Stress Ultrasound Evaluation of Medial Elbow Instability in a Cadaveric Model

Abstract

Background: An injury of the ulnar collateral ligament (UCL) is potentially career threatening for elite overhead-throwing athletes. Stress ultrasonography (SUS) allows for a rapid, cost-effective, and noninvasive evaluation of the UCL and elbow joint both at rest and with applied stress. Purpose/Hypothesis: To determine the amount of cadaveric elbow valgus gapping with sequential sectioning of medial elbow structures as measured by SUS. It was hypothesized that the greatest increase in ulnohumeral joint gapping would be noted with release of the anterior bundle of the UCL. Study Design: Descriptive laboratory study. Methods: Twelve cadaveric elbows were divided into 2 groups and dissected in reverse sequences under the direct supervision of an experienced orthopaedic surgeon. Baseline ultrasound and SUS with applied valgus loads were performed by an experienced radiologist. A valgus load was applied at each sectioning interval using a standardized device. Ulnohumeral joint gapping in millimeters was measured by SUS for each step as the width of the medial joint from the trochlea to the sublime tubercle. The mean increases in joint gapping (Δ) between each step were calculated to quantify the additional gapping achieved with release of each sequential stabilizer. Results: Release of the anterior band of the anterior bundle resulted in a mean Δ of 2.0 mm (95% CI, 1.1-2.8 mm). Release of the posterior band of the anterior bundle resulted in a mean Δ of 1.4 mm (95% CI, 0.6-2.2 mm). Release of the entire anterior bundle caused a mean increase in ulnohumeral valgus joint gapping of 3.4 mm (95% CI, 2.4-4.3 mm). Release of the remaining individual structures each resulted in a mean increase in valgus joint gapping of ≤0.8 mm. Conclusion: The results of the current cadaveric study suggest that different amounts of gapping are seen on SUS with sectioning of the medial elbow stabilizers. The hypothesis was confirmed with release of the anterior bundle of the UCL resulting in the greatest increase in joint gapping as measured by SUS. Clinical Relevance: This study illustrates that SUS can identify the contributions of each anatomic portion of the UCL and the flexor-pronator mass to ulnohumeral joint stability in a cadaveric model.