Hazard of Arm Injury in Professional Starting and Relief Pitchers

Context: How different pitching roles affect the risk of arm injury in professional pitchers is currently unclear. Objectives: To investigate differences between professional baseball starting and relief pitchers in the hazard of (1) arm injury and (2) elbow and shoulder injury. Design: Prospective cohort study. Setting: Minor League Baseball (MiLB) from 2013 to 2019. Patients or Other Participants: Pitchers in MiLB. Main Outcome Measure(s): Pitchers were followed for the entire MiLB season, and athlete-exposures 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 conducted for elbow and shoulder injuries. Results: A total of 297 pitchers were included, with 85270 player-days recorded. The incidence of arm injuries was 11.4 per 10000 athlete-exposures. Starting pitchers demonstrated a greater risk ratio (1.2 [95% CI = 1.1, 1.3]), risk difference (13.6 [95% CI = 5.6, 21.6]), and hazard of arm injury (2.4 [95% CI = 1.5, 4.0]) than relief pitchers. No differences were observed for the hazard of elbow injury between starting and relief pitchers (1.9; 95% CI = 0.8, 4.2). Starting pitchers had a greater hazard of shoulder injury than relief pitchers (3.8 [95% CI = 2.0, 7.1]). Conclusions: Starting pitchers displayed a 2.4 times greater hazard of arm injury than relief pitchers. Subgroup analyses indicated that starters exhibited a greater hazard of shoulder injury than relievers, but no differences occurred for the hazard of elbow injury. However, due to the wide CIs, 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 the risk of pitching arm injury.