gms | German Medical Science

Objectives/Interrogation: The distal radioulnar ligaments (DRUL) are considered major stabilizers of the DRUJ. The DRUL can be separated into superficial and deep layers and the dorsal and volar portions of each tighten reciprocally during forearm pronation and supination. Ulnar styloid fractures (USF) may affect the insertions of these ligaments and therefore the mechanics of the DRUJ. Knowledge of the topography of the DRUL insertions is essential to better understand possible instability that could accompany ulnar styloid fractures. The purpose of this study was to anatomically evaluate the location and size of the footprints of each portion of the DRUL in relation to the bony landmarks of the styloid.

Methods: 24 fresh cadaver forearm-wrist-hand complex were dissected free of soft tissue while taking care to retain the TFCC and the DRUJ capsule. Characteristic bony points were digitized to define the geometry of the ulnar styloid and head. The superficial and deep ligaments were sharply transected sequentially at their base and the circumference of each footprint was digitized. The area and distances between the footprints and bony landmarks were then calculated. Distances were also calculated in two dimensions along the long axis of the ulna to simulate a plain radiograph projection onto a 2D plane.

Results and Conclusions: The average styloid height (length from base to tip) was 17 mm, the average anterior-posterior width was 6.5mm and the average fovea depth was 1.8 mm. In the coronal plane, the superficial DRUL inserted from the tip of the styloid down to 87% of the styloid height. The deep DRUL inserted from 81% of the styloid height down to the fovea. The superficial footprint had an area of 10.6 mm² on the radial face of the ulnar styloid. The deep DRUL attachment had two distinguishable parts: the dorsal portion (2 3mm²) and the volar portion (7.8mm^2). The dorsal portion had a separate footprint in 47% of the cases.

This study quantified the relationships between the footprints of each of the component parts of the DRUL relative to the bony landmarks of the ulnar styloid. The deep portion attaches from the fovea up to 81% of the styloid. USF more distal that 81% may only minimally affect the DRUJ stability. Furthermore, the deep portion has distinct dorsal and volar footprints with the dorsal portion inserting more dorsal and radial. In the setting of an USF, whether the fracture traverses each of these footprints may result in preferential detachment of the DRUL and thus affect stability of the DRUJ.