Post-Operative Assessment of Ulnar Nerve Tension Using Shear-Wave Elastography

Abstract

Background: Ulnar nerve compression at the elbow level is the second-most common entrapment neuropathy. The aim of this study was to use shear-wave elastography for the quantification of ulnar nerve elasticity in patients after ulnar nerve decompression with anterior transposition and in the contralateral non-operative side.

Method: Eleven patients with confirmed diagnosis and ulnar nerve decompression with anterior transposition were included and examinations were performed on an Aixplorer^TM ultrasound system (Supersonic Imagine, Aix-en-Provence, France).

Results: We observed significant differences at 0-degree (p < 0.001), 45-degree (p < 0.05), 90-degree (p < 0.01) and 120-degree (p < 0.001) elbow flexion in the shear elastic modulus of the ulnar nerve in the operative and non-operative sides. There were no statistically significant differences between the elasticity values of the ulnar nerve after transposition at 0-degree elbow flexion and in the non-operative side at 120-degree elbow flexion (p = 0.39), or in the ulnar nerve after transposition at 120-degree elbow flexion and in the non-operative side at 0-degree elbow flexion (p = 0.09).

Conclusion: Shear-wave elastography has the potential to be used postoperatively as a method for assessing nerve tension noninvasively by the estimation of mechanical properties, such as the shear elastic modulus.

Keywords: elastography; nerve compression; nerve transposition; ulnar nerve.

Figure 1

Sketches detailing ulnar nerve (yellow) entrapment in the cubital tunnel (a), which is where Obsorne’s ligament is located (asterix). The ulnar nerve is transposed anteriorly (blue arrow) and stabilized with a fascial sling (b). Intraoperative photograph after complete release of all points of ulnar nerve with elevation of the soft tissue above the flexor-pronator muscle mass (c); the ulnar nerve is transposed subcutaneously and stabilized anteriorly with a fascial sling (d).

Figure 2

Examples of shear elastic modulus measurement of the ulnar nerve at 0- (image at top), 45-, 90- and 120-degree flexion of the elbow in an Elbo™ brace (A). The colored region represents the shear elasticity map in a healthy ulnar nerve (B) and an ulnar nerve after anterior transposition (C) with a color scale (see bottom right), with blue representing lesser stiffness and red greater stiffness. The software allowed us to measure the mean shear elasticity value over a 2 mm² Q-Box focus area.

Figure 3

Box plot of the shear elastic modulus of the ulnar nerve (kPa) at 0, 45, 90 and 120 degrees of elbow flexion in operative side (red) and non-operative side (blue). Box (interquartile range (IQR); 75th–25th percentile), central line (median; 50th percentile), lower whisker (5th percentile), upper whisker (95th percentile).