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.
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.
