midtarsal joints consist of the articulations between tarflexion and phalangeal flexion (61). Two sesamoid the calcaneus and the cuboid (calcaneocuboid joint) and the talus and bones lie under the first metatarsal and reduce the load on the navicular (talonavicular joint). Each joint has an axis of rotation that one of the hallucis muscles in the propulsive phase. The runs obliquely across the joint. When the two axes are parallel to each movements at the metatarsophalangeal joints are similar other, the foot is flexible and can freely move. If the axes do not run par- to those seen in the same joints in the hand except that allel to each other, the foot is locked in a rigid position. This occurs with greater extension occurs in the foot as a result of require- supination. ments for the propulsive phase of gait. The interphalangeal joints are similar to those found in the hand (Fig. 6-28). These uniaxial hinge joints allow for flexion and extension of the toes. The toes are much smaller than the fingers. They are also less developed, probably because of continual wearing of shoes (75). The toes are less functional than the fingers because they lack an opposable structure like the thumb. ARCHES OF THE FOOT The tarsals and metatarsals of the foot form three arches, two running longitudinally and one running transversely across the foot. This creates an elastic shock-absorbing

CHAPTER 6 Functional Anatomy of the Lower Extremity 229 Right foot Forefoot Subtalar joint Subtalar joint Subtalar joint inverted neutral neutral neutral Calcaneous Calcaneous Calcaneous vertical vertical inverted Non–weight bearing Non–weight bearing Non–weight bearing Right foot Subtalar joint Calcaneous Forefoot Subtalar joint Subtalar joint pronated supinated pronated everted stable Calcaneous Forefoot Calcaneous vertical on surface inverted Weight bearing A Weight bearing B Weight bearing C FIGURE 6-34 The metatarsal head should be perpendicular to the heel in a normal alignment in the foot. There are many variations in this alignment, including forefoot valgus (B), in which the medial side of the forefoot drops below the neutral plane; forefoot varus (A), in which the medial side lifts; and rear foot varus (C), in which the calcaneus is inverted. In weight bearing, these alignments occur with different movements. system. In standing, half of the weight is borne by the heel at toe contact with the ground. The medial arch short- and half by the metatarsals. One third of the weight borne ens at midsupport and then slightly elongates and again by the metatarsals is on the first metatarsal, and the remain- rapidly shortens at toe-off (61). Flexion at the trans- ing load is on the other metatarsal heads (61). The arches verse tarsal and tarsometatarsal joints increases the form a concave surface that is a quarter of a sphere (75). height of the longitudinal arch as the metatarsopha- The arches are shown in Figure 6-35. langeal joints extend at pushoff (147). The movement of the medial arch is important because it dampens The lateral longitudinal arch is formed by the calca- impact by transmitting the vertical load through deflec- neus, cuboid, and fourth and fifth metatarsals. It is rela- tion of the arch. tively flat and limited in mobility (61). Because it is lower than the medial arch, it may make contact with the Even though the medial arch is very adjustable, it usu- ground and bear some of the weight in locomotion, thus ally does not make contact with the ground unless a per- playing a support role in the foot. son has functional flat feet. The medial arch is supported by the keystone navicular bone, the calcaneonavicular The more dynamic medial longitudinal arch runs ligament, the long plantar ligament, and the plantar across the calcaneus to the talus, navicular, cuneiforms, fascia (38,62). and first three metatarsals. It is much more flexible and mobile than the lateral arch and plays a significant role The plantar fascia, illustrated in Figure 6-36, is a strong, in shock absorption upon contact with the ground. At fibrous plantar aponeurosis running from the calcaneus to heel strike, part of the initial force is attenuated by com- the metatarsophalangeal articulation. It supports both pression of a fat pad positioned on the inferior surface of arches and protects the underlying neurovascular bundles. the calcaneus. This is followed by a rapid elongation of The plantar fascia can be irritated as a result of ankle the medial arch that continues to maximum elongation motion through extreme ranges of motion because the

230 SECTION II Functional Anatomy AB C FIGURE 6-35 Three arches are formed by the tarsals and metatarsals: the transverse arches (A), which support a significant portion of the body weight during weight bearing; the medial longitudinal arch (B), which dynam- ically contributes to shock absorption; and the lateral longitudinal arch (C), which participates in a support role function during weight bearing. arch is flattened in dorsiflexion and increased in plan- The transverse arch is formed by the wedging of the tarflexion. These actions place a wide range of tensions on tarsals and the base of the metatarsals. The bones act as the fascial attachments (38). Also, if the plantar fascia is beams for support of this arch, which flattens with weight short, the arch is likely to be higher. bearing and can support three to four times body weight (152). The flattening of this arch causes the forefoot to spread considerably in a shoe, indicating the importance of sufficient room in shoes to allow for this spread. Individuals can be classified according to the height of the medial arch into foot types that are normal, high- arched or pes cavus, and flat-footed or pes planus. They can be further classified as being rigid or flexible. The midfoot of the high-arched rigid foot does not make any contact with the ground and usually has little or no inver- sion or eversion in stance. It is a foot type that has poor shock absorption. The flat foot, on the other hand, is usu- ally hypermobile, with most of the plantar surface making contact in stance. This weakens the medial side. It is a foot type usually associated with excessive pronation through- out the support phase of gait. FIGURE 6-36 The plantar fascia is a strong fibrous aponeurosis that runs MOVEMENT CHARACTERISTICS from the calcaneus to the base of the phalanges. It supports the arches and protects structures in the foot. The range of motion at the ankle joint varies with the application of loads to the joint. The range of motion in dorsiflexion is limited by the bony contact between the neck of the talus and the tibia, the capsule and ligaments, and the plantar flexor muscles. The average range of dor- siflexion is 20°, although approximately 10° of dorsiflex- ion is required for efficient gait (24). More dorsiflexion can be attained up through 40° plus when performing a full squat movement using body weight. Healthy elderly individuals typically exhibit less passive dorsiflexion range of motion but more dorsiflexion in gait than their younger counterparts. Any arthritic condition in the ankle also reduces passive and increases active dorsiflexion range of motion. The

CHAPTER 6 Functional Anatomy of the Lower Extremity 231 increase in dorsiflexion in the arthritic joint is primarily At the stage of foot flat in stance, the knee joint begins because of a decrease in flexibility in the gastrocnemius or to externally rotate and extend, and because the forefoot a weakness in the soleus. With the maintenance of the is still fixed on the ground, these movements are trans- knee flexion angle during the support period of gait, a col- mitted to the talus (62). The subtalar joint should begin lapse into greater dorsiflexion is observed (89). With to supinate in response to the external rotation and exten- increased dorsiflexion and knee flexion, more weight is sion that occurs up through heel-off. Many injuries of the maintained on the heel. lower extremity are thought to be associated with a lack of synchrony between these movements at the knee and sub- Plantarflexion is movement of the foot away from the talar joint. leg (e.g., rising up on the toes) or moving the leg away from the foot (such as in leaning back, away from the Excessive pronation has been speculated to be a major front of the foot) (Fig. 6-30). Plantarflexion is limited by cause of injury, but it is not necessarily the maximum the talus and the tibia, the ligaments and the capsule, and degree of pronation but rather the percentage of support the dorsiflexor muscles. The average range of motion for in which pronation is present and the synchronization plantarflexion is 50°, with 20° to 25° of plantarflexion with the knee joint movements. Pronation can be present used in gait (24,29,109). for as much as 55% to 85% of stance, creating problems when the lower limb moves into external rotation and In an arthritic or pathological gait, plantarflexion range extension as the subtalar joint is still pronating (104). The of motion is less for both passive and active measurements. lack of synchrony between the subtalar and knee joint The reduction of plantarflexion in gait is substantial motions has been shown to increase with increasing veloc- because of weak calf muscles. Healthy elderly people do ities (155) and increases in stride length (154). not demonstrate substantial loss in either passive or active plantarflexion range of motion (89). ALIGNMENT AND FOOT FUNCTION In the rear foot, subtalar eversion and inversion can be Foot function can be altered significantly with any variation measured by the angle formed between the leg and the in alignment in the lower extremity or as a result of abnor- calcaneus. In the closed-chain weight-bearing movement, mal motion in the lower extremity linkage. Typically, any the talus moves on the calcaneus, and in the open chain, varum alignment in the lower extremity increases the the calcaneus moves on the talus. Calcaneal inversion and pronation at the subtalar joint in stance (67). A Q-angle at eversion are the same regardless of weight-bearing or the knee greater than 20°, tibial varum greater than 5°, rear open-chain motion. This makes calcaneal inversion and foot varum (calcaneus inversion) greater than 2°, and fore- eversion measurements very useful in quantifying subtalar foot varum (forefoot adduction) greater than 3° are all motion (Fig. 6-32). Subtalar inversion is possible through deemed to be significant enough to produce an increase in 20° to 32° of motion in young healthy individuals and 18° subtalar pronation (89). in healthy elderly individuals (89,105). Inversion is greatly reduced in individuals with osteoarthritis in the ankle Rear foot varus is usually a combination of subtalar joint. Eversion, measured passively, averages 5° and 4° for varus and tibial varum in which the calcaneus inverts and healthy young and elderly individuals, respectively (89). the lower third of the tibia deviates in the direction of In 84% of arthritic patients, excessive calcaneal eversion inversion. Forefoot varus, the most common cause of creates what is known as a hindfoot valgus deformity. excessive pronation, is the inversion of the forefoot on the rear foot with the subtalar joint in the neutral position COMBINED MOVEMENTS OF THE KNEE (24). It is caused by the inability of the talus to derotate, AND ANKLE/SUBTALAR leaving the foot pronated at heel lift and preventing any supination. This shifts the body weight to the medial side Movements at the knee and foot need to be coordinated to of the foot, creating a hypermobile midtarsal joint and an maximize absorption of forces and minimize strain in the unstable first metatarsal. lower extremity linkage. For example, during the support phase of gait, pronation and supination in the foot should Both rear foot and forefoot varus double the amount correspond with rotation at the knee and hip. At heel of pronation in midstance compared with normal foot strike, the foot typically makes contact with the ground in function and continue pronation into late stance (67). In a slightly supinated position, and the foot is lowered to the some cases, the pronation continues until the very end of ground in plantarflexion (39). The subtalar joint begins to the support period. This is a major injury-producing immediately pronate, accompanying internal rotation and mechanism because the continued pronation is contrary flexion at the knee and hip joints (62). The talus rotates to the external rotation being produced in the leg. It is medially on the calcaneus, initiating pronation as a result of the primary cause of discomfort and dysfunction in the lateral heel strike and putting stress on the medial side foot and leg. The transverse rotation being produced by (140). Pronation continues until it reaches a maximum at the hypermobile foot, still in pronation late in stance, is approximately 35% to 50% of the stance phase (9,155), and absorbed at the knee joint and can create lateral hip pain this corresponds to the achievement of maximum flexion through an anterior tilt of the pelvis or strain the invertor and internal rotation at the knee. muscles (39).

232 SECTION II Functional Anatomy A plantarflexed first ray can also produce excessive and absorb energy during movement. The ligaments and pronation (67). The first ray is usually plantarflexed by the tendons of the muscles store some of the energy for later pull of the peroneus longus muscle and is commonly seen return. For example, the Achilles tendon can store 37 joules in both rear foot and forefoot varus alignments. This (J) of elastic energy, and the ligaments of the arch can store alignment causes the medial side of the foot to load pre- 17 J as the foot absorbs the forces and body weight (142). maturely, with greater than normal loads limiting forefoot inversion and creating supination in midstance. However, Plantarflexion is used to propel the body forward and sudden pronation is generated at heel-off, developing upward, contributing significantly to the other propelling high shear forces across the forefoot, especially at the first forces generated in heel-off and toe-off. Plantar flexor and fifth metatarsals (67). muscles are also used eccentrically to slow down a rapidly dorsiflexing foot or to assist in the control of the forward Hypermobility of the first ray is generated because the movement of the body, specifically the forward rotation of peroneus longus muscle cannot stabilize the first the tibia over the foot. metatarsal. During pronation, the medial side is hypermo- bile, placing a large load and shear force on the second Plantarflexion is a powerful action created by muscles metatarsal. This is a common cause of stress fracture of the that insert posterior to the transverse axis running second metatarsal and subluxation of the first metatar- through the ankle joint. The majority of the plantarflexion sophalangeal joint (1,24). force is produced by the gastrocnemius and the soleus, which together are referred to as the triceps surae muscle Although it is not common, a person may have a fore- group. Because the gastrocnemius also crosses the knee foot valgus alignment. This may be caused by a bony joint and can act as a knee flexor, it is more effective as a deformity in which the plantar surfaces of the metatarsals plantar flexor with the knee extended and the quadriceps evert relative to the calcaneus with the subtalar joint in the femoris activated. neutral position (24). Forefoot valgus causes the forefoot to be prematurely loaded in gait, creating supination at In a sprint racing start, the gastrocnemius is maximally the subtalar joint. This alignment is typically seen in high- activated with the knee extended and the foot placed in arched feet. full dorsiflexion. The soleus, called the workhorse of plan- tarflexion, is flatter than the gastrocnemius (38). It is also Foot type, as mentioned previously, can also affect the the predominant plantarflexor during a standing posture. amount of pronation or supination. In the normal foot A tight soleus can create a functional short leg, often seen with a subtalar axis of 42° to 45°, the internal rotation of in the left leg of people who drive a car a great deal. As the leg is equal to the internal rotation of the foot (70). In explained in an earlier section, an inflexible or tight soleus a high-arched foot, the axis of the subtalar joint is more limits dorsiflexion and facilitates compensatory pronation vertical and is greater than 45°, so that for any given inter- that creates the functionally shorter limb. nal rotation of the leg, there is less internal rotation of the foot, creating less pronation for any given leg rotation. The action of these plantarflexor muscles is mediated through a stiff subtalar joint, allowing for an efficient In the flat foot, the subtalar joint axis is less than 45°, transfer of the muscular force. The gastrocnemius and that is, closer to the horizontal. This has the opposite possibly the soleus have also been shown to produce effect to an axis that is greater than 45°. Thus, for any supination when the forefoot is on the floor during the given internal rotation of the leg, there is greater internal later stages of the stance phase of gait. Plantarflexion is rotation of the foot, creating greater pronation (70). usually accompanied by both supination and adduction. A final alignment consideration is the equine foot, in The other plantar flexor muscles produce only 7% of which the Achilles tendon is short, creating a significant the remaining plantarflexor force (38). Of these, the per- limitation of dorsiflexion in gait. The equinus deviation oneus longus and the peroneus brevis are the most signif- can be reproduced with a tight and inflexible gastrocne- icant, with minimal plantarflexor contribution from the mius and soleus. Because the tibia is unable to move for- plantaris, flexor hallucis longus, flexor digitorum longus, ward on the talus in midsupport, the talus moves anteriorly and tibialis posterior. The plantaris is an interesting mus- and pronates excessively to compensate (39). An early heel cle, similar to the palmaris longus in the hand, in that it is rise and toe walking are symptoms of this disorder. absent in some individuals, very small in others, and well developed in yet others. Overall, its contribution is usually MUSCLE ACTIONS insignificant. Twenty-three muscles act on the ankle and the foot, 12 Dorsiflexion at the ankle is actively used in the swing originating outside the foot and 11 inside the foot. All of phase of gait to help the foot clear the ground and in the the 12 extrinsic muscles, except for the gastrocnemius, stance phase of gait to control lowering of the foot to the soleus, and plantaris, act across both the subtalar and mid- floor after heel strike. Dorsiflexion is also present in the mid- tarsal joints (50). The insertion, actions, and nerve supply dle part of the stance phase as the body lowers and the tibia of all of these muscles are presented in Figure 6-37. travels over the foot, but this action is controlled eccentri- cally by the plantarflexor muscles (46). The dorsiflexor mus- The muscles of the foot play an important role in sus- cles are those that insert anterior to the transverse axis taining impacts of very high magnitude. They also generate running through the ankle (50) (see Fig. 6-37).

CHAPTER 6 Functional Anatomy of the Lower Extremity 233 Gastroc- Tibialis Biceps Iliotibial nemius posterior femoris tract muscle (band) Flexor (long head) digitorum Rectus Popliteus femoris longus muscle tendon Peroneus Biceps longus femoris muscle Flexor (short hallucis head) longus Soleus Peroneus brevis Achilles tendon AB CD E Muscle Insertion Nerve Supply Flexion/ Extension/ Abduction Adduction Inversion Eversion Dorsiflexion Plantarflexion Abductor Lateral calcaneus TO Lateral plantar PM: digiti minimi base of proximal phalanx nerve Little toe of 5th toe Abductor Medial plantar PM: hallucis Medial calcaneus TO nerve Big toe medial base of proximal phalanx of 1st toe Adductor 2nd, 3rd, 4th metatarsal Lateral plantar PM: hallucis TO lateral side of proximal nerve Big toe phalanx of big toe Dorsal Sides of metatarsals TO Lateral plantar PM: PM: PM: interossei lateral side of proximal nerve proximal Toes 2–4 2nd toe phalanx phalanx Extensor Lateral calcaneus TO Deep peroneal PM: digitorum proximal phalanx of 1st, nerve Toes 1–4 brevis 2nd, 3rd toes Deep peroneal Asst: PM PM Extensor Lateal condyle of tibia; digitorum fibula; interosseus nerve Ankle DF Toe 2–5 longus membrane TO dorsal expansion of toes 2–5 Extensor Anterior fibula; interos- Deep peroneal Asst: PM: PM: hallucis seous membrane TO Forefoot longus distal phalanx of big toe nerve Ankle DF Big toe Flexor digiti 5th metatarsal TO Lateral plantar PM: minimi brevis proximal phalanx of little toe nerve Little toe Flexor Medial calcaneus TO Medial plantar PM: digitorum brevis middle phalanx of toes nerve Toe 2–5 2–5 Flexor Posterior tibia TO distal Tibial nerve PM: Asst: Asst digitorum phalanx of toes 2–5 Toe 2–5 Ankle PF longus Flexor Cuboid TO medial side Medial plantar PM: hallucis brevis of proximal phalanx of big toe nerve Big toe Flexor hallucis Lower 2–3 of posterior Tibial nerve PM: Asst: PM: Asst longus fibula, interosseous Big toe Ankle PF Forefoot membrane FIGURE 6-37 Muscles acting on the ankle joint and foot, including superficial posterior muscles (A) and surface anatomy (B) of posterior lower leg; deep posterior muscles of the lower leg (C), muscles (D) and surface anatomy of the lower leg (E); anterior muscle (F) and surface anatomy (G); surface anatomy of the foot and ankle (H); and muscles in the dorsal (I, J, K) and ventral (L) surface of the foot.

234 SECTION II Functional Anatomy Lumbricals Hallucis longus Flexor Flexor Extensor digitorum hallucis hallucis brevis brevis longus Extensor Peroneus Quadratus Extensor digitorum longus plantae hallucis brevis longus Tibialis Gastroc- H J Adductor hallucis anterior nemius (transverse head) L muscle Lumbricales Peroneus Abductor Opponens Adductor brevis Soleus digiti digiti hallucis muscle minimi (oblique Extensor minimi head) digitorum Flexor digitorum Flexor Flexor longus brevis digiti hallucis brevis Extensor Abductor minimi hallucis hallucis longus FG IK Muscle Insertion Nerve Supply Flexion/ Extension/ Abduction Adduction Inversion Eversion Dorsiflexion Plantarflexion Gastrocnemius Medial, lateral condyles Tibial nerve; PM: of femur TO calcaneus S1, S2 Ankle PF Medial, lateral Lumbricales Tendon of flexor planter nerve PM: Asst: digitorum longus TO proximal Ankle PF base of proximal phalanx Superficial phalanx of toes 2–5 peroneal 2–5 nerve Peroneus Lower lateral fibula TO PM brevis 5th metatarsal Peroneus Lateral condyle of tibia, Superficial Asst: PM: PM longus upper lateral fibula TO peroneal Ankle PF Forefoot PM 1st cuneiform; lateral 1st nerve Peroneus metatarsal tertius Lower anterior fibula; Deep peroneal PM Plantar interossei interosseous membrane nerve Plantaris TO base of 5th metatarsal Medial side of 3–5 meta- Lateral plantar PM: tarsal TO medial side of nerve Toes 3–5 proximal phalanx of toes 3–5 Asst: Ankle PF Linea aspera on femur Tibial nerve TO calcaneus Quadratus Medial lateral inferior Lateral plantar PM: plantae calcaneus TO flexor digitorum tendon nerve Toes 2–5 Soleus Upper posterior tibia, Tibial nerve PM: Ankle PF Tibialis fibula, interosseous mem- anterior Asst: brane TO calcaneus Ankle PF Tibialis posterior Upper lateral tibia, intero- Deep peroneal PM: PM sseous membrane TO nerve Ankle DF PM medial plantar surface of 1st cuneiform Upper posterior tibia, Tibial nerve fibula, interosseous mem- brane TO inferior navicular FIGURE 6-37 (CONTINUED)

CHAPTER 6 Functional Anatomy of the Lower Extremity 235 The most medial dorsiflexor is the tibialis anterior, Inversion is created primarily by the tibialis anterior and whose tendon is farthest from the joint, thus giving it a the tibialis posterior, with assistance from the toe flexors, significant mechanical advantage and making it the most flexor digitorum longus, and flexor hallucis longus. The powerful dorsiflexor (38). The tibialis anterior has a long extensor hallucis longus works with the flexor hallucis tendon that begins halfway down the leg. It is also the longus to adduct the forefoot during inversion. largest muscle and provides additional support to the medial longitudinal arch. Assisting the tibialis anterior in The intrinsic muscles of the foot work as a group and dorsiflexion are the extensor digitorum longus and the are very active in the support phase of stance. They basi- extensor hallucis longus. These muscles pull the toes up in cally follow supination and are more active in the later extension. The peroneus tertius also contributes to the portions of stance to stabilize the foot in propulsion (70). dorsiflexion force. In a foot that excessively pronates, they are also more active as they work to stabilize the midtarsal and subtalar Eversion is created primarily by the peroneal muscle joints. There are 11 intrinsic muscles, and 10 of these are group. These muscles lie lateral to the long axis of the on the plantar surface arranged in four layers. Figure 6-37 tibia. They are known as pronators in the non–weight- has a full listing of these muscles. bearing position because they evert the calcaneus and abduct the forefoot. The peroneus longus is an everter STRENGTH OF THE ANKLE AND FOOT that is also responsible for controlling the pressure on the MUSCLES first metatarsal and some of the finer movements of the first metatarsal and big toe, or hallux. The strongest movement at the ankle or foot is plantarflex- ion. This is because of the larger muscle mass contributing The lack of stabilization of the first metatarsal by the to the movement. It is also related to the fact that the peroneus longus leads to hypermobility of the medial side plantarflexors are used more to work against gravity and of the foot. The peroneus brevis also contributes through maintain an upright posture, control lowering to the the production of eversion and forefoot abduction, and the ground, and add to propulsion. Even standing, the plan- peroneus tertius contributes through dorsiflexion and tarflexors, specifically the soleus, contract to control dor- eversion. Both the peroneus tertius and peroneus brevis siflexion in the standing posture. stabilize the lateral aspect of the foot. Pronation in the weight-bearing position is primarily generated by weight Plantarflexion strength is greatest from a position of bearing on the lateral side of the foot in heel strike. This slight dorsiflexion. A starting dorsiflexion angle of 105° drives the talus medially, producing pronation. Figure 6-38 increases plantarflexion strength by 16% from the neutral shows how pronation is produced through weight bearing. 90° position. Plantarflexion strength measured from 75° and 60° of plantarflexion is reduced by 27% and 42%, The inverters of the foot are the muscles lying medial respectively compared with strength measured in the neu- to the long axis of the tibia. These muscles generate inver- tral position (152). Additionally, plantarflexion strength sion of the calcaneus and adduction of the forefoot (38). can be increased if the knee is maintained in an extended position, placing the gastrocnemius at a more advanta- geous muscle length. Dorsiflexion is incapable of generating a large force because of its reduced muscle mass and because it is min- imally used in daily activities. The strength of the dorsi- flexor muscles is only about 25% that of the plantarflexor muscles (152). Dorsiflexion strength can be enhanced by placing the foot in a few degrees of plantarflexion before initiating dorsiflexion. FIGURE 6-38 When the heel strikes the ground on the lateral (L) aspect, a CONDITIONING OF THE FOOT AND ANKLE vertical force is directed on the outside of the foot. The force of body MUSCLES weight is acting down through the ankle joint. Because these two forces do not line up, the talus is driven medially (M), producing the pronation Both stretching and strengthening exercises for selected movement. movements at the foot and ankle are presented in Figure 6-39. The plantarflexor muscles are exercised to a great extent in daily living activities: They are used to walk, get out of chairs, go up stairs, and drive a car. Strengthening the plantarflexors by using resistive exercises is also rela- tively easy. Any heel-raising exercise offers a significant amount of resistance because body weight is lifted by this muscle group. With the weight centered over the foot, the leverage of the plantarflexors is very efficient for handling

236 SECTION II Functional Anatomy Muscle Group Sample Stretching Exercise Sample Strengthening Exercise Other Exercises Standing calf raise Ankle Dumbbell heel raise Plantarflexors Barbell heel raise Seated calf raise Ankle Dorsiflexion with tubing dorsiflexors Ankle Eversion with elastic band eversion/inversion Ankle tubing inversion FIGURE 6-39 Sample stretching and strengthening exercises for selected muscle groups are illustrated.