Three-dimensional geometric analysis of the metacarpophalangeal joint.

No prosthesis yet designed for replacement of the metacarpophalangeal (MCP) joint incorporates all considerations of anatomy and geometry of the natural joint to restore the normal kinematics. Loss of stability, recurrent deformity, and early loosening are persistent problems. In this study, a detailed three-dimensional geometric analysis of the MCP joint was performed. The sagittal contours of both metacarpal heads and base of the proximal phalanx under loaded and unloaded conditions were analyzed. The geometric parameters of the MCP joint articulating surfaces were analyzed, including the center and radius of curvature and the location and size of the contact area. The pressures on articulating surfaces during various hand functions were also established. These findings provided important information for better understanding the kinematics of finger joint articulation, as well as the cause of joint degeneration.