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Posterior Compartment of the Thigh Anatomy


Posterior Compartment of the Thigh Anatomy
The posterior compartment is enclosed by the fascia lata (Fig. 6.34) and extends from the gluteal region above to the popliteal fossa below. It contains the poste­ rior cutaneous nerve of thigh, hamstring muscles, sciatic nerve and terminal branches of the profunda femoris artery.


Hamstring muscles
These three muscles, semimembranosus, semitendinosus and biceps femoris (long head) (Fig. 6.35), attach proximally to the ischial tuberosity (Fig. 6.36) and distally to the upper end of the tibia or fibula and are innervated by the sciatic nerve. They span the entire length of the femur and act on two joints, the hip for extension and the knee for flexion. After flexion of the trunk, the hamstrings act as antigravity muscles by pulling on the ischial tuberosities, thus extending the trunk into an upright position at the hip. Tears of the hamstrings occur in sports involving jumping, running and kicking.
Semimembranosus
This muscle is attached to the upper and lateral parts of the ischial tuberosity by a wide, flat tendon, which is overlapped by the tendons of biceps and semitendinosus close to the tuberosity, and descends on the medial side of the popliteal fossa to its main attachment into a horizontal groove on the posteromedial aspect of the medial tibial condyle. Some of its fibres pass upwards and laterally behind the knee joint to form the oblique posterior ligament; others descend to reinforce the fascia over popliteus (Fig. 6.39).
Semitendinosus
Proximally, semitendinosus is attached to the medial part of the ischial tuberosity. It descends on the medial side of the popliteal fossa, forming a narrow tendon, which overlies semimembranosus, and attaches to the medial surface of the upper end of the tibial shaft close to the attachments of sartorius and gracilis (Fig. 6.79). Besides contributing to the common actions of the hamstring group, semitendinosus and semimembranosus produce medial rotation of the leg at the knee.
Biceps femoris
This muscle has two heads. Proximally, the long head is attached to the medial part of the ischial tuberosity close to the semitendinosus and descends to the lateral side of the popliteal fossa, where it fuses with the short head, which originates from the lateral lip of the linea aspera and lateral supracondylar ridge of femur (Fig. 6.35). Inferiorly, the tendon of biceps is attached to the head of the fibula. In addition to the general actions of the hamstrings, biceps produce lateral rotation of the leg at the knee.

Sciatic nerve
The sciatic nerve emerges at the lower border of gluteus maximus lying just beneath the deep fascia, passes deep to the long head of biceps and descends in the midline of the limb. In the distal third of the thigh, it usually divides into two terminal branches, the tibial and common fibular (common peroneal) nerves, which continue into the popliteal fossa (Fig. 6.40). Division may occur more proximally in the thigh, within the buttock or even the pelvis. In the latter case, the common fibular nerve may pass through the piriformis where it may be compressed. Proximally, fibres from the medial (tibial) part of the sciatic nerve supply the hamstrings (Fig. 6.35) and the ischial head of adductor magnus. More distally, a branch from the lateral (common fibular) part of the nerve supplies the short head of biceps.

Posterior cutaneous nerve of thigh
The nerve enters the thigh superficial and slightly medial to the sciatic nerve and descends beneath the fascia lata to the upper part of the popliteal fossa (Fig. 6.37). Apart from branches arising near the lower border of gluteus maximus, the nerve gives sensory fibres to the skin on the back of the thigh, popliteal fossa and proximal part of leg.

Profunda femoris artery
Perforating branches of the profunda femoris artery penetrate adductor magnus and terminate in the posterior compartment. They anastomose with branches from the inferior gluteal artery above and the popliteal artery below.