Page 271 - Clinical Anatomy

ECA4 7/18/06 6:48 PM Page 256

256 The lower limb

Branches
While still in the popliteal fossa, the common peroneal nerve gives
off the lateral cutaneous nerve of the calf, a peroneal (sural) communicating
branch and twigs to the knee joint, but has no muscular branches.

The deep peroneal (fibular) nerve
The deep peroneal nerve pierces extensor digitorum longus, then descends,
in company with the anterior tibial vessels, over the interosseous mem-
brane and then over the ankle joint. Medially lies tibialis anterior, while lat-
erally lies first extensor digitorum longus, then extensor hallucis longus. Its
branches are:
•◊◊muscular — to the muscles of the anterior compartment of the leg —
extensor digitorum longus, extensor hallucis longus, tibialis anterior, per-
oneus tertius—and extensor digitorum brevis;
•◊◊cutaneous — to a small area of skin in the web between the 1st and
2nd toes.

The superficial peroneal (fibular) nerve

The superficial peroneal nerve runs in the lateral compartment of the leg.
Its branches are:
•◊◊muscular — to the lateral compartment muscles (peroneus longus and
brevis);
•◊◊cutaneous—to the skin of the distal two-thirds of the lateral aspect of the
leg and to the dorsum of the foot (apart from the small area between the 1st
and 2nd toes supplied by the deep peroneal nerve).

Clinical features

The common peroneal nerve is in a particularly vulnerable position as
it winds around the neck of the fibula. It may be damaged at this site by the
pressure of a tight bandage or plaster cast or may be torn in severe adduc-
tion injuries to the knee. Damage to this nerve is followed by foot drop (due
to paralysis of the ankle and foot extensors) and inversion of the foot due to
paralysis of the peroneal muscles with unopposed action of the foot flexors
and invertors). There is also anaesthesia over the anterior and lateral
aspects of the leg and foot, although the medial side escapes, since this is
innervated by the saphenous branch of the femoral nerve.

Segmental cutaneous supply of the lower limb
(Fig. 185)

The arrangement of root segments supplying the lower limb is as follows:
•◊◊L1, 2 and 3—supply the anterior aspect of the thigh from above down;
•◊◊L4—supplies the frontomedial aspect of the leg;