Ulnar drift and metacarpophalangeal joint subluxation in the rheumatoid hand: review of the pathogenesis.

Ulnar drift and metacarpophalangeal joint subluxation are complicated abnormalities with a wide variety of causes. This paper reviews certain anatomic and mechanical features of the normal hand which predispose toward these abnormalities. In the rheumatoid hand, the major deforming forces include extensor forces, flexor forces, intrinsic forces, and forces from the wrist and carpometacarpal joints. Ulnar drift and metacarpophalangeal joint subluxation result not from any singular cause, but from a combination of all or many of these forces acting upon a joint rendered unstable by rheumatoid synovitis.