Popliteal Fossa Anatomy
The popliteal fossa is a
diamondshaped space behind the knee joint. It contains the principal blood
vessels and nerves passing between the thigh and the leg. It has a roof, four
walls and a floor.
Roof
The roof is formed by the investing
layer of deep fascia. In the subcutaneous tissue overlying the roof are the
posterior cutaneous nerve of the thigh, which continues into the proximal part
of the leg, and the small saphenous vein (Fig. 6.37). The vein usually penetrates the roof to
drain into the popliteal vein but may drain more proximally into the great
saphenous vein (Fig. 6.34).
Walls
The walls overhang the fossa.
Superiorly, they are formed by the diverging tendons of the hamstrings, namely
semitendinosus and semimembranosus lying medially and biceps laterally.
Inferiorly are the medial and lateral heads of gastrocnemius, which converge at
the inferior angle (Fig. 6.38). Adjacent to the lateral head of gastrocnemius
is the small plantaris muscle. On each side of the popliteal fossa the
hamstring tendons overlap the
heads of gastrocnemius, and between the medial head of
gastrocnemius and semimembranosus there is frequently a bursa (Fig. 6.39).
Contents
The principal contents of the fossa
are embedded in fat and comprise the popliteal artery and vein together with
the two terminal branches of the sciatic nerve, the common fibular and tibial
nerves (Fig. 6.40). These vessels and nerves are responsible for the blood and
nerve supply of most of the leg and foot.
The popliteal artery lies deepest
and is the continuation of the femoral artery from the thigh. It enters through
the opening in adductor magnus and descends vertically on the floor of the
fossa to the inferior angle, where it leaves beneath the fused heads of
gastrocnemius. The artery is so deep
that it is difficult to palpate unless the knee is flexed to relax the
boundaries and roof of the fossa. The artery supplies the
surrounding muscles and also forms a substantial plexus of articular branches
anastomosing symmetrically around the knee joint (Fig. 1.27).
The popliteal vein lies superficial
to the artery and is formed at the inferior angle of the fossa by the union of
the venae comitantes that accompany the tibial arteries in the leg. It
continues proximally with the artery through the opening in adductor magnus to
enter the adductor canal and become the femoral vein.
The tibial and common fibular
nerves (Fig. 6.40), entering the fossa from the posterior
compartment of the thigh, lie just beneath the roof, superficial to the
popliteal vessels. The tibial nerve enters from beneath the hamstrings and
descends vertically, bisecting the fossa, and leaves beneath the gastrocnemius
at the inferior angle of the fossa, where it enters the posterior compartment
of the leg. The tibial nerve is mainly motor in its distribution, supplying
gastrocnemius, plantaris, popliteus and soleus. All these branches arise within
the fossa. The nerve also gives sensory branches to the knee joint and a large
cutaneous branch, which passes into the calf to form the sural nerve. The
common fibular nerve descends under cover of the tendon of biceps to reach the
lateral angle of the fossa, where it enters the lateral (fibular or peroneal)
compartment of the leg. Here it winds around the neck of the fibula where it is
vulnerable to damage and compression, resulting in footdrop. It supplies
sensory branches to the knee joint and two cutaneous nerves, one to the lateral
side of the calf and the other, the lateral sural cutaneous nerve, joining the
sural nerve in the calf.
The remaining contents of the
popliteal fossa are the deeply placed popliteal lymph nodes, which lie close to
the popliteal artery. They drain the deep structures of the leg and foot and
the knee joint and receive superficial lymphatics, which accompany the short
saphenous vein from the lateral side of the foot and leg.
The floor of the fossa is formed,
from above downwards, by the popliteal surface of the femur, the capsule of the
knee joint reinforced by the
oblique popliteal ligament and popliteus (Fig. 6.39).
Popliteus
This muscle is attached to a
triangular area on the posterior surface of the proximal end of the tibia above
the soleal line. The tendon passes upwards and laterally, penetrating the capsule of the knee joint (Fig.
6.77) to become attached to a pit below the lateral epicondyle of the femur.
Its action is to ‘unlock’ the knee joint
by producing lateral rotation of
the femur on the tibia during flexion of the joint from the fully extended
position. Popliteus is supplied by the tibial nerve.
