Causes of locking metacarpophalangeal joint of the thumb and its non-operative treatment.

The non-operative method of reduction of locking metacarpophalangeal joint of the thumb is described, and illustrated by four case reports. Experimental studies in the hands of a fresh cadaver are also described. Locking of the metacarpophalangeal joint of the thumb can be produced by slight external forces, insufficient to damage strong tissues. Incarceration of the sesamoid bone is anatomically impossible, but incarceration of the proximal portion of the volar plate is believed to be the true cause. This incarceration can be reduced easily by our non-operative method along with intra-articular injection of local anaesthetics.