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ACL Return-to-Sport: Am I Ready?

By: Dr. Daniel Chillianis, PT, DPT

An ACL injury is a substantial and life-altering event for competitive athletes that leads to a sustained period of uncertainty in the future and strips away the ability for an athlete to do what they love...Be an Athlete. You're forced to reluctantly take your hands off the wheel and place your trust and athletic career in the hands of a clinical team with the looming fear of “Will I ever be the same again?” As you work your way through the arduous process that is ACL Rehab you will eventually reach a point where you follow up with your surgeon around the 12-16 week post-op period and the surgeon will provide you with a form or verbal confirmation that you are “Cleared to return to sport activities” and you will rejoice however, your mind will quickly snap back to “am I actually ready? How do I even begin to start playing again? If I step wrong will my knee support me or is it going to betray me again?” These are all extremely normal reservations and questions to have and something every athlete returning from a major reconstructive procedure goes through. What I always tell my patients is that “How could you trust your knee right now? The last time you did that we ended up here! Now we have to get your knee to earn that trust back and prove to you it’s ready!”

Return to Sport testing is a polarizing subject in the rehabilitation world. I feel confident saying all rehab professionals agree that in order to return to dynamic activities we must test you dynamically first, however, the next part of that is where disagreements lie and that’s the question of “How?” With this blog I hope to shed some light on where the most current and up to date research is on effective return to sport testing.

● Overview:

○ Athletes who sustain an Anterior Cruciate Ligament (ACL) injury often subsequently undergo ACL Reconstruction Surgery (ACL-R) with the goal and expectation of making a full return to sports at their pre-injury level. While over the past 2 decades tremendous improvements have been made in procedures/grafting and options for specific repair protocols and rehab processes, unfortunately the proportion of athletes who successfully return to pre-injury sport level is low meanwhile the re-tear (or reinjury) rate of a second ACL injury in athletes under 20 y/o has been reported as high as 40%(!) (3)

● Return To Sport Testing:

○ While variation exists between therapists and testing protocols most validated and respectable RTS testing consists of similar properties which we will review below.

○ Limb Symmetry Index:

■ LSI or Limb Symmetry Index is another widely accepted and clinically meaningful portion of RTS testing. This process consists of performing prompted actions (ie. Balance/Strength/Stability) on the uninvolved side (non-surgical knee) and then performing the same prompted tasks on the involved side (surgically repaired knee) and analyzing/comparing and unilateral performance to reach a percentage of symmetry

● IE. LSI = (uninvolved side) / (involved side)

■ An LSI of >90% is the usual cut of score demonstrating within normal limits of symmetry bilaterally, however newer research recommends LSI of strength testing and functional performance should reach near 100% prior returning to cutting/pivoting and contact competitive sports.

● The issue here lies in the sobering reality that only 14% (!!!) of all patients s/p ACL-R achieve 100% symmetry for strength testing alone as far as 2 years post surgery! (3)

● Another prominent issue is the validity of using the uninvolved side as the control in this testing. RTS testing is typically done >9 months post-surgery which means your “Control” leg has not been subject to these dynamic bouts and demands in almost a full year and recent studies show there are detrimental neuromuscular effects on the uninvolved side following a unilateral injury therefore the uninvolved side is “weaker” and exhibits deficits as a result leading to a poor control for our testing! (3)

○ Strength Testing

■ 56% of Therapists in the USA still use Manual Muscle Testing as their only method of evaluating strength. The concern here lies in the subjective nature of manual muscle testing, meaning if you asked every Therapist to measure Mr. Jones’ Quadricep Strength there's a good chance you will receive a range of numbers which leads to doubt in the efficacy of this testing procedure.(3)

■ The Gold Standard in RTS Testing remains Isokinetic Dynamometry, however these machines are vast, space/time consuming, financially burdensome and frankly hard to find!

■ Testing can be done in more of an objective manner with use of portable isometric dynamometry testing (force plates and pull tension monitors) or via 1-RM 5-RM testing on leg press/hamstring curl machines etc.

○ Hop Tests/Movement Quality:

■ There are 4 commonly used “Hop Tests” in RTS Testing

● Single Hop For Distance

● Triple Hop For Distance

● Triple Crossover Hop

● 6m Timed Hop

■ We measure these one leg at a time and yup you guessed it measure it in the form of Limb Symmetry (ie. R Single Hop Distance/ L Single Hop Distance)

■ Issues:

● As you’ll see in the header for this section hop tests must not only be qualified by distance but also the quality of motion/landing

● This brings in two issues with the validity of this testing method

○ The deficits in the uninvolved side provide an overestimate of functional improvement.

○ The quality assessment remains subjective and therapist dependent with limited reliability between testers.

● Depending on the Graft used for surgical repair, compensations in movement quality of landing mechanics.

○ A study by Welling et. Al showed that although out of the testing subjects >70% “passed” RTS testing. >60% of these “RTS cleared” athletes continued to demonstrate altered landing mechanics leading to compensatory offloading motions, poor trunk and pelvis positioning in unplanned change of direction drills which are offered as predispositions for increased re-injury rates. (2)

● Psychological Factors and Testing:

○ Beyond the litany of physical, measurable and mechanical deficits an athlete must overcome throughout ACL-R Rehab there is a MAJOR psychological effect on an athlete throughout this experience.(1)

○ A recent Systematic Review looked at 999 athletes who underwent ACL-R and subsequent rehabilitation process. Of those 999 athletes 63.4% returned to play in their respective sports. Of the 56.6% of athletes who did not return to play >65% of them reported “fear of reinjury” as their reason for not making a full return. (1)

○ While we don’t currently endorse any type of specific intervention that will abolish fear of reinjury, this only furthers the previous points that we must conduct a global, measurable, objective and methodical testing evaluating all aspects of an athletes readiness prior to transitioning back to sport participation.



(1) Gokeler, A., Dingenen, B., & Hewett, T. E. (2022, January 28). Rehabilitation and return to sport testing after Anterior Cruciate Ligament Reconstruction: Where are we in 2022?. Arthroscopy, sports medicine, and rehabilitation.

(2) Nwachukwu BU;Adjei J;Rauck RC;Chahla J;Okoroha KR;Verma NN;Allen AA;Williams RJ;, B. (2022, May). How much do psychological factors affect lack of return to play after Anterior Cruciate Ligament Reconstruction? A systematic review. Orthopaedic journal of sports medicine.

(3) Welling W;A;Seil R;Lemmink K;Gokeler A;, B. (2018, October). Altered movement during single Leg Hop Test after ACL reconstruction: Implications to incorporate 2-D video movement analysis for hop tests. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA.

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