Association of Changes in Game Pitch Count, Pitching Velocity, and Arm Injuries in Collegiate Pitchers.

BACKGROUND: Baseball pitchers experience a high rate of shoulder and elbow injuries. While there have been several factors associated with arm injuries among pitchers, pitch volume and pitch velocity have garnered a great deal of attention. The associations among pitch counts, pitch velocity, and arm injury have not been well studied.

PURPOSE: To assess the association between changes in game pitch count and arm injuries in collegiate baseball pitchers over 1 summer season. The secondary aim was to assess the association between mean in-game fastball pitch velocity and arm injuries in the same baseball pitchers.

METHODS: Collegiate pitchers were prospectively followed throughout the summer season for game pitch count, pitch velocity, and arm injuries. Bayesian joint models, including time-to-event Cox regressions and multilevel mixed effects regressions, were performed to assess the associations of interest, while competing risks of release and/or retirement were controlled for. Nonlinear relationships were modeled using natural splines. Change in pitch count and pitch velocity was modeled by the change in each pitcher's mean seasonal pitch count or pitch velocity.

RESULTS: A total of 187 pitchers were included in this study and followed for a total of 9890 baseball exposure days. A total of 22 pitchers (12%; 95% CI, 7.5%-17.2%) experienced an arm injury, and 4 pitchers (2%; 95% CI, 0.6%-5.4%) were released, voluntarily retired, or reached their innings limit for the season. There was a nonlinear (parabolic shape) positive association of an increased change in pitch count as compared with the pitcher's mean pitch count and arm injuries. Additionally, there was a nonlinear (parabolic shape) positive association between arm injury hazard and a decrease in fastball pitch velocity when compared with the pitcher's mean fastball pitch velocity.

CONCLUSION: There was an increased risk for shoulder and elbow injuries with an increase in pitch count as compared with a pitcher's mean pitch count over pitch appearances. Additionally, there was an association between arm injuries and decreased pitch velocity as compared with a pitcher's mean pitch velocity.

STUDY DESIGN: Cohort study; Level of evidence, 2.