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75 (); 184-190
doi:
10.1016/j.jor.2026.02.051

The impact of isolated ACL and MCL injuries on career longevity and performance metrics in elite rugby union players

, , , , , , , ,
a Department of Orthopaedic Surgery, NYU Langone Health, New York, NY, 10022, USA
b Fortius Clinic, London, UK
c FIFA Medical Centre of Excellence, London, UK
d Imperial College, London, UK
e Department of Orthopaedic Surgery and Sports Medicine, Amsterdam Movement Sciences, Amsterdam UMC, Location AMC, University of Amsterdam, Amsterdam, the Netherlands
f Academic Center for Evidence-Based Sports Medicine, Amsterdam UMC, Amsterdam, the Netherlands
g Amsterdam Collaboration for Health and Safety in Sports, International Olympic Committee Research Center, Amsterdam UMC, Amsterdam, the Netherlands

⁎Corresponding author: John G. Kennedy. john.kennedy@nyulangone.org

Received: , Accepted: ,
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

Knee ligament injuries are common in elite rugby union players and are associated with performance limitations. However, comparative data on long-term performance and career patterns after isolated anterior cruciate ligament (ACL) versus medial collateral ligament (MCL) injuries remain limited.

A retrospective review of elite rugby union players who sustained an isolated partial or complete ACL or MCL tear from 2013 to 2025 was performed. Data were collected from rugby databases and media reports, and included player demographics, injury characteristics, and performance metrics. A Wilcoxon signed rank test was used to compare pre-injury and post-injury performance metrics, with a p value < 0.05 determined as statistically significant.

Twenty-eight players sustained ACL injuries and 23 sustained MCL injuries. At 9.8 ± 3.1 months, 96.4% of ACL-injured players returned to sport, while 100% of MCL-injured players returned at 1.9 ± 2.1 months. ACL-injured players demonstrated significant declines in games played, tries, and points scored in the season following injury. Over time, performance largely stabilized, but total seasons played decreased. Players with MCL injuries demonstrated short-term performance declines but played a. similar number of seasons before and after injury. Re-injury occurred in 17.9% of ACL cases and 13.0% of MCL cases, with greater re-injury frequency and shorter intervals between injuries in the ACL cohort.

ACL injuries in elite rugby union players were associated with longer return to sport (RTS) times and fewer post-injury seasons despite recovery of performance metrics. MCL injuries allowed faster RTS and preserved career length but were associated with decreased performance. Re-injury led to further performance decline in both cohorts. These findings highlight distinct patterns of career and performance impact following ACL versus MCL injury in elite rugby union players.

IV

Keywords

Rugby
Anterior cruciate ligament
Medial collateral ligament
Return to sport
Player performance metrics
1

1 Introduction

Rugby is played by approximately 8.5 million people across 132 countries, ranking it among the one of the most popular and fastest growing sports.1 Characterized by its physicality, rugby involves constant tackling, scrums, rucks and high-impact collisions between players with little to no protective equipment. Due to the physical demands of the sport, rugby players often experience higher rates of in-match injuries compared to other team sports.2,3 Of these reported injuries, the lower extremities are the most frequently affected, with an incidence of 47 injuries per 1000 player-match-hours.4 Specifically, knee injuries account for the highest number of playing days missed due to injury, with anterior cruciate ligament (ACL) and medial collateral ligament (MCL) injuries accounting for 25-29% of playing days missed.5,6

ACL and MCL tears in athletes pose complex rehabilitation challenges, influencing both return to sport (RTS) timelines and long-term performance outcomes. In rugby, 57% of ACL injuries have been reported to occur from contact mechanisms, while non-contact ACL injuries most often arise during a side-stepping maneuver in which the heel strikes the ground first.7 MCL tears occur at an even higher rate among rugby players, typically resulting from direct valgus stress during collisions that force the knee inward. Previous research has demonstrated that rugby players returning to competition after injury demonstrate slower running speeds and overall performance.8 Despite these findings, comprehensive data comparing incidence rates and long-term performance outcomes between rugby players who injured their ACL or MCL remain limited.

The purpose of this study was to assess outcomes following ACL or MCL injuries sustained by elite rugby union players. This study evaluated the RTS and various performance metrics for elite rugby union players who suffered ACL or MCL injuries. We hypothesized that ACL injuries would result in longer time to RTS, greater short-term performance decline, and shorter career longevity compared with MCL injuries in elite rugby union players.

2

2 Methods

2.1

2.1 Patient identification

A retrospective review of all elite rugby union players who sustained an isolated partial or complete tear of their ACL or MCL from 2013 to 2025 was performed. Injuries from the 2013-2025 elite rugby union seasons were identified through analysis of injury reports, transactions, and reserve placements. Data were obtained from three publicly available databases (all.rugby, ESPN.com, and Rugbypass.com), previously established as credible sources for injury-related information in professional sports research.9–12 Data were extracted by authors with extensive knowledge of elite rugby. Three independent authors accessed the databases, and all entries were subsequently cross-referenced to ensure accuracy. Any discrepancies in extraction were resolved by the senior author after data evaluation. ACL and MCL injuries were verified through historical reports from Englandrugby.com, world.rugby, and NRL.com. Exclusion criteria consisted of non-elite rugby players, injuries that occurred outside of club or international matches, cases with additional concomitant injuries, and reports dated before 2013. The year 2013 was selected as the cutoff because online statistics prior to this time were reported inconsistently. After 2013, the databases used in this study such as all.rugby, ESPN.com, and Rugbypass.com provided comprehensive and reliable data. As the data analyzed was publicly accessible, research ethics approval was not required for this study.

2.2

2.2 Data extraction

A sports database was established to extract the following data: player demographics, competition match, positions, and management of injuries (Table 1). Injury characteristics including number of minutes in the match a player got injured, mechanism of injury, competitions, RTS, and re-injury rates were reported (Table 2). Performance metrics included games played, tries scored, and points scored the season directly before and after injury (Table 3). For all seasons before and after injury, the performance metrics were also reported (Table 4). These metrics were calculated by the performance metric divided by the number of seasons or games played. For patients with re-injuries, mechanism of injury, time between injuries, and performance metrics were also recorded (Table 5).

Table 1 Demographic characteristics of professional rugby players with ACL and MCL Injuries.
Table 2 Injury characteristics of professional rugby players with ACL and MCL Injuries.
Table 3 Performance metrics of professional rugby players with ACL and MCL injuries directly one season pre- and post-injury.
Performance Metrics ACL Injuries (n = 28) p value MCL Injuries (n = 23) p value
Pre-Injury Post-Injury Pre-Injury Post-Injury
Games Played (n) 21.0 (16.0-27.3) 17.0 (10.0-20.0) <0.001a 27.0 (22.0-32.0) 22.0 (16.0-24.0) 0.018a
Tries (n) 2.5 (2.0-6.0) 3.0 (1.0-5.0) 0.018a 4.0 (3.5-5.5) 2.0 (1.0-4.0) 0.082
Tries per Game (n) 0.2 (0.1-0.3) 0.2 (0.1-0.3) 0.361 0.2 (0.1-0.2) 0.1 (0-0.2) 0.520
Points (n) 20.0 (10.0-47.8) 15.0 (5.0-37.0) 0.049a 25.0 (20.0-87.0) 15.0 (5.0-70.5) 0.085
Points per Game (n) 1.0 (0.5-2.0) 1.3 (0.6-1.9) 0.517 1.1 (0.8-3.0) 1.0 (0.3-3.9) 0.689
a indicate significant value, values reported as median with interquartile ranges; N, number; ACL, anterior cruciate ligament; MCL, medial collateral ligament.
Table 4 Mean performance metrics of professional rugby players with ACL and MCL injuries in the total seasons pre- and post-injury.
Performance Metrics ACL Injuries (n = 28) p value MCL Injuries (n = 23) p value
Pre-Injury Post-Injury Pre-Injury Post-Injury
Seasons (n) 5.0 (4.0-7.0) 3.0 (1.0-6.0) 0.117 5.0 (3.5-7.0) 5.0 (2.5-7.5) 0.663
Games Played per Season (n) 16.0 (10.6-19.9) 15.9 (13.3-19.6) 0.279 21.4 (19.3-22.8) 22.5 (17.2-23.9) 0.436
Tries per Season (n) 2.8 (1.3-5.0) 2.8 (1.4-4.3) 1.00 3.4 (2.0-4.8) 2.0 (1.3-4.1) 0.119
Tries per Game (n) 0.2 (0.1-0.3) 0.2 (0.1-0.3) 0.603 0.2 (0.1-0.2) 0.1 (0.1-0.2) 0.168
Points per Season (n) 15.0 (6.4-30.6) 15.0 (7.3-34.8) 0.773 23.1 (13.6-107.4) 17.5 (6.8-67.1) 0.088
Points per Game (n) 1.0 (0.7-2.4) 0.9 (0.6-1.9) 0.534 1.1 (0.7-4.6) 1.3 (0.4-3.8) 0.223
Table 5 Mean performance metrics of professional rugby players with ACL and MCL Re-injuries in the total seasons pre- and post-injury.
Performance Metrics ACL Re-Injury (n = 5) p value MCL Re-Injury (n = 3) p value
Mechanism of Re-Injury 1 player while being tackled, 4 players with non-contact injury 2 players while being tackled, 1 player with non-contact injury
Time Between Injuries (mo) 23.6 ± 15.5 30.3 ± 37.0
Season Before and After Pre-Injury Post-Injury Pre-Injury Post-Injury
Games Played (n) 12.0 (3.0-16.8) 13.5 (0-20.5) 0.610 21.5 (14.8-21.5) 21.0 (15.5-21.0) 0.343
Tries (n) 2.0 (0-4.0) 1.5 (0-2.8) 0.285 4.0 (2.5-4.0) 3.0 (0.5-3.0) 0.713
Tries per Game (n) 0.2 (0-0.3) 0.1 (0-0.2) 0.173 0.1 (0.1-0.1) 0.1 (0-0.1) 0.600
Points (n) 10.0 (0-20.0) 7.5 (0-13.8) 0.008a 111.5 (41.5-111.5) 85.5 (20.0-85.5) 0.753
Points per Game (n) 1.1 (0-1.5) 0.6 (0-0.8) 0.214 5.8 (2.4-5.8) 4.1 (2.0-4.1) 0.600
Total Seasons
Tries per Season (n) 2.0 (0-3.0) 2.5 (0-3.3) 0.766 2.4 (2.0-2.4) 1.7 (0.7-1.7) 0.249
Tries per Game (n) 0.2 (0-0.3) 0.2 (0-0.2) 0.441 0.1 (0.1-0.1) 0.1 (0.1-0.1) 0.248
Points per Season (n) 10.0 (0-15.0) 12.5 (0-16.7) 0.765 120.3 (45.9-120.3) 68.3 (25.4-68.3) 0.600
Points per Game (n) 0.9 (0-1.5) 0.8 (0-1.0) 0.440 5.1 (2.4-5.1) 5.8 (2.3-5.8) 0.345
a indicate significant value, values reported as mean ± standard deviation and median with interquartile ranges; N, number; ACL, anterior cruciate ligament; MCL, medial collateral ligament; mo, months.
2.3

2.3 Statistical analysis

All statistical analyses were performed using SPSS Statistics 28.0.1.1 (IBM, Armonk, NY, USA). Descriptive statistics were generated, with categorical variables presented as frequencies and percentages. Continuous variables were expressed as mean ± standard deviation or median and interquartile range (IQR), as appropriate based on data distribution. The Wilcoxon signed-rank test was used to compare paired pre-injury and post-injury performance metrics when data did not meet assumptions of normality. Since non-parametric outcomes were summarized using medians and IQRs and effect size estimates with corresponding confidence intervals were not calculated, 95% confidence intervals were not reported. A p value of <0.05 was determined to be statistically significant.

3

3 Results

3.1

3.1 Demographic data and player characteristics

Demographic data and player characteristics can be found in Table 1. There was a total of 28 elite rugby union players included in this study who had isolated ACL injuries between 2013 and 2025. The mean age of players was 25.3 ± 2.0 years, with a mean body mass index (BMI) of 30.1 ± 3.4. In the 28 games players were injured, 7 (25%) were international matches and 21 (75%) were club matches. In terms of player positions, 13 (46.4%) forwards and 15 (53.6%) backs experienced ACL injuries. The most common injured positions were 4 (14.3%) hookers, 3 (10.7%) fly-halves, 3 (10.7%) inside centers, and 3(10.7%) fullbacks. All 28 (100%) players underwent surgical management for their injuries.

There was a total of 23 elite rugby union players included in this study who had isolated MCL injuries between 2013 and 2025. The mean age of players was 27.0 ± 3.5 years, with a mean BMI of 28.9 ± 2.9. In the 24 games players were injured, 4 (17.4%) were international matches and 19 (82.6%) were club matches. In terms of player positions, 10 (43.5%) forwards and 13 (56.5%) backs experienced MCL injuries. The most common injured positions were 5 (21.7%) fly-halves, 4 (17.4%) scrum-halves, 3 (13.0%) locks, and 3 (13.0%) fullbacks. Of the 23 players with MCL injuries, 1 (4.3%) underwent surgical management for his injury and 22 (95.7%) did not undergo surgical management. There was a statistically significant difference between ACL and MCL players who underwent surgical management for their respective injuries (p < 0.001).

3.2

3.2 Injury characteristics

Injury characteristics can be found in Table 2. For players with ACL injuries, the mean number of minutes players were injured into a match was 35.1 ± 16.5 min. In terms of mechanism of injury, 9 (32.1%) were non-contact injuries, 8 (28.6%) were while being tackled, 5 (17.9%) were during a ruck, 2 (7.1%) were while making a tackle, and 4 (14.3%) were unable to be determined. The most common competitions that players injured their ACL was 7 (25.0%) in a Ruper Rugby match and 5 (17.9%) in a Premiership match. The mean time to RTS was 9.8 ± 3.1 months. Of all the players who injured their ACL, 27 (96.4%) returned to sport. Five (17.9%) players re-injured their ACL later in their career.

For players with MCL injuries the mean number of minutes players were injured into a match was 42.5 ± 22.1 min. In terms of mechanism of injury, 13 (56.5%) were while being tackled, 6 (26.1%) were during a ruck, 1 (4.3%) was while making a tackle, and 3 (13.0%) were unable to be determined. The most common competitions that players injured their MCL was 7 (30.4%) in a Super Rugby match and 7 (30.4%) in an European Rugby Champions Cup match. The mean time to RTS was 1.9 ± 2.1 months. There was a statistically significant difference in RTS time between players who injured their ACL and MCL (p < 0.001). All 23 (100%) players who injured their MCL returned to play. Three (13.0%) players re-injured their MCL later in their career.

3.3

3.3 Performance metrics season prior and season post-injury

Performance metrics in the season directly prior to injury and directly post-injury can be found in Table 3. For players who injured their ACL, the median number of games from the season before injury and the season after injury significantly decreased from 21.0 (IQR 16.0-27.3) to 17.0 (IQR 10.0-20.0) (p < 0.001), respectively. The median number of tries from the season before injury and the season after injury significantly increased from 2.5 (IQR 2.0-6.0) to 3.0 (IQR 1.0-5.0) (p = 0.018), respectively. The median number of tries per game the season before injury and the season after injury stayed the same at 0.2 (IQR 0.1-0.3) and 0.2 (IQR 0.1-0.3) (p = 0.20), respectively. The median number of points from the season before injury and the season after injury significantly decreased from 20.0 (IQR 10.0-47.8) to 15.0 (IQR 5.0-37.0) (p = 0.049), respectively. The median number of points per game the season before injury and the season after injury increased from 1.0 (IQR 0.5-2.0) to 1.3 (IQR 0.6-1.9) (p = 0.29), respectively.

For players who injured their MCL, the median number of games from the season before injury and the season after injury significantly decreased from 27.0 (IQR 22.0-32.0) to 22.0 (IQR 16.0-24.0) (p = 0.018), respectively. The median number of tries from the season before injury and the season after injury decreased from 4.0 (IQR 3.5-5.5) to 2.0 (IQR 1.0-4.0) (p = 0.07), respectively. The median number of tries per game the season before injury and the season after injury decreased from 0.2 (IQR 0.1-0.2) to 0.1 (IQR 0-0.2) (p = 0.39), respectively. The median number of points from the season before injury and the season after injury decreased from 25.0 (IQR 20.0-87.0) to 15.0 (IQR 5.0-70.5) (p = 0.14), respectively. The median number of points per game the season before injury and the season after injury decreased from 1.1 (IQR 0.8-3.0) to 1.0 (IQR 0.3-3.9) (p = 0.92), respectively.

3.4

3.4 Performance metrics prior to injury and post-injury

Performance metrics in all the seasons prior to injury and all the seasons post-injury can be found in Table 4. For players who injured their ACL, the median number of seasons played pre-injury and post-injury decreased from 5.0 (IQR 4.0-7.0) to 3.0 (IQR 1.0-6.0) (p = 0.11), respectively. The median number of games played per season pre-injury and post-injury decreased from 16.0 (IQR 10.6-19.9) to 15.9 (IQR 13.3-19.6) (p = 0.78), respectively. The median number of tries per season pre-injury and post-injury stayed the same at 2.8 (IQR 1.3-5.0) and 2.8 (IQR 1.4-4.3) (p = 0.65), respectively. The median number of tries per game pre-injury and post-injury stayed the same at 0.2 (IQR 0.1-0.3) and 0.2 (IQR 0.1-0.3) (p = 0.85), respectively. The median number of points per season pre-injury and post-injury stayed the same at 15.0 (IQR 6.4-30.6) and 15.0 (IQR 7.3-34.8) (p = 0.59), respectively. The median number of points per game pre-injury and post-injury decreased from 1.0 (IQR 0.7-2.4) to 0.9 (IQR 0.6-1.9) (p = 0.96), respectively.

For players who injured their MCL, the median number of seasons played pre-injury and post-injury stayed the same at 5.0 (IQR 3.5-7.0) and 5.0 (IQR 2.5-7.5) (p = 0.58), respectively. The median number of games played per season pre-injury and post-injury increased from 21.4 (IQR 19.3-22.8) to 22.5 (IQR 17.2-23.9) (p = 0.75), respectively. The median number of tries per season pre-injury and post-injury decreased from 3.4 (IQR 2.0-4.8) to 2.0 (IQR 1.3-4.1) (p = 0.28), respectively. The median number of tries per game decreased from 0.2 (IQR 0.1-0.2) to 0.1 (IQR 0.1-0.2) (p = 0.10), respectively. The median number of points per season pre-injury and post-injury decreased from 23.1 (IQR 13.6-107.4) to 17.5 (IQR 6.8-67.1) (p = 0.13), respectively. The median number of points per game increased from 1.1 (IQR 0.7-4.6) to 1.3 (IQR 0.4-3.8) (p = 0.54), respectively.

3.5

3.5 Performance metrics for players with Re-injuries

Performance metrics in players with re-injuries can be found in Table 5. There were 5 (17.9%) players who re-injured their ACL after initial injury. Of these 5 players, 4 players were injured due to non-contact injury, and 1 player was injured while being tackled. The mean time between ACL re-injuries was 23.6 ± 15.5 months. The median number of games played the season directly before and after re-injury increased from 12.0 (IQR 3.0-16.8) to 13.5 (IQR 0-20.5) (p = 0.20), respectively. The median number of tries the season directly before and after re-injury decreased from 2.0 (IQR 0-4.0) to 1.5 (IQR 0-2.8) (p = 0.11), respectively. The median number of tries per game the season directly before and after re-injury decreased from 0.2 (IQR 0-0.3) to 0.1 (IQR 0-0.2) (p = 0.64), respectively. The median number of points the season directly before and after re-injury significantly decreased from 10.0 (IQR 0-20.0) to 7.5 (IQR 0-13.8) (p = 0.008), respectively. The median number of points per game the season directly before and after re-injury decreased from 1.1 (IQR 0-1.5) to 0.6 (IQR 0-0.8) (p = 0.31), respectively. The median number of tries per season before and after re-injury significantly increased from 2.0 (IQR 0-3.0) to 2.5 (IQR 0-3.3) (p = 0.02), respectively. The median number of tries per game before and after re-injury stayed the same at 0.2 (IQR 0-0.3) and 0.2 (IQR 0-0.2) (p = 0.46), respectively. The median number of points per season before and after re-injury increased from 10.0 (IQR 0-15.0) to 12.5 (IQR 0-16.7) (p = 0.64), respectively. The median number of points per game before and after re-injury decreased from 0.9 (IQR 0-1.5) to 0.8 (IQR 0-1.0) (p = 0.95), respectively.

There were 3 (13.0%) players who re-injured their MCL after initial injury. Of those 3 players, 2 players were injured while being tackled and 1 player was injured due to a non-contact injury. The mean time between MCL re-injuries was 30.3 ± 37.0 months. The median number of games played the season directly before and after re-injury decreased from 21.5 (IQR 14.8-21.5) to 21.0 (IQR 15.5-21.0) (p = 0.44), respectively. The median number of tries the season directly before and after re-injury decreased from 4.0 (IQR 2.5-4.0) to 3.0 (IQR 0.5-3.0) (p = 0.71), respectively. The median number of tries per game the season directly before and after re-injury stayed the same at 0.1 (IQR 0.1-0.1) and 0.1 (IQR 0-0.1) (p = 0.84), respectively. The median number of points the season directly before and after re-injury decreased from 111.5 (IQR 41.5-111.5) to 85.5 (IQR 20.0-85.5) (p = 0.69), respectively. The median number of points per game the season directly before and after re-injury decreased from 5.8 (IQR 2.4-1.5.8) to 4.1 (IQR 2.0-4.1) (p = 0.69), respectively. The median number of tries per season before and after re-injury decreased from 2.4 (IQR 2.0-2.4) to 1.7 (IQR 0.7-1.7) (p = 0.31), respectively. The median number of tries per game before and after re-injury stayed the same at 0.1 (IQR 0.1-0.1) and 0.1 (IQR 0.1-0.1) (p = 0.31), respectively. The median number of points per season before and after re-injury decreased from 120.3 (IQR 45.9-120.3) to 68.3 (IQR 25.4-68.3) (p = 0.69), respectively. The median number of points per game before and after re-injury increased from 5.1 (IQR 2.4-5.1) to 5.8 (IQR 2.3-5.8) (p = 0.44), respectively.

4

4 Discussion

The most important finding of this study was that ACL injury was associated with a reduction in post-injury career duration yet preserved post-injury performance in elite rugby union players. In contrast, MCL injury was associated with longer careers, but players demonstrated deterioration in performance metrics. The results of this study underscore the impacts of ACL and MCL injuries on elite rugby union players.

Most ACL injuries occur through non-contact cutting, deceleration, or pivoting movements that overload the knee's internal rotation.13,14 In elite rugby union players, non-contact ACL injuries occur during side-stepping with low knee flexion at initial contact and heel-strike,7 which was the most common mechanism of injury for the ACL cohort in this review. Given the intra-articular location and limited healing capacity of the ACL, management of these injuries typically consists of surgical intervention with reparative or reconstructive techniques.15 In the current review, surgery was performed for 100% of elite rugby union players with ACL injuries. Furthermore, ACL injuries require longer time to RTS, with English professional rugby union players averaging 9 months of absence from play.5 The current review found a comparable mean time to RTS of 9.8 months. In contrast, most MCL injuries are contact related, typically during a tackle that places a large valgus load to the knee, which was the most common mechanism of injury for the MCL cohort in this review. Compared to ACL injuries, MCL injuries have much shorter RTS times,5,16 averaging 1.9 months in the current review. The MCL's extra-articular location and robust vascularity favor nonoperative management such as bracing and progressive rehabilitation, rather than surgical intervention.17,18 In the current review, only 1 (4.3%) player underwent surgical management for his MCL injury.

The season following an ACL injury is consistently associated with reduced performance among professional athletes. Early performance deficits following ACL injuries are reported in other professional sports such as the National Basketball Association (NBA) in which post-injury players demonstrate notable first-year deficits in points, rebounds, and assists.19 Similarly, in women's professional soccer, players who returned after ACL injury had a significant decrease in assists and goals from pre- and post-injury seasons.20 The current review found that elite rugby union players with ACL injuries experienced significant declines in games played, tries scored, and points scored the season after their injury. These early performance deficits may be attributed to the long recovery process, muscular and proprioceptive impairments, and psychological factors such as diminished confidence or fear of re-injury.21–23 Encouragingly, over successive post-injury seasons, tries and points per season were not significantly different from pre-injury levels for elite rugby union players. Across other sports, NBA players show a 19.3% first year efficiency decline after ACL injury but return to baseline by year two, and professional soccer players often match or exceed pre-injury performance by year three.24,25 Early post-ACL deficits in performance may be transient, as pre-injury baselines are established for successive seasons after returning to sport for professional players. Despite these findings, career duration demonstrated a reduction following ACL injury, decreasing from an average of 5 seasons before injury and 3 seasons after injury. Similarly, previous studies have demonstrated that professional soccer players who underwent ACL reconstruction had significantly shorter careers than players without ACL injury.26,27 Overall, the data in the current review indicates that the performance impact of an ACL injury is largely short-term, with most players returning to pre-injury production in successive seasons. Even though performance metrics return to baseline, there is a trend toward fewer post-injury seasons for elite rugby union players after ACL injury. Cumulative joint degeneration following ACL injury, in addition to the demands of extensive surgical management and prolonged rehabilitation, may be potential contributors to reduced long-term training capacity and earlier career termination in elite rugby union players, even when short-term performance recovers.

The current review found that elite rugby union players with MCL injuries only experienced a significant decrease in points scored the season directly after injury. Isolated MCL tears are less debilitating in comparison to other knee injuries, often healing well with only conservative management.28 In a cohort of professional soccer players, Lavoie-Gagne et al. found that 64% returned in the first post-injury season at or near pre-injury performance.29 Elite rugby union players with MCL injuries similarly maintained on-field performance upon returning the following season. Interestingly, this cohort played a similar number of seasons after injury but demonstrated reduced per-season productivity, opposite of what was found for players with ACL injuries. Since MCL injuries are managed nonoperatively and allow for a rapid RTS, players do not face the prolonged surgical recovery burden that is seen with ACL injuries. Therefore, career longevity is generally preserved with players participating in the same number of seasons before and after their MCL injuries. However, these players may experience residual valgus micro-instability and medial sided symptoms, ultimately leading to worse performance metrics.30 In addition, professional athletes with MCL injuries often have concomitant meniscal or chondral damage.31 While not career-shortening, the cumulative effects of these intra-articular lesions can decrease season to season productivity for elite rugby union players. In summary, MCL injuries in elite rugby union players are output-costing, as players demonstrate decreased performance metrics despite a similar number of seasons played post-injury. In contrast, ACL injuries are time-costing, in which players perform at pre-injury levels at the expense of a trend toward fewer post-injury seasons. The difference in injury patterns calls for prioritization of player management strategies for MCL injuries versus long-term joint preservation strategies for ACL injuries.

Elite rugby union players in the current review had a secondary ACL re-injury rate of 17.9%. Studies evaluating other elite athletes have demonstrated similar findings, with secondary ACL injury rates of approximately 20%.32,33 The high rate of re-injury can be attributed to the sport's demanding pivoting movements and residual biomechanical deficits that persist after ACL reconstruction.23 Furthermore, re-injury tends to occur earlier in these players, often within 24 months in professional athletes,34 confirmed with a 23.6 month time to reinjury in the present review. In contrast, elite rugby union players with MCL re-injuries demonstrated lower re-injury rates and longer time in between successive injuries. The ACL has inferior intrinsic healing capacity than the MCL, thus players may face a higher and often earlier risk of re-injury.17 Regardless of injury type, re-injury was followed by declines in performance metrics for elite rugby union players. Re-injury of the ACL or MCL may limit overall strength and proprioceptive properties of the knee, ultimately preventing players from being able to tolerate the high-intensity movements involved in elite rugby and performing worse overall.35,36 While ACL re-injuries may occur at a faster and higher rate than MCL re-injuries, both are detrimental to the overall performance of elite rugby union players.

The current review has several associated limitations. First, the retrospective nature of the study limits data completeness and precision of follow-up performance assessment. Further follow-up was restricted to publicly available online sources, which may have missed unreported injuries and statistics. Second, relying on publicly available sources may yield incomplete reporting of injury details and various performance metrics. Third, there was a small cohort for the re-injury subgroup, of which one player's exceptionally high metrics may have disproportionally adjusted the results. Finally, as the data was drawn from sports databases and online sources, key clinical details such as injury grade, concomitant pathology, and rehabilitation protocols were generally unavailable.

5

5 Conclusion

This retrospective review found that ACL injuries in elite rugby union players were associated with a mean RTS time of 9.8 months and a reduction in post-injury seasons played despite recovery of performance metrics after injury. In contrast, MCL injuries had a mean RTS time of 1.9 months, and although they were associated with decreased performance metrics after injury this injury did not affect career longevity. Re-injury occurred in 17.9% of ACL cases and 13.0% of MCL cases, with all re-injured players demonstrating decline in performance metrics after re-injury. The findings of this study demonstrate the distinct detrimental effects of knee ligament injuries for elite rugby union players, in which ACL injuries are associated with a trend toward fewer post-injury seasons, while MCL injuries primarily decrease performance rather than career duration.

IRB statement

No IRB approval was required as this was a systematic review of published peer reviewed studies.

Ethics approval statement

No ethical approval was required for this study.

CRediT authorship contribution statement

Jared Rubin: Writing – review & editing, Writing – original draft, Investigation, Formal analysis, Data curation, Conceptualization; Alexander Tham: Writing – review & editing, Supervision, Project administration, Methodology, Data curation, Conceptualization. Ryan Rutherford: Writing – original draft, Writing – review & editing, Validation, Supervision, Investigation, Conceptualization. Charlotte Walls: Writing – review & editing, Data curation, Validation. Bradley Lezak: Writing – original draft, Writing – review & editing, Data curation. Nathaniel Mercer: Writing – original draft, Writing – review & editing, Data curation. James Calder: Writing – review & editing, Validation, Supervision, Project administration, Methodology, Investigation. Gino Kerkhoffs: Writing – review & editing, Validation, Supervision, Project administration, Formal Analysis. John Kennedy: Writing – review & editing, Writing – original draft, Validation, Supervision, Resources, Project administration, Methodology, Investigation.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

There was no guardian or patient consent for this study as it was a systematic review and did not use primary patient data.

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