Effect of Extension Osteotomy of the 1st Metacarpal on Laxity of the Thumb Carpometacarpal Joint

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 (Figure1) [1–4]. Previous investigations of laxity and stability of the human thumb CMC joint have been performed visually, with no quantitative measures of joint laxity recorded [5–7]. Surgical treatment has been a common solution to reduce the pain associated with CMC OA. One treatment, extension osteotomy of the 1^st metacarpal, has been suggested not only to reduce the pain of OA, but also improve hand function [8], 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.