Osteoarthritis (OA) of the human thumb carpometacarpal (CMC) joint is a debilitating disease. It has been proposed in the clinical literature that joint ligamentous laxity, or joint looseness, is a major etiological factor in OA of the CMC joint (Figurel) Previous investigations of laxity and stability of the human thumb CMC joint have been performed visually, with no quantitative measures of joint laxity recorded Surgical treatment has been a common solution to reduce the pain associated with CMC OA. One treatment, extension osteotomy of the 1st metacarpal, has been suggested not only to reduce the pain of OA, but also improve hand function, however, little is known about its biomechanical effects. A complete description of joint laxity requires that all physiological directions of motion be fully tested. A custom-designed, 4 degree of freedom tester was constructed and instrumented for displacement and load in the distraction-compression, dorsal-volar, pronation-supination, and radial-ulnar directions. The purpose of this study was to use this device to: 1) Measure the joint laxity and compliance of non-OA human thumb CMC joints and 2) Determine the effect that a simulated extension osteotomy has on joint laxity and joint stiffness. This study provides an accurate baseline for future comparisons with osteoarthritic, surgically corrected, and otherwise non-healthy CMC joints.
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