Metacarpophalangeal joint motion and the role of the collateral ligaments.

A three stage study of the metacarpophalangeal joint was performed. First, a triaxial goniometer was designed which allowed direct measurement of joint motion in living and cadaveric hands. Then, based on the above data, a computer simulated model of the joint was developed. This permitted an analysis of the orientation of the joint for any given point in the axis of motion, the effects of the collateral ligaments and their contribution to joint motion and stability. Finally the metacarpal head was analysed using a shadow profilometer and anatomical dissections. From 0 degree to 70 degrees, the metacarpal head demonstrated a curved configuration. At approximately 70 degrees, the metacarpal head assumed a bicondylar shape which produced a bony block to lateral deviation. Dissection of the collateral ligaments demonstrated that they ran diagonally from the metacarpal head to the proximal phalanx. We conclude that the metacarpophalangeal joint has an instant axis. From 0 degree to 70 degrees of flexion, in any given hand, the angle of lateral deviation is constant. Beyond 70 degrees there is a marked decrease in lateral deviation. The joint has two degrees of freedom and the collateral ligament is taut in all positions.