ACL Return to Sport: What Passing the Test Doesn’t Tell You
Written by Dr. Josh Funk, DPT
If you’ve had ACL reconstruction and you’re working your way back to sport, passing your return-to-sport tests is the goal. It isn’t the whole story. Paterno and colleagues followed young athletes for two years after ACL reconstruction and return to sport, reporting in the American Journal of Sports Medicine that 29.5 percent sustained a second ACL injury. More of those were tears in the other knee (20.5 percent) than graft tears in the reconstructed one (9 percent), and most happened soon after returning. Criteria-based return to sport lowers that risk. Understanding what the tests can miss is how you lower it further.
This article is general education, not a return-to-sport clearance for any individual. Whether you’re ready to return depends on your surgery, your sport, your timeline, and your functional testing results. Work with a licensed physical therapist or physician to make that call.
A quick refresher on what “cleared” actually means
Most return-to-sport testing after ACL reconstruction centers on a limb symmetry index, comparing strength and hop performance on the surgical leg to the other leg, with 90 percent symmetry treated as the standard benchmark. For a full walkthrough of the ACL recovery timeline itself, from surgery through each rehab phase, see our complete guide to ACL recovery. This article picks up from there: what happens once you’re cleared, and why that clearance doesn’t fully close the book on risk.
Why passing the test isn’t the finish line
Second ACL injury is common, not a footnote. In the Paterno study, nearly 3 in 10 athletes returning to pivoting and cutting sports had a second ACL injury within two years, most of them early in their first stretch of practices and games back. The part most athletes miss: the other knee was injured more than twice as often as the graft. Timing matters too. Grindem and colleagues, in the Delaware-Oslo ACL Cohort study published in the British Journal of Sports Medicine, found knee reinjury rates dropped 51 percent for each month return to sport was delayed, up to 9 months after surgery. Time and testing both matter, and neither one alone tells the whole story.
What a testing battery measures, and where it can fall short
Criteria-based return to sport, instead of a calendar date, is the right instinct, but the standard approach has a real limitation worth understanding:
- Strength symmetry (limb symmetry index). Quadriceps and hamstring strength on the surgical leg compared to the other leg, typically requiring 90 percent or better.
- Functional hop testing. Single-leg hop distance and control, again compared side to side.
- Psychological readiness. Confidence and trust in the knee during cutting, pivoting, and landing, often measured with a questionnaire called the ACL-RSI.
Here’s the catch: limb symmetry index compares the surgical leg to the other leg as it is right now, not to how strong either leg was before the injury. Wellsandt and colleagues, writing in the Journal of Orthopaedic & Sports Physical Therapy, found that limb symmetry indexes frequently overestimate knee function after ACL reconstruction, because the “healthy” comparison leg often loses strength too during the months an athlete spends rehabbing the surgical one. An athlete can hit 90 percent symmetry and still be meaningfully weaker on both sides than they were before the injury ever happened. That’s a testing blind spot, not a reason to distrust testing altogether, and it’s exactly why the standard alone shouldn’t be the last word.
What the research says about passing the test
Webster and Hewett, in a systematic review and meta-analysis in Sports Medicine, found only 23 percent of athletes passed their return-to-sport test battery. Among those who did, passing was linked to a 60 percent lower risk of graft rupture. It was not linked to protection for the other knee. Researchers still debate the exact numbers, and a later reanalysis in the British Journal of Sports Medicine challenged the review’s methods. The takeaway holds either way: testing is linked to lower risk for the knee it measures. A plan built only around the surgical leg leaves the other one unaccounted for.
How Rehab 2 Perform builds an ACL return-to-sport plan
We treat the standard limb symmetry test as a floor, not a finish line. Using isokinetic strength testing (HUMAC NORM) and force plate data (VALD), we measure strength and control on both legs, not just how they compare to each other, so a quietly weakened “healthy” leg doesn’t hide behind a passing symmetry score. From there we build Movement Health around the full picture: competency (movement quality and control under fatigue and fear), capacity (quadriceps and hamstring strength measured against body weight and the demands of your sport, not just leg to leg), and conditioning (readiness for the actual pace and cutting demands of your sport). Timing matters too: we don’t rush the 9-month mark, and we don’t treat time alone as a substitute for testing.
That’s Assess, Don’t Guess, applied through our Sports Rehabilitation program to every athlete returning from ACL reconstruction.
It’s the same standard behind an NPS of 94 and more than 2,700 five-star Google reviews across our 16 DMV locations.
Getting back to the bigger picture
The same principle applies to every injury, not just the ACL: clearance on paper and readiness on the field are separate questions, and closing the gap between them is how re-injury risk comes down. For a broader look at why criteria-based return to sport is the evidence-based standard across injuries, not just this one, see our full guide to returning to sport after injury.
Frequently Asked Questions
Either a tear or graft failure in the reconstructed knee, or a new ACL tear in the other, uninjured knee. Both count, and the second is more common than most people expect.
How common is a second ACL injury after return to sport?
Research following young athletes for two years after return to sport found that close to 1 in 3 sustained a second ACL injury, and more of those injuries were to the other knee than to the graft.
Standard testing compares your surgical leg to your other leg, not to how strong either leg was before the injury. Research shows this comparison can overestimate readiness, since the “healthy” leg often loses strength too during recovery, letting real deficits hide behind a passing score.
It’s a comparison of strength or hop performance between your surgical and non-surgical leg, usually with 90 percent as the passing threshold. It can be misleading because it only measures the two legs against each other, not against your actual pre-injury baseline.
Research on timing after ACL reconstruction has linked returning before 9 months to meaningfully higher reinjury rates, with knee reinjury rates dropping 51 percent for each month return was delayed, up to 9 months. Time alone isn’t sufficient, but it’s a real factor alongside testing, not a separate issue.
In Maryland and Virginia, no. Direct access laws let you book a physical therapy evaluation without a physician’s referral.
Ready to Perform at Your Best?
If you’re heading back to your sport after ACL reconstruction, a passing test score doesn’t have to be the last word on how ready you actually are. Book an evaluation at one of our 16 DMV locations, and we’ll test what a standard symmetry check can miss, build a plan around your actual capacity, not just leg-to-leg comparison, and help you protect both knees, not just the one that was surgically repaired. No referral needed in Maryland or Virginia. That’s Ready 2 Perform, and Assess, Don’t Guess.
Not sure where to start? Use our Injury Finder.
About the author: Dr. Josh Funk, DPT, is the founder and CEO of Rehab 2 Perform. He captained Ohio State’s Division I men’s lacrosse team, played professionally in the National Lacrosse League, and earned his Doctor of Physical Therapy from the University of Maryland.