PROFESSIONAL STARTING BASEBALL PITCHERS DEMONSTRATE INCREASED TIME TO ARM INJURY RISK COMPARED TO RELIEVERS: A SURVIVAL ANALYSIS

G. Bullock¹, C. Thigpen^2,3, G. Collins⁴, N. Arden⁵, T. Noonan⁶, M. Kissenberth⁷, D. Wyland⁷, E. Shanley^3,2

Background: Baseball arm injuries are a substantial problem and continue to rise. It is currently unclear how different pitching roles affect arm injury risk in professional pitchers. Understanding this relationship will allow greater precision in physical examination and shared decision making with coaches and athletes when evaluating injury risk and creating personalised injury prevention programs.

Purpose: To 1) Investigate the differences in arm injury hazard between professional baseball starting and relief pitchers; 2) To separately investigate elbow and shoulder injury hazard professional baseball starting and relief pitchers.

Methods: A prospective cohort study was conducted from 2013 to 2019 on Minor League Baseball (MiLB) pitchers in one Major League Baseball (MLB) organisation. Pitchers (Starter=164 Reliever=133; Age: 23.0±2.2 years; BMI: 24.8±2.2) were preseason tested (i.e. Spring training) for shoulder total range of motion (TROM), horizontal adduction (HA), and humeral torsion (HT) prior to participating in baseball related activities. Pitchers were then followed for the entire MiLB season and athletic exposures (AE’s) and injuries were recorded. An arm injury was defined as missing at least one day of missed practice or games. A survival analysis was performed in relation to time to arm injury between starting and relieving MiLB pitchers. Linearity was not assumed, with continuous variables assessed through restricted cubic splines. Hazard risk ratios with 95% CI’s were reported. Models controlled for age, body mass index (BMI), seasonal pitch load, number of pitching appearances, arm dominance, shoulder TROM, shoulder HA, difference of dominant and non-dominant HT, previous arm injury, and year of data collection. Subgroup analyses were performed for elbow and shoulder. Sensitivity analyses included Cox analyses with arm injury defined as seven days or more and 28 days or more lost to injury, a Cox analysis with linearity assumed, and a logistic regression.

Results: A total of 85,270 player days recorded with an overall arm injury incidence of 11.4 arm injuries per 10,000 AE’s, 4.8 elbow injuries per 10,000 AE’s, and 7.9 shoulder injuries per 10,000 AE’s. Starting pitchers demonstrated greater hazard of arm injury compared to relief pitchers (2.4 (95% CI: 1.5, 4.0), P < 0.001). There was no difference in hazard of elbow injury between starting and relief pitchers (1.9 (95% CI: 0.8, 4.2), P = 0.130). Starting pitchers demonstrated greater hazard of shoulder injury compared to relief pitchers (3.8 (95% CI: 2.0, 7.1), P < 0.001). Sensitivity analyses demonstrated similar results to primary analysis.

Conclusion(s): Starting pitchers were almost two and a half times as likely to sustain an arm injury compared to relief pitchers. Subgroup analyses demonstrated that starters were more likely to sustain a shoulder injury compared to relievers, but no differences were observed for time to elbow injury. However, due to the wide confidence intervals, these subgroup analyses should be interpreted with caution.

Implications: Clinicians should consider the different cumulative exposure for different pitching roles when assessing arm injury risk. Future research is required to understand how acute changes in pitch load affect injury risk.

Funding, acknowledgements: None 

Keywords: Shoulder, Elbow, Playerload

Topic: Sport & sports injuries

Did this work require ethics approval? Yes

Institution: University of South Carolina

Committee: Prisma Health Institutional Review Approved Board

Ethics number: 4915