Ultrasound evaluation of ulnar nerve anatomy in the pediatric population

Ulnar nerve instability has been reported in up to 17% of children. Accurate assessment is important to achieve because of potential nerve complications that can arise from treatment of common pediatric fractures, including supracondylar humerus fractures. The objective of our study was to evaluate our ability to use ultrasonography to determine the extent of ulnar nerve dislocation in the normal pediatric population and to determine if there is a relationship between ulnar nerve instability and ligamentous laxity.

We conducted a prospective ultrasound evaluation of 51 children, examining the excursion of the ulnar nerve through full range of motion. On the basis of its movement during flexion, the ulnar nerve was categorized as stable, subluxating, or dislocating. In addition, we assessed all subjects for ligamentous laxity using the Wynne-Davies signs of joint laxity. The subjects were then divided into groups based on age or ligamentous laxity, and statistical analysis was performed.

Most of the elbows evaluated had stable ulnar nerves (64/102, 62.7%), 27.5% (28/102) had subluxating nerves, and 9.8% (10/102) had dislocating nerves. Patients aged between 6 and 10 showed the highest rate of dislocating or subluxating nerves, with 50%, and also the highest average laxity score, 2.0. When grouped according to ligamentous laxity, patients who had multiple signs of ligamentous laxity had statistically higher numbers of subluxating and dislocating nerves (91.6%, 11/12) than those with lower laxity scores (25.6%, 10/39).

There are a substantial number of subluxating or dislocating ulnar nerves in children, and the incidence is often bilateral. Patients with ligamentous laxity are more likely to possess unstable ulnar nerves. Ultrasound evaluation and assessment of ligamentous laxity are additional tools that can be used to assess elbow anatomy and identify children at risk for iatrogenic nerve injury.

Level III, diagnostic study.