Chapter 10The Lower Limb
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.
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.
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.
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.
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.
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.
The talus, or anklebone, consists of a body, a short neck, and a head. The body is clamped by and articulates with the fibula (lateral malleolus) and the tibia (medial malleolus). The body also articulates with the calcaneus below. A short neck attaches the body to a head, which articulates with the navicular bone anteriorly and the calcaneus inferiorly.
The calcaneus, or heel bone, is the largest of the tarsal bones. It articulates with the body of the talus and the head of the talus. A bony shelf, or sustentaculum tali, helps to support the head of the talus. The posterior third of the talus projects backward beyond the ankle joint as the weight-bearing portion of the heel inferiorly. Superiorly this portion acts as a lever for extensor muscles.
As the name suggests, the navicular bone is boat-shaped. The concavity of the boat faces posteriorly and articulates with the rounded head of the talus. The navicular bone articulates anteriorly with three cuneiform bones and laterally with the cuboid bone.
Cuneiform means wedge-shaped, and there are three of these bones arranged anterior to the navicular bone. The medial cuneiform articulates with the head of the first metatarsal, the intermediate cuneiform with the head of the second metatarsal, and the lateral cuneiform articulates with the third metatarsal.
There are five metatarsal bones that form the skeleton of the anterior sole of the foot. Metatarsals 1, 2, and 3 articulate with the three cuneiform bones; metatarsals 4 and 5 articulate with the cuboid bone.
Each metatarsal features an expanded base, which articulates with the tarsals behind and provides attachments for muscles of the foot. A rounded head on the distal end of the shaft articulates anteriorly with the phalanges of the toes.
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.
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.
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.
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.
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.
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.
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:
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.
Smooth, glassy hyaline cartilage coats the articular surfaces of the femoral and tibial condyles. When moistened with synovial fluid, the articulating surfaces move smoothly over each other. The condyles of the femur and the tibia are partially separated by two interposing fibrocartilaginous discs, or menisci, the medial and lateral menisci. Each meniscus is C-shaped, and a transverse ligament joins their anterior margins.
The capsular ligament or articular capsule is a thin, strong fibrous membrane that forms a sleeve around the knee, and it is strengthened considerably by medial and lateral collateral ligaments and overlying muscle tendons that help to stabilize the knee and limit movements of the knee to normal ranges. The medial meniscus is attached to the inner aspect of the medial collateral ligament. Contributing significantly to the stability of the knee are two strong, internal anterior and posterior cruciate ligaments that join the intercondylar areas of the femur and the tibia. The ligaments are named according to their attachments on the tibia. The anterior crucia/>