Observation
Look for:
- high-stepping gait
- foot slap
- muscle wasting
- scars or deformity
Motor examination
Test separately:
- ankle dorsiflexion — tibialis anterior
- great-toe extension — EHL
- toe extension — EDL
- eversion — peroneal muscles
- inversion — tibialis posterior
- plantar flexion
Localisation
Common peroneal nerve lesion
- weak dorsiflexion
- weak toe extension
- weak eversion
- inversion usually preserved
L5 radiculopathy
- dorsiflexion and toe extension weak
- inversion may also be weak
- hip abduction may be weak
Preserved inversion is therefore useful when differentiating a common peroneal lesion from an L5 root lesion.
Sensory examination
Assess:
- first dorsal web space — deep peroneal nerve
- dorsum of foot — superficial peroneal nerve
- L5 dermatomal distribution
Additional examination
- reflexes
- Tinel sign around fibular neck
- straight-leg raise and lumbar examination
- knee stability and proximal tibiofibular region
Investigations
Nerve conduction studies and EMG help localise the lesion and determine severity. MRI is directed by the suspected level of pathology.