Cross-sectional area reference values for peripheral nerve ultrasound in adults: a systematic review and meta-analysis-Part I: Upper extremity nerves.

BACKGROUND AND PURPOSE: Measurement of the cross-sectional area (CSA) of peripheral nerves using ultrasound is useful in the evaluation of focal lesions like entrapment syndromes and inflammatory polyneuropathies. Here, a systematic review and meta-analysis of published CSA reference values for upper extremity nerves was performed.

METHODS: Available to date nerve ultrasound studies on healthy adults were included and a meta-analysis for CSA was provided of the following nerves: median nerve at the wrist, forearm, upper arm; ulnar nerve at the Guyon's canal, forearm, elbow, upper arm; radial nerve at the upper arm. Regression and correlation analyses for age, gender, height, weight, geographic continents and publication year are reported.

RESULTS: Seventy-four studies with 4186 healthy volunteers (mean age 42.7 years) and 18,226 examined nerve sites were included. The calculated mean pooled CSA of the median nerve at the wrist was 8.3 mm2 (95% confidence interval [95% CI] 7.9-8.7, n = 4071), at the forearm 6.4 mm2 (95% CI 5.9-6.9, n = 3021), at the upper arm 8.3 mm2 (95% CI 7.5-9.0, n = 1388), of the ulnar nerve at the Guyon's canal 4.1 mm2 (95% CI 3.6-4.6, n = 1688), at the forearm 5.2 mm2 (95% CI 4.8-5.7, n = 1983), at the elbow 5.9 mm2 (95% CI 5.4-6.5, n = 2551), at the upper arm 6.6 mm2 (95% CI 5.1-6.1, n = 1737) and of the radial nerve 5.1 mm2 (95% CI 4.0-6.2, n = 1787). Substantial heterogeneity across studies (I2 > 50%) was found only for the radial nerve. Subgroup analysis revealed a positive effect of age for the median nerve at the wrist and for height and weight for different sites of the ulnar nerve.

CONCLUSION: The first meta-analysis on CSA reference values for the upper extremities with no or only low heterogeneity of reported CSA values in most nerve sites is provided. Our data facilitate the goal of an international standardized evaluation protocol.