Factors Related to Increased Ulnar Collateral Ligament Thickness on Stress Sonography of the Elbow in Asymptomatic Youth and Adolescent Baseball Pitchers

Background: Stress ultrasound (SUS) of the elbow has demonstrated changes in the anterior band of the ulnar collateral ligament (UCL) in professional and high school-aged pitchers. However, there have been no large reports correlating pitching history data with SUS changes in youth and adolescent baseball pitchers. Hypothesis: Changes of the UCL on SUS will correlate with pitching volume in youth and adolescent baseball pitchers. Study Design: Cross-sectional study; Level of evidence, 3. Methods: SUS of the elbow was performed in both elbows of 102 youth and adolescent baseball pitchers. UCL thickness and the width of the ulnohumeral joint, at rest and with 150 N of valgus stress, were measured using a standardized, instrumented device. Demographic data, arm measurements, and a pitching history questionnaire were recorded as well. The pitchers were separated into 2 groups based on age: group 1 (12-14 years) and group 2 (15-18 years). SUS findings of the dominant elbows were compared between the 2 groups. Correlation analysis and linear regression were used to identify relationships between SUS findings and pitching history data. Results: In all pitchers, the mean UCL thickness was 4.40 mm in the dominant elbow and 4.11 mm in the nondominant elbow (P =.03). There was no significant difference between elbows in any joint space characteristics. A comparison of group 1 versus group 2 demonstrated significant differences in UCL thickness (4.13 vs 4.96 mm; P <.001), resting joint space width (6.56 vs 4.04 mm; P <.001), and stressed joint space width (7.68 vs 4.07 mm; P <.001). There was no difference in the change in joint space width between the 2 groups (1.11 vs 0.76 mm; P =.05). The UCL was significantly thicker in pitchers who threw more than 67 pitches per appearance (4.69 vs 4.14 mm), who pitched more than 5 innings per appearance (4.76 vs 4.11 mm), and who had more than 5.5 years of pitching experience (4.71 vs 4.07 mm; P <.001). Linear regression demonstrated that age, weight, and pitches per appearance (R ² = 0.114, 0.370, and 0.326, respectively) significantly correlated with UCL thickness. Conclusion: These findings suggest that UCL thickness increases as pitchers get older and heavier and as they increase their pitch volumes.