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

Ledibabari M Ngaage; Peter M Casey; Aviram M Giladi

doi:10.1016/j.jhsg.2023.03.013

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

J Hand Surg Glob Online. 2023 Apr 21;5(4):430-434. doi: 10.1016/j.jhsg.2023.03.013. eCollection 2023 Jul.

Authors

Ledibabari M Ngaage^{1

2}, Peter M Casey¹, Aviram M Giladi¹

Affiliations

¹ The Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD.
² Department of Plastic and Reconstructive Surgery, Johns Hopkins University School of Medicine, Baltimore, MD.

Abstract

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 mm² vs 6.3 ± 1.2 mm², P < .001). Under ACTS-level pressures, the thresholds for CSA and HWR were 8.5 mm² and 0.41, respectively. HWR significantly increased with distraction compared with baseline (0.47 ± 0.10 vs 0.28 ± 0.09, P = .006). Most neutral DRF models (n = 8, 80%) met the CSA threshold for ACTS, whereas all specimens with a DRF extended or under traction had CSAs above the ACTS threshold. Compared to the baseline, the shape of the median nerve was more circular in all DRFs, including neutral (0.28 ± 0.09 vs 0.39 ± 0.13), under traction (0.43 ± 0.09), and extended (0.45 ± 0.09).

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.

Keywords: Carpal tunnel syndrome; Cross-sectional area; Distal radius fracture; Median nerve; Ultrasonography.