Normal Values of Distal Radioulnar Joint Kinematics during a Dynamic Press Test

Background Measurement of in vivo distal radioulnar joint (DRUJ) pathomechanics during simple activities can represent the disability experienced by patients and may be useful in diagnostics of DRUJ instability. A first step is to describe the physiological normal limits for DRUJ kinematics in a reproducible and precise test setup, which was the aim of this study. Methods DRUJ kinematics were evaluated in 33 participants with dynamic radiostereometry (RSA) while performing a standardized press test examination. AutoRSA software was used for image analyses. Computed tomography (CT) forearm bone models were generated, and standardized anatomical axes were applied to estimate kinematic outcomes including, DRUJ translation, DRUJ position ratio, and changes in ulnar variance. Repeatability of dynamic RSA press test double examinations was evaluated to estimate the precision and intraclass correlation coefficient (ICC) test-retest agreement. Results The maximum force during the press test was 6.0 kg (95% confidence interval [CI]: 5.1-6.9), which resulted in 4.7 mm (95% CI: 4.2-5.1) DRUJ translation, DRUJ position ratio of 0.40 (95% CI: 0.33-0.44), and increase in ulnar variance of 1.1 mm (95% CI: 1.0-1.2). The mean maximum DRUJ translation leveled off after a 5 kg force application. The DRUJ translation ICC coefficient was 0.93 within a prediction interval of +/- 0.53mm. Conclusions This clinical study demonstrates the normal values of DRUJ kinematics and reports excellent agreement and high precision of the press tests examination using an automated noninvasive dynamic RSA imaging method based on patient-specific CT bone models. The next step is the application of the method in patients with arthroscopic verified triangular fibrocartilage complex injuries.