Once you’ve sprained an ankle, there’s a good chance you’ll sprain it again. And each time the ankle is injured, the more likely it is that you’ll develop chronic ankle sprains. The orthopedic term for this condition is functional ankle instability (FAI). People with FAI report episodes where the foot and ankle just collapse, give way, or roll under them.
Lateral ankle sprains are the most common. Lateral refers to the outside ankle or the side away from the other leg. Physical therapists and athletic trainers help patients regain normal muscle activation and joint proprioception after ankle sprains. This type of rehab program is a strategy for preventing future (repeat) ankle sprains. Joint proprioception refers to the joint’s sense of its own position.
But sometimes even after rehab, people end up spraining the ankle again. This is a puzzle. If rehab isn’t effective, is it because it’s the wrong rehab program? Or is there something else going on in the nervous system that can’t be changed with rehab? Or maybe there’s a need for a different approach altogether.
To test out this idea, experts in the area of kinesiology (movement) set up an experiment to test and measure ankle stability and function. They specifically focused on muscle activation of the peroneal muscles. The peroneal muscles evert the foot and ankle. Evert means to move it away from the other foot. The idea was to check for a deficit of muscle activation called arthrogenic muscle inhibition (AMI).
AMI refers to the fact that the peroneal muscles are not being activated with sufficient force for a strong muscle contraction. Without this dynamic activation, the ankle is more likely to be unstable, giving way without warning. If the muscle isn’t getting the nerve messages needed to contract, why not? Is there a problem with local control of the nerve to muscle communication pathway? Or is the breakdown occurring more centrally in the spinal cord of the nervous system?
Here’s what they did. First, they built a walkway with special trapdoors that could be triggered simulating ankle eversion or the giving way experience of chronic ankle sprain sufferers. Then they measured the electromyographic (EMG) output of the peroneal muscles while walking on the flat walkway and when the trapdoors were activated.
They compared one ankle to the other for two groups of people. The first group was made up of patients with functional ankle instability (FAI). They were accepted for the FAI group based on results of two testing tools: the Functional Ankle Instability Questionnaire and the <i Ankle Instability Instrument. The second (control) group had no ankle sprain (past or present). EMG measurements were compared from one leg to the other in both groups.
EMG can be used to calculate H-reflexes (H) and M-waves (M) for the peroneal muscles as an indication of muscle inhibition. The control group (no ankle sprains) had equal measurements from side to side. Their H:M ratios were the same on both sides. The ankle sprain group had larger peroneal H:M ratios on the uninjured side. The ankle sprain group also had lower EMG readings than normal when the foot/ankle was dropped unexpectedly. This suggests that the peroneal muscles weren’t firing as they should be to stabilize the foot and hold the ankle stiff when the person is suddenly off balance.
After conducting the experiment, it became clear that the problem was still in the peroneal muscles. It wasn’t a matter of neuromuscular inhibition or processing at the central nervous system interfering with ankle stability. That means we are back to the drawing board reviewing rehab protocols. Obviously current approaches are not restoring peroneal muscle function as needed to prevent reinjury.
This study helps point researchers in the right direction when evaluating what’s best for functional ankle rehab. Future studies are needed now to identify specific exercises, activities, or interventions that target and return peroneal muscle activation to normal.