Clear view of the index sesamoid: a sign of irreducible metacarpophalangeal joint dislocation.

If the index sesamoid bone is clearly seen in the joint following significant injury to the index metacarpophalangeal joint on radiographic examination, there is the probability of incarceration of the volar plate. In almost all cases, an open reduction will be necessary to re-establish the normal relationship between the second metacarpal and the proximal phalanx. In a case of irreducible dislocation of the index metacarpophalangeal joint, attempted reduction caused the injury to appear as a subluxation.