Patellofemoral syndrome (PFS) is one of the most common causes of anterior knee pain – it is also commonly known as runner’s knee.
Knee pain can be difficult to treat and has stopped many runners from enjoying the exercise.
Researchers from the University of Connecticut suggest that what may work for one runner won’t necessarily help another.
The study highlights the importance of personalised rehabilitation to effectively address chronic knee pain on an individual basis.
Neal Glaviano, assistant professor of kinesiology in the College of Agriculture, Health and Natural Resources, in collaboration with Sungwan Kim, a PhD student, discovered that rehabilitation to address chronic knee pain may not be targeting all the right muscles.
Professor Glaviano has been studying “runner’s knee” for many years. Approximately 23 per cent of the global population suffers from this kind of pain, which affects the area around the kneecap.
While present in the general population, this condition is especially common for runners and those in the military.
“Across the board it’s a pretty significant impairment in [people’s] ability to lead happy and healthy lives,” Professor Glaviano says.
Studies have shown that patients who suffer from patellofemoral pain, some muscles in their legs and hips are weaker in terms of strength and endurance, as well as a decreased ability to generate their maximal muscle contraction.
“It all comes back to there being some potential deficit in the muscle for some reason,” Professor Glaviano says in the university release.
Professor Glaviano theorised that these deficits may be related to the size of certain muscles around the knee. Researchers were specifically interested in the glute and quad muscles.
“A lot of the research shows consistent evidence that there’s weakness in those muscles,” Professor Glaviano says.
“So, I expected those are the four muscles that we would discover are smaller in size compared to the healthy database.”
To understand “runner’s knee” better, the team worked with the Brain Imaging Research Center (BIRC) at UConn to conduct MRI scans of 13 female patients with patellofemoral pain. They then worked with Springbok, a company developed by researchers at the University of Virginia, to analyse individual muscle volumes.
Professor Glaviano and Mr Kim decided to focus on female patients as women are 2.2 times more likely to experience this kind of pain than men – though researchers have not quite figured out why this might be.
“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,” Professor Glaviano says.
Researchers expected to see differences in muscle size in the quads and glutes but that was not the case. Results showed no significant differences in the size of these muscles in patients with patellofemoral pain compared to the healthy samples.
Instead, the results revealed that the muscles at the front of patients’ hips, their deep external hip rotators, and hamstrings were smaller. But, not all patients had impairments in the same muscles.
“The four main muscles that a lot of the research prioritises as the target for rehabilitation were not actually smaller in size,” Professor 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.”
In hopes of finding further answers, researchers want to continue researching this topic in order to understand if rehabilitation interventions for patellofemoral pain can be better tailored and personalised for individual patients.
Most patients who receive rehabilitation for patellofemoral pain do not experience long-term pain relief and these findings may be a key to addressing this shortcoming and improving their quality of life.
“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,” Professor Glaviano adds. “While we’re targeting their quads and their hip muscles, we might be missing other muscles that might also be important.”
Professor Glaviano plans to investigate muscle inhibition, where a muscle is unable to perform optimally because not all the connected nerves are firing.
In his previous studies, Professor Glaviano found that patients with patellofemoral pain experience inhibition in their glute and quad muscles.
“Maybe it’s not that the muscle is smaller. 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,” Professor Glaviano says.
What is ‘runner’s knee’ and what are the symptoms?
“Runner’s knee” or patellofemoral pain (PFP), is an injury that causes pian to the front of the knee or around the kneecap.
According to Cedars Sinai, a runner’s knee may be caused by a structural defect or may be due to a certain way or walking or running.
Other causes may include:
• Malalignment of the kneecap
• Excessive training or overuse
• Injury or trauma
• Weak thigh muscles
• Tight hamstrings
• Tight Achilles tendons
• Poor foot support
• Walking or running with the feet rolling in while the thigh muscles pull the kneecap outward
The symptoms of runner’s knee include:
• Pain in and around the kneecap when you are active.
• Pain after sitting for a long time with the knees bent, which can sometimes cause weakness or feeling of instability.
• Rubbing, grinding of clicking sound of the kneecap
• Kneecap that is sensitive to touch.
