Context: It is currently unclear how different pitching roles affect arm injury risk in professional pitchers.
Objective: 1) Investigate the differences in arm injury hazard between professional baseball starting and relief pitchers; 2) Separately investigate elbow and shoulder injury hazard between professional baseball starting and relief pitchers.
Study Design: Prospective cohort
Setting: Minor League Baseball (MiLB) from 2013–2019
Patients or Other Participants: Pitchers
Main Outcome Measures: Pitchers were followed for the entire MiLB season and athletic exposures (AE's) and injuries were recorded. Risk ratios and risk difference were calculated between starting and relieving MiLB pitchers. A cox survival analysis was then performed in relation to time to arm injury between starting and relieving MiLB pitchers. Subgroup analyses were performed for elbow and shoulder.
Results: 297 pitchers were included with a total of 85,270 player days recorded. Arm injury incidence was 11.4 arm injuries per 10,000 AE's. Starting pitchers demonstrated greater risk ratio (1.2 (95% CI: 1.1–1.3)) and risk difference (13.6 (95% CI: 5.6–21.6)) and hazard of arm injury (2.4 (95% CI: 1.5–4.0)) compared to relief pitchers. No differences were observed for hazard of elbow injury between starting and relief pitchers (1.9 (95% CI: 0.8–4.2)). Starting pitchers demonstrated greater hazard of shoulder injury compared to relief pitchers (3.8 (95% CI: 2.0–7.1)).
Conclusions: Starting pitchers demonstrated almost two and a half times greater hazard of arm injury compared to relief pitchers. Subgroup analyses demonstrated that starters exhibited greater hazard of shoulder injury compared to relievers; but, no differences were observed for hazard of elbow injury. However, due to the wide confidence intervals, these subgroup analyses should be interpreted with caution. Clinicians may need to consider cumulative exposure and fatigue and how these factors relate to different pitching roles when assessing pitching arm injury risk.