Abstract
Background:
Abdominal musculature injuries comprise the third most prevalent time-loss injury across professional baseball. Despite increased awareness and prevention attempts in the recent decade, the trends of these abdominal injury numbers in Major League Baseball (MLB) are not fully understood.
Purposes:
To update the trends in oblique and intercostal injuries, analyze the impact of these injuries based on time out of play, and identify factors that correlate with increased injury severity to help with recovery time prognostication for the sports medicine community.
Study Design:
Descriptive epidemiology study.
Methods:
Using the MLB Health and Injury Tracking System, the authors identified all abdominal and core musculature injuries that resulted in time out of play in MLB and Minor League Baseball (MiLB) between the 2011 and 2021 seasons. These were filtered for injuries that resulted in ≥1 days missed (DM) during spring training, the regular season, and postseason. A Student t test was utilized to assess for significant differences for all normally distributed values. Regression analysis was utilized for determining change over time. For all statistical comparisons, the threshold for alpha was set to P < .05.
Results:
During the study period between 2011 and 2021, there were 4560 total abdominal injuries among 3401 athletes. When filtered for in-season, time-loss injuries defined as spring training, regular season, and postseason, there were 2890 injuries. Of these, 1928 were oblique injuries, 453 were intercostal injuries, and 115 were rectus injuries. The number of oblique injuries each season increased for all of baseball (P < .001), as well as for MLB (P = .009) and MiLB (P = .012) individually. Of the 1928 oblique injuries, 498 (26%) oblique injuries occurred at the MLB level and 1430 (74%) occurred at the MiLB level. Batting and pitching-related injuries comprised 860 (45%) and 729 (38%) oblique injuries, with a total of 18,455 DM and 20,891 DM, respectively. This corresponded to a mean of 22 DM for batting injuries and 29 DM for pitching injuries (mean difference, 7.2; 95% CI, 5.27-9.13; P < .001).
Conclusion:
This decade-long study on professional baseball revealed a significant increase in abdominal oblique injuries across MLB and MiLB, with the largest number of injuries observed in the 2021 season. Meanwhile, there was a significant decrease in intercostal injuries across professional baseball during these years. Such injuries continue to pose challenges, leading to substantial DM per injury and affecting players from various positions.
Since the first epidemiological report on the topic in 2011, injuries to the musculature of the abdominal region have been a central focus in baseball athletes because of the high injury rate and time out of play.1,5,12 Specifically, the abdominal muscles are key to the transfer of power in rotational activity that is pivotal to the generation of forces seen during throwing and batting.1,6 Camp et al 2 noted that oblique muscle strains were a top 5 time-loss injury in Major League Baseball (MLB). When combined with intercostal muscle strains, these abdominal injuries were behind only hamstring strains and rotator cuff strains as the third most prevalent time-loss injury across professional baseball. 2 Oblique muscle and intercostal strains were responsible for 1642 injuries and 31,730 days missed (DM) between 2011 and 2016, consistent with other trends establishing the epidemic nature of these injuries.1,2 In the United States, pitcher and position player incidence rates were found to be about even; however, in Japan, the incidence of oblique injuries was found to be significantly higher in fielders. 8 Despite these differences in injury occurrence, pitchers continuously miss more time than other positions once sustaining an oblique injury.1,5,8,12
As our understanding of these injuries continues to evolve, there is increasing attention to injury mechanisms, risk factors, prevention strategies, and alternative treatment options. One factor that has been correlated with an increased risk of abdominal muscle injuries is hip internal rotation deficits, which were found to be a predictor of abdominal injuries, potentially identifying a targeted area of treatment to mitigate oblique injury risk. 3 Some authors have reported mixed results on utilization of corticosteroids to try to optimize healing and decrease return-to-play times. 10 Newly utilized treatments and preventions have the potential to reduce the impact of abdominal injuries, but further research is needed to evaluate the current state of these player health trends in professional baseball.
In 2012, Conte et al 5 reported an overall upward trend of abdominal injuries in MLB between 1991 and 2010; however, rates declined at the MLB level between 2011 and 2015 while remaining stable in Minor League Baseball (MiLB). 1 Given the variations in these trends and the increase in attention being paid to injury prevention, an updated review is necessary to better understand the current scope of abdominal injuries in MLB. Accordingly, the purpose of this study was to provide a robust review of abdominal oblique injuries in professional baseball between 2011 and 2021. More specifically, we sought to (1) provide an update on the trends in oblique and intercostal injuries, (2) analyze the impact of these injuries based on time out of play to assess the efficacy of more contemporary treatment strategies, and (3) identify factors that correlate with increased injury severity to help with recovery time prognostication for the sports medicine community. We hypothesized that the incidence of abdominal oblique and intercostal strains, as well as time to return to play, would have declined since prior studies because of the increased awareness, focus on prevention, and improved treatment strategies across MLB and MiLB.
Methods
This study was approved by the MLB Research Committee and reviewed and deemed exempt by the Mayo Clinic Institutional Review Board. The MLB Health and Injury Tracking System (HITS) database was queried to identify injuries that occurred in MLB and MiLB players between the 2011 and 2021 seasons. Player data were anonymized, and the deidentified player data were filtered for abdominal and core musculature injuries. The sports medicine diagnostic codes oblique muscle strain, intercostal muscle strain, rectus abdominus strain, abdominal “stitch”/exercise-induced diaphragmatic spasm, abdominal wall strain, sports hernia, and hernia were used as initial search criteria. Data indicating abdominal injuries but not coded into the previous categories were manually sorted. These were filtered for oblique injuries that resulted in ≥1 DM during spring training, the regular season, and the postseason. Season-ending injuries were removed as data on return to sports are difficult to validate. Player characteristics included age at injury, handedness, position, and level of play. Other data, such as injury description, injury date, clearance date, mechanism, and level of play were collected and reported. Comparison and analysis were done across a multitude of factors. Analysis was repeated for intercostal and rectus injuries, and results were reported when numbers were sufficient.
Statistical Analysis
All epidemiological data are reported using descriptive statistics (mean, standard deviation, median, range, frequency, and percentage) where indicated. When making pairwise comparisons between means of continuous variables such as number of DM, a Student t test was utilized to assess for significant differences for all normally distributed values, and mean differences (MDs) with 95% confidence intervals were provided. Regression analysis was utilized for determining change over time. For all statistical comparisons, the threshold for alpha was set to P < .05.
Results
Between 2011 and 2021, there were 4560 abdominal/core injuries among 3401 athletes (Figure 1). When filtered for in-season, time-loss injuries defined as spring training, regular season, and postseason, there were 2890 injuries among 2400 athletes. Of these, 1928 were oblique injuries, 453 were intercostal injuries, and 115 were rectus injuries. Other injuries including abdominal “stitch”/exercise-induced diaphragmatic spasm (n = 12), hernias (n = 44), other abdominal injuries not specified (n = 82), and other injuries (n = 256) were not included in the analysis. The year 2020 was included in the total analysis, but data from that year were removed for any per annum–based analysis because of the shortened season due to the COVID-19 pandemic. The number of oblique injuries each season increased for all of baseball (P < .001), as well as for MLB (P = .009) and MiLB (P = .012) individually (Figure 2). Between 2011 and 2021, there was a mean of 188 oblique injuries each year with a low of 165 in 2012 and a maximum of 214 in 2021 (Table 1). The mean number of DM per season was 4153 for a total of 45,687 DM across the 2011-2021 seasons (Table 1). DM per season peaked in 2021, with 5968 total DM, and was at its lowest in 2012, with 3234 DM. On the other hand, the number of intercostal injuries each season underwent a steady decline for all professional baseball (P = .010), as well as for MLB (P = .034) and MiLB (P = .026) (Figure 3). In contrast to oblique injuries, between 2011 and 2021, there was a mean of 44 intercostal injuries each year, with a low of 23 occurring in 2018 and a maximum of 65 occurring in 2011 (Table 2). The mean number of DM per season was 771 for a total of 7814 DM between 2011 and 2021 (Table 2). DM per season peaked in 2011 with 1444 DM and was at its lowest in 2018 with 240 DM.
Flowchart demonstrating included and excluded injuries. DM, days missed.
Annual oblique injuries across levels of professional baseball, Minor League Baseball (MiLB), and Major League Baseball (MLB). R2 = 0.796, R2 = 0.620, and R2 = 0.524 for all injuries, MiLB injuries, and MLB injuries, respectively.
Comparison of Oblique Injuries by Season a
DM, days missed; MiLB, Minor League Baseball; MLB, Major League Baseball.
Shortened 2020 season is not included in annual mean.
Annual intercostal injuries across levels of professional baseball, Minor League Baseball (MiLB), and Major League Baseball (MLB). R2 = 0.582, R2 = 0.480, and R2 = 0.448 for all injuries, MiLB injuries, and MLB injuries, respectively.
Comparison of Intercostal Injuries by Season a
DM, days missed; MiLB, Minor League Baseball; MLB, Major League Baseball.
Shortened 2020 season is not included in annual mean.
Level of Play: MLB Versus MiLB
Of the 1928 oblique injuries, 498 (26%) occurred at the MLB level and 1430 (74%) occurred at the MiLB level (Table 3). MLB players had 24 DM per injury as compared with 24 DM per injury for MiLB players, for a mean of 24 DM in all professional baseball (P = .921). The mean age at the time of injury for MLB players was 29 years and 24 years for MiLB players (MD, 5.2 years, 95% CI 4.87-5.53 years; P < .001) (Table 3). Total oblique injuries for both MLB and MiLB players increased over time, as depicted in Figure 4, when compared with intercostal injuries that decreased over the same period between 2011 and 2021 (Figure 5).
Summary of Oblique Injuries by Level of Play, Most Common Mechanisms, Pitching Role, and Days Missed a
Boldface values signify statistical significance (P < .05). DM, days missed; MiLB, Minor League Baseball; MLB, Major League Baseball.
Major League Baseball (MLB) versus Minor League Baseball (MiLB) oblique injuries divided into batting, pitching, and defensive throwing injuries.
Major League Baseball (MLB) versus Minor League Baseball (MiLB) intercostal injuries divided into batting, pitching, and defensive throwing injuries.
Batting Injuries Versus Pitching Injuries
Batting and pitching-related injuries comprised 860 (45%) and 729 (38%) oblique injuries, with a total of 18,455 DM and 20,891 DM, respectively. This corresponded to a mean of 22 DM for batting injuries and 29 DM for pitching injuries (MD, 7.2 days; 95% CI, 5.27-9.13 days; P < .001) (Table 3). The mean DM per year were 1816 and 2023 for batting and pitching injuries, respectively (MD, 207.1 days; 95% CI, 163.7-250.5 days; P < .001). There were 416 (57%) injuries to starting pitchers compared with 313 (43%) injuries to relief pitchers, corresponding to 12,699 and 8192 DM, respectively. The mean DM for starting pitchers was 31 days vs 26 days for relief pitchers (MD, 4.3 days; 95% CI, 1.07-7.53 days; P = .009) (Table 3). Batting and pitching combined made up 82% of all injuries. This was followed by nonpitching throwing injuries (5%) and fielding injuries (5%). The mean DM for all oblique injuries was 24 (median, 20; range, 1-175). The maximum DM per injury was seen in pitchers (mean, 29 days), while the minimum, when defined, was seen in fielders (mean, 16 days) (Table 4). Regarding intercostal injuries, batting and pitching combined made up 68% of all injuries. This was followed by other injuries (10%) and weight lifting/conditioning injuries (7%) (Table 5). The mean DM was 16 days (median, 13; range, 1-182) (Table 5). The maximum DM per injury was seen in pitchers (mean, 21 days), while the minimum was seen in nonpitching throwers (mean, 10 days).
Summary of Oblique Injuries Based on Mechanism
Summary of Intercostal Injuries Based on Mechanism
Timing Injuries
The number of injuries varied by time of year. Of the 1928 oblique injuries, 380 (20%) occurred in spring training, 1526 (79%) in the regular season, and 22 (1%) in the postseason. There were more injuries that occurred during the months of March through May as compared with June through August (P < .001) (Figure 6).
Oblique injuries by month. R2 = 0.275.
Body Side Injuries
A total of 1373 oblique injuries were defined for lead versus trailing side. This was divided into batters, pitchers, and defensive throwers, resulting in 644 batters, 646 pitchers, and 83 defensive throwers. Of batters, 460 (71%) had lead-side injuries and 184 (29%) had trailing-side injuries (Table 6). Pitchers were divided into 544 (84%) and 102 (16%) for lead- and trailing-side injuries, respectively. There was a difference in DM per injury between pitchers with lead-side injuries and trailing-side injuries (MD, 6.0 days; 95% CI, 1.3-10.7 days; P = .012). Of the 1373 side-defined injuries, 1072 (78%) were lead side, and 301 (22%) were trailing side, corresponding to total DM of 27,604 and 6191, respectively. A total of 259 intercostal injuries were defined for lead versus trailing side. When divided by positions, these instances occurred across 90 batters, 134 pitchers, and 35 defensive throwers. Of batters, 56 (62%) had lead-side injuries and 34 (38%) had trailing-side injuries (Table 7). Pitchers were divided into 78 (58%) and 56 (42%) for lead- and trailing-side injuries, respectively. A difference was not seen across these intercostal injuries in pitchers regarding lead- and trailing-side time loss due to injury. Overall, of the 259 side-defined injuries, 157 (61%) were lead side and 102 (39%) were trailing side, which corresponded to total DM of 3323 and 1811 days, respectively.
Comparison of Oblique Injuries Based on Body Side a
P values were calculated by comparing the lead-side and trailing-side variables for each column. Boldface values signify statistical significance (P < .05). DM, days missed.
Switch hitters were excluded from this analysis.
Defensive players with unlisted throwing dominance were excluded from this analysis.
Lead side is defined as the opposite side of hitting or throwing dominance (ie, left side for right-handed thrower/hitter).
Trailing side is defined as the same side as hitting or throwing dominance (ie, right side for right-handed thrower/hitter).
Comparison of Intercostal Injuries Based on Body Side a
P values were calculated by comparing the lead-side and trailing-side variables for each column. Boldface values signify statistical significance (P < .05). DM, days missed.
Switch hitters were excluded from this analysis.
Defensive players with unlisted throwing dominance were excluded from this analysis.
Lead side is defined as the opposite side of hitting or throwing dominance (ie, left side for right-handed thrower/hitter).
Trailing side is defined as the same side as hitting or throwing dominance (ie, right side for right-handed thrower/hitter).
Discussion
Abdominal musculature injuries, in regard to both DM and absolute number, result in some of the most significant treatment and management issues for professional baseball clubs.2,11 The purpose of this work was to utilize HITS data to provide an update to abdominal injuries and identify their impact over the last decade (2011-2021) of professional baseball. The major findings within our analysis were an overall upward trend in oblique injuries across professional baseball (R2 = 0.796), along with an overall downward trend of intercostal injuries (R2 = 0.582), over the 2011-2021 seasons. The peak number of oblique injuries across the leagues was found to occur in 2021, while the peak number of intercostal injuries occurred in 2011. The hypothesis regarding oblique injuries was not confirmed; however, intercostal injuries did decline overall in both MLB and MiLB.
In 2017, Camp et al 1 identified that the incidence of oblique injuries appeared to be declining in MLB across the 2011-2015 seasons and speculated that the reduction was secondary to an increased focus on core strengthening. The 2011-2015 research publication noted conclusions about abdominal injuries in MLB such that (1) pitchers required 5.1 days longer to recover from injury than batters, (2) the mean time out of play was 22.2 DM per abdominal injury across professional baseball, and (3) 77% of abdominal injuries occurred on the lead side. 1 On our decade review of the HITS data, (1) pitchers required 7.2 days longer to recover than batters for oblique injuries; (2) the mean times out of play due to abdominal injuries were 23.7 and 16.1 days, respectively, for oblique and intercostal injuries; and (3) 71.4% and 62.2% of injuries occurred on the lead side for oblique and intercostal injuries, respectively. These comparisons help evaluate risk factors for abdominal injuries over time. First, as throwing velocity has increased over the past decade, higher pitch velocity has been demonstrated to be the most predictive factor of ulnar collateral ligament reconstruction in MLB pitchers. 4 This correlation may be associated with other body regions, as pitchers experienced longer time out of play for abdominal injuries as compared with previous studies. Next, the 2011-2015 study reported a mean of 22.2 DM per injury for abdominal oblique injuries; meanwhile, we were able to stratify oblique versus intercostal DM per injury in the last decade. Using advanced imaging to better identify these abdominal injuries can give greater insight on how the stratification of these injuries has led to better player-specific care and outcomes. Lastly, these concepts carry over to the difference in lead-side injuries. An increased focus on sidedness and abdominal injury type has allowed teams to focus on decreasing lead-side injuries, as demonstrated by the comparison of our data with the previous study. 1 Rate changes like these ultimately lead to decreased time out of play, as trailing-side injuries result in a mean reduction of 3.5 DM per injury when comparing our data with previously published data. These direct comparisons are important toward labeling how the treatment of abdominal musculature injuries over the past decade in professional baseball has led to improved outcomes for players.
In the past, abdominal region injuries were often labeled as general strains because of the sparsity of medical imaging conducted by club medical professionals at the time. 5 As a result, it was difficult to critically analyze and determine the exact abdominal musculature injury. Similar to the medical terminology shift that occurred in the late 1990s when magnetic resonance imaging usage allowed previous “rib cage injuries” or “lower chest injuries” to be termed oblique injuries, we must continue to differentiate abdominal injuries from each other for better injury prevention. 9 As compared with 28 DM per oblique injury, on average, in its maximal injury season (2021), intercostal injuries had a mean of 14 DM per intercostal injury in 2021. Therefore, using medical imaging techniques to specifically stratify oblique versus intercostal injuries, for example, may result in more targeted therapy and 2 weeks less of time loss on average. These results indicate that more robust abdominal injury imaging can have drastic effects on athlete return-to-play rates, front office injury designation decisions, and insight for better focused injury prevention and treatments by club medical staffs.
The impact of these injuries on time out of play demonstrates the significance of these injuries, as the mean DM per injury for MLB players was similar to that of MiLB. The similarity in these numbers assists with providing an accurate benchmark to which we can compare oblique injury prevention strategies. Between 2011 and 2015, the mean DM per injury for MLB and MiLB were 24 and 22 days, respectively. 1 Although our study identified a greater number of DM per injury in MiLB (24 as compared with 22 days in previous research), the values are approximately equal across MLB specifically. These comparisons show that despite the increased trend of oblique injuries across professional baseball, DM means per injury are not increasing. Data like these are important to provide insight to how more contemporary treatment strategies seem to be curbing the increased injury rates.
Additional factors that correlate with increasing injury severity are pivotal to identify as they help with recovery time prognostication for the sports medicine community. The extreme angular acceleration and high-demand rotational movements of batting and pitching positions contribute to the reasons these represent the most common injury mechanisms. 1 Batters and pitchers had 82% of oblique injuries over the 2011-2021 study period and almost 40,000 DM because of injury. These trends were consistent with previous research and reemphasize the importance of targeted injury prevention for these extreme force baseball activities.1,2,5,12 When looking specifically at pitchers, starters sustained the majority (57%) of injuries as compared with relievers with mean of 31 and 26 DM, respectively. The usage schedule of starters and relievers may provide a confounding variable to DM per injury that needs further research, whereas the greater absolute number of injuries to starters needs immediate attention. New research has demonstrated that “hidden pitches,” including warm-up and between-inning throws, do not statistically contribute to increased pitcher injury risk. 7 Most importantly, starters log greater innings pitched throughout the course of the season. Inning limits or the introduction of 6-man rotations may be the most important currently identifiable factor to minimize injury in starting pitchers. These variables point toward the specialized attention needed to reduce the impact of oblique injuries on starting pitchers as compared with relievers.
The timing of these injuries over the course of the season demonstrated similar trends to prior research,1,2,5 as significantly more abdominal injuries occurred from March through May (908 injuries) compared with the last 3 months of full activity, June through August (831 injuries; P < .001). Of note, the month of July had the second-highest incidence of oblique injuries seen across the baseball schedule (the highest was March). July provides clubs with rest halfway through the 162-game season; however, these conclusions emphasize the educational need for medical staff and players on exercise and treatments to maintain player health during the season halfway point. Our research points toward recommendations that clubs should increase the roles of stretching and strengthening therapies around the All-Star break.
The decade-long study on professional baseball abdominal injuries provides a foundational benchmark for future monthly tailored injury prevention programs aimed at reducing oblique injuries. Also, similar to previous research, the lead side was responsible for more injuries and more DM than trailing-side injuries.1,5 These trends were consistent across oblique and intercostal injuries when analyzed separately. The difference in time loss due to injury sidedness for oblique versus intercostal injuries is unique to the 2011-2021 abdominal injury analysis and may represent new targets for prevention and strengthening programs after advanced imaging to better localize specific abdominal injuries. These findings point toward lead-side oblique strengthening and laxity programs, as the lead-side oblique muscles are at increased risk of injury when compared with the contralateral region. The importance of focusing on prevention and distinguishing between abdominal musculature may be especially true for pitchers, as compared with batters, given the increased time lost due to injury depending on muscle and sidedness.
Limitations
There are a few limitations to the current study. Because of the change in International Classification of Diseases, 9th Revision to International Classification of Diseases, 10th Revision codes in the electronic medical record, the HITS data extraction was missing body region details to define injuries further than abdominal. Data were manually combed through to identify injury musculature to mitigate these variants, but some data points may remain unaccounted for. Additionally, given that the analysis was done on in-season injuries only, any season-ending event was not included. These injuries can at times result in many DM; thus, as presented, the data may underestimate the length of recovery. Lastly, this research relies on data from the MLB HITS database. While this is one of the most robust professional sports databases to date, the data are entered by medical staffs, including athletic trainers, physical therapists, and team physicians, across 30 professional teams with >120 affiliate MiLB clubs. The differences regarding diagnostic imaging usage, injury documentation, and return-to-play protocols may affect the consistency of the data analyzed.
Conclusion
This decade-long study on professional baseball revealed a significant increase in abdominal oblique injuries across MLB and MiLB, with the largest number of injuries observed in the 2021 season. Meanwhile, there was a significant decrease in intercostal injuries across professional baseball during these years. Such injuries continue to pose challenges, leading to substantial DM per injury and affecting players from various positions.
Footnotes
Acknowledgements
The authors extend their gratitude to the athletic trainers for their dedicated care of professional baseball players, as well as to MLB staff members for their relentless work in maintaining the MLB HITS database. It is through the combined contributions of everyone involved that we gain valuable insights into how to best treat these players.
Final revision submitted April 14, 2024; accepted May 3, 2024.
One or more of the authors has declared the following potential conflict of interest or source of funding: C.L.C. has received research support from Major League Baseball and Springer, education payments from Arthrex, consulting fees from Arthrex, nonconsulting fees from Arthrex, and royalties from Springer. T.B.G. has received education payments from United Orthopedics. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
Ethical approval for this study was waived by Mayo Clinic.
