Mechanical wearing down of flexor tendons in rheumatoid arthritis as a result of extreme volar-flexed intercalated segment instability.

We report the case of a 72-year-old patient with rheumatoid arthritis complicated by spontaneous ruptures of the flexor digitorum superficialis and profundus tendons of the left index finger. Extreme volar-flexed intercalated segment instability resulted in protrusion of the head of the capitate bone into the carpal tunnel and rupture of both tendons caused by wear. Reconstruction of the flexor digitorum profundus tendon, interposition of a tendon graft, and radiolunate arthrodesis restored function.