A simple clinical test of flexor pollicis longus rupture.

Rupture of the tendon of flexor pollicis longus is suspected when active flexion of the interphalangeal joint of the thumb is not possible. This can be a result of trauma but, when spontaneous, diagnostic confusion can exist as incomplete palsy of the anterior interosseous nerve can present in a similar way. We describe a simple clinical sign which can differentiate between these conditions.