Summary

ACL injuries in Major League Soccer players saw reduced recovery times and lower re-injury rates from 2016-2021, with most athletes returning to pre-injury performance levels by the third season post-injury, except for attackers who continued to show performance decline.

Abstract

Introduction

Anterior cruciate ligament (ACL) injuries are a significant concern in elite sports, particularly in high-impact athletics, such as soccer, where the demands on the knee joint are substantial. In Major League Soccer (MLS), ACL injuries pose a threat to an athlete’s immediate ability to participate in the sport but also long-term performance and career longevity. This study aims to provide a comprehensive analysis of ACL injuries in MLS athletes over a decade, offering insight into the factors influencing return-to-play (RTP) and evaluating performance outcomes of injured players compared to their uninjured controls.

Methodology

The MLS Injury Surveillance database was queried for athletes with ACL injuries from 2011-2021. An ACL injury was defined as an incident involving the ACL, with possible additional co-ligament involvement, that required medical attention. Demographic characteristics and injury characteristics (setting, activity, and re-injury) were used for descriptive analysis. The athletes were then matched by position, age, season of injury, baseline statistics and then compared to uninjured control players in a 1-to-3 ratio. The difference between performance metrics for the first 4 full seasons following injury were calculated by comparing to player metrics 1 season before injury. Univariate 2-group comparisons were performed by using independent t-tests.

Results

A total of 146 ACL injuries were recorded between 2010 and 2021 in 138 MLS players, with 9 (6%) re-injuries. The median absence from sport per injury was 240 days (mean: 246.5). The average number of games missed, and practices missed per injury, were 17.4 ±13.3 and 52.8 ± 50.6, respectively. The average injured player age was 24.8 ± 4.3 years. Time to RTP significantly decreased from 269.6 days in 2010-2015 to 219.0 days in 2016-2021 (p=0.044), and the re-injury rate (sprain or tear) following initial ACL injury decreased from 8% (6/76) to 4% (3/73) when comparing between the same time intervals. Additionally, acute contact injury (vs non-contact), lead to increased games missed (20.7 games vs 15.6 games, p = 0.024). Concurrent ligamentous and meniscal pathology, position, home vs away games, weather, and field type, did not significantly affect time to RTP or average games missed.
51 total athletes, who at least played in one season prior to injury, were matched to 153 control athletes. Injured athletes played and started significantly fewer games and recorded inferior performances for the first season after their injury (P < 0.05). However, in subsequent years the game performance of injured players was either not statistically significant in difference or had significantly improved compared to control athletes across several performance metrics, except for attackers, who demonstrated a continued decline in performance beyond the initial 1-2 years following injury (P < 0.03). Notably, when compared to control players, a higher percentage of injured players had remained in the league for the first 1-2 years following the injury index year. However, by the 4th post-injury season, the rate of players still in the league were similar between both cohorts.

Conclusion

Comparing injuries between 2010-2015 and 2016-2021, there was a 50-day average decrease in days missed, and a 5-game average decrease in games missed. The statistically significant decrease in days missed and clinically significant decrease in reinjury rate noted from 2016-2021 may indicate an acceleration of ACL injury rehabilitation. Except for attackers, player performance largely equaled or exceeded that of matched controls by the third post-injury season, a result shared by prior studies investigating player metrics in UEFA soccer athletes.