Shear wave elastography ultrasound assessment of the ulnar collateral ligament in the elbow of college baseball players.

Abstract

Background: The ulnar collateral ligament (UCL) stabilizes the elbow during overhead throwing activities. Repetitive throwing can cause valgus laxity even without injury. Shear-wave ultrasound elastography (SWE) is a novel imaging technique that assesses tissue elasticity. This study aimed to assess UCL elasticity in college baseball players using SWE under resting and valgus stress conditions.

Methods: The study included 30 healthy male college baseball players (mean age 20.48 ± 1.34 years). The dominant and non-dominant arms of participants were examined, excluding those with a history of UCL injury. UCL thickness was measured using conventional ultrasound, and elastography was conducted at the same sites. Measurements were repeated under valgus stress, and the ulnohumeral joint gap was recorded. Participants were categorized into throwing and non-throwing arm groups. A subgroup analysis of the throwing arm was conducted based on joint laxity, defined as an increase of >1 mm in the ulnohumeral joint gap under valgus stress, which is associated with UCL injury and joint laxity. Correlations between UCL evaluation parameters and changes in ulnohumeral gap were analyzed.

Results: Out of 54 elbows, 26 were classified as throwing and 28 as non-throwing. The throwing group had a significant increase in the ulnohumeral gap compared to the non-throwing group. The ulnohumeral gap under valgus stress increased from 0.59 to 0.72 cm (p=0.01). There was no significant difference in shear-wave velocity (SWV) between the two groups. Within the throwing group, 13 elbows were classified as lax arms and 15 as non-lax arms. The SWV of the lax arms (6.71 ± 4.59 m/s) was significantly lower than that of the non-lax arms (8.54 ± 5.17 m/s) (p=0.045). Multiple regression analysis showed that UCL thickness and SWV were independently correlated with the rate of change in the ulnohumeral gap (ß=0.335, p=0.018 and ß=-0.319, p=0.013, respectively).

Conclusion: Valgus laxity of the elbow joint can be evaluated based on the elasticity of the UCL measured above the joint line using SWE at rest. Thickened UCL may exhibit a decrease in function; therefore, physicians should not evaluate the joint status solely on the basis of the structural properties on conventional ultrasound.