Experimental investigation of finger dynamics before and after metacarpophalangeal joint arthroplasty.

PURPOSE: The purpose of this study was to quantify the changes in the arc of digital flexion before and after metacarpophalangeal (MCP) silicone arthroplasty with a 30 degrees preflexed design.

METHODS

Index, middle, and ring fingers of 4 fresh-frozen cadaver hands were used. Each hand was attached (palmar side up) to a custom test apparatus. The tendon was drawn by a small winch-type servomotor. Micropotentiometers that were attached to the centers of rotation of the MCP, distal interphalangeal, and proximal interphalangeal joints measured angular displacement before and after MCP arthroplasty as a function of tendon excursion. The data were analyzed comparing the angle of flexion initiation and the angular displacement as a function of tendon excursion before and after joint arthroplasty.

RESULTS

There were no statistical differences in the angles of the MCP joints at rest, the order of initiation of joint flexion, and the overall degree of flexion between the unoperated fingers and the fingers that had surgery. There was, however, a trend toward delay in flexion initiation, an increase in the MCP angle at rest, and a decrease in torque after implant arthroplasty.

CONCLUSIONS

The decrease in initiation of flexion of the MCP joint, although not statistically significant, probably was related to the 30 degrees of preflexion built into the implant. We also noted a trend of decreased flexion at the MCP joint and increased flexion at the proximal interphalangeal and distal interphalangeal joints. This trend may be advantageous in the reconstruction of hands that initially have an MCP joint flexion deformity.

TYPE OF STUDY/LEVEL OF EVIDENCE: to come.