Variations in the Minimum Joint Distance During Flexion and Abduction of the Thumb Carpometacarpal Joint: Potential Implications for Joint Degeneration.

BACKGROUND: The type of movement leading to osteoarthritis of the thumb carpometacarpal joint remains unclear. This study investigated changes in the joint distance during thumb flexion and abduction. METHODS: Five healthy adult men underwent computed tomography imaging at eight different limb positions. The joint distances perpendicular to the articular surfaces of the metacarpal (Dm) and trapezium (Dt) were measured. RESULTS: For Dm, the minimum joint distance was the smallest in both the flexion and abduction positions with narrowing predominantly observed on the volar side of the metacarpal. Similarly, for Dt, the minimum joint distance was also smallest in the flexion and abduction positions. Dm was mainly distributed on the volar side in all limb positions and tended to shift toward the radial side during abduction. Dt was generally located at the center and shifted toward the volar side in the flexion position. CONCLUSION: Flexion and abduction of the thumb may contribute to degeneration of the volar side of the metacarpal articular surface. In particular, during maximum flexion, narrowing on the volar side of the trapezium was observed, indicating that flexion may contribute to degeneration not only in the central region but also on the volar side of the trapezium.