Ulnar Styloid Base Fractures Cause Distal Radioulnar Joint Instability in a Cadaveric Model

Abstract

Background: The deep portion of the distal radioulnar ligaments (DRUL) inserts on the ulnar fovea and is the most important stabilizer of the distal radioulnar joint (DRUJ). Ulnar styloid base fractures that include the ulnar fovea may cause DRUJ instability. Methods: DRUJ stability in pronosupination was evaluated in 12 fresh-frozen upper extremities (4 female) aged 52 to 68 years (mean: 58.8 years) using a custom fixture, which allowed free rotation of the radius around the fixed ulna. Optical motion capture was used to record rotation of the radius with respect to the ulna. Each specimen was subjected to 3 N m of torque in both supination and pronation under 4 conditions: intact, ulnar styloid osteotomy with disruption of the foveal insertion of the DRUL, ulnar styloid fixation, and DRUL transection. Group differences were compared using a 1-way repeated-measures analysis of variance and Tukey multiple comparison post hoc tests. Results: When compared with the intact condition, both ulnar styloid osteotomy and DRUL transection significantly increased mean pronation (by 9.40° and 15.21°, respectively) and supination (by 9.05° and 17.42°, respectively) of the forearm. Screw fixation only significantly reduced pronation compared with osteotomy (by 2.62°). Screw fixation did not significantly affect supination. Conclusions: Ulnar styloid fractures that disrupt the fovea cause instability of the DRUJ in pronation and supination under 3 N m of torque in a cadaveric model. Screw fixation of ulnar styloid base fractures achieves anatomic reduction; however, it only partially returns rotational stability acutely to the DRUJ and only during pronation.