What Should Inform My Return-to-Sport Decision-Making After ACL Reconstruction?

By Dr. Matt Ithurburn

How many athletes after ACL reconstruction safely return to sports participation?

Unfortunately, you’ve probably heard the stats. Only about 60% of patients after anterior cruciate ligament (ACL) reconstruction actually return to their preinjury level of sport.(2) And then, when we look at athletes in competitive sports, only 40-50% return to their previous level.(2,4) Despite this, our patients consistently expect to return to sport after ACL reconstruction. Specifically, a recent study found that 88% of patients undergoing their first ACL reconstruction expected that they would return to sport at their preinjury level.(23) Dealing with this gap between expectations and reality for our ACL reconstruction patients is especially challenging. Maybe even more alarmingly, on average, somewhere between 20-30% of young athletes (think - those younger than 25, returning to high-level sports) sustain 2nd ACL injuries in either knee (Figure 1).(18,26) Because of all of these things, it’s no wonder the topic of ACL reconstruction return-to-sport testing and decision-making has huge interest! We as clinicians want to know: How do we decide an athlete has sufficiently recovered to allow safe return-to-sport? What should we test and what thresholds should be reached? How do we best involve the patient and other stakeholders in this decision?

What typically guides return-to-sport clearance decisions?

To provide some background information relevant to this topic, I think it’s important to understand what has historically been used to guide return-to-sport clearance decisions. Generally, these decisions have been guided by: post-operative time, clinical examination findings, clinician opinion, patient-reported readiness or function, and/or objective measures of function or performance. Digging into the recent evidence in this area, a comprehensive scoping review from Burgi and colleagues(5) found that post-operative time was far and away the most reported criterion for allowing return-to-sport (included in 85% of the 178 included studies), and was the sole criterion used in 42% of the included studies. While we know that recovery over normal knee function and overall knee homeostasis (think - strength, movement patterns, graft ligamentization, bone bruise healing) does take time after ACL reconstruction,(16) it’s critical we not neglect impairment, performance, and other important factors and only focus on time in the return-to-sport decision-making process. So, when objective measures are tested, most commonly, measures of thigh strength (quads, hamstrings) and performance measures like single-leg hop tests are used. And these measures are often evaluated for recovery based on limb-symmetry, comparing injury limb performance to the uninjured limb (and we won’t go into the potential limitations of limb-symmetry indices here, but there definitely are some to consider..), or based on absolute performance.

How do I measure these things in the clinic?

OK, great. So I’m going to objectively test as a part of my return-to-sport decision-making. The next question is: how do I test what I need to test in the clinic? Starting with strength testing, we know that our gold standard for evaluating strength is an isokinetic dynamometer (perhaps the most common example being a Biodex). However, because these dynamometers, when new, typically cost somewhere in the neighborhood of a Tesla Model 3, most clinics don’t have access to them. Fortunately, there are other potential options that are more clinically-accessible. Handheld dynamometers are good clinical correlates of isokinetic dynamometry.(21,25) When handheld dynamometer testing in the clinic, it’s important to use consistent positioning, constrain the lower leg and thigh, and make sure your patient isn’t having discomfort due to the dynamometer pressing against their leg – as it might impact their maximal performance. For more about this, see some of Terry Grindstaff’s work in this area (one specifically here: https://www.ncbi.nlm.nih.gov/pubmed/25709864). Even without a handheld dynamometer, a 1-rep max on the knee extension can work. Although, using a 1-rep max does often underestimate differences between limbs,(21) and it’s probably a good idea to shoot for 100% symmetry if that is what you use.

Testing single-leg hop tests in the clinic is generally fairly straight forward, and the tried and true ones are the single hop, triple hop, crossover hop, and 6-meter timed hop. However, an important consideration with single-leg hop testing beyond evaluating only distance, is also evaluating movement quality/control. Several recent studies have shown that despite symmetric distance performance on single-leg hop tests, the takeoff and landing strategies are altered in the ACL-reconstructed limb.(9,10,27) While we don’t know what ‘ideal’ movement patterns are, generally, what we don’t want to see during single-leg tasks are: stiff knee, overly stiff or excessive trunk movement (in both planes), and a general lack of knee control or balance. You could consider taking videos of your patients performing single-leg hop tests or other sport-related tasks using user-friendly apps like Dartfish and others. There are also some developed movement assessments to consider for double-leg jumping and landing tasks, such as the LESS (Landing Error Scoring System) and the repeated tuck jump test. Overall, we need more work in this area to develop movement quality screening tools with good clinical utility to include in our return-to-sport testing.

So far, we’ve focused a lot on physical, performance, and movement quality evaluation. But another critical domain to evaluate in these patients, beyond physical factors, are psychological readiness-related factors. We know from a large body of research that fear of reinjury/lack of confidence/psychological readiness/motivation to return play a huge role in successful return-to-sport.(1,3,14) While we won’t do a deep dive on how we to integrate psychologically-informed interventions into our ACL reconstruction rehabilitation, we absolutely should evaluate psychological readiness and other related constructs as a part of our return-to-sport testing. Currently, the most commonly used tool to evaluate psychological readiness in individuals after ACL injuries is the ACL-Return to Sport after Injury (ACL-RSI) scale,(24) or a recently described short-version of the ACL-RSI with only 6 questions.(22)

So, what evidence do we have to support our return-to-sport criteria?

To briefly answer this question, we have a good chunk of evidence supporting individual items within the typical return-to-sport testing battery. For example, we see in the literature that having quadriceps strength symmetry >90% is associated with lower risk of subsequent additional knee injury risk(6,11) and better knee-related function.(7,20) We also see that more symmetric landing mechanics are associated with decreased 2nd injury risk,(19) and that more symmetric single-leg hop test performance and mechanics (>90%) are associated with better knee-related function.(8,12) Regarding psychological factors, several recent studies have shown that less psychological readiness or greater fear of reinjury are associated with higher risk of a 2nd ACL injury.(14,15,17) However, a recent systematic review and meta-analysis by Losciale and colleagues(13) found no overall association between passing return-to-sport criteria and risk of sustaining a 2nd ACL injury after returning to activity. Clearly, we have work left to do in this space.

Overall, what should I aim for in my ACL reconstruction return-to-sport testing?

And really, this question prompts more questions, such as: What specific thresholds should we aim for? How does that differ based on the specific sport the athlete is returning to? How do psychological readiness factors and physical factors interact to contribute to risk or success in the return-to-sport process? How do we use return-to-sport testing to differentiate risk of 2nd injury? Despite these remaining questions, we do know that the first steps are performing a multidimensional battery of objective tests, involving all stakeholders while using clear communication (e.g., the patient, clinicians, coaches, and family), and considering relevant contextual factors specific to the individual athlete in front of you (e.g., sport-specific demands; workload; timing of the season; outside pressure).

Matt Ithurburn

Matt Ithurburn, PT, DPT, PhD is the Director of Clinical Research at the American Sports Medicine Institute (ASMI). ASMI is an international leader in sports medicine research, focused on studying surgical and rehabilitation outcomes, biomechanics, and injury mechanisms to improve the prevention and treatment of sports-related injuries. In his role at ASMI, Dr. Ithurburn leads a multidisciplinary clinical research team managing multiple externally-funded studies and ongoing outcomes data repositories. Additionally, he further collaborates on several studies seeking to improve rehabilitation and return-to-sport success in individuals recovering from lower extremity injuries, including those with ACL reconstruction, femoroacetabular impingement, and hip dysplasia. In addition to his research involvement, Dr. Ithurburn is an adjunct Assistant Professor at the University of Alabama at Birmingham (UAB), teaching in the DPT program and mentoring PhD students.

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