LAUSR

Few studies have described extents of subluxation, applied stresses, and assessing postures during trapeziometacarpal stress-view radiography, which probably has led to unsatisfactory reliability of the Eaton classification for determining arthritis. To address this problem, this study examined the effects of applied forces and thumb position on levels of trapeziometacarpal subluxation during stress-view radiography. Thirty-two volunteers allowed our team to quantify their trapeziometacarpal subluxation ratio (TSR) via fluoroscopic images while stress was applied to their thumbs under 3 different positions (Stress_IP, Stress_MP, and Stress_KP). The results were recorded synchronously using a force transducer embedded in a custom stress-view evaluation system (SvES). The differences in TSR under different stress levels and thumb positions and the relationships between TSRs and applied stresses on the joint were analyzed. The findings show acceptable reliability and validity with use of the SvES for trapeziometacarpal stress-view tests. There were significant correlations between applied stresses and TSRs (r = 0.8 − 0.989, P < 0.001), and different levels of applied stress significantly contributed to different TSRs. Assessing the thumb in various postures significantly influenced the TSRs and corresponding stresses. Although Stress_KP could produce larger forces, the greater TSRs were found under Stress_IP and Stress_MP conditions. This study clearly indicates relationships among the extents of subluxation, applied stresses, and assessing postures when trapeziometacarpal stress-view radiographs are performed with use of the SvES. These findings might provide information for further clinical or research use and should be useful as a basis for better understanding and precise diagnosis of joint mechanics.