In Vivo 3-Dimensional Kinematics of Thumb Carpometacarpal Joint During Thumb Opposition

This study primarily aimed to demonstrate the screw-home rotation of the thumb carpometacarpal (CMC) joint and the function of surrounding ligaments during thumb oppositional motion.

A 3-dimensional kinematic analysis of the thumb CMC joint was conducted using data derived from computed tomography of 9 healthy volunteers. Scans were obtained in the neutral forearm and wrist position and the thumb in maximum radial abduction, maximum palmar abduction, and maximum opposition. The movements of the first metacarpal and the palmar and dorsal bases on the trapezium during thumb oppositional motion from radial abduction through palmar abduction were quantified using a coordinate system originating on the trapezium. In addition to the kinematic analyses, the length of virtual ligaments, including the anterior oblique, ulnar collateral, dorsal radial, dorsal central (DCL), and posterior oblique ligament (POL), were calculated at each thumb position.

From radial abduction to opposition of the thumb through palmar abduction, the first metacarpal was abducted, internally rotated, and flexed on the trapezium. The palmar base of the first metacarpal moved in the palmar-ulnar direction, and the dorsal base moved in the palmar-distal direction along the concave surface of the trapezium. Although the DCL and POL lengthened, the lengths of other ligaments did not change significantly.

During thumb oppositional motion, internal rotation of the first metacarpal occurred, with the palmar base rotating primarily with respect to the dorsal base. The DCL and POL may be strained in thumb functional positions.

Kinematic variables indicated a screw-home rotation of the thumb CMC joint and the contribution of the dorsal ligaments to the stability of the rotation on the pivot point.