A Biomechanical Analysis of the Distal Radioulnar Joint Ballottement Test Using Stress CT

TDetection of distal radioulnar joint (DRUJ) instability has proven inconsistent despite numerous examination maneuvers. Computed tomography (CT) has been suggested as a modality for evaluating DRUJ instability; however, without stress across the DRUJ, it fails to reliably identify this. No study has simultaneously assessed stress CT with clinical stress maneuvers. As such, the purpose of this study was to compare both methods in stable and unstable wrists.

An arthrometer was developed to evaluate a clinical stress test of the DRUJ in various degrees of forearm rotation. In each forearm position, specimens were subjected to standardized volar and dorsal loads to simulate clinical stress to the DRUJ. Computed tomography images were acquired in each position with additional unstressed images. The triangular fibrocartilage complex (TFCC) was then sectioned to simulate DRUJ instability.

Nine upper extremities were used. The arthrometer could detect a significant difference between sectioned and intact TFCCs in the supinated forearm position. A large proportion of the translation measured by the arthrometer was due to rotation within the clamps. In the unstressed state, CT analysis using the radioulnar ratio failed to show significant differences in DRUJ stability for any forearm orientation. By applying stress across the DRUJ, CT analysis of ulnar translation along the sigmoid notch showed significant differences between TFCC intact and sectioned wrists.

Clinical examination maneuvers and arthrometers are observing a rotational component that occurs due to the inability to directly clamp the underlying bone, whereas stress CT is more accurate for quantifying underlying bony translation. Unstressed CT analysis did not identify instability.