Page 348 - Medicine and Surgery

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344 Chapter 7: Nervous system

Clinical features Prognosis
Flexion of the knee is markedly impaired and all the This is a disabling injury. In walking, quadriceps weak-
muscles below the knee are paralysed, causing drop foot. ness can be compensated for to some extent by the ad-
The calf is wasted. Sensation is absent in most of the skin ductor muscles.
below the knee.
Peroneal nerve lesions
Management Definition
Intraumaticdamage,explorationandrepairofthenerve The common peroneal nerve is the smaller terminal
should be carried out. A footdrop splint is worn to keep
branch of the sciatic nerve which supplies muscles which
the ankle in a safe position, but the lower leg is very
act on the ankle joint.
vulnerable to neuropathic ulceration and development
of Charcot’s joint, which may necessitate a below-knee
Aetiology/pathophysiology
amputation.
This nerve is easily damaged because it runs down
in the popliteal fossa, then winds laterally around the
neck of the fibula. It can be compressed by a plaster
Femoral nerve injuries
cast, in compartment syndrome, by lying unconscious
Definition with the leg externally rotated or it may be stretched
The femoral nerve is a branch of the lumbar plexus, from when the knee is forced into varus with lateral ligament
nerve roots L1–4, and it supplies flexors of the hip and injuries.
extensors of the knee. It has two terminal branches, the superficial and deep
peroneal nerves. The superficial nerve supplies peroneus
longus and peroneus brevis, which plantarflex and evert
Aetiology/pathophysiology
the foot, and the skin on the lower, lateral side of the
Complete division of the femoral nerve is rare. It may be
leg and foot. The deep nerve supplies muscles which
injured by a gunshot wound, traction in an operation or
dorsiflextheankleandasmallareaofskinonthedorsum
bleeding into the thigh.
of the foot around the first web space.
In the abdomen, the femoral nerve is related to the
psoas muscle and supplies iliopsoas. It enters the thigh
Clinical features
lateral to the femoral to supply the hamstring muscles
Common peroneal nerve injury: Drop foot, both dorsi-
in the thigh. Its two divisions, then supply all the ante-
flexion of the ankle and eversion of the foot are weak but
rior compartment muscles of the thigh, namely quadri-
not plantarflexion (gastrocnemius and soleus are much
ceps femoris, which is a powerful extensor of the knee,
more powerful plantarflexors of the foot). Sensation is
and the skin of the medial and anterior surfaces of the
lost over the front and outer leg and the dorsum of the
thigh.
foot.
Superficial branch injury: Foot eversion is lost, but
dorsiflexion is intact. Sensation is lost over the outer
Clinical features
side of the leg and foot.
Weakness of knee extension and numbness of the medial
Deep branch injury: This tends to occur in anterior
and anterior aspect of the thigh, the medial aspect of the
compartmentsyndrome.Thereisweakeneddorsiflexion
lower leg and the medial border of the foot. The knee
and a small area of sensory loss on the dorsum of the
jerk is depressed or absent. Hip flexion is only slightly
foot.
affected and adduction is preserved.
Management
Management Most cases resolve spontaneously if due to compression.
Evacuationofahaematomaordirectsuturingorgrafting Compartment syndrome however requires emergency
of a cut nerve. decompression. If the nerve is cut or torn, it should be