Baseball-related throwing injuries in Japan versus the United States: A comprehensive comparison

Throwing-related arm injuries are very common in baseball, and their incidence continues to rise. The United States and Japan-two of the largest baseball participation populations in the world-have developed unique nationwide initiatives to address these throwing injury "epidemics." Given the substantial interest and research in baseball and throwing injuries in both countries, curiosity about throwing injuries with respect to similarities and differences between the countries has been growing. When taking into account heterogeneous definitions of injury and injury collection methods, this review found higher rates of youth elbow injuries in Japan. Unlike Japan, U.S. injury surveillance methods included large national databases, whereas Japanese injury surveillance focused primarily on annual physical examinations, often with ultrasound. Biomechanically, U.S. pitchers threw faster and had greater joint torques, which increased injury risk. Regarding workload, the United States was the first of the two countries to implement pitch count regulations in hopes of mitigating injury risk. In Japan, smaller youth baseballs and a workload-limiting professional league structure may reduce injury risk factors. Furthermore, cultural differences appear to impact youth workload. Lastly, Japan's health care structure may provide better access to orthopedic sports medicine physicians but limits access to primary care sports medicine physicians. We present injury rates, risk factors, screening practices, and management approaches in both countries to inform strategies to address the throwing-injury epidemic.