A simple clinical test to differentiate rupture of flexor pollicis longus and incomplete anterior interosseous paralysis.

Incomplete anterior interosseous nerve paralysis and spontaneous rupture of flexor pollicis longus tendon are conditions which mimic each other closely and have been mistaken for each other, leading to unnecessary surgery. This is a report of a simple and reliable clinical test to differentiate between the two conditions. A search of the literature has not revealed a previous description of this test.