Summary

A 43-year-old man presented with weakness of the interphalageal joint of his right thumb following the use of forearm crutches. On examination he was unable to oppose his thumb and index finger to form the ‘ok’ sign. Nerve conduction showed anterior interosseous nerve (AIN) damage along its path to the flexor pollicis longus. The patient was managed conservatively with little clinical improvement seen at 4 months. AIN palsies are very rare and account for <1% of all upper limb lesions. Although AIN palsies resulting from other causes such as surgery and blunt trauma are more common, we report the second case of AIN palsy following crutch use, and the first case in which clinical identification was confirmed using electrodiagnosis. Usual clinical practice recommends a prolonged period of conservative management with surgical management withheld for a minimum of 12 months. Correct crutch fitting and early identification of signs of associated injuries are of paramount importance.