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I'm trying to put together the pieces of my own knee problem. So far I know I have a problem with the kneecap tracking up and down properly over the knee. The pain I'm having while going up stairs, squatting, or running has been diagnosed as patellofemoral pain syndrome. It looks to me like the muscles around the painful knee are smaller than the other leg. Is that what's causing this problem?

No one knows for sure what causes patellofemoral pain syndrome (PFPS). It's likely that the problem is multifactorial -- in other words, it has many factors. Some experts think that when enough contributing factors are present, the problem develops. There could be some anatomical changes, overuse and repetitive motions, and even muscle atrophy (wasting) that when added together kick in this problem. In fact, a recent study from Belgium has just added some new information to help us better understand PFPS. They used MRIs to measure the size of the vastus medialis obliquus (VMO) in two groups of people. The VMO is one part of the quadriceps muscle along the front of the thigh. It is the section of muscle closest to the other knee. When the quadriceps muscle contracts and pulls evenly on the patella, it moves up and down over the knee joint in the middle where it belongs. But if the lateral quadriceps along the outside edge of the patella pulls more than the medial quadriceps along the inside border, then maltracking and eventually patellofemoral pain syndrome (PFPS) can occur. To find out more about the role of the vastus medialis obliquus (referred to as the "VMO") a group of researchers from Belgium conducted a new study. They used MRIs to measure the size of the VMO in two groups of people. Group one were patients diagnosed with PFPS. They ranged in ages from 12 to 40 years old. Group two were considered "normal" controls -- they did not have any knee pain and no sign of PFPS. They were matched by age, similar body type, activity level and sex (male and female). Special equipment was used to hold the legs still so no muscle contraction would occur during the MRI test. The results were sent to a computer that had a special software program to measure and compare the size of the vastus medialis obliquus (VMO). The measurement was just muscle fibers without any fat, blood vessels, or nerves included. They found that the cross-sectional area of the VMO was indeed smaller at the patellar level in the patients diagnosed with patellofemoral pain syndrome (PFPS). In fact, the entire quadriceps muscle was smaller in the PFPS group when measured at the midthigh level. But these findings don't answer the question: which came first -- the PFPS or the change in muscle size? Maybe people born with a smaller vastus medialis obliquus (VMO) are more likely to develop PFPS. Or maybe the pain of PFPS leads to inactivity and the muscle begins to waste away and get smaller. Understanding the cause and effect of VMO size and PFPS will be the focus of a future study. The authors of that study we mentioned also suggest looking at muscle strength as it relates to the size of the VMO in different people.


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