Wellsandt E, Failla MJ, Snyder-Mackler L. (2017) Journal of Orthopaedic & Sports Physical  Therapy; 47(5): 334–338

Abstracted by Adam Schwent SPT, Missouri State University, Springfield, MO

Background: The reoccurrence of anterior cruciate ligament (ACL) injuries after return to sport (RTS) poses a high-risk for athletes and the evaluation of whether an athlete is ready to RTS is a clinical decision that is often debated among many physical therapists. Many RTS criteria are based on whether the involved limb is symmetrical (or nearly so) to the uninvolved limb throughout certain testing protocols. The product of measuring the differences between limbs is called a limb symmetry index. In other words, the uninvolved limb at the time of the testing is essentially used as the goal for RTS. 

Objective: The aim of this randomized controlled trial study was to evaluate the effectiveness of limb symmetry indexes (LSI) utilized in RTS testing and its relationship with ACL injury reoccurrence. Furthermore, LSI’s were also compared to estimated preinjury capacity (EPIC) levels in their abilities to predict ACL injury reoccurrence.

Methods:  In this study, 70 athletes had their quad strength and 4 single-leg hop tests (single, crossover, and triple hop tests for distance, and 6-meter timed hop test) measured both before and 6 months after ACL reconstruction (ACLR). 6-month post-operative testing was chosen due to this being noted in the literature as a common time to RTS after ACLR. RTS criteria based on LSI’s used a 90% (85-90% being a common cutoff in other RTS criteria) or greater cutoff for all the measured tests, as well as at least 90% on the Knee Outcome Survey Activities of Daily Living Scales and on a global rating score of knee function. EPIC levels were calculated by comparing the involved-limb function at 6 months to the uninvolved-limb scores prior to ACL reconstruction and, similarly, a 90% cutoff for RTS was used for EPIC level measurements as well. There was then a minimum 2-year follow with the patients on whether they had sustained a subsequent ACL injury. 

Results: Of the 70 patients, 40 (57.1%) patients met the RTS criteria of at least 90% based on LSI in quadriceps strength and all 4 single-limb hop tests 6 months after ACL reconstruction, but only 16 of these 40 achieved the 90% EPIC levels RTS criteria cutoff, meaning a merely 22.9% of the patients met the EPIC levels cutoff. 

After follow-up, 11 patients (16% of original patients) had sustained a subsequent ACL injury. 8 of these 11 patients (72.7%), had passed the 90% LSI RTS criteria cutoff; however, 6 of these 8 (75%) did not achieve the 90% EPIC levels RTS criteria cutoff. Therefore, the 90% EPIC levels RTS criteria cutoff, where the quad strength and single leg hop tests 6 months after initial ACL reconstruction were compared to preoperative levels, was more sensitive in predicting a second ACL tear than the 90% LSIs RTS criteria cutoff (LSIs, 0.273; 95% confidence interval [CI]: 0.010, 0.566 and EPIC, 0.818; 95% CI: 0.523, 0.949).

Personal Commentary

This article was of particular interest to me because of personal experience with an ACL injury, subsequent reconstruction, and the many months of strenuous rehab that follow. Luckily, I have not suffered a recurrent ACL injury myself; however, I have witnessed many fellow athletes, as well as many professional athletes, suffer another ACL tear shortly after their seemingly dedicated ACL rehab regimens. Knowing this highly prevalent reoccurrence rate, I couldn’t help but ponder what responsibility must the profession of physical therapy take in all this or whether it is just some biomechanical anomaly that cannot be accounted for? With accountability being one of the seven core values of the profession of physical therapy, I think PT’s must take a hard look in the mirror in this particular scenario.   

So, why should recurrent ACL tears be concerning for PT’s? Beyond the fact that a recurrent ACL tear is physically, mentally, and financially draining, as a future PT, I have concerns for these patient’s health much later down the road. Research has shown that current ACL re-rupture rates after RTS are around 1-11%2, with other sources saying up to even 28%1. With recurrent ACL tears, come worse functional and also radiological outcomes .1 Furthermore, with recurrent ACL tears and subsequent ACLR revisions, there is evidence that those with recurrent tears have a higher incidence of tibial and femoral chondral defects, and, therefore, even higher increased risk for knee arthritis later in life than those with just a one-time ACL tear.4 Moreover, one can assume that with a higher incidences of knee arthritis, there will be an increased likelihood for a potential need for knee arthroplasty later in life. The American Academy of Orthopedic Surgeons reports over 680,000 total knee arthroplasty’s (TKA’s) done in 2014 (likely even more annually now) and at an average cost of between $35,000-$50,000, TKA’s are costing the U.S. and our citizens billions of dollars annually. So, with that said, anything we can do as PT’s to reduce these numbers would be beneficial to all parties involved. 

Now that I’ve stated why I find recurrent ACL tears so concerning, it reinforces why a study like the one above is so important. It is highly valuable to us and to our patients to find the most accurate ways we can to determine whether they are truly ready to RTS. This study highlights the fact that using the LSI’s may not be as accurate as intended with the reason being that after an ACL injury the uninvolved limb will likely experience a large decrease in activity compared to pre-injury status. With this decrease in activity, there are likely to be compensatory adaptions such as a decrease in muscle strength, even in the “uninvolved” limb.3 Consequently, it would be irrational to assume that the uninvolved limb after injury would serve as a valid standard or goal for the reconstructed limb to reach, and rather, pre-injury uninvolved limb measurements would be much better. 

This is one example of how to improve RTS criteria selection. Another thought mentioned in the article would be to establish age, sex, and sports matched norms that the individual’s involved limb could be compared to, but with the extremely large number of factors to consider, these norms are not widely developed yet. Regardless, there are ways to improve our outcomes with our patients and it is our professional duty to bring our minds together to collectively establish better standardized criteria for RTS for post-ACLR patients. 

In my experience as an SPT, I have not had the pleasure to see many of my patients prior to surgery, so, while using EPIC levels may be shown in this study to be a better frame of reference, it may not always be realistic to assume we’ll see many of these ACLR patients before surgery. Regardless, I think that through more strict and less time or subjective based RTC criteria, in addition to ACLR rehab programs that include an extensive focus on muscle strengthening, refinement of landing and deceleration biomechanical patterns, improving balance and proprioception, and plyometrics, I truly believe we can improve our outcomes and reduce tear reoccurrence for ACLR patients [5]. 


[1] Ahmed I, Salmon L, Roe J, Pinczewski L. (2017) The long-term clinical and radiological outcomes in patients who suffer recurrent injuries to the anterior cruciate ligament after reconstruction. Bone Joint J. 99-B(3):337–343.

[2] Gans, I., Retzky, J. S., Jones, L. C., & Tanaka, M. J. (2018). Epidemiology of recurrent anterior cruciate ligament injuries in national collegiate athletic association sports: the injury surveillance program, 2004-2014. Orthopaedic Journal of Sports Medicine, 6(6), 2325967118777823. 

[3] Hiemstra LA, Webber S, MacDonald PB, Kriellaars DJ. (2007) Contralateral limb strength deficits after anterior cruciate ligament reconstruction using a hamstring tendon graft. Clin Biomech; 22:543-550. 

[4] Mitchell, J. J., Cinque, M. E., Dornan, G. J., Matheny, L. M., Dean, C. S., Kruckeberg, B., Laprade, R. F. (2018). Primary versus revision anterior cruciate ligament reconstruction: patient demographics, radiographic findings, and associated lesions. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 34(3), 695–703.

[5] Voskanian, N. (2013). ACL Injury prevention in female athletes: review of the literature and practical considerations in implementing an ACL prevention program. Current Reviews in Musculoskeletal Medicine, 6(2), 158–163. doi: 10.1007/s12178-013-9158-y