Abstract
Background:
Arthrogenic muscle inhibition (AMI) is a complex neurological phenomenon that is actually very common. AMI can appear following a knee injury or knee surgery. If it is not addressed, the patient's function can be negatively affected. There is currently no specific tool for the diagnosis and treatment of AMI.
Indications:
Following surgery or injury to the knee, AMI causes defective activation of the quadriceps, sometimes combined with a knee extension deficit. A clinical classification of AMI has been proposed recently to help with making the diagnosis and to guide treatment. In this article, we describe how biofeedback and surface electromyography (EMG) can be used in the early diagnosis and treatment of knee AMI.
Technique Description:
Biofeedback is based on transformation of physiological variables into a visual or auditory signal. This allows the patient to learn how to control physical and bodily functions, which were previously considered as involuntary processes. This technique requires the use of a specific device that transforms the measured physiological signals—neuromuscular activation in this instance—into visual signals. This tool incorporates surface EMG, with electrodes connected to a measuring unit. This unit is connected to a screen that shows the neuromuscular activation in real time. Thus, EMG biofeedback can be used to help clinicians make a diagnosis and to specifically treat the AMI.
Results:
We have used biofeedback in patients who have a knee injury or who have undergone knee surgery. Both the therapist and patient were able to objectively see the presence of AMI using the biofeedback device. For treatment, the therapist works with a patient by providing clear instructions and increasingly more challenging goals. We show examples of how patients were able to eliminate their AMI by using biofeedback.
Discussion/Conclusion:
EMG biofeedback is a promising tool for the diagnosis and treatment of AMI after an anterior cruciate ligament (ACL) tear and ACL reconstruction surgery. The next steps are to define thresholds and a rehabilitation protocol that will be used in a clinical trial.
Patient Consent Disclosure Statement:
The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.
This is a visual representation of the abstract.
Video transcript
In this video, we will describe how biofeedback with surface electromyography can contribute to the diagnosis and treatment of arthrogenic muscle inhibition in the knee.
These are our disclosures.
Background
This article is a follow-on to the recent article in the Video Journal of Sports Medicine by Bertrand Sonnery-Cottet and colleagues 6 titled “Arthrogenic Muscle Inhibition Following Knee Injury or Surgery.” We will give detailed examples on how biofeedback can be used to diagnose and treat arthrogenic muscle inhibition. Biofeedback provides real-time information about muscle activity based on surface electromyography that is visible to the therapist and patient. Our group has successfully used biofeedback to retrain the vastus medialis oblique (VMO) and eliminate hamstring contracture, especially in patients with grade 2 arthrogenic muscle inhibition.
Arthrogenic muscle inhibition, or AMI, is a complex neurological phenomenon in which the neuromuscular pathways are disrupted. It interferes with the activation of VMO and sometimes also causes involuntary over-activation of the hamstring muscles.3-5 AMI frequently appears following a knee injury or during the postoperative course of surgery, especially anterior cruciate ligament (ACL) reconstruction.1,7 AMI is known to hinder a patient's postoperative recovery and slow their rehabilitation. If AMI becomes entrenched, it can have serious consequences for a patient due to quadriceps weakness and also interfere with proprioception and gait. 8
But there is currently no tool, other than clinical examination, which can be used to diagnose and quantify AMI in patients. In addition, there is no specific tool that can be used to solve this clinical problem. The treatments recommended today are rehabilitation exercises, cryotherapy, and joint aspiration in the event of initial hemarthrosis. 9
The objective of this video article is to describe how biofeedback using surface electromyography can be used to confirm the presence of AMI at the knee, classify it, and treat it.
The best known neuromuscular biofeedback technique is one that incorporates electromyography, or EMG. 10 EMG electrodes are placed on the surface of the muscle of interest. EMG can detect a change in a muscle's electrical activity because depolarization occurs before a muscle contracts. The electrical signals produced during a muscle's contraction are transformed into a visual signal by the biofeedback unit, which is actually a highly sensitive voltmeter. Thus, surface EMG provides real-time information about the timing and excitation level of the muscles of interest.
Biofeedback has been used for many years in rehabilitation. Providing patients with biofeedback during rehabilitation will help them take control of physiological processes that were previously considered automatic. It has a neurophysiological basis: it reactivates underused neuronal and synaptic pathways. 2 At our sports injury clinic, we use the NeuroTrac MyoPlus 2 Pro EMG biofeedback system. It has 2 channels that show the excitation level in both legs simultaneously.
This is the AMI classification proposed by Sonnery-Cottet in 2022. In this article, we will focus on Grade 1: VMO contraction inhibited with no knee extension deficit and Grade 2: VMO contraction inhibited with associated knee extension deficit due to hamstring contracture.
Technique Description
This patient tore his left ACL 1 month ago and has Grade 1 AMI. He has full knee extension but inadequate VMO activation. The therapist can confirm his clinical impression of grade 1 AMI by comparing the injured to the healthy contralateral leg. The patient was asked to contract his quadriceps muscle while looking at the biofeedback screen. His left side is clearly deficient, and he can barely reach 80 mV, while on his right side, he can generate more than 500 mV.
This patient underwent ACL reconstruction in her left knee and has Grade 2 AMI. We asked her to relax completely, but it is clear that her left hamstring muscle is activated and that it cannot fully relax. Her right hamstring activity is normal at rest. Comparing the injured to the healthy contralateral leg helps the therapist confirm the presence of grade 2 AMI.
Biofeedback can be used to treat AMI. The patient can learn how to consciously re-activate their pathological VMO muscle and to fully relax their hamstring muscles. Guidance from a therapist is crucial in many respects. The therapist sets the goal on the biofeedback unit. This goal must be achievable by the patient during the contraction, but still require a true effort. Once the patient achieves the goal easily, the therapist will increase the threshold to ensure the patient continues to improve. The instructions given to the patient by the therapist are also important. The patient must understand the work required to make a 100% effort to complete the task. These are elements of neurological and motor retraining that will ensure a patient can overcome their AMI and optimize their rehabilitation after a knee injury or surgery. Some studies seem to point to the superiority of rehabilitation with the use of biofeedback versus usual rehabilitation.
Here is a patient who has Grade 1 AMI in his left knee; the goal is to re-activate his left VMO. This is done through a series of contractions. The patient is instructed to focus on achieving the highest possible signal during each contraction, visible on the biofeedback unit.
Here is a patient who has grade 2 AMI with an obvious hamstring contracture. The goal is to eliminate the involuntary hamstring activity in his left leg. We asked him to contract and relax his hamstrings while looking at the biofeedback unit and to focus on letting the colored bar drop after each contraction. You can see that the hamstring activity eventually drops to zero.
Here is the progress made by a patient who has grade 2 AMI postoperatively. After using the biofeedback system for 15 days, the VMO activation in his left leg has improved. The biofeedback unit confirms our clinical impression as his activation went from 0 mV to about 80 mV in 15 days. We can also see that full extension has been restored in his left knee.
Discussion
Biofeedback with surface EMG is being used every day at the sports rehabilitation clinic associated with our teaching hospital for all patients who have signs of AMI, after knee injury or surgery. Using this biofeedback system has also allowed us to classify the severity of AMI in patients.
Biofeedback training is done every session until the AMI is gone, in addition to the usual rehab exercises. The objective is to achieve values identical or close to the contralateral healthy side. This treatment targets the pathophysiology of AMI by addressing the motor cortex dysfunction and retraining the spinal reflex pathways. It is one component of our comprehensive treatment approach to address AMI.
The pitfalls of co-contraction are avoided by measuring the VMO's true contraction level. Even if the patient has regained full knee extension, their VMO may not be functioning normally. Thus, biofeedback is a qualitative approach that is focused on a muscle's activity, not its action.
One of the limitations for biofeedback for AMI is the lack of EMG reference values (μV) to use as a standard. Also, we have found that therapists vary in how they apply the EMG electrodes to a muscle and how they modify the biofeedback goals over time. There are no published studies yet on the outcomes of using biofeedback with surface EMG to treat AMI. Finally, we did not find any real contraindications or adverse effects but this tool can be expensive, is not widely used today, it requires a precise understanding of the patient, and sometimes the treatment does not work.
We are grateful for the editorial support provided by Joanne Archambault.
These are our references. Thank you.
Footnotes
Submitted November 21, 2023; accepted February 28, 2024.
The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
