Abstract Title Factors predictive of season-ending upper extremity injuries in MLB pitchers and the implementation of the pitch clock.

Background The 2024 MLB season has seen high profile pitchers succumb to season ending upper extremity injuries (SEI), raising concerns regarding pitcher injuries. The sports community remains divided between factors such as the newly initiated pitch clock, banning of sticky substances and increasing pitch velocity as the main culprit. No study has yet demonstrated a correlation between any one factor and pitcher injuries. This study attempts to identify specific factors associated with season ending injuries in MLB pitchers.

Methods A retrospective cohort study of all MLB pitchers from 2015–2023 was performed utilizing publicly available data on MLB injuries (prosportstransactions.com) and pitch-by-pitch metrics (baseballsavant.mlb.com). Pitcher demographics, average number of pitches thrown per game, and pitch-specific metrics were analyzed for each pitcher. Multivariable binary logistic regression was utilized to determine metrics predictive of SEI. Comparison of seasons surrounding the initiation of the pitch clock were done utilizing Pearson's Chi-squared test.

Results 6,569 pitcher-seasons were analyzed with 405 instances resulting in an SEI from the 2015 - 2023 seasons, excluding 2020. Multivariable logistic regression showed SEI is significantly associated with increasing number of pitches per game (OR, 1.011, 95% CI, 1.008-1.015, p < 0.001), pitch velocity (OR, 1.049, 95% CI, 1.009-1.091, p < 0.05) and acceleration (OR, 1.034, 95% CI, 1.003-1.065, p < 0.05) in the x-dimension. SEI’s were not associated with pitch release speed, release extension, velocity/acceleration in the y- or z-dimension or pitcher demographic measures (pitcher height, weight, BMI). SEI decreased significantly following initiation of the pitch clock from 50 (5.9%) in 2022 to 17 (2.0%) in 2023 (p<0.0001). SEI did not significantly change after banning of sticky substances.

Conclusion Increasing SEI’s with increasing pitch count, velocity, and acceleration per game reflects an expected consequence of higher volume and faster pitching in the MLB year-over-year. The significant decrease in upper extremity SEI’s after introduction of the pitch clock could be due to anything from teams managing pitchers more carefully, to biomechanical differences with less rest between pitches. More seasons with the pitch clock will help elucidate the cause. Banning of sticky substances had no effect on injuries likely because sticky substance helps pitchers add spin and movement which are not associated with SEI’s. Further research is underway to evaluate injuries further by anatomic location and/or structure, as well as other positions.