Predictors for nonunion of unrepaired ulnar styloid fracture associated with distal radius fractures in patients treated with volar locking plate fixation and their effect on functional outcomes

Introduction: Nonunion of ulnar styloid fractures after radius stabilisation by volar locking plate (VLP) fixation without surgical fixation on ulnar styloid fractures is quite common. However, the factors affecting the nonunion of ulnar styloid fractures and their effect on functional outcomes in patients with distal radius fractures (DRFs) treated with VLP fixation are unclear. Hypothesis: The purpose of this study was to investigate the predictors affecting nonunion of unrepaired ulnar styloid fractures in patients with DRFs and the effect of nonunion and its predictors on functional outcomes. Materials and methods: We retrospectively reviewed data from 84 patients with DRF who underwent VLP fixation. None of the accompanying ulnar styloid fractures were manipulated during the surgery. Postoperative evaluation included the measurement of the grip strength, wrist range of motion, and Disabilities of the Arm, Shoulder, and Hand score at a minimum of one year postoperatively. Patients were divided into the nonunion and union groups according to the presence of union of ulnar styloid fracture. Demographic and radiologic parameters, including age, sex, bone mineral density, location and displacement distance of ulnar styloid fracture, and fracture pattern of DRFs, were analysed to identify predictors of nonunion. Functional outcomes were compared between the two groups and were compared according to the presence of predictors of nonunion. Results: Univariate analysis revealed that the nonunion rate was higher in ulnar styloid non-base fractures, substantial displacement (≥ 1.9 mm) of ulnar styloid fracture, and AO/OTA C-type DRF. However, multivariate logistic regression analysis showed that non-base fractures and substantial displacement were significant predictors. Accompanying ulnar styloid fracture nonunion and its predictors were found not to influence functional outcomes. Discussion: Substantial displacement and non-base fracture are predictive factors for nonunion of unrepaired ulnar styloid fractures after DRF treatment with VLP fixation. However, nonunion and its predictors do not influence the overall wrist function. These findings suggest that the ulnar styloid fracture accompanying DRF should not be considered a fracture affecting the wrist function when treating with VLP fixation. Level of evidence: III, Retrospective, Case Control study.