Surgeons and engineers in collaboration studied biomechanical disturbances in the rheumatoid hand. Experiments with freshly amputated fingers, combined with mathematical models of finger movement, have established that there is a pin-axis of flexionextension in the metacarpophalangeal (MP) joint. Forces active on normal and abnormal joint restraints have been examined, bearing forces and their resultant shear lines on the phalanx and metacarpal have been described, and the knowledge combined to consider the effectiveness of the various man-made joint substitutes currently available.
It is concluded that prosthetic substitution of the rheumatoid MP joint provides better function than fusion of the MP joints, but that prostheses are not suitable for long-term use in a solitary joint in an otherwise normal hand.
Flatt AE. Studies in Finger Joint ReplacementA Review of the Present Position. Arch Surg. 1973;107(3):437-443. doi:10.1001/archsurg.1973.01350210069019