Three-dimensional displacement analysis of the thumb CM joint based on the bone axis using X-ray CT images

Abstract

Thumb carpometacarpal (CM) joint osteoarthritis is a common disease in elderly. To clarify the thumb CM joint motion is critical to reveal the factor of disease and improve treatment methods. The thumb CM joint, which has a specific structure called the saddle joint, consists of the first metacarpal bone and the trapezium. The saddle-shaped articular surface allows us to perform a wide range of motion and screw home torque rotation. However, the kinematics of the thumb CM joint is not clarified. The factor of disease and the optimal treatment is also unclear. Recent motion analysis often uses the Euler angle method with three-dimensional CT, whose calculated value may be inaccurate because the coordinate axis used for evaluation does not always coincide with the actual rotation axis. Besides, previous analyses do not capture localized motion changes due to the limited number of limb positions for analysis. Therefore, this study proposed a new analysis method to calculate the rotation axis and performed the 3-dimensional analysis of the thumb by dividing its motion into several segments with CT imaging. As a result, the conventional method often underestimates the motion of the thumb CM joint motion more than our method. The screw home torque rotation occurred in the specific flexion segment. This kinematics may cause a heavy load on the joint surface and be a factor in diseases.