Increasing Dorsal Tilt in Distal Radius Fractures Does Not Increase Median Nerve Strain

Abstract

Background: Although extensive research shows an association between distal radius fractures and the development of median nerve related pathologies such as carpal tunnel syndrome, none directly track how the resulting angular deformity relates to likelihood of development of median nerve pathology. Methods: Median nerve strain was measured with a custom-built system using a camera, optical markers, and a proprietary segmentation algorithm. After initial validation of the system in a cadaver model, our system was used to assess strain in 10 cadaver arms with a simulated distal radius fracture and increasing dorsal angulation. The measured strain at each angle was then analyzed using a linear regression model. Results: The linear regression model in the validation experiment demonstrated a regression coefficient of 1.00067 (P < 0.0001) with r2= 0.899, thus validating the use of the optical tracking system. The average strain at maximum dorsal angulation (50 degrees) across all specimens was -0.2%. Linear regression analysis of the effect of increasing dorsal angulation on strain in the osteotomy model yielded a regression coefficient of -0.000048 (P = 0.714), r2= 0.00129, suggesting no significant correlation between increasing dorsal tilt and median nerve strain. Conclusions: Increases in median nerve strain at the wrist are negligible with increasing dorsal tilt in a distal radius fracture model. It is therefore likely that other factors, such as increased pressure within the carpal tunnel, are the primary cause of median neuropathy in distal radius malunions. Therefore, correction of dorsal tilt may not be required to improve neurologic symptoms.