An athlete returning to sport after an ACL reconstruction surgery (ACLR) is one of the most challenging decisions a sports medicine team has to make. What makes it even harder is there is not yet any universal return-to-sport criteria for resuming athletic activity following ACLR.
No athlete after an ACLR has the same recovery. There are such a variety of factors that one has to consider when releasing an athlete back to sports after ACLR, including both intrinsic (genetics, biology, inflammation, lesion type, anatomical features, motivation, psychology) and extrinsic (graft type, surgical techniques, rehabilitation, biological support) factors, that it might be impossible to create a protocol that will be able to consider all of the relevant variables.
A recent analysis by Ardern et al. shows that only 82% of patients who underwent ACLR resumed sports activity, even though 90% of those patients presented with normal or nearly normal knee function.
So where is this discrepancy coming from?
Czuppon et al. attempted to explain this in a systematic review of current research on the subject, but only weak evidence supported pain, quadriceps strength, effusion (swelling), range of motion, instability, kinesiophobia (fear of movement), confidence in knee, and self-motivation as having an influence on returning to sport.1-3
ACLR Return to Sport Testing
Prior to initiating any sort of return to sport program, athletes must present with quadriceps strength index greater than or equal to 90%, no to minimal effusion, full knee ROM, and no pain with single leg hopping.4 See Table 1 below.
Table 1. Return to Sport. Adapted from Adams et al.
Athletes should be able to complete hop testing (See Figure 1 below).4 Based on Logerstedt et al.5, the 6-m timed hop was the best predictor of knee function after ACLR. This was also confirmed in another study by Fitzgerald.6
While hop testing is an excellent objective measure that will simulate the demands of higher level activities, these tests may not be sensitive enough to pick up on functional limitations that may be present in multi-directional movements.
Figure 1. Hop Testing. From Adams et al.
Vail Sport TestTM
Per Garrison, et al., the Vail Sport Test™ has been shown to have excellent reliability between graders during the return-to-sport period of rehab.
This test is a battery of single-leg squatting, lateral bouncing, and forwards and backwards jogging against resistance from the sportcord®, giving a clinician a lot of information about a athlete’s movement patterns, neuromuscular control, and endurance in many different directions.7
The anterior reach direction (ANT) of the Y Balance Test™ is similar to a single leg squat, and because the ANT requires significant quadriceps muscle activation, the ability to perform the movement correctly has been used as an indicator of readiness for exercise progression following ACL reconstruction.8
Per Garrison et al, athletes following ACLR who exhibited > 4 cm Y Balance ANT deficits at 12 weeks on their involved limb did not tend to achieve 90% limb symmetry for single hop and triple hops (see Figure 1 above) at time of return to sport, suggesting the Y-balance test may be used as a tool to predict future success in return-to-sport endeavors.9
So I Passed? Now Can I Go Play?
It is important to understand that even once an athlete is cleared by passing some sort of battery of functional return to sport testing, it is not recommended that athletes immediately return to competition.
Functional testing must be satisfactorily passed and then typically, the athlete must be cleared by the physical therapist as well as the surgeon to initiate return-to-sport progression.
Athletes begin with no contact in practice and progressively work up to limited contact before full contact, monitoring knee effusion, ROM, and pain at each level. Figure 2 adapted from Fitzgerald et al. is a visual representation of this process.
Figure 2. Progression to sports-related activities. From Fitzgerald et al.6
Copers versus Noncopers
There have been very few studies looking at whether or not an athlete NEEDS his or her ACL reconstructed after an ACL injury. ACL rupture may result in increased knee joint instability and dysfunction, including the inability to participate in cutting and pivoting sports. Individuals who decide to get surgery to address these deficits are called “noncopers.”
However, athletes who injure their ACL and now have an ACL-deficient knee without functional limitations or instability and successfully can return to all activities without surgery are described as “copers.”
A group from Delaware has been attempting to come up with an algorithm for determining the subset of athletes with an ACL injury who could potentially be “copers.” Potential copers were individuals who met all the following criteria: (1) hop test index of 80% or more for the timed 6-meter hop test, (2) Knee Outcome Survey activities of daily living scale score of 80% or greater, (3) global rating of knee function of 60 or greater, and (4) no more than 1 episode of giving-way since the injury.
While 57% of potential copers still went on to have reconstruction surgery in this study, it is important to note that it is possible to expect good knee function even without surgical intervention in combination with a rehabilitation program that includes perturbation training. 6,10
The problem we tend to see more often is patients, especially high school athletes who only have a finite amount of time, don’t want to spend the time doing 3 months of physical therapy if they’re just going to end up having surgery anyways.
Obviously, the decision to undergo ACL reconstruction is a complex one and will be an individualized process for each athlete.
Males vs. Females and ACL Injury
It is well studied that females are far more likely to tear their ACL compared to males; however, at this point in time, there is little consensus on why this is.
While there are anatomical differences between males and females (females typically have smaller femoral notches and smaller ACLs), as well as hormonal considerations, the biggest difference between males and females to explain the increased number of female ACL injuries seems to be neuromuscular differences and muscle activation patterns.
Hip position influences knee position and if the hips aren’t doing their job, the knee will never be in a “good” position.
Females have both less hamstring and less gluteus medius activation and are less effective at knee stiffening compared to males.
Females also seem to have weak hip extensors, causing them to land a jump in a more upright hip position, resulting in an altered knee angle on landing. Decreased hip muscle activation also decreases maximal possible quadriceps and hamstring activation.
Similarly, females show a significantly shorter duration of gluteus medius activation in load-absorbing phase when executing a cutting maneuver. This results in higher loads per unit of body weight on the knee in females, which may also contribute to ACL injury.
Strength programs to prevent ACL injury should emphasize hip control and appropriate landing mechanics in order to avoid ACL injury in female cutting sports, like soccer and basketball.13,14
I Finished Formal Physical Therapy: Now I Can Stop Doing My Exercises At Home, Right?!
The median time to return to play after ACLR is getting longer: around 9 months at the minimum.15 The athletes who can return in 4 months are anomalies who have the resources, genetics, and time to rehabilitate in a way that the majority of us cannot.
Continued strength training and neuromuscular control training needs to continue for as long as one plans on participating in higher-level sporting activities, given the fact that an ACL injury is “permanent,” so to speak, even with a reconstruction.12
Timestamps after ACL surgery just do not matter: if you haven’t worked on your knee control or your balance, it will not be better. Physical therapy intervention is imperative for optimal knee function, especially if you plan to return to sport, no matter how far out you are from your injury, whether you had surgery or not.
After finishing rehab with a physical therapist, you'll need to continue taking care of your knee to avoid developing excessive arthritis in the knee. The risk of long-term arthritis increases after an ACL surgery so it's your best interest to control inflammation and take care of your joints.