Isolated closed rupture of the bony insertion of the flexor digitorum superficialis tendon: an unusual case.

We describe a case of isolated rupture of the flexor digitorum superficialis tendon due to middle phalangeal cortical bone avulsion with a 4-month delay in treatment. X-ray examination revealed an area of calcification in the flexor tendon sheath proximal to the proximal interphalangeal joint. Excision of the bone fragment and surrounding scar tissue corrected nearly all the 60 degrees extension lag at the proximal interphalangeal joint, which was the most notable functional loss.