Sonographic normal values for the cross-sectional area of the ulnar nerve: a systematic review and meta-analysis

Abstract

Purpose Nerve size is a commonly used sonographic parameter when assessing suspected entrapment of the ulnar nerve. We aimed to create a robust set of normal values, based on a critical review of published normal values. Methods We performed a systematic evaluation of studies on normal ulnar nerve sizes, identified in PubMed, Embase, and Cochrane databases. Using meta-analyses, we determined pooled mean cross-sectional area (CSA) values for different anatomical locations of the ulnar nerve throughout the arm. Subgroup analyses were performed for gender, probe frequency, in- or exclusion of diabetic patients, position of the elbow and Asian versus other populations. Results We identified 90 studies of which 77 studies were included for further analyses after quality review, resulting in data from 5772 arms of 3472 participants. Subgroup analyses show lower CSA values at at the wrist crease and proximal to the wrist crease when using low frequency probes (< 15 MHz) and at the wrist crease, proximal to the wrist crease, proximal forearm and the distal upper arm in Asians. CSA values were lower when in flexed position compared to extended position for the cubital tunnel inlet only. No difference was found for gender. Conclusions Our systematic review provides a comprehensive set of normal values at sites along the entire length of the ulnar nerve. This provides a foundation for clinical practise and upon which future studies could be more systematically compared.

Comparison of distortion correction preprocessing pipelines for DTI in the upper limb

“…All ROIs were checked independently by RGW, TG and RF. Around the elbow, the normal cross‐sectional area of the ulnar nerve is ∼7mm 2 , 45 , 46 the median ∼7 mm 2 , and the radial nerve is ∼5.1mm 2 . 46 To minimize partial volume effects, the ROI was limited to 1.5 mm 2 (one voxel) and centered over the cross‐section of the nerve, which typically had the highest regional QA value.…”

Updates in diagnostic tools for diagnosing nerve injury and compressions

“…The international agreement is that nerve size is best measured as a cross-sectional area (CSA) within the hyperechoic outer epineurial rim (Tawfik et al, 2023). CSA reference values (Figure 2) are available for most limb nerves in different populations and should be used to interpret CSA findings (Abdelnaby et al, 2023;Boers et al, 2023;Cartwright et al, 2008Cartwright et al, , 2013Fisse et al, 2021). It is strongly advised to scan the nerve all the way along its accessible length, looking for sudden changes in size and/or appearance.…”

The use and misuse of sonographic reference values in neuromuscular disease

“…In addition, age, body mass index, ethnicity and race, exact measurement location along the length of the nerve, technical factors such as the insonation frequency (i.e., <15 or >15 MHz), the use of zoom magnification, and patient positioning have all been reported to influence the ultrasound measurements of nerve size. [20][21][22][23][24] Unfortunately, the authors were not able to address the influence of many of these items in their meta-analysis (e.g., lack of important demographic details, technical factors, exact anatomic and patient positioning). Also, the method they used to pool the published mean nerve size values gave different weights to studies with different sample sizes and outliers, which resulted in more accurate confidence intervals for the mean values, but not a better delineation of the upper and lower limits of normal that would be used to determine abnormality.…”

“…The authors also faced considerable challenges when collating all the published normal values, including the lack of access to the raw data, the heterogeneity of the populations sampled, and the lack of standardization in the sonographic protocols. In addition, age, body mass index, ethnicity and race, exact measurement location along the length of the nerve, technical factors such as the insonation frequency (i.e., <15 or >15 MHz), the use of zoom magnification, and patient positioning have all been reported to influence the ultrasound measurements of nerve size 20–24 . Unfortunately, the authors were not able to address the influence of many of these items in their meta‐analysis (e.g., lack of important demographic details, technical factors, exact anatomic and patient positioning).…”