Sonographic Measurements of the Ulnar Nerve at the Elbow With Different Degrees of Elbow Flexion

Objective: To determine whether there were differences in the cross-sectional area (CSA) and the flattening ratio of the normative ulnar nerve as it passes between the medial epicondyle and the olecranon at 30 degrees of elbow flexion versus 90 degrees of elbow flexion. Design: Bilateral upper extremities of normal Dial healthy adult volunteers' were evaluated with ultrasound. The CSA and the flattening ratio of the ulnar nerve at the elbow as it passes between the medial epicondyle and the olecranon were measured, with the elbow flexed at 30 degrees and at 90 degrees, by 2 operators with varying ultrasound scanning experience by using ellipse and direct tracing methods. The results from the 2 different angles of elbow flexion were compared for each individual operator. Finally, intraclass correlations for absolute agreement and consistency between the 2 raters were calculated. Setting: An outpatient clinic room at a regional rehabilitation center. Participants: Twenty-five normal. healthy adult volunteers. Main Outcome Measurement: The mean CSA and the mean flattening ratio of the ulnar nerve at 30 degrees of elbow flexion and at 90 degrees of elbow flexion. Results: First, for the ellipse method, the mean CSA of the ulnar nerve at 90 degrees (9.93 mm(2)) was slightly larger than at 30 degrees (9.77 mm(2)) for rater 1. However, for rater 2, the mean CSA of the ulnar nerve at 90 degrees (6.80 mm(2)) was slightly smaller than at 30 degrees (7.08 mm(2)). This was found to be statistically insignificant when using a matched pairs t test and the Wilcoxon signed-rank test, with a significance level of .05. Similarly, the difference between the right side and the left side was not statistically significant. The intraclass correlations for absolute agreement between the 2 raters were not very high due to different measurement locations, but the intraclass correlations for consistency were high. Second, for the direct tracing method, the mean CSA at 90 degrees (7.26 mm(2)) was slightly lower than at 30 degrees (7.48 mm(2)). This was found to be statistically nonsignificant when using the matched pairs t test and the Wilcoxon signed-rank test with a significance level of .05. There was no significant difference in the average flattening ratio between the 2 angles for the left arm (0.54 at 30 degrees vs 0.56 at 90 degrees; P = .619 for the matched pairs t test and .274 for the Wilcoxon signed-rank test). However, for the right arm, the flattening ratio at 90 degrees was significantly higher than that at 30 degrees (0.58 at 90 degrees vs 0.50 at 30 degrees; P = .007 for both the matched pairs t test and the Wilcoxon signed-rank test). Conclusions: The mean CSA of the ulnar nerve at the elbow at 30 degrees was not significantly different than at 90 degrees. However, the average flattening ratio at 90 degrees was found to be significantly higher than at 30 degrees for the right arm.