Injury Trends in Major League Baseball Over 18 Seasons: 1998-2015

Discussion

To date, a number of studies have been published on injuries in professional baseball. These can primarily be categorized as either studies with a detailed focus on a single injury type or body region^6-13,17,19 or broader reviews that are limited by the relatively short time span covered.^4,5 The purpose of this work was to provide a comprehensive review of injury trends in MLB since the league expanded to 30 teams in 1998 while paying special attention to the financial impact of those injuries. Additionally, we sought to provide an up-to-date review of MUCL injuries and surgeries since the procedure was first developed in 1974. Ultimately, this data demonstrates that injuries continue to rise in MLB and this increase is accompanied by increased expense for teams. Thankfully, the rates of DL assignments for shoulder injuries are on the decline; however, this decrease is countered by a reciprocal increase in elbow injuries. Similarly, the rates of MUCL reconstruction have also risen dramatically in recent years.

The fact that injury rates are on the rise is confirmed by other published reports. This trend was demonstrated in prior analyses of DL data from the 1989 to 1998⁴ and 2002 to 2008 seasons.⁵ These 2 studies represent the only comprehensive reviews of MLB injury trends to date, and each provides valuable information. Both are consistent with the current study findings that pitchers are the most commonly injured players and that shoulder and elbow injuries represent about half of all injuries.^4,5 Similar injury rates and characteristics have been reported at the collegiate²⁰ and minor league levels.²¹ Despite this consistency, this analysis of injuries from 1998 to 2015 is the first to report that DL designations for shoulder injuries are on the decline while designations for elbow injuries continue to rise. Although the exact etiology of this decline in shoulder injuries remains unknown, there are a number of possible explanations. In recent years, increased emphasis has been placed on shoulder rehabilitation, reduction of glenohumeral internal rotation deficits, scapular stabilization, and overall kinetic chain balance and coordination. However, this does not explain why elbow injuries continue to rise annually.

With this increase in injuries, the cost of maintaining an active 25-man roster is also climbing. As expected, this growing expense is primarily due to the increased number of DL days each year as well as the increase in league salaries. Fortunately, this increased financial strain has been met with steadily increased annual revenues in professional baseball. In 2014, the prorated salary cost to players designated to the DL and their replacements was $579,568,059. This figure represents an estimated 6.4% of the $9 billion in total revenue for MLB that same year.²² Although this may represent a small percentage of the whole, it still embodies an exceptionally large financial responsibility. This does not include the medical expenses incurred to treat and rehabilitate the players’ injuries.

Every injury that occurs in MLB players has the potential to adversely affect players, teams, and MLB as a whole. With its increasing prevalence, need for surgical treatment, and prolonged return to play, injuries to the MUCL of the elbow may represent the most costly of all injuries. Although a multitude of reports on MUCL injuries, treatments, techniques, rehabilitation, and outcomes have been reported,^{8,9,12,14-19,23-25} to our knowledge, a comprehensive and longitudinal incidence study in MLB players has not yet been published. By including every MUCL reconstruction that has been performed on a MLB player, our study demonstrates the dramatic increase in the annual incidence of MUCL surgeries. Studies performed over shorter time intervals corroborate these findings. A recent review of a privately insured patient database revealed an annual increase in MUCL reconstructions of 4.2% in that cohort.²⁶ When looking specifically at the MLB, a recent survey of all 30 clubs found that 25% (96 of 382) of MLB pitchers and 15% (341 of 2324) of minor league pitchers have undergone MUCL reconstruction.⁸ Because it occurs so frequently and requires a mean of 17 months to return to sport, MUCL injuries represent a very significant cause of time out of play.

While this study represents a unique epidemiologic report on injuries in baseball, it is certainly not without its limitations. As stated previously, it relies on DL data that was initially intended to serve as a roster management tool rather than an injury database. Accordingly, detailed and specific information about every injury is not always available. The limitations of DL data will largely be overcome in future studies thanks to the implementation of the HITS database in 2010. Moving forward, this system will allow for more detailed analysis of injury patterns, characteristics, time out of play, treatments rendered, etc. Its main limitation is that the earliest data dates back to 2010, making it less applicable for longitudinal studies like the present one. Another limitation of this study is the estimations used for the cost of replacing players designated to the DL. For each injury, it was assumed that the replacement player was paid a prorated portion of the league minimum salary while on the major league roster, but in some instances, that may not have been the case. It is possible that some players filling roster spots were already under contract for amounts higher than the league minimum. Since that player would be making that amount regardless of the level of play, the team may not have paid them any additional salary while filling the position of the injured player. The strengths of this study are its comprehensive nature and inclusion of 18 years of data, making it the longest such study of injuries in MLB. It also represents the first report of cost of replacement for players designated to the DL. To our knowledge, this study also represents the first comprehensive report of every MUCL surgery that has been performed on MLB players.