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
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