In Vivo Three-Dimensional Displacement of the Distal Radioulnar Joint During Resisted Forearm Rotation

Purpose: The in vivo displacement of the distal radioulnar joint (DRUJ) while under resisted pronation or supination has never been previously quantified. Being a joint with 3 dimensions of motion (dorsopalmar translation, changes in ulnar variance, and radioulnar coaptation), our purpose was to determine its 3-dimensional (3D) displacement during resisted rotational torque. Methods: Ten normal subjects (aged 31.8 years ± 7.8; F, 5; M, 5) were recruited. Computed tomography scans of a subjects' distal forearms were obtained while grasping the handles of a custom apparatus to keep the fist and forearm in neutral rotation. Scanning was performed in 3 conditions: no rotational torque (control), maximum isometric supination, and maximum isometric pronation. The 3D displacement of the DRUJ, using the ulnar fovea as the reference point, during isometric rotational torque was determined using markerless bone registration techniques. Results: The mean 3D displacement of the ulnar fovea during maximum isometric pronation and maximum isometric supination was 3.09 mm ± 0.94 and 2.17 mm ± 1.55, respectively. During maximum isometric pronation, the ulnar fovea displaced a mean of 0.51 mm ± 1.79 dorsally. During maximum isometric supination, the ulnar fovea displaced a mean of 0.13 mm ± 2.07 volarly. In both conditions, ulnar variance increased (0.23 mm ± 2.52 for isometric pronation and 0.44 mm ± 1.57 for isometric supination), and there was increased radioulnar coaptation (0.37 mm ± 0.86 for isometric pronation, 0.039 mm ± 0.66 for isometric supination). Conclusions: Resisted rotational torque can be applied to the DRUJ while in neutral rotation during computed tomography imaging, producing measurable displacements in 3D. This technique of studying the DRUJ has the potential to improve our ability to detect and quantify instabilities of the DRUJ.