Dynamic analysis of the ulnar nerve and cubital tunnel morphology using ultrasonography: a cadaveric study

Background: The causes of ulnar neuropathy at the elbow are unclear. The authors hypothesized that the humeral trochlea protrudes into the cubital tunnel during elbow flexion and causes a dynamic morphologic change of the ulnar nerve in the cubital tunnel. Methods: An ultrasonic probe was fixed to the ulnar shafts of 10 fresh cadavers with an external fixator, and dynamic morphology of the cubital tunnel and ulnar nerve was observed. The distance from the Osborne band to the trochlea (OTD), distance from ulnar nerve center to the trochlea (UTD), and the short-and long-axis diameters of the nerve at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of elbow flexion were recorded. We compared the OTD, UTD, and the flattening of the ulnar nerve at the different angles of flexion using single-factor analysis of variance. Correlation between the ulnar nerve flattering, OTD, and UTD was examined using Spearman correlation coefficient. A P value less than .05 was used to denote statistical significance.Results: Flattening of the ulnar nerve progressed with increasing elbow flexion and was significantly different between 0 degrees and 60 degrees, 90 degrees, and 120 degrees (P = .03 at 60 degrees, P < .01 at 90 degrees and 120 degrees). OTD decreased with elbow flexion, and there was a significant difference at all elbow flexion angles (all P < .01). UTD decreased significantly from 0 degrees flexion to 90 degrees flexion (P = .03). Flattening of the nerve was signif-icantly correlated with the OTD (r = 0.66, P < .01).Conclusions: A positive correlation was found between the protrusion of the humeral trochlea into the cubital tunnel during elbow flexion and ulnar nerve flattening using cadaveric elbow and ultrasonography.Level of evidence: Basic Science Study; Kinesiology; Cadaver Model (c) 2022 Journal of Shoulder and Elbow Board of Trustees. All reserved.

Automated summary

During elbow flexion, the protrusion of the humeral trochlea into the cubital tunnel causes dynamic morphological changes in the ulnar nerve. The flattening of the ulnar nerve increases with increasing elbow flexion.