Sports Medicine Research: In the Lab & In the Field: What’s Really Causing Those Knee Stability Deficits Following an ACL Reconstruction? (Sports Med Res)


Wednesday, July 2, 2014

What’s Really Causing Those Knee Stability Deficits Following an ACL Reconstruction?

Long-term deficits in quadriceps strength and activation following anterior cruciate ligament reconstruction.

Otzel DM, Chow JW, and Tillman MD. Physical Therapy in Sport. 2014. [Epub ahead of Print].

Take Home Message: Following anterior cruciate ligament reconstruction (ACLR) rehabilitation patients continue to experience muscular strength and stability deficits in the affected limb compared with the unaffected limb. This is potentially caused by the loss of neuromuscular control following ACLR and the rehabilitation process.

The goals of rehabilitation after an anterior cruciate ligament (ACL) reconstruction (ACLR) are to restore range of motion, strength, and neuromuscular control. This is done in an effort to return a patient to pre-injury activity levels. Despite these efforts, we often see long-term strength deficits in the muscles responsible for dynamic knee stabilization. Therefore, Otzel and colleagues completed a study to comprehensively analyze the long-term post-surgical outcomes following ACLR. Twenty-four patients (13 female, 11 male, age ~ 20.2 years of age, ~ 3.3 years post-surgery) who underwent unilateral ACLR and completed a rehabilitation regime were recruited for the study. The researchers matched all patients to a control group with respect to gender, height, and weight. All ACLR patients completed rehabilitation and returned to recreational physical active. Prior to any testing all participants completed a 5 minute warm-up on a treadmill. During each testing session, an investigator measured bilateral thigh circumference. Participants then completed strength and neuromuscular control testing on a KinCom AP125 dynamometer. All participants completed 2 sets of 3 trials of maximal effort for knee flexion and extension movements at 180⁰/s followed by 60⁰/s. After maximum voluntary contractions were recorded, researchers placed electrodes in a bipolar configuration over the rectus femoris and vastus medialis. Participants performed maximal effort isometric knee-extension and as their force output was steady, the researchers delivered an electrical impulse to assess central activation deficits of the quadriceps muscles. Overall, knee-extensor strength deficits and central activation deficits of the quadriceps were detected in the involved limb compared with the uninvolved limb. Further, no difference in quadriceps size was found in ACLR patients compared with controls.

Overall, the current study demonstrates that patients with an ACLR have strength and central activation deficits. However, the participants with ACLR and control participants had similar quadriceps size, which indicates that central activation deficits may be a key issue following ACLR. These deficits could reduce the patient’s ability to stabilize the joint, which may increase the risk for a new joint injury or further joint damage. These findings should raise awareness for the need to continue, and even expand neuromuscular recruitment training throughout the rehabilitation process. However, we need to identify how long these deficits persist, if they ever resolve, and if they resolve then the time-frame in which this is accomplished. This would be a key piece in identifying how intensely and how often neuromuscular training should continue in the rehabilitation process or if the rehabilitation process should be lengthened to sufficiently correct these deficits. Until then, clinicians should look to limit neuromuscular activation deficits following ACLR and rely more on inter-limb strength levels instead of muscle atrophy measurements when considering return-to-activity decisions.

Questions for Discussion: How long in the rehabilitation process do you have patients work on neuromuscular activation? At what point do you as a clinicians feel comfortable discontinuing neuromuscular activation training? Should we teach patients how to promote better muscle activation after they leave our care so that they can avoid activation deficits?

Written by: Kyle Harris
Reviewed by:  Jeffrey Driban

Related Posts:
Predictors of Failure After ACL Reconstructions

Otzel, D., Chow, J., & Tillman, M. (2014). Long-term deficits in quadriceps strength and activation following anterior cruciate ligament reconstruction Physical Therapy in Sport DOI: 10.1016/j.ptsp.2014.02.003


Meaghan McMillen said...

I greatly agree that neuromuscular deficits should be considered within rehabilitation programs. I think that these deficits should be looked into more to determine the actually source of the deficit. Is this a deficit that is arising from a global movement pattern or from a fine motor control unit. This could help dictate the rehabilitation route to take, for if the global neuromuscular control were addressed but they were not the original or source of the problem nothing would be solved. Also, it will be important to learn where in the body this deficit begins, within sensory feedback, the message from the brain to the motor unit, or within the motor unit itself.

This study was also particularly helpful because it compared the subjects to a similar control, as opposed to using the subject contralateral uninvolved limb. Many studies that look at similar measures use the contralateral limb for baseline or normative data ranges. This may skew results as the contralateral limb still received neurological input from the same single brain. This may cause deficits that were in the injured limb prior to injury to be measured as normal within the uninjured limb. It would be more beneficial to compare the subject to a person of similar weight and height, or even similar activity involvement.

Stacy Schurr said...

This was a very interesting study, and you made a lot of good points. The most interesting part to me is that there were no differences in quadriceps size between ACLR subjects and the controls. The deficits that are present should tell us that clinicians are on point with strengthening the musculature, but something is obviously still missing. I would be interested in seeing a study looking at the longer time-frame post-injury to see if symptoms ever do resolve. I think we should look to educate patients on proper neuromuscular activation after they complete their rehabilitation, but further research will be key moving forward.

Chelsea Williamson said...

As Stacy commented earlier, it is very interesting that there were no size differences found in the quadriceps between the ACLR and controls. I'm curious as clinicians how do we recognize this neuromuscular deficit, or if we can at all. Clinically we should see the strength deficits, but have no way of measuring the central activation deficits. I am curious if adding in modality use for the specific purpose of trying to wake up the neuromuscular component more quickly would help during the rehab process.

Jeffrey Driban said...

Hi Chelsea: You are right that it can be challenging to identify neuromuscular deficits. It is important to note here that they authors detected differences in limb strength between limbs. This deficit is something we can detect. We could even quantify it in a school that has a weight room. It might not capture a neuromuscular deficit perfectly but it will help us detect issues. The CAR is really helping us look at why the person has the deficit. There is work being done to identify modalities that can help wake up the neuromuscular component during rehab. Stay tuned :)

Rachel Koldenhoven said...

Hey Jeffrey,

I was also thinking along the same lines as Chelsea and Stacy. It's very interesting that there weren't size differences between the two groups, but there were strength and CAR deficits. From an observation stand point, the legs may look to be about the same size, but what is going on inside the muscle themselves is the problem. As clinicians we need to pay special attention to correcting those strength deficits on the injured side, but also make sure that they return to pre injury strength. When it comes to CAR, clinically we haven't found a way to look at it, but it is still an issue that we need to address. I look forward to hearing about modalities in the future that can help us assess clinically. I definitely think we're on the right track though in helping those ACLR patients by staying up to date on the current research.

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