Description of Project
Osteoarthritis of the thumb trapeziometacarpal (TM) joint is a common yet controversial problem. Although the prevalence of this disease in the USA is over 84% in those over age 80, the mechanics leading to osteoarthritic degeneration of the TM joint are poorly understood. Several studies have attributed the pathophysiology of TM osteoarthritis to ligament laxity and subluxation, but there remains uncertainty as to whether the forces causing subluxation are greater during pinch or grip functions. In addition, the volar and dorsal TM ligaments provide additive support to the joint, but there is controversy as to which set provides the primary restraint to dorsal subluxation. This study aimed to explore these two unknowns by examining the TM joints of 5 mid-humerus cadaver specimens in static and dynamic key pinch and power grip configurations. The ultimate goal of this work was to apply the biomechanical discoveries to design improvements for the Stablyx Arthroplasty device, a hemi-trapeziometacarpal joint replacement developed by Skeletal Dynamics.
Results of Project
Kinematic analysis of the trapeziometacarpal joint in cadaver specimens revealed that the saddle-on-saddle architecture of the articular surfaces provides more stability in the key pinch function than in the power grip function when all joint ligaments are excised. CMC joint stability was difficult to obtain in the power grip configuration due to dorso-ulnar subluxation and dislocation. Serial resection of dorsal and volar ligaments demonstrated that the dorsal ligaments of the TM joint are larger, stronger, and more important for maintaining articular alignment during power grip. Ligament resection had little to no effect on articular alignment during key pinch. These findings led to the extension of the volar lip of the Stablyx device and a change in the surgical protocol to preserve some of the dorsal TM ligaments.