Purpose: The purpose was to investigate the relationship between distal radius fracture malunion and arm-related disability.

Methods: This prospective population-based cohort study included 143 patients above 18 years with acute distal radius fracture treated at one emergency hospital with either closed reduction and cast (55 patients) or with closed reduction and external and/or percutaneous pin fixation (88 patients). The patients were evaluated with the disabilities of the arm, shoulder and hand (DASH) questionnaire at baseline (inquiring about disabilities before fracture) and at 6, 12 and 24 months after the fracture. The 12-month follow-up also included the SF-12 health status questionnaire as well as clinical and radiographic examination. The patients were classified according to the degree of malunion (defined as dorsal tilt > 10 degrees or ulnar variance > 0 mm) into three groups; no malunion, malunion involving either dorsal tilt or ulnar variance, and malunion involving both dorsal tilt and ulnar variance. A Cox regression analysis was performed to determine the relationship between the 1-year DASH score (≥ 15 or < 15) and malunion adjusting for age, sex, fracture AO type, and treatment method and the relative risk (RR) of obtaining the higher DASH score was calculated. The number needed to harm (NNH) associated with malunion was calculated.

Results: The mean DASH score at 1 year after fracture was about 10 points worse with each degree of increased malunion. The degree of malunion also correlated with SF-12 score, grip strength and supination. The regression analysis showed significantly higher disability with each degree of malunion compared to no malunion; for malunion involving either dorsal tilt or ulnar variance the RR was 2.4 (95% CI 1.0–5.7; p=0.038), and for malunion involving both dorsal tilt and ulnar variance the RR was 3.2 (95% CI 1.4–7.5; p=0.007). The NNH was 2.5 (95% CI 1.8–5.4).

Conclusion: Malunion after distal radius fracture was associated with higher arm-related disability.