Sport specialization is associated with upper-extremity overuse injury in high school baseball players

Background and hypothesis: Sport specialization is increasingly common in youth sports and is a risk factor for lower-extremity overuse injuries. However, limited data exist on whether specialization is associated with upper-extremity (UE) overuse injuries, specifically in youth baseball players. We hypothesized that specialization in baseball and being a pitcher would be associated with poorer arm health and UE overuse injury history in the previous year. Methods: During the 2019 spring baseball season, 551 high school baseball athletes (aged 15.9 +/- 1.3 years) from 3 states (Alabama, n =200; California, n=188; and Michigan, n=163) completed an anonymous questionnaire. Athletes were recruited from 5 high schools in each state, with schools matched based on factors that influence specialization rates. The questionnaire consisted of (1) demographic characteristics, (2) baseball participation information (including sport specialization status), and (3) throwing-arm health and UE injury history in the previous 12 months. Throwing-arm health was assessed using the Youth Throwing Score (YTS), a validated and reliable outcome measure for youth baseball players. Multivariate regression analyses were used to examine the association between variables of interest and the YTS or UE overuse injury history, adjusting for covariates. Results: After adjustment for covariates, highly specialized athletes were more likely to report a UE overuse injury in the previous year compared with low-specialization athletes (odds ratio [OR], 3.77; 95% confidence interval [CI], 1.39-10.2, P=.009). Both athletes who reported playing baseball for more than 8 months per year (OR, 2.03; 95% CI, 1.12-3.65; P=.019) and athletes who reported being a pitcher (OR, 2.11; 95% CI, 1.20-3.72; P=.010) were more likely to report a history of UE overuse injury. Highly specialized players reported lower (worse) YTS values compared with low-specialization players (least-squares mean estimate +/- standard error, 56.5 +/- 1.1 vs. 53.3 +/- 0.7; P=.034). Players who reported pitching as one of their positions scored worse on the YTS than non-pitchers (leastsquares mean estimate +/- standard error, 51.6 +/- 0.8 vs. 57.2 +/- 0.6; P <.001). Conclusion: Although baseball recommendations that discourage sport specialization are widely available for parents, athletes, and coaches, high rates of sport specialization were reported in our sample. We found that being highly specialized in baseball was associated with UE overuse injury history and worse throwing-arm health in high school baseball athletes. Continued education for baseball parents, athletes, and coaches is necessary to raise awareness of the risks associated with high specialization. Level of evidence: Level III; Cross-Sectional Design; Epidemiology Study (C) 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.