We experienced a relatively rare case of rupture of the flexor pollicis tendon resulting from an nonunited scaphoid fracture. A seventy-two year old man suddenly lost the ability to flex the interphalangeal joint of his right thumb while he was writing. On examination, there was no active flexion of the interphalangeal joint of his right thumb. No neurological deficits could be found. Roentgenograms revealed an old scaphoid nonunion.
We recognized the rupture of his flexor pollicis longus tendon in the preoperative MRI and echograhy. It can be suggested that MRI and echogram investigations are valuable for distinguishing between rupture of the flexor pollicis longus tendon and an incomplete type of anterior interosseous nerve palsy.
