Common, Superficial & Deep Peroneal (Fibular) Nerve Anatomy

This is a common peroneal nerve palsy, almost certainly from compression at the fibular neck by the cast - the nerve is subcutaneous on the fibula and is the most commonly compressed nerve in the lower limb. I would confirm loss of dorsiflexion (deep peroneal) and eversion (superficial peroneal) with sensory loss over the dorsum and first web space, and importantly check that inversion and plantarflexion are preserved. To distinguish an L5 radiculopathy I would test tibialis posterior (inversion) and hip abduction, which are L5 but spared in a peroneal lesion, and look for back/radicular pain; a Tinel sign at the fibular neck supports a peripheral cause. Management: remove the compressing cast immediately, protect the foot with an ankle-foot orthosis and maintain range, and obtain electrodiagnostics if it does not recover. Most compressive palsies recover; persistent cases may need decompression or, if irreversible, a tibialis posterior tendon transfer.