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Ulnar Styloid Fractures: Is Their Neglect Truly Benign
Tyler S. Pidgeon, MD; Joseph Crisco, PhD; Alexander T. Wilson, BS; Gregory Waryasz, MD, Douglas Moore, MS; Manuel F. DaSilva, MD
Brown University/Rhode Island Hospital, Providence, RI

Introduction: Fractures involving the base of the ulnar styloid may disrupt the foveal insertion of the deep portion of the distal radioulnar ligaments (DRUL). This component of the triangular fibrocartilage complex is theorized to assist with stabilization of the distal radioulnar joint (DRUJ). Thus, we hypothesize that ulnar styloid base fractures involving the ulnar fovea in a cadaveric model destabilize the DRUJ. Additionally, we predict that DRUJ stability is restored with reduction and fixation of the styloid fragment.
Methods: DRUJ stability in pronosupination was evaluated in six fresh-frozen upper extremities (4 females) aged 52-68 years (Mean: 58.7) using a custom jig, which allowed free rotation of the radius around the fixed ulna (Figure 1). Optical motion capture was used to record rotation and translation of the radius with respect to the ulna. Marker clusters were rigidly secured to the distal radius and ulna via threaded K-wires. Each specimen was subjected to 4 Nm of torque in both supination and pronation under four conditions: Intact, ulnar styloid osteotomy, ulnar styloid fixation, and DRUL transection. The styloid osteotomy freed the foveal insertion of the DRUL. Styloid fixation was performed with a headless compression screw under fluoroscopy to confirm anatomic alignment. DRUL transection was performed with a scalpel under direct visualization. Group differences were compared using a one-way repeated-measures ANOVA and Dunnett's multiple comparison post hoc tests.
Results (Table I): Ulnar styloid osteotomy and DRUJ disruption significantly increased pronation of the radius compared to the intact condition by averages of 10.0 degrees and 21.0 degrees, respectively. In contrast, only DRUJ disruption significantly increased supination of the radius compared to the native condition, by an average of 19.9 degrees. Pronation and supination after headless screw fixation were comparable to those seen after osteotomy. There were no observable differences in the translation of the radius.
Discussion: Ulnar styloid fracture treatment is controversial. Our study confirms that such fractures involving the fovea cause instability of the DRUJ in pronation. Thus, we conclude that ulnar styloid base fractures involving the fovea should be reduced and fixed to return stability to the DRUJ. In our experiment, fixation with a headless compression screw achieved anatomic reduction; however, it did not acutely return stability to the DRUJ as defined by limitation of pronation under 4 Nm of torque. While headless compression screws may adequately fixate these fractures in conjunction with forearm immobilization until healing, this will need to be confirmed.

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