Return-to-sport criteria after ACL reconstruction: what the evidence shows

Deciding when to return to sport after an anterior cruciate ligament (ACL) reconstruction can be a complex process. Research suggests that both the amount of time since surgery and how well a person meets specific physical criteria may relate to the risk of re-injury [1, 2]. Understanding these factors can help guide discussions with healthcare professionals about when it might be appropriate to return to activity.

Timing of Return to Sport and Reinjury Risk

One study, known as the Delaware-Oslo ACL cohort study, explored the relationship between knee re-injury after ACL reconstruction and factors like returning to sport, the timing of that return, and knee function before returning [1]. This was a prospective cohort study that followed 106 patients who participated in pivoting sports, over a two-year period [1]. Researchers recorded sports participation and any knee re-injuries each month [1].

A prospective cohort study follows a group of people (a "cohort") over time to see how certain factors relate to outcomes [1]. In this type of study, researchers observe what happens naturally without intervening or assigning treatments [1]. Because researchers are observing rather than directly controlling variables, these studies show "associations" or "relationships" between factors and outcomes, rather than proving that one factor directly "causes" another [1]. For example, if a study finds that delaying return to sport is "associated with" a lower re-injury rate, it means these two things tend to happen together [1]. It does not mean that delaying return to sport guarantees a lower risk, or that it is the only factor involved [1]. Other unmeasured factors could also play a role. This distinction is important for understanding the implications of the findings.

The Delaware-Oslo study found that patients who returned to "level I sports"—which are sports involving pivoting, such as soccer or basketball—had a 4.32 times higher re-injury rate over two years compared to those who did not return to these sports [1].

The timing of return to sport also appeared to be a factor. The study observed that the re-injury rate was significantly reduced by 51% for each month return to sport was delayed, up to 9 months after surgery [1]. After 9 months, the study did not observe any further reduction in risk [1]. This suggests that waiting a certain amount of time after surgery may be associated with a lower re-injury rate [1].

The Role of Meeting Functional Criteria

Beyond the time since surgery, a person's physical function before returning to sport may also be important. The Delaware-Oslo ACL cohort study also assessed knee function using several measures [1]. These included: * The Knee Outcome Survey-Activities of Daily Living Scale: This scale typically assesses how knee problems affect a person's ability to perform everyday tasks [1]. * A global rating scale of function: This involves the patient giving an overall score of their knee's function [1]. * Quadriceps strength: This measures the power of the thigh muscles, which are crucial for knee stability [1]. * Hop test symmetry: This compares how well a person can jump on their injured leg versus their uninjured leg, indicating functional recovery and balance [1].

The researchers defined "passing return-to-sport criteria" as scoring above 90 on all these tests [1]. Failing any of these tests meant failing the criteria [1]. The study found that 38.2% of patients who failed these return-to-sport criteria experienced re-injuries, compared to 5.6% of those who passed all the criteria [1]. This indicates that meeting these functional benchmarks was associated with a lower re-injury rate [1]. Specifically, the study noted that having more symmetrical quadriceps strength before returning to sport was associated with a significantly reduced knee re-injury rate [1].

Another study, by Kyritsis and colleagues, also investigated whether a set of objective discharge criteria, including muscle strength and functional tests, were associated with the risk of ACL graft rupture after returning to sport [2]. This study included 158 male professional athletes who had undergone ACL reconstruction and returned to their previous professional level of sport [2]. Before returning to sport, these athletes completed a series of discharge tests [2]. These tests included: * Isokinetic strength testing at three different speeds (60°, 180°, and 300° per second): This measures muscle strength and endurance throughout a range of motion, focusing on the quadriceps and hamstrings [2]. The different speeds assess muscle performance under various conditions, from slow, powerful movements to faster, more dynamic ones [2]. * A running T-test: This is a measure of agility, involving sprinting forward, shuffling sideways, and running backward around cones [2]. * A single hop test: This assesses explosive power and balance by measuring the distance a person can hop on one leg [2]. * A triple hop test: This measures the total distance covered in three consecutive hops on one leg, indicating power and endurance [2]. * A triple crossover hop test: This is similar to the triple hop but involves hopping over a central line three times, adding an element of lateral control and agility [2].

The athletes were monitored for ACL re-ruptures after they returned to sport, with a median follow-up of 646 days [2]. The study found that 26 out of 158 athletes (16.5%) experienced an ACL graft rupture, on average 105 days after returning to sport [2].

The researchers identified two factors associated with an increased risk of ACL graft rupture in this group [2]: 1. Not meeting all six discharge criteria before returning to team training was associated with a 4.1 times greater risk of ACL graft rupture [2]. 2. A decreased hamstring-to-quadriceps ratio in the involved leg at 60° per second was also associated with an increased risk of ACL graft rupture [2]. For every 10% difference in this ratio, the risk was 10.6 times greater [2].

These findings suggest that a comprehensive assessment of strength and functional movement before returning to sport may be important for identifying potential risks [2].

Younger Patients and Reinjury Rates

Younger age has been recognized as a factor that may influence the risk of re-injury after ACL reconstruction [3]. A cohort study by Webster and colleagues looked at re-injury rates in 354 patients who were younger than 20 years old when they had their first ACL reconstruction using a hamstring tendon autograft [3]. The patients were followed for an average of 5 years [3].

The study found a high rate of subsequent ACL injuries in this younger patient group [3]. Overall, 110 patients (35%) had at least one further ACL injury after their initial surgery [3].

Specific findings included: * Graft ruptures: 57 patients (18%) experienced a graft rupture, on average 1.8 years after surgery [3]. Almost half of these ruptures (47%) occurred within the first year after surgery, and 74% occurred within the first two years [3]. * Age and sex differences: The highest graft rupture rate was observed in males younger than 18 years old, at 28.3% [3]. This rate was significantly higher compared to females in the same age group (12.9%) and males aged 18-19 years (13.8%) [3]. * Contralateral ACL injuries: 56 patients (17.7%) experienced an injury to their other, unoperated ACL, at an average of 3.7 years after surgery [3]. The study did not find significant age- or sex-based differences for these contralateral ACL injuries [3].

These findings highlight that younger patients, particularly males under 18, may face a higher risk of graft rupture after ACL reconstruction [3].

Return to Sport as a Continuum and Shared Decision

The decision to return to sport after an injury is often complex and involves many factors. It is seen as an exercise in managing risk [4]. A 2016 consensus statement from the First World Congress in Sports Physical Therapy, held in Bern, Switzerland, brought together 17 expert clinicians to discuss and make recommendations for return-to-sport decision-making [4].

The experts agreed that return to sport should not be seen as a single decision made at the end of the recovery process [4]. Instead, it should be viewed as a continuous process that happens alongside recovery and rehabilitation [4]. Ideally, this decision is made collaboratively by clinicians, athletes, and coaches [4].

The consensus statement suggested that using "biopsychosocial models" can help clinicians understand the individual factors that might influence an athlete's return to sport [4]. These models consider biological factors (like physical healing), psychological factors (like fear of re-injury), and social factors (like pressure from coaches or teammates) [4]. The "Strategic Assessment of Risk and Risk Tolerance" framework may also help decision-makers gather information to make an informed return-to-sport decision [4].

The experts noted that there is limited research evidence to fully support all return-to-sport decisions in clinical practice [4]. They recommended that future research should focus on a standardized way to define, measure, and report return-to-sport outcomes, and to identify valuable factors that predict successful return to sport [4].

Limitations of the Research

When considering the findings of these studies, it is important to understand their limitations: * Cohort Study Design: The studies discussed are prospective cohort studies [1, 2, 3]. As noted earlier, this type of study can show associations or relationships between factors and outcomes, but it does not prove that one factor directly causes another [1]. Other factors not measured by the researchers could also influence the results. * Specific Study Populations: The groups of people studied were specific: * The Delaware-Oslo study included 106 patients who participated in pivoting sports [1]. * The Kyritsis study focused on 158 male professional athletes [2]. * The Webster study examined 354 patients who were younger than 20 years old at the time of their surgery [3]. * Generalizability: Because these studies focused on particular groups (e.g., professional athletes, young individuals, those in pivoting sports), their findings may not directly apply to all individuals recovering from ACL reconstruction [1, 2, 3]. For example, the risks and optimal return-to-sport timing for a recreational athlete or an older individual might differ from those observed in these specific cohorts. * Evidence Gaps: The research itself acknowledges that there is "sparse evidence to guide return to sport (RTS) decisions" [1] and that "commonly used RTS criteria have not been validated" [2]. The Bern consensus statement also highlighted that "research evidence to support return to sport decisions in clinical practice is scarce" [4]. This means that while these studies provide valuable insights, they are part of an ongoing effort to build a stronger evidence base for return-to-sport decisions.

What this means for you

Returning to sport after an ACL reconstruction involves careful consideration of several factors. Research suggests that delaying your return to sport for a certain period, such as at least 9 months, may be associated with a lower risk of re-injury [1]. Additionally, meeting specific functional criteria, including having symmetrical quadriceps strength and passing a battery of physical tests, appears to be associated with a reduced risk of re-injury or graft rupture [1, 2]. Younger individuals, especially males under 18, may also have a higher risk of graft rupture after ACL reconstruction [3].

The decision to return to sport is not a simple one-time event, but rather a process that should ideally involve collaboration between you, your healthcare providers, and potentially your coaches [4]. A licensed physiotherapist can assess your individual situation, evaluate your physical readiness, and help you understand the potential risks involved in returning to your chosen activities [4]. They can guide you through the rehabilitation process and help you work towards meeting objective criteria that may be associated with a safer return to sport.

Consider asking your physiotherapist or surgeon specific questions such as: * "What are the objective criteria that you use to assess readiness for return to sport, and how do my current test results compare to those benchmarks?" * "Based on my age, activity level, and the demands of my sport, what is a reasonable timeframe to consider for returning to full activity, and what are the potential risks of returning earlier?" * "How will we monitor my quadriceps strength and hamstring-to-quadriceps ratio to ensure they are symmetrical and within a safe range for my sport?" * "What psychological factors, such as fear of re-injury or pressure to return, should we discuss as part of my return-to-sport plan?" * "What are the specific risks involved in returning to my particular sport, and how can we work together to manage those risks effectively?"

If you are recovering from an ACL reconstruction, speaking with a physiotherapist can help you understand your options and develop a personalized plan. You can find physiotherapy clinics in Calgary or physiotherapy clinics in Vancouver through Clinic Directory. To verify that a physiotherapist is registered, contact their provincial regulatory college — in Alberta, that is the College of Physiotherapists of Alberta [5]. The Canadian Physiotherapy Association is a national professional association rather than a regulator, so it cannot confirm a registration, though it is a useful starting point for understanding the profession [6].