This dissertation addresses the quantitative analysis of the biomechanical behavior of the thumb carpometacarpal joint, particularly with regard to articular topography, ligament mechanics, articular contact, and joint kinematics in various thumb functions, using experimental testing and biomechanical modeling. The objective is to answer the basic questions of how various etiologic factors effect the biomechanical behavior of the carpometacarpal joint and which factors may play major roles in the initiation and development of osteoarthritis in this joint.

This study systematically and quantitatively investigates the topography of the carpometacarpal joint and its variations related to gender, age, and progression of osteoarthritis. The results indicate that the carpometacarpal joint becomes more congruent in geometry with the progression of osteoarthritis and with the increase of age, and that female joints are less congruent than male joints.

The mechanical functions of capsular ligamentous structures in stabilizing the carpometacarpal joint are investigated, using tensile testing of the ligaments and multibody modeling of the carpometacarpal joint. The results indicate that:​ 1) no significant difference is found in mechanical properties among major capsular ligaments;​ and 2) during passive metacarpal pronation, all major capsular ligaments contribute to stabilizing the carpometacarpal joint, each in different ways.

Articular contact and kinematics of the carpometacarpal joint in various pinch functions are performed experimentally. It is found that articular contact is mostly located at the dorso-radial and/or volar-ulnar sites of the articular surfaces in lateral pinch, tip pinch, and grasp, sometimes extending to volar and radial sites of the joint. No significant difference in articular contact areas is found among the three joint functions tested.

Finally, a multibody biomechanical model of the entire thumb is developed, with an emphasis on analyzing the mechanical environment of the carpometacarpal joint. Using this model, the biomechanical environment inside the joint in various active functions can be predicted, including articular contact area, contact force, contact stresses, and ligament forces. As an application of the model, the effects of selective surgical procedures on articular contact are reported.