Structural abnormalities of the elbow joint in high school baseball players exposed to the COVID-19 pandemic during their elementary and junior high school years: a sonographic analysis of 354 players at high school entry.

Background and Hypothesis: Previous studies have shown that increased pitching load during growth is associated with medial epicondyle hypertrophy and ulnar collateral ligament thickening. The COVID-19 pandemic caused prolonged restrictions on sports activities among youth, especially during their elementary and junior high school years. We hypothesized that pandemic-related reductions in pitching opportunities would result in a lower prevalence of these structural adaptations in high school baseball players. Methods: Of the 354 high school baseball players enrolled between 2015 and 2025, 119 were pitchers and 235 were fielders. All participants had undergone ultrasound screening at the time of high school enrollment. We categorized them into a Pandemic group (entered high school between 2021 and 2025) and a pre-pandemic group (entered high school in 2020 or earlier). Medial elbow structures were assessed for 5 abnormalities: hypertrophy, irregularity, bone fragment, hypoechoic findings, and thickening. Group differences were analyzed using chi-square tests and odds ratios. Stepwise multivariable logistic regression was conducted to identify independent factors associated with medial epicondyle hypertrophy. Results: The Pandemic group demonstrated a significantly higher prevalence of medial epicondyle hypertrophy compared with the pre-pandemic group (41.1% vs. 28.3%, Discussion and Conclusion: High school baseball players who experienced the COVID-19 pandemic during crucial growth periods exhibited a paradoxical increase in medial epicondyle hypertrophy along with a decrease in ligamentous abnormalities. Supplemental questionnaire data from a subset of participants suggested that abrupt increases in pitching volume after restrictions, rather than total cumulative load, may have contributed to hypertrophy. These findings indicate that sudden changes in throwing load and inadequate physiological adaptation during pandemic-related restrictions may have disrupted normal remodeling processes in the developing elbow. To prevent elbow abnormalities in growing baseball players, comprehensive throwing load management-including frequency and intensity, not just pitch count-is essential, with particular attention to gradual return-to-throwing programs after prolonged inactivity.