Abstract
Background:
Anterior cruciate ligament (ACL) injuries are among the most debilitating injuries in professional soccer, often leading to extended recovery times and performance impacts. While much is known about ACL injury outcomes in European leagues, data specific to the Major League Soccer (MLS) remains limited.
Purpose/Hypothesis:
This study aimed to assess the return to play (RTP) times, RTP rates, and performance outcomes after ACL reconstruction in MLS athletes. It was hypothesized that RTP times would improve over the study period and that player performance would stabilize by the third post-injury season, consistent with findings from other professional soccer leagues.
Study Design:
Cohort study; Level of evidence, 3.
Methods:
The MLS Injury Surveillance database was queried for ACL injuries from 2010 to 2021. Player characteristics, injury characteristics, and performance metrics were collected for 132 players with ACL injuries and compared with 396 uninjured controls matched by age, position, and seasons played. The injured cohort was divided into 2 groups: 2010-2015 and 2016-2021 to compare changes in RTP times, performance outcomes, and trends over time. RTP was defined as participation in at least 1 MLS match after injury. Statistical analyses, including the chi-square and t tests, were performed to evaluate differences between the 2 time periods and matched controls, with significance set at P < .05.
Results:
RTP time decreased significantly from 269.6 days (2009-2015) to 219 days (2016-2021) (P = .044). Forwards experienced significant performance declines starting in the third post-injury year, with reductions in goals scored, minutes played, and offsides (P < .05). Midfielders showed improved performance in goals scored by the third post-injury year, while defenders exhibited recovery by the second year, with no significant long-term performance deficits.
Conclusion:
Our study demonstrated that while overall RTP times have improved, position-specific performance outcomes vary significantly, with forwards exhibiting long-term deficits compared with midfielders and defenders. These findings suggest that position-specific rehabilitation protocols may be beneficial for athlete education in RTP and for potential prevention strategies.
Soccer is one of the most widely played sports worldwide, with an estimated 270 million participants, including over 24.4 million in the United States. 11 The growing popularity of the Major League Soccer (MLS) has led to an increase in competition intensity, placing greater physical demands on athletes. Among lower extremity injuries, anterior cruciate ligament (ACL) tears represent one of the most severe, often necessitating surgical reconstruction and prolonged rehabilitation.5,22 ACL injuries can have significant career implications, as they are associated with extended time away from play, potential performance decline, and an increased risk of reinjury.14,23
ACL injuries in soccer are predominantly noncontact, often occurring during rapid deceleration, pivoting, or improper landing mechanics.6,10 However, they are also commonly caused by direct contact or contact leading to poor landing. Given the vital role of the ACL in stabilizing the knee joint, surgical intervention followed by an extensive rehabilitation program is typically required for return to play (RTP). 20 Previous studies in elite European soccer leagues have reported variable RTP rates after ACL reconstruction (ACLR), with most players returning to competition within 6 to 12 months.9,25 However, despite medical advancements, there is evidence that ACL injuries can lead to long-term performance declines, particularly among attacking players who rely on explosive movements.1,12
The literature has primarily focused on European leagues, such as the English Premier League (EPL) and the Union of European Football Associations (UEFA), competitions,8,15 with limited data available regarding ACL injuries in the MLS. Studies have suggested that differences in training methodologies, rehabilitation protocols, and playing surfaces may influence RTP times and post-injury performance outcomes across leagues.13,16 As the MLS continues to grow in stature and competitiveness, understanding injury patterns and recovery trajectories in this league is critical for optimizing player health and performance.
By providing a comprehensive assessment of ACL injury outcomes in the MLS, this study aimed to contribute valuable insights to team physicians, rehabilitation specialists, and coaching staff involved in player recovery and injury prevention. This study aimed to analyze ACL injury trends in MLS players over 10 years (2010-2021), with a focus on RTP rates, RTP times, and post-injury performance outcomes. We hypothesized that RTP times have improved over the study period. Additionally, we seek to evaluate position-specific differences in post-injury performance, particularly whether ACL injuries disproportionately affect certain playing roles.
Methods
An ACL injury was defined as an incident involving the ACL, with possible additional co-ligament involvement, that required medical attention. The database utilized did not detail concomitant injuries. Descriptive data captured for each player from the injury included age, player position, team played, year of injury (2010-2015 vs 2016-2021), field type, competitive setting, injury onset, field location, in-game time of injury, and weather conditions. Injury and RTP data documented included the date of injury, days/games missed, practices missed, date of RTP, and subsequent injuries, as has been performed in previous investigations on professional soccer athletes. RTP was calculated as the time difference between the injury date and the date the athlete returned to sport.
A player was included in the injured cohort if he was drafted or signed to a team in the MLS, participated in at least 1 game before sustaining a complete ACL rupture, and had a minimum of 1-year follow-up after injury. Players were excluded if their ACL injury could not be identified as a complete rupture or if they had no baseline characteristics or statistics. Demographic data for each player, including age, height, position, and number of seasons played, were recorded. Utilizing Microsoft Power Automate, player age, team during injury year, and position were used as inputs to blindly extract player baseline performance, which was defined as 1 season before the injury year, and any post-injury performance statistics from the publicly available MLS website (MLSsoccer.com/stats). Performance metrics, such as games played, minutes per game/season, goals scored, assists, shutouts, and goals conceded, were subsequently collected for each injured player.
A group of soccer players who had not experienced a complete ACL rupture was selected from the MLS website and matched to injured players at a 3-to-1 ratio (ie, 3 control players for each injured player). Players identified were compared with the MLS injury database to ensure they did not sustain any other lower-extremity injuries; otherwise, they were excluded from the control group. Matching was based on position, age (within ±2 years), the same season year, and total seasons played in the league (within ±1 season). Additional performance factors, such as minutes played per season, goals, and assists, were used to refine the matching process when multiple control players were available. A matched-cohort analysis was then conducted to assess the performance of injured players, compared with their uninjured counterparts.
Changes in performance metrics for 1, 2, and 3 years after the index year were compared with metrics 1 season before the index year. Injured players who did not RTP in the MLS were excluded from performance analysis. Athletes who returned to play were only included in the performance analysis if they actively participated in a single MLS game after injury. Given the prolonged recovery time for ACL tears, removing the index year (year of the ACL injury) and comparing metrics with those of the previous year minimized the confounding effect of missed game time on season performance in the injured cohort. Performance changes at the various post-injury timepoints were compared between the injured and matched control groups by position to account for the differing roles of player positions on the field. Injury history data were summarized utilizing means ± standard deviations. All other continuous data were summarized as medians and interquartile ranges. Univariate 2-group comparisons were performed using independent 2-group t tests and the Wilcoxon rank-sum test when normality was violated. Chi-square tests were used to compare categorical data. All analyses were performed using RStudio software Version 3.6.2 (R Foundation for Statistical Computing), with statistical significance set at P < .05.
Results
A total of 132 MLS soccer players with 144 ACL tears that occurred between 2010 and 2021 were analyzed and compared with matched noninjured controls. The mean age of injury among players was 24.8 ± 4.3 years. Defenders constituted the largest percentage of injured players at 38.7% (n = 43), followed by midfielders at 32.4% (n = 36), forwards at 26.1% (n = 29), and goalkeepers at 2.7% (n = 3). The mean time to RTS significantly decreased from 269.6 days in 2009-2015 to 219 days in 2016-2021 (P = .04). Similarly, the mean number of games missed significantly decreased from 19.4 games in 2009-2015 to 14.4 games in 2016-2021 (P = .02).
Field type did not have a significant effect on RTP, with players injured on grass averaging 246.7 days compared with 243.9 days on artificial turf (P = .460). Field location and player age did not significantly influence RTP times. Players injured at home averaged an RTP of 245 days, compared with 257 days for those injured away (P = .380). Athletes aged ≤25 years had an RTP of 234 days, while those >25 years averaged 258 days (P = .424). Concurrent ligamentous or meniscus pathology also did not significantly affect RTP, with RTP times of 245 days for injuries with concurrent pathology, and 240 days with isolated ACL injuries (P = .432). Weather conditions, comparing sunny or clear conditions to rainy or snowy conditions, were also found to be not significant (P = .209). Similarly, no significant differences were observed between positions, with midfielders averaging 276 days, forwards 267 days, and defenders 229 days (P = .5728).
In contrast, a competitive setting was a significant factor, with athletes injured during a game or match having a significantly longer RTP (259 days) compared with those injured during practice (207 days; P = .039). Additionally, injury onset also played a significant role, as acute contact injury (vs noncontact), lead to increased games missed (20.7 games vs 15.6 games; P = .02). However, injury onset did not play a significant role with respect to the mean time to RTP, as acute contact injuries had a similar RTP (262 days) when compared with acute noncontact injuries (230 days) (P = .35). Player characteristics and RTP statistics are further detailed in Table 1.
Return to Sport Time in MLS Athletes With ACL Tendon Injuries Between 2010 and 2021 a
Data are presented as mean ± SD, unless otherwise indicated. Bold values indicate statistical significance. The independent Student t test and ANOVA were used to compare means, where appropriate. ACL, anterior cruciate ligament; ANOVA, analysis of variance; MLS, Major League Soccer; RTP, return to play.
Multivariate regression analysis was conducted to assess the influence of various factors on the number of days missed after ACL injuries. None of the included variables, such as age, position, injury type, injury onset, field type, weather conditions, or reinjury, demonstrated statistically significant associations with days missed. Variables such as reinjury status (P = .93) and weather conditions (P = .27) did not reach significance.
Injury rates remained stable in the 2010-2015 period to the 2016-2021 period (P = .087). The mean time to RTP decreased significantly, with athletes in 2016-2021 returning in 197.71 ± 126.60 days, compared with 283.28 ± 249.13 days in 2010-2015 (P = .050). Reinjury had no statistically significant difference (Table 2). Among athletes who sustained a second injury, the mean RTP time post-second injury was comparable in 2016-2021 (244.4 ± 4.95 days) to 2010-2015 (357.50 ± 204.35 days) (P = .516).
Details Comparing 2010-2015 With 2016-2021 a
Data are presented as mean ± SD or %. The bold P value indicates significance. RTP, return to play.
The performance metrics of players who experienced ACL injuries were assessed against uninjured controls, with changes in performance expressed as delta values calculated as the difference between the index year/year of injury and the year post-injury. The findings are organized by player positions, including forwards, midfielders, and defenders. Goalkeepers were not included in the performance data because the total injured population was too small, with only 3 players.
Forwards with ACL injuries did not exhibit significant differences in games played per season when compared with controls across the first 2 years post-injury. For instance, 1 year after injury, injured forwards had a change of −7.8 games compared with −5 for controls (P = .59). There was no significant difference in goals scored per season 1-year post-injury, with injured forwards recording −3.5 goals versus −1.8 for controls (P = .24). Assists per season similarly showed no significant differences, with a change of −1 for injured forwards and −1 for controls at 3 years post-injury (P = .50). However, injured attackers did show significant performance deficit in the third and fourth year after injury. There were decreases in scoring attempts (P = .01), goals scored (P = .03), minutes played (P = .04), and total offsides by the third year (P = .01) (Table 3A).
Forward Metrics Compared With 1 Year Before Index Year a
ACL, anterior cruciate ligament; Y, year.
Midfielders similarly showed no significant differences in performance metrics in the first 2 seasons after injury. However, by the third and fourth years post-injury, the injured cohort showed significantly improved performance in scoring attempts and goals scored, respectively. For instance, the injured players had a mean increase of +3 goals, versus −1.7 for the control group (P = .03). Similarly scoring attempts increased by 2.8 for in the injured cohort versus −12.25 for the control group by the third year (P = .3). Four years post-injury, injured midfielders recorded a change of −7.43 games, while controls showed a change of −5.5 (P = .45). Assists scored per season did not differ significantly between injured and uninjured midfielders, with a nonsignificant delta of −1.57 for injured players versus 0.25 for controls 4 years after injury (P = .13) (Table 3B).
Midfielder Metrics Compared With 1 Year Before Index Year a
ACL, anterior cruciate ligament; Y, year.
Defenders exhibited a pronounced decrease in games played in the first year after ACL injury (–4.6 [injured] vs 0.46 [uninjured]; P = .05); however, performance quickly recovered by the second post-injury year and beyond. Two years after injury, injured defenders experienced a significant improvement in games and minutes played per season (2.5 [injured] vs −3.78 [uninjured], P = .04; 122 [injured] vs −381 [uninjured]; P = .05, respectively). Goals, assists, scoring attempts, and accurate pass % largely remained the same across both cohorts over the 4 years after injury (Table 3C).
Defender Metrics Compared With 1 Year Before Index Year a
ACL, anterior cruciate ligament; Y, year.
Discussion
The major findings of our study was that RTP times significantly improved over the past decade, decreasing from 269.6 days in 2010-2015 to 219 days in 2016-2021 (P = .04), with a concurrent reduction in average games missed from 19.4 to 14.4 games (P = .02). Players injured during matches experienced longer recovery (259 vs 207 days; P = .039), and acute contact injuries led to significantly more games missed than noncontact injuries (20.7 vs 15.6 games; P = .02). Performance analysis revealed that forwards experienced significant declines by the third post-injury year in goals scored (−3.5 vs +2.4; P = .03), minutes played (−787 vs +445; P = .04), and scoring attempts (−28.5 vs +18.6; P = .01) compared with controls. In contrast, midfielders demonstrated improved outcomes in later seasons, with a significant increase in goals scored 4 years after injury (+3 vs −1.7; P = .03) and scoring attempts 3 years after injury (+2.8 vs −12.15; P = .03). Defenders showed a pronounced early drop-in games played (−4.6 vs −0.46; P = .05), but recovered by the second year with improved games played (+2.5 vs −3.8; P = .04) and minutes played (+122 vs −381; P = .05). These results highlight significant improvements in recovery time and underscore position-specific differences in long-term performance after ACLR in MLS athletes. This trend aligns with advancements in surgical techniques, rehabilitation protocols, and sports medicine strategies that aim to optimize recovery and reduce time lost to injury.3,19
RTP Rates and Timing
The RTP rate in our cohort remains comparable to previously reported rates in elite soccer players, including those in European professional leagues such as the UEFA Champions League and the EPL.8,18 Lai et al 17 conducted a systematic review and found that 83% of elite athletes returned to their preinjury level of sport after ACLR, with a mean RTP time of 6 to 13 months. Our study's mean RTP time of 219 days for the 2016-2021 cohort is slightly lower, suggesting that improvements in rehabilitation strategies tailored to MLS athletes are warranted. Furthermore, competitive settings and injury onset significantly influenced RTP: players injured during matches required longer recovery times than those injured in practice, and acute injuries resulted in more games missed than noncontact injuries. These trends suggest that mechanics and context of injury may play critical roles in the recovery timeline. The lack of significant findings in our multivariate regression analysis suggests that recovery time is likely influenced by a combination of factors rather than any single variable. Our findings support those of Waldén et al, 24 who observed that players returning from ACLR often face an increased risk of reinjury within the first 2 seasons after RTP. 24 The positional performance declines observed in forwards in our study suggest that the physical demands of high-intensity play may contribute to an elevated risk of secondary injuries. 22
Positional Differences in Performance Recovery
Our results highlight significant differences in post-injury performance trajectories based on player position. Forwards demonstrated substantial declines in scoring attempts, goals scored, and minutes played beginning in the third post-injury year, whereas midfielders exhibited improved goal-scoring metrics over time, and defenders recovered to baseline performance by the second post-injury year. These findings are consistent with previous research indicating that the explosive, high-intensity movements required of attacking players place them at greater risk of prolonged performance impairment after ACLR. 2
Ekstrand et al 8 previously reported that forwards are particularly susceptible to post-injury performance declines due to the reliance on cutting, sprinting, and pivoting motions. Similarly, Webster and Feller 25 found that midfielders and defenders demonstrate more favorable recovery trajectories due to the relative stability of their positional demands, which require less frequent high-intensity accelerations. Our study's findings further reinforce these observations, suggesting that position-specific rehabilitation protocols may be warranted to address the distinct recovery needs of different player roles.
Comparisons to Other Soccer Leagues
The differences in RTP times and performance outcomes between the MLS and European leagues may be influenced by several factors, including playing surface, medical resources, and training methodologies. Previous studies have suggested that artificial turf may increase the risk of ACL injuries and potentially affect RTP outcomes.1,8 However, our study found no significant difference in RTP times between players injured on natural grass versus artificial turf. These results are in agreement with the findings of Brophy et al, 1 who reported no statistically significant differences in RTP rates between playing surfaces in professional soccer players.
Moreover, the MLS differs from European leagues in terms of its competitive schedule and travel demands. The longer distances traveled for away matches and the varied climatic conditions in North America may contribute to differences in injury recovery and performance adaptation compared with other leagues.7,21 Future studies should consider examining how these league-specific factors influence ACL recovery and long-term outcomes.
Implications for Rehabilitation and Injury Prevention
Given our findings, tailored rehabilitation approaches could be considered to optimize RTP and long-term performance outcomes. The positional disparities in post-injury performance may underscore the need for individualized rehabilitation plans. Forwards may benefit from extended return-to-performance phases that emphasize explosive strength, agility, and sprint mechanics to compensate for the long-term declines observed in our study. Additionally, load management strategies may be employed to gradually reintegrate high-intensity play and minimize reinjury risk in the critical first 2 post-injury seasons. 10 Additionally, Buckthorpe et al3,4 suggest that late-stage rehabilitation protocols incorporating sport-specific movements can facilitate smoother reintegration into competitive play. Further research into implementing these strategies within MLS rehabilitation protocols could provide a better understanding of how to enhance recovery outcomes and mitigate performance deficits.
Limitations
This study has several limitations. First, its retrospective design relies on historical data, which may lead to inaccuracies in injury reporting and RTP timelines. Additionally, the calculation of injury rates did not account for individual player exposure, such as minutes played or games participated in, which could lead to imprecise estimates. However, by focusing on the number of unique injuries per year, the study still provides valuable insights into overall trends in injury occurrence. Furthermore, the analysis used a database that may lack detailed information on injury severity (specifically isolated ACL injuries and multiligament injuries), specific rehabilitation protocols, or player compliance. This limits our ability to assess the full effect of individualized recovery efforts on RTP and performance outcomes. Additionally, the performance metrics analyzed, such as goals, assists, and minutes played, may not equally reflect the effect of ACL injury across all positions; in particular, these metrics may underestimate performance deficits in defenders, whose primary contributions may not be captured by offensive statistics.
Another limitation is that this study exclusively focuses on MLS players, and therefore, the results may not be generalizable to other leagues or sports with differing physical demands or rehabilitation practices. The lack of statistically significant findings in the multivariate analysis is likely due to the small sample size, which limited the study's power to detect meaningful associations. Wide confidence intervals across several variables suggest substantial variability, highlighting the need for larger cohorts in future studies to provide more robust and definitive conclusions. Lastly, while efforts were made to minimize confounding factors, unmeasured variables such as team medical resources or player fitness could have influenced the findings. Future prospective studies with more detailed exposure data and standardized rehabilitation protocols are needed to confirm these findings and provide further insights into long-term outcomes.
Conclusion
Our study demonstrated that while overall RTP times have improved, position-specific performance outcomes vary significantly, with forwards exhibiting long-term deficits compared with midfielders and defenders. These findings suggest that position-specific rehabilitation protocols may be beneficial for athlete education in RTP and for potential prevention strategies.
Footnotes
Final revision submitted April 11, 2025; accepted May 12, 2025.
One or more of the authors has declared the following potential conflict of interest or source of funding: B.F. is a board or committee member of the American Orthopaedic Society for Sports Medicine; has received research support from Arthrex, Inc, Smith & Nephew, and Stryker; has received publishing royalties and financial or material support from Elsevier; has stock or stock options in iBrainTech, Sparta Biopharma, and Zuno Medical; is a paid consultant for Smith & Nephew and Stryker; and is an editorial or governing board member of The Video Journal of Sports Medicine. E.G. is a paid consultant for Arthrex, Inc, and Zimmer. R.B. is a board or committee member of the American Academy of Orthopaedic Surgeons, American Orthopaedic Association, and American Orthopaedic Society for Sports Medicine; is an editorial or governing board member of The American Journal of Sports Medicine and Journal of the American Academy of Orthopaedic Surgeons; and a paid consultant for Syneos. D.N. is a paid consultant for CONMED Linvatec and Newclip USA. B.M. is an editorial or governing board member of The American Journal of Sports Medicine and Cartilage; receives IP royalties from Arthrex, Inc; is a paid consultant for Arthrex, Inc; and is a board or committee member of the Biologic Association, International Cartilage Regeneration & Joint Preservation Society, and Kerlan-Jobe Institute. AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
Ethical approval was not sought for the present study.
