Rehab Planning for Unplanned Movement: Challenges in Neuromuscular Control After ACLR

Postural Adjustments Following ACL Rupture and Reconstruction: A Longitudinal Study

International Journal of Sports Medicine, July 2018

Labanca Et. Al   

Università Degli Studi di Roma ‘Foro Italico’, Department of Movement, Human and Health Sciences, Roma, Italy

Here we go, Ortho Hub’s first rundown of an article out of Italy! Now, I have to admit, Italy does hold a special place for me as I was fortunate enough to do a clinical rotation there during PT school and I have to say it was quite the experience – in a positive way, of course. It’s definitely rewarding to see healthcare from different cultural perspectives.

Okay, enough about the blogger, let’s get on to the good stuff.

We’ve seen that individuals who have undergone ACLR can present with both short and long-term deficits in neuromuscular control. See here, here, and here. Furthermore, problems with neuromuscular control could lead to ACL re-tear and revision, so it’s something we definitely want to address throughout the course of rehab.

From a neuromuscular standpoint, we have two, amongst many, mechanisms that help maintain joint stability to movement perturbations: anticipatory postural adjustments (APA) and compensatory postural adjustments (CPA). Basically, APAs involve pre-firing muscles to help minimize anticipated perturbations. Meanwhile, CPAs involve compensatory activation of muscles to minimize and restore posture in response to unplanned perturbations.

Early on in rehab, it would be pretty risky to expose an individual with an ACLR to an unplanned perturbation, making research difficult in this domain. Thankfully, one research study did find a means to do this.  These researchers performed perturbations to subjects in a seated, non-weight-bearing position at 2 months s/p ACLR where they saw neuromuscular control deficits.

The authors of this study explored how the knee responds, through mechanisms of APA and CPA in the quad muscles, to planned and unplanned perturbations during a prehab time period, 2 months after ACLR, and 6 months after ACLR compared to healthy controls.

How Were The Subjects Challenged?

24 individuals participated in the study (12 in the ACLR group with bone-patella-bone grafts and 12 healthy controls). Testing was performed at three different times: pre-surgery (T1), 2 months post (T2), and 6 months post (T3). The ACLR group performed a standardized rehab program 5x per week throughout the study.

All of the participants sat in a semi-reclined position to about 40 degrees with their knee and lower leg off the table. They were then given either a predictable or unpredictable perturbation. The unpredictable perturbation involved a researcher holding the leg in full extension in the air and then at an unplanned time, dropping the leg and leaving the subject to restore and/or maintain knee extension. The planned perturbation involved the subject holding their own leg up in full extension using the big toe of their contralateral leg.

The study used surface EMG to make sure the quad muscles were relaxed prior to the perturbation and to collect data related to quad activity.  The angular displacement of the knee was collected by an electrogoniometer.

Neuromuscular Control of ACLR Vs. Healthy Control

Unpredictable condition

  • In the ACLR group, quadriceps muscles (vastus medialis and lateralis) took longer to contract (CPA) than the healthy control’s quadriceps muscles at all 3 times:
    • Pre-Surgery: VL (39 milliseconds) and VM (42 milliseconds)
    • 2 Months Post: VL (31 ms) and VM (23 ms)
    • 6 Months Post: VL (34 ms) and VM (28 ms)

Predictable Condition

  • In the ACLR group, the quadriceps muscles needed more time prior to the planned perturbation to fire (APA) than the healthy control’s quadriceps at T1 and T2.
    • Pre-Surgery: VL (-69 ms vs. -12 ms)
    • 2 Months Post: VL (-47 ms vs. -16 ms)
  • However, at 6 months out, there were no significant differences between groups, demonstrating that perhaps the APA mechanism improves over time.

What Might Explain Delayed Responses To Unplanned Perturbations?

The authors suggest 2 possible reasons why the compensatory postural adjustments may continue to be affected at 6 months post-surgery.

  • 1) The quad muscles could have delayed detection of a sudden change in quad length. In the ACL bundle, there are afferent neurons (sensory) that have a direct effect and action on the muscle spindles of the quadriceps. Injury to the ACL could affect the sensitivity of the spindles, which impairs the ability of the quadriceps to detect sudden muscle length changes, thereby not being able to have a quick reflexive contraction.
  • 2) There could be a delay in the ability of the quads to generative quick muscle activation due to post-surgical arthrogenic muscle inhibition. Basically, this involves more of our higher threshold motor units, think bigger type-II fibers, and puts a damper on the CNS from being able to really utilize the knee extensors to their full capacity.


  • At 6 months, when you begin to consider advancing your patient’s activity level towards more sport-specific activity, it’s possible that their neuromuscular control, with regards to a decreased ability to respond to unplanned perturbations, can still be significantly affected.
  • Make sure to challenge your patient’s neuromuscular control with unplanned movements and perturbations throughout rehabilitation in addition to their strengthening, ROM, and other rehab goals.
  • You could consider this study in relation to a former featured study on Ortho Hub that discusses knee extensor compensation in squats to help with decision making during the rehab process.

Tyler Cope

Forever Disclaimers:

1): Readers –  If any of these articles peak your interest, please click the link to the original source to read the full text! It’s important to interpret research for yourself and as it pertains to you and your practice. Not to mention, we should support our journals and authors that provide this content.
2): Journals and authors – I do my best job to help promote the message from the research you provide to help clinicians improve. This is not a platform to try and promote my own individual views. I can promise you that I will not always have everything right, so please, if you have any feedback for me or if I misinterpreted anything then let me know!




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