The human thumb carpometacarpal (CMC) joint is located radially at the base of the hand and is largely responsible for the prehensile abilities of the hand. The thumb CMC joint is also a primary location for osteoarthritis (OA) in the human body. Understanding the source of thumb CMC OA, its progression and treatment by using quantitative biomechanical analysis, as presented in this thesis, is essential in helping a growing portion of the population cope with, and possibly prevent, the symptoms of thumb CMC OA.
To elucidate the progression of OA in the human thumb CMC joint, sequential arthritic wear patterns of the thumb CMC joint from cadaveric specimens are calculated. Stereophotogrammetry (SPG) is used to calculate the cartilage thickness of one-hundred four specimens representing the various stages of thumb CMC OA. Cartilage thinning is seen in the volar portions of the joint during the initial stages of OA, while average cartilage thickness maps display a gradual progression of thinning radially as the arthritic stage increases.
Since many investigators have proposed that ligamentous laxity is an etiological factor in thumb CMC OA, a novel custom-designed thumb CMC joint laxity tester is constructed as part of the investigation of thumb CMC OA. Capable of measurements with high linear and angular accuracy, the laxity tester is used to evaluate the effects of an Eaton-Littler style ligament reconstruction and an extension osteotomy (10°, 15° and 30°) of the first metacarpal on laxity and contact areas within the thumb CMC joint in the position of lateral pinch. The results indicate that both procedures significantly reduce joint laxity, however, only the extension osteotomy alters the contact mechanics within the joint post-operatively.
The laxity tester is also used to predict the stiffness of the thumb CMC joint capsular ligaments during distraction. This is performed by using the multi-directional force-displacement data recorded during laxity testing in conjunction with measured ligament insertion points on the trapezium and thumb metacarpal and static force balance equations. The anterior oblique ligament and dorsal-radial ligament were found to be the primary restraints during distraction of the joint. The calculated stiffnesses of the ligaments may indicate their individual restraining capabilities of the thumb CMC joint during activities of daily living.
Finally, two species were evaluated as animal models for OA in the human. First, the Papio anubis (grey baboon) was selected as an animal model to study the human thumb CMC joint. Curvature characteristics were calculated for the trapezium and thumb metacarpal of the baboon and human species. Significant similarities were found between the two species for all but one value of surface wide joint curvature. Differences in joint curvature were found in the volar regions of the metacarpal. The similarities in joint curvature indicate the potential of the baboon thumb to be used as an animal model of the human thumb. In the second study, the equine species was evaluated as a model for general OA in the human. Joint kinematics, contact areas and a computer joint model were created based on the in vivo gait patterns of a horse. The results of this study are beneficial for research involving large joints in the human body.
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