CMC Biomechanics and OA Progression: An Update on Our Research Program

Introduction Thumb carpometacarpal (CMC) osteoarthritis (OA) is a widespread, disabling disease of undetermined etiology that is far more prevalent in woman than in men. The disease affects 15% of adults over age 30, and two-thirds of women over age 55. Loss of thumb function alone imparts a 40 to 50% impairment to the upper extremity due to its central role in nearly all grasp and handling tasks. Although recent studies suggest genetics, increased BMI and environmental factors (such as hand use) are likely associated with the development of thumb CMC OA. There is strong empirical and experimental data indicating that altered biomechanics plays a central role in the disease and, importantly in its treatment. CMC OA is far more prevalent in women than men, and women have flatter joint surfaces, smaller areas of cartilage contact, and higher contact pressures. Our study is designed to generate foundational data on thumb CMC biomechanics in vivo by quantifying and comparing the differences in CMC biomechanics across sex and age using a cross-sectional experimental design (Aim 1), and, using a longitudinal experimental design, to determine if CMC joint laxity is positively associated with CMC OA progression 1.5 and 3 years after initial diagnosis in patients who initially present with CMC pain and minimal radiographic evidence of OA (Aim 2). Materials and Methods Aim 1 . Determine the in vivo biomechanics and morphometry of the CMC joint in asymptomatic young and old men and women ( N = 44; 18 to 25 years; and 45 to 75 years.) during functional tasks using well-established methodologies. Hierarchical Linear Models (HLMs) are used to evaluate differences as a function of age and gender, with task and loading as covariates. Aim 2 . Measure temporal changes in the in vivo biomechanics and morphometry of the CMC joint during functional tasks in women and men ( N = 80; 45 to 75 years.) presenting with Early OA at baseline and 1.5 and 3 years follow-up. OA progression is measured at follow-up primarily via radiographic classification (Eaton) and compared with the baseline CMC joint laxity measure using HLMs. Results Our results to date include CMC kinematics, subchondral shape analyses, AOL and DRL ligament elongation and function, joint-space measures and standardized pain and function outcomes. A summary of these findings for normals and for early OA at baseline will be presented. Acknowledgments NIH/NIAMS AR059185