The tibial nerve innervates: all muscles in the posterior compartment of the leg, all intrinsic muscles in the sole of the foot including the first two dorsal interossei muscles, which also may receive innervation from the deep fibular nerve, and skin on the posterolateral side of the lower half of the leg and lateral side of the ankle, foot, and little toe, and skin on the sole of the foot and toes.
The common fibular part of the sciatic nerve innervates the short head of the biceps femoris in the posterior compartment of the thigh and then continues into the lateral and anterior compartments of the leg and onto the foot (Fig. 6.70).
The common fibular nerve innervates: all muscles in the anterior and lateral compartments of the leg, one muscle (extensor digitorum brevis) on the dorsal aspect of the foot, the first two dorsal interossei muscles in the sole of the foot, and skin over the lateral aspect of the leg, and ankle, and over the dorsal aspect of the foot and toes.
The knee joint is the largest synovial joint in the body. It consists of: the articulation between the femur and tibia, which is weight-bearing, and the articulation between the patella and the femur, which allows the pull of the quadriceps femoris muscle to be directed anteriorly over the knee to the tibia without tendon wear (Fig. 6.71).
Two fibrocartilaginous menisci, one on each side, between the femoral condyles and tibia accommodate changes in the shape of the articular surfaces during joint movements.
The detailed movements of the knee joint are complex, but basically the joint is a hinge joint that allows mainly flexion and extension. Like all hinge joints, the knee joint is reinforced by collateral ligaments, one on each side of the joint. In addition, two very strong ligaments (the cruciate ligaments) interconnect the adjacent ends of the femur and tibia and maintain their opposed positions during movement.
Because the knee joint is involved in weight-bearing, it has an efficient “locking” mechanism to reduce the amount of muscle energy required to keep the joint extended when standing.
The articular surfaces of the bones that contribute to the knee joint are covered by hyaline cartilage. The major surfaces involved include: the two femoral condyles, and the adjacent surfaces of the superior aspect of the tibial condyles.
The surfaces of the femoral condyles that articulate with the tibia in flexion of the knee are curved or round, whereas the surfaces that articulate in full extension are flat (Fig. 6.72).
The articular surfaces between the femur and patella are the V-shaped trench on the anterior surface of the distal end of the femur where the two condyles join and the adjacent surfaces on the posterior aspect of the patella. The joint surfaces are all enclosed within a single articular cavity, as are the intraarticular menisci between the femoral and tibial condyles.
There are two menisci, which are fibrocartilaginous C-shaped cartilages, in the knee joint, one medial (medial meniscus) and the other lateral (lateral meniscus) (Fig. 6.73). Both are attached at each end to facets in the intercondylar region of the tibial plateau.
The medial meniscus is attached around its margin to the capsule of the joint and to the tibial collateral ligament, whereas the lateral meniscus is unattached to the capsule. Therefore, the lateral meniscus is more mobile than the medial meniscus.
The menisci are interconnected anteriorly by a transverse ligament of the knee. The lateral meniscus is also connected to the tendon of the popliteus muscle, which passes superolaterally between this meniscus and the capsule to insert on the femur.
The menisci improve congruency between the femoral and tibial condyles during joint movements where the surfaces of the femoral condyles articulating with the tibial plateau change from small curved surfaces in flexion to large flat surfaces in extension.