SN6 SHORT NOTE 5M

Common Peroneal Nerve Palsy

General Surgery · Final Professional

Definition & Cause

Common peroneal (fibular) nerve palsy produces foot drop. The nerve is very vulnerable where it winds superficially around the neck of the fibula, so it is injured by fractures of the fibular neck, tight plaster casts, direct pressure (prolonged leg-crossing, coma, poor positioning) and knee dislocations.

Clinical Features

The common peroneal nerve supplies the dorsiflexors and evertors of the foot. Its paralysis causes foot drop — the inability to dorsiflex and evert the foot — producing a high-stepping (‘steppage’) gait (the patient lifts the knee high to clear the dropped foot) and sensory loss over the dorsum of the foot and lateral leg.

CLINICAL PEARL

Foot drop from a common peroneal palsy is painless and shows a steppage gait; protect the vulnerable nerve at the fibular neck by careful padding of casts and positioning of the unconscious or bed-bound patient.

Management

A palsy from compression (cast, positioning) often recovers once the cause is removed; the foot is supported with an ankle-foot orthosis (foot-drop splint) and physiotherapy while awaiting recovery, preventing a fixed equinus contracture. A divided nerve is repaired; irrecoverable foot drop may be treated by tendon transfer (e.g. Tibialis posterior) or ankle stabilisation.

Assessment & Prevention

Examination confirms weak dorsiflexion and eversion with preserved inversion and plantarflexion (helping to localise the lesion to the common peroneal nerve rather than the sciatic nerve or an L5 root), and maps the sensory loss. Because so many cases are avoidable pressure palsies, prevention is emphasised: careful padding of casts around the fibular neck, and correct positioning of the anaesthetised, comatose or bed-bound patient to keep pressure off the lateral aspect of the knee.

CLINICAL PEARL

Painless foot drop with a steppage gait points to the common peroneal nerve at the fibular neck — much of it is avoidable pressure palsy, so pad casts and position patients with care.

DANGER / REMEMBER

Distinguish a common peroneal palsy from an L5 radiculopathy and a sciatic lesion: in a peroneal palsy inversion and plantarflexion are preserved and there is no back pain, whereas an L5 root lesion often causes back and radicular pain with weakness of inversion too. Getting this right avoids imaging the wrong level and directs treatment.

Most vulnerable where it winds round the fibular neck.

KEY POINT

Key points TO remember

Common peroneal palsy = foot drop; nerve vulnerable at the fibular neck.
Causes: fibular neck fracture, tight cast, pressure/positioning, knee dislocation.
Loss of dorsiflexion/eversion → steppage gait; dorsal foot/lateral leg sensory loss.
Remove cause + AFO/foot-drop splint; repair division; tendon transfer if irrecoverable.

EXAM TIP

Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.

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