Signs of palsy of tibial and peroneal nerves

1. Big picture

The tibial nerve and peroneal/fibular nerve are the two main terminal branches of the sciatic nerve. Their lesions are common exam topics because they cause very recognizable gait and foot deformity patterns.

The key contrast is:

Peroneal nerve palsy = foot drop, steppage gait, weak dorsiflexion and eversion. Tibial nerve palsy = weak plantar flexion, difficulty standing on toes, sensory loss on the sole.

The most common clinical trap is confusing common peroneal nerve palsy with L5 radiculopathy, because both can cause foot drop. The best differentiating point is that in common peroneal palsy, foot inversion is preserved, while in L5 radiculopathy it may be weak because tibialis posterior is also L5 but supplied by the tibial nerve.

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