Implant arthroplasty of the hand: retrospective and prospective considerations.

Small joint arthroplasty has lagged behind the development of that in large joints because of their small sizes, different shapes, presence within kinetic chains, complex soft tissue investments, presence of adjacent rays, secondary displacement and contracture, and the differing requirements of degenerative and rheumatoid arthritis. Prosthetic development must take into consideration range of motion, stability, tendon moment arms, fixation, ease of implantation, biocompatibility, wear and strength characteristics, and soft tissue reconstruction. The metacarpophalangeal, interphalangeal, and trapeziometacarpal joints each present different problems in the design of kinematic equivalent prostheses. One-piece polymeric designs have advantages in cost, adaptability, and known performance but show degradation of function with time. Total joint designs have the potential of better simulating normal joint function but have shown tendencies to subsidence, loosening, and breakage. The rigidity of hinge joints limits the damping of out-of-plane forces and places greater stress on bone-stem interfaces, whereas global designs have poor constraint features.