Paper 56: Impact of youth baseball rule changes on elbow screening for osteochondritis dissecans of the humeral capitellum during annual elbow examinations

Objectives: Osteochondritis dissecans (OCD) of the humeral capitellum is a serious overuse injury affecting young baseball players, especially those who frequently pitch or catch. Early detection and intervention are critical to prevent progression and long-term disability. In recent years, awareness of elbow injuries in youth sports has led to regulatory efforts aimed at injury prevention. In Japan, new rules in youth baseball were introduced in a stepwise manner: beginning with pitch count limits in 2019, followed by inning/time restrictions and enlargement of the home plate in 2022. These measures were expected to reduce stress on the elbow joint by limiting excessive throwing and gameplay time.The purpose of this study was to evaluate the impact of these rule changes on the incidence of suspected OCD as identified through a mass ultrasound screening program for youth baseball players. By categorizing participants into groups based on the timing of the rule implementations, we aimed to clarify whether the introduction of pitch and play restrictions was effective in reducing early signs of OCD in the humeral capitellum.
Methods: This study was approved by the Ethics Review Committee of our institute. This study involved a total of 3,057 elementary school students (age 9 to 12) who were actively participating in youth baseball and had no prior diagnosis of OCD or other major elbow disorders. The participants were divided into three groups according to the timing of the elbow examination in relation to the rule changes: - Group A: Players screened before the implementation of pitch count restrictions (2017-2018, n = 832) - Group B: Players screened after pitch count limits were introduced (2019-2021, n = 909) - Group C: Players screened after inning/time limits and home plate enlargement were implemented in addition to pitch count restrictions (2022-2024, n = 1,316)Ultrasound screening of the throwing elbow was performed by experienced examiners using standardized protocols. Players with findings suggestive of OCD (including subchondral irregularity or fragmentation at the capitellum) were referred for secondary examinations and were recorded as 'suspected OCD cases.' Data were analyzed by screening year, group, and player position, with particular attention to pitchers and catchers, who are known to be at higher risk.
Results: The number of suspected OCD cases in each group was: - Group A: 43 players (5.2%) - Group B: 23 players (2.5%) - Group C: 29 players (2.2%)There was a statistically significant reduction in the proportion of suspected OCD cases following the implementation of pitch count limits in 2019 (p < 0.01). This trend continued after the additional inning/time restrictions and home plate modifications in 2022, although the decrease from Group B to Group C was not statistically significant. (Table1)When analyzed by player position, pitchers and catchers showed a marked reduction in suspected OCD prevalence after the rule changes were introduced. (Table2)
Conclusions: Previous studies have identified repetitive valgus stress and high throwing volume as key contributors to the development of OCD in young athletes. Our findings support the hypothesis that administrative intervention through rule enforcement can play a significant role in reducing the risk of such injuries. The early implementation of pitch count limits was particularly effective, and while the subsequent inning/time restrictions had less dramatic effects, they may provide additional protective benefit through cumulative load management.Additionally, this study underscores the value of routine ultrasound screening in identifying asymptomatic or minimally symptomatic cases of OCD, allowing for early management before irreversible joint damage occurs.In conclusion, stepwise rule changes in youth baseball-especially pitch count restrictions-were associated with a significant reduction in suspected OCD cases among elementary school players, particularly pitchers and catchers. These findings suggest that policy-level interventions are effective strategies for injury prevention in young athletes. Continued surveillance and evaluation will be important to optimize protective measures and promote safe sports participation.