Risk Factors for an Ulnar Collateral Ligament Injury Resulting in Surgery: A Prospective Longitudinal Study of 305 Professional Baseball Pitchers.

Background: The number of ulnar collateral ligament (UCL) surgical procedures in professional baseball players continues to increase.

Hypothesis: Performance, injury history, physical characteristics, pitching velocity, elbow torque, and amount of pitching are associated with the risk of a UCL injury resulting in surgery.

Study design: Cohort study; Level of evidence, 2.

Methods: All 30 Major League Baseball (MLB) clubs were contacted for recruitment at Spring Training and the Fall Instructional League in 2015, 2016, and 2017. Pitchers were eligible if they were from the most recent draft and were healthy. Participants completed a questionnaire, a physical examination, magnetic resonance imaging (MRI), and biomechanical testing. The questionnaire included date of birth, previous elbow surgery, and self-reported fastball velocity. The physical examination included measurements of height, weight, and passive range of motion in both shoulders. Elbow MRI assessed for abnormalities of the UCL. During biomechanical testing, fastball velocity was measured, and elbow varus torque was calculated. Pitching volume and injuries resulting in UCL surgery were monitored until the end of 2019. Continuous variables were compared between pitchers with and without UCL surgery using the Student t test. For binary risk factors, significant differences in proportions were determined with the chi-square test. Cox proportional hazards regression was used to model hazard ratios for the associations between risk factor variables and time to injury. An alpha level of .05 was used for all tests.

Results: Overall, 31 of 305 participants required UCL surgery during the follow-up period. Elbow varus torque was significantly higher for pitchers with a subsequent injury requiring UCL surgery (100.8 ± 18.1 N·m) compared with pitchers without such an injury (94.3 ± 16.1 N·m). The risk of UCL surgery increased 26% for every 10-N·m increase in elbow varus torque. No statistically significant association was found between UCL surgery and body size, history of surgery, fastball velocity, percentage of games pitched as a starter, or UCL abnormalities on MRI, although the 2 pitchers with a full-thickness UCL tear on MRI subsequently underwent UCL surgery.

Conclusion: High elbow varus torque was associated with a greater risk of UCL surgery. With motion capture technology and biomechanists now part of MLB organizations, teams can analyze and improve the biomechanics of their pitchers to reduce elbow varus torque and the injury risk.