Performance-Based Outcomes Following Symptomatic Pars Injuries in American Professional Baseball Players
Authors: Gould Heath P. , Winkelman Robert Daniel , Tanenbaum Joseph , Hu Emily , Haines Colin M. , Hsu Wellington , Kalfas Iain H. , Savage Jason W. , Schickendantz Mark S. , Mroz Thomas E. 
Published: July 2019

Objectives: Previous studies in the evidence-based literature suggest that lumbar spine injuries can lead to a significant decrease in athletic performance. This phenomenon is particularly evident in sports that require repetitive truncal rotation, such as baseball. Although we have previously characterized the natural history of symptomatic spondylolysis and spondylolisthesis in professional baseball players, no prior study has investigated the impact of pars injuries on player performance in this patient population. The purpose of this study was to report performance-based outcomes following symptomatic pars injuries in elite-level baseball athletes. Methods: A retrospective cohort study was conducted among all professional baseball players who presented with a symptomatic pars defect between 2011 and 2016. Both Major League and Minor League players were enrolled using a de-identified injury surveillance database maintained by the MLB. Lumbar spine imaging reports were reviewed to confirm the radiologic diagnosis of spondylolysis or spondylolisthesis. Players were stratified according to baseball position (pitcher vs. position player). Primary outcome measures for pitchers were earned run average (ERA) and walks plus hits per inning pitched (WHIP), while primary outcomes for position players were batting average (AVG) and on-base plus slugging (OPS). Paired t tests were used to compare pre-injury statistical performance to post-injury performance, with p < 0.05 treated as statistically significant. Results: During the defined study period, 75 players presented with low-back pain in the setting of a pars defect. 47 players were diagnosed with spondylolysis (62.7%), while 28 were diagnosed with spondylolisthesis (37.3%). Of those individuals, 19 players were excluded due to incomplete statistical data in the MLB injury surveillance system. Pre-injury vs. post-injury statistical comparisons are presented in Table 1. Pitching performance after the pars injury did not significantly differ with regard to the primary outcome measures, ERA (3.45 vs. 4.73; p = 0.25) and WHIP (1.28 vs. 1.47; p = 0.26). There was also no significant difference in any of the secondary outcomes - runs per 9 innings (R/9), hits per 9 innings (H/9), walks per 9 innings (BB/9), strikeouts per 9 innings (K/9), home runs per 9 innings (HR/9), and strikeout-to-walk ratio (K/BB). Similarly, batting performance among position players did not significantly differ from pre-injury to post-injury with regard to the primary outcomes, AVG (.261 vs. .256; p = 0.59) and OPS (.672 vs. .667; p = 0.87), or any of the secondary outcomes - on-base percentage (OBP), slugging percentage (SLG), runs per plate appearance (R/PA), hits per plate appearance (H/PA), runs batted in per plate appearance (RBI/PA), extra-base hits per plate appearance (XBH/PA), home runs per plate appearance (HR/PA), and walk-to-strikeout ratio (BB/K). Conclusion: This study represents the most comprehensive analysis of the impact of symptomatic pars injuries on MLB player performance. While previous studies suggest that lumbar injuries lead to shorter careers in both pitchers and position players, our current data demonstrate that pars defects do not cause a significant decrease in performance when MLB athletes return to play following these injury episodes. Given the limitations of our study design, larger prospective investigations are needed to validate these conclusions. [Table: see text]