Chapter 10The Lower Limb

4. Nerve Supply: The Lumbar and Sacral Plexuses 444

The lower limb can be compared to the upper limb, bearing in mind that, during development, both limbs rotate 90 degrees in opposite directions. This results in the big toe ending up on the medial side, whereas its upper limb equivalent, the thumb, is on the radial side. The bones, joints, and musculature of the lower limb are relatively larger and sturdier because they are modified for weight bearing and mobility.

1 Skeleton

PELVIC GIRDLE

The lower limb girdle consists of the right and left os coxae, the sacrum, and the coccyx (Figure 10-1). The bones of the pelvis were considered in Chapter 4, Section 1.

Figure 10-1 Bones of the lower right limb. A, Anterior view. B, Posterior view.

The femur is the only bone of the thigh (Figure 10-2). It is a large, long bone with a rounded head superiorly that articulates with the os coxae and two large knuckles, or condyles, that articulate inferiorly with the tibia.

Figure 10-2 Right femur. A, Anterior aspect. B, Posterior aspect.

Features

1. The head is somewhat spherical and fits in the cup-shaped acetabulum of the os coxae; approximately three fifths of the spherical head is covered with articular, hyaline cartilage except for a small pit, or fovea, for the attachment of the round ligament (ligament teres) of the head of the femur.

2. A neck fixes the head to the upper medial aspect of the shaft at an angle of about 130 degrees; at the junction of head and neck are two traction prominences or trochanters that serve as attachments for large lower limb muscles.

3. The greater trochanter is the larger of the two; it points superiorly, occupies a superolateral position, and can be palpated just below the skin in the hip region.

4. The lesser trochanter is a smaller projection that faces medially and posteriorly.

5. The intertrochanteric line is a ridge joining the bases of the two trochanters on the anterior aspect.

6. The intertrochanteric crest is a more prominent ridge seen from the posterior aspect that runs from the greater to the lesser trochanter.

7. The shaft of the femur angles downward medially and toward its distal end diverges to end as two large knuckles, or condyles.

8. The medial and lateral condyles of the femur are two large spherical structures that articulate below with the tibia.

9. A deep intercondylar notch separates the two condyles. Anteriorly the notch diverges into a smooth patellar fossa for articulation with the patella.

10. The lateral and medial epicondyles are small projections on the lateral and medial aspects of the condyles.

11. The adductor tubercle is another bony projection just above the medial epicondyle that can be palpated easily.

12. The linea aspera is actually a double ridge on the posterior shaft that extends from the greater and lesser tubercles, converges as a fine double line, and then diverges inferiorly to pass to the medial and lateral epicondyles. It serves as a muscle attachment.

Patella

The patella is a sesamoid bone embedded within the tendon of the quadriceps femoris muscle (Figure 10-3). The anterior surface is roughened for the tendinous attachments to the quadriceps femoris muscle. The medial and lateral borders converge inferiorly as the apex. The posterior aspect of the patella is lined with articular cartilage that articulates with the trochlea of the femur. The articular surface is divided into several facets.

Figure 10-3 Right patella. A, Anterior aspect. B, Posterior aspect.

LEG

There are two long bones of the leg, the tibia on the medial aspect and the fibula on the lateral.

Tibia

Description

The tibia is relatively strong and massive because it bears all of the weight transmitted inferiorly from the femur and, in turn, transfers the weight to the ankle below (Figure 10-4).

Figure 10-4 Right tibia and fibula. A, Anterior aspect. B, Posterior aspect.

Features

1. The medial and lateral condyles of the tibia are expanded knuckles that articulate with the femoral condyles superiorly through two flattened circular, articular surfaces; the medial condyle is the larger of the two.

2. The intercondylar eminence lies between the condyles superiorly.

3. An articular facet for the head of the fibular is a shallow, circular depression on the posterolateral aspect of the lateral condyle.

4. The tibial tuberosity is a prominent bony projection on the anterior aspect just below the condyles; it is palpable just below the anterior aspect of the kneecap, or patella, and it provides attachment for the patellar ligament.

5. The shaft of the tibia has a sharp anterior border that may be palpated because it is just below the skin (for this reason, it is vulnerable to painful bumps and bruises). Attached to the lateral or interosseous border of the shaft is an interosseous membrane that extends to the shaft of the fibula and provides an area for muscular attachment.

6. The medial malleolus is the medial prominence of the ankle.

7. The inferior end of the tibia articulates below with the talus of the ankle and laterally with the inferior end of the fibula.

Fibula

Description

The fibula is the thin lateral bone of the leg. It is not weight-bearing but does provide surface area for muscle attachments. It articulates superomedially with the tibia and inferomedially with the tibia and the talus.

Features

1. An expanded head sits atop the thin shaft of the fibula, and it articulates with the articular facet of the tibia described previously.

2. The lateral malleolus is the prominent lower end of the fibula that acts as a lateral splint to clamp the talus of the ankle laterally, whereas the medial malleolus of the tibia clamps it medially.

ANKLE AND FOOT

Tarsal Bones

The tarsal bones in the ankle correspond to the carpal bones of the wrist, but there are seven tarsals in the ankle compared to eight carpals in the wrist (Figure 10-5). The tarsals occupy the posterior half of the foot. Two tarsals, the talus and calcaneus, are considerably larger, weight-bearing bones and comprise the entire posterior aspect of the foot.

Figure 10-5 Bones of the right foot. A, Dorsal aspect. B, Plantar aspect. M, Metatarsal; P, phalanx.

2 Joints

THE PELVIC GIRDLE

Features

Two joints anchor the pelvic girdle to the axial skeleton: (1) the sacroiliac joint and (2) the hip joint (Figure 10-6).

Figure 10-6 Joints of the pelvic girdle and hip.

Sacroiliac Joint

The sacroiliac joint is a fairly rigid joint binding the ear-shaped, or auricular, surfaces of the sacrum to a reciprocally shaped area on the iliac portion of the os coxae. It has the features of two joints; it is a synovial joint anteriorly and a fibrous joint posteriorly.

Symphysis Pubis

The symphysis pubis is a midline joint between the pubic portions of the right and left os coxae. It is a typical symphysis in that the bony surfaces are lined with hyaline cartilage. Fibrous tissue binds the cartilaginous surfaces in the midline, forming a joint with little movement.

Movements

There is some movement in the sacroiliac joint that imparts some resilience as weight is transferred from the sacrum to the pelvis, but this resiliency tends to decrease with age. During pregnancy, the fibrous elements of both the sacroiliac and the symphysis pubis joints become lax, allowing the pelvis to widen and facilitate passage of the head through the birth canal.

HIP JOINT

Features

The hip joint is an extremely stable yet moveable ball-and-socket joint (Figure 10-7). It is an articulation between the spherical head of the femur (ball) and the cup-shaped acetabulum of the os coxae (socket). The articular surface of the acetabulum is horseshoe-shaped. The concavity of the acetabulum is further deepened by the acetabular labrum, a fibrocartilage ring that encircles the rim of the fossa. A joint capsule surrounds the joint, affording it a fair degree of movement. The capsule is thickened and reinforced by three strong ligaments running from each component of the os coxae to the neck of the femur to prevent dislocation of the joint. The ligaments include the iliofemoral ligament anteriorly, the ischiofemoral ligament posteriorly, and the pubofemoral ligament inferiorly and anteriorly. The ligament of the head of the femur is a rather weak ligament that runs from the lower end of the acetabulum to the fovea on the head of the femur. It may contain a small nutrient artery to the head of the femur.

Figure 10-7 Coronal section through the right os coxae (hip bone) to display opened hip joint.

CLINICAL NOTES

Fracture of the Femoral Neck

Fractures of the femoral neck are more common in older people, particularly women suffering from osteoporosis. The nutrient arterial supply to the head of the femur arises mainly from vessels that continue through the joint capsule as retinacula. Should the fracture damage these vessels, the head of the femur undergoes degeneration or avascular necrosis, a situation that necessitates surgical replacement.

Hip Replacement

Osteoarthritis of the hip is a degenerative disease that results in pain and limited movement to a point at which surgical hip replacement is the treatment of choice. The damaged elements of the joint, the femoral head and the acetabulum, are removed and replaced by inert prostheses.

Movements

The following movements are described in relation to the anatomical position (Figure 10-8). This assumes that the foot is moved from the ground with resultant movement of the femur at the hip. If the foot remains on the ground, however, the os coxae moves in relation to the femur. The hip joint is capable of six movements:

1. Flexion of the thigh at the hip swings the thigh anteriorly and superiorly in the sagittal plane from the anatomical position; this is accomplished by the rectus femoris, sartorius, iliopsoas, pectineus, and adductor muscles.

2. Extension swings the thigh back to the anatomical position; hyperextension swings the thigh even farther posteriorly. Muscles that extend the thigh include the hamstrings, gluteus maximus, and adductor magnus muscles.

3. Abduction swings the thigh laterally and superiorly away from the trunk in the coronal plane; the gluteus medius, gluteus minimus, tensor fasciae latae, iliopsoas, piriformis, and sartorius muscles abduct the thigh at the hip.

4. Adduction swings the thigh back toward the trunk through the actions of the adductors (longus, brevis, and magnus), pectineus, gracilis, gemelli, obturator internus, and obturator externus muscles.

5. Medial rotation is the rotation of the thigh about its long axis turning its anterior surface toward the median plane; this movement is performed by the glutei medius and minimus, adductors (longus, brevis, and magnus), and tensor fasciae latae muscles.

6. Lateral rotation rotates the thigh about its long axis so that the anterior surface turns laterally away from the median plane; contributing muscles are the gluteus maximus, iliopsoas, piriformis, obturator externus and internus, gemelli, and quadratus femoris.

Figure 10-8 Movements at the hip joint. A, Flexion and extension. B, Hyperextension. C, Abduction and adduction. D, Medial and lateral rotation.

Circumduction is a combination of flexion, extension, abduction, and adduction in a wide conical arc about the hip.

THE KNEE JOINT

The knee joint is the largest and perhaps the most complicated joint in the body (Figure 10-9). It is classified as a synovial joint with interposing fibrocartilage discs, or menisci. The knee is really a complex of three joints: (1) between the lateral condyles of the femur and tibia, (2) between the medial condyles of the femur and the tibia, and (3) between the patella and the femur. The joints between the tibia and femur represent the weight-bearing portion of the knee. They are moveable, synovial joints that allow a combined hinge and sliding type movement and limited rotation. The joint between the patella and the femur allows a sliding type of movement.