Posted on Sep 26, 2023, 8 p.m.
Around 23% of the global population suffers from chronic knee pain, but it is especially common for runners and those in the military. Recent research published in the journal Physical Therapy in Sport suggests that there may not be a universal way to treat runner’s knee or chronic knee pain, discovering that rehabilitation to address them may not be targeting all the right muscles in every person.
“Across the board, it’s a pretty significant impairment in [people’s] ability to lead happy and healthy lives,” says Neal Glaviano, assistant professor of kinesiology in the College of Agriculture, Health and Natural Resources. Glaviano has been studying patellofemoral pain, sometimes called “runner’s knee” for years.
In those with chronic patellofemoral pain, some leg and hip muscles are weaker in terms of endurance and strength, in addition to a decreased ability to generate maximal muscle contraction. These deficits are hypothesized to be related to the size of certain muscles around the knee, specifically with interest to the glute and quad muscles.
“It all comes back to there being some potential deficit in the muscle for some reason,” Glaviano says. “A lot of the research shows consistent evidence that there’s weakness in those muscles,” Glaviano adds. “So, I expected those are the four muscles that we would discover are smaller in size compared to the healthy database.”
For this study, the researchers conducted MRI scans of 13 female participants with patellofemoral pain. Women were focused on because they are 2.2 times more likely to experience this kind of pain than men. The researchers were surprised to find no significant differences in the size of these muscles in those with pain when compared to healthy samples. Interestingly, they did find that the muscles at the front of the hips, the deep external hip rotators, and the hamstrings were smaller, and to add to this, not all participants had impairments in the same muscles.
“We thought trying to control for [sex] would allow us to answer our question a little more straightforwardly rather than having to worry about known differences in muscle size between males and females,” Glaviano says.
“The four main muscles that a lot of the research prioritizes as the target for rehabilitation were not actually smaller in size,” Glaviano says. “I think it demonstrates the need to individualize patients’ treatment. We as clinicians and researchers need to quantify which muscles have impairment and target those in a patient’s treatment.”
“There’s very little work on the muscles that were identified as being smaller, so that might explain why there’s such poor long-term outcomes in these patients,” Glaviano says. “While we’re targeting their quads and their hip muscles, we might be missing other muscles that might also be important.”
When it comes to muscle inhibition, where a muscle is unable to perform optimally because not all of the connected nerves are firing, previous research found that those with patellofemoral pain experience inhibition in their quad and glute muscles. Those who undergo rehabilitation for patellofemoral pain often do not experience long-term pain relief, these findings may help to address the issue to improve quality of life.
“Maybe it’s not that the muscle is smaller,” Glaviano says. “It’s that the muscle isn’t able to recruit all the motor units available to be able to produce that force, and that’s why the weakness is present, not purely from a volumetric standpoint. We’ll have to continue to work to find out.”
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