KINEMATICS OF THE TRAPEZIOMETACARPAL JOINT - A BIOMECHANICAL ANALYSISCOMPARING TENDON INTERPOSITION ARTHROPLASTY AND TOTAL-JOINT ARTHROPLASTY

The kinematics of the trapeziometacarpal joint were studied in 15 cada ver hands; normal joints were compared with simulated arthroplasties-e ither a total-joint arthroplasty of the ball-and-socket variety or a f ibrous suspension arthroplasty of ligament reconstruction with tendon interposition. The motion of the thumb metacarpal was analyzed based o n a trapezial coordinate system, using a magnetic tracking system. The pivot point (instantaneous center of rotation) for the thumb metacarp al changed during active and passive circumduction. Compared with norm al trapeziometacarpal joint motion, the pivot point after ligament rec onstruction with tendon interposition shifted significantly in palmar and ulnar directions in reference to the trapezial coordinate system, whereas after total-joint arthroplasty, the pivot point shifted slight ly palmarly and radially. The axes of rotation were also compared for ligament reconstruction with tendon interposition and total-joint arth roplasty during thumb flexion-extension and abduction-adduction motion s. After ligament reconstruction with tendon interposition, the center of flexion-extension shifted palmarly and the center of abduction-add uction shifted ulnarly. After total-joint arthroplasty, the center of rotation For flexion-extension shifted distally and palmarly and that for abduction-adduction shifted palmarly and proximally. in comparison with the normal joint, passive circumduction increased after tendon i nterposition arthroplasty but was less with total-joint arthroplasty. Changes in kinematics suggest a suspensory ligament function of ligame nt reconstruction with tendon interposition arthroplasty, whereas tota l-joint arthroplasty results in axes of rotation that reflect the join t replacement rather those of the normal joint.