Osteoarthritis (OA) of the thumb carpometacarpal (CMC) joint is a common and disabling condition. Controversies surround the etiology of CMC OA because the internal mechanics of the joint is poorly understood. Several studies have been reported where mathematical modeling was used to study the biomechanical behavior of the CMC joint. Cooney et al (1977) developed a 3D static thumb model. An et al (1985) modified this model to simulate abnormal conditions of the thumb such as tendon laceration. Esteki (1995) developed a dynamic model to study neuromuscular stimulation of the hand. However, these previous studies have mostly employed idealized kinematic representations of the CMC joint (e.g., as a universal joint), and their results have focused primarily on the calculation of joint reactions forces. The biomechanical parameters which are believed to play key roles in CMC joint degeneration, such as contact area patterns of articular surfaces and complex higher pair kinematics, cannot be predicted by these models. Moreover, Imaeda et al (1994) demonstrated that the CMC joint may not be adequately modeled as a universal joint, emphasizing the need for employing the actual geometry of CMC articular surfaces for kinematic analyses.
The objective of this study is to develop a mathematical model of the thumb CMC joint which accounts for the complex topography of its articular surfaces as well as the capsular ligaments spanning the joint. This mathematical model can be employed to study complex 3D joint kinematics, contact forces and articular contact areas. When using accurate geometric and material data, this model can be used to elucidate the internal biomechanics of the CMC joint and to parametrically simulate processes which are hypothesized to play a role in the etiopathogenesis of CMC joint OA, such as capsular laxity and articular incongruence.