Page 270 - Clinical Anatomy

ECA4 7/18/06 6:48 PM Page 255

Course and distribution of nerves 255

dislocation of the hip associated with fracture of the posterior lip of the
acetabulum, to which the nerve is closely related (Fig. 168).
Damage to the sciatic nerve is followed by paralysis of the hamstrings
and all the muscles of the leg and foot (supplied by its distributing branches);
there is loss of all movements in the lower limb below the knee joint with foot
drop deformity. Sensory loss is complete below the knee, except for an area
along the medial side of the leg, over the medial malleolus and down to the
hallux, which is innervated by the saphenous branch of the femoral nerve.
2◊◊The sciatic nerve is accompanied by a companion artery (derived from
the inferior gluteal artery) which bleeds quite sharply when the nerve is
divided during an above-knee amputation. The artery must be neatly iso-
lated and tied without any nerve fibres being incorporated in the ligature,
since this would be followed by severe pain in the stump.

The tibial nerve (Fig. 178a and b)
The tibial nerve (L4, 5, S1–3) is the larger of the two terminal branches of the
sciatic nerve; it traverses the popliteal fossa superficial to the popliteal vein
and artery, which it crosses from the lateral to the medial side.

Branches
a) in popliteal fossa
•◊◊muscular—to gastrocnemius, soleus and popliteus;
•◊◊cutaneous — the sural nerve, which descends over the back of the calf,
behind the lateral malleolus to the 5th toe; it receives a communicating
branch from the common peroneal nerve and supplies the lateral side of the
leg, foot and 5th toe;
•◊◊articular—to the knee joint.
It then descends deep to soleus, in company with the posterior tibial
vessels, passes on their lateral side behind the medial malleolus to end by
dividing into the medial and lateral plantar nerves.
b) in the leg
The tibial nerve supplies flexor hallucis longus, flexor digitorum longus
and tibialis posterior. Its terminal plantar branches supply the intrinsic
muscles and skin of the sole of the foot, the medial plantar nerve having an
equivalent distribution to that of the median nerve in the hand, the lateral
plantar nerve being comparable to the ulnar nerve.

The common peroneal (fibular) nerve
The common peroneal nerve (L4, 5, S1, 2) is the smaller of the terminal
branches of the sciatic nerve. It enters the upper part of the popliteal fossa,
passes along the medial border of the biceps tendon, then curves around
the neck of the fibula where it lies in the substance of peroneus longus and
divides into its terminal branches, the deep peroneal and superficial peroneal
nerves (Fig. 155).