Utility of Ultrasound for Identifying Median Nerve Changes Indicative of Acute Carpal Tunnel Syndrome After Distal Radius Fracture.

Purpose: Ultrasound offers a fast and inexpensive way to evaluate the median nerve. However, there is a paucity of data assessing ultrasound in acute trauma. Our study aimed to characterize median nerve changes indicative of acute carpal tunnel syndrome (ACTS) in a cadaveric distal radius fracture (DRF) model. Methods: We used 10 upper-extremity specimens. We induced ACTS (carpal tunnel pressure >40 mm Hg) in a distraction-only model and then used a DRF model as a neutral position, under traction, or wrist extension. We measured the median nerve cross-sectional area (CSA), height, and width with ultrasound in each model. We used a novel calculation, height-width ratio (HWR), to describe nerve shape. A low HWR indicates an elliptical shape; as the HWR increases toward one, the shape becomes more circular. The CSA measurements and HWR at pressures >40 mm Hg were used to calculate a 95% confidence interval, which defined the threshold for ACTS. Results: Wrist distraction created carpal tunnel pressures >40 mm Hg in all specimens. Distraction increased CSA compared with baseline (9.1 ± 0.9 mm Conclusions: ACTS should be suspected in patients with median nerves demonstrating increased CSA and adopting a more circular shape. Fracture positioning impacts median nerve CSA with wrist extension, causing the greatest change. Median nerve HWR may offer an easier ultrasonographic alternative to CSA. Type of study/level of evidence: Diagnostic III.