No Backing to Suggest Patellofemoral Pain Syndrome is NeuropathicPatients who live with patellofemoral pain syndrome (PFPS), pain in the anterior, or front of the knee, find that it gets worse as they walk up or down hill, squat, kneel, or sit with their knees folded in. It's a fairly common pain syndrome, say researchers, with about 20 percent of the population experiencing it at one time or another.
At this point, there is no set guideline for assessing, diagnosing or managing PFPS, but there have been several theories about what causes the pain. One such theory is that it is caused by a local nerve injury and results from pressure from neighboring bones. When researching the physical aspects, x-rays have not shown any definite findings that could explain the pain and what causes it.
The authors of this study assessed whether PFPS could be classified as neuropathic pain, or pain that is related to the nerves.
Researchers recruited patients with PFPS in one knee and 56 men and 35 women between the ages of 18 and 40 years participated in the study. A control group of 12 women and 11 men also participated. None of the subjects in the control group had any knee pain and all had normal knee function.
To assess the pain, researchers used quantitative sensory testing (QST), a method that is used to evaluate sensory nerve fiber function, and various instruments to check sensations to vibration and heat. The researchers used the visual analog scale (VAS) a score of 0 to 100, with 0 being reports of no pain and 100 being the most severe pain possible. The Cincinnati Rating System was used to determine level of knee function by evaluating symptoms of knee pain, swelling, giving-way, and function (walking, stairs, running, jumping/twisting). A functional performance test is also performed. The Step-Down test assesses the ability of the knee to function stepping up and down a 20 centimeter platform.
When gathering the results, the researchers found that the average age of the study subjects was 31 years and the average length of time they had the knee pain was about 70 months. The average body mass index of the subjects was 25.3. No-one had not taken any medication for their knee pain on the day of testing, but four had taken NSAIDs (non steroidal anti-inflammatory drugs) within the week before the test.
Comparing the results of sensation and the results from the scale measurements, the findings did not show any differences in sensation between the knees of the study group and the knees of the control group. The researchers did find that there was localized damage to the nerve channels, but they were unable to âidentify a subgroup with probably neuropathic pain.â
The authors of this article note that there is no gold standard for identifying neuropathic pain so there are no real tests for it. However, using certain criteria, it is possible to form a profile. Comparing the test results between the group with pain and the control group, the researchers found that, although the patients with pain had altered nerve sensation in the knee, there was no clear subgroup of patients who had features of neuropathic pain.
Roar Jensen, PT, MHlthSc (OMT), Alice Kvale, PT, PhD, and Anders Baerheim, MD, PhD. Is Pain in Patellofemoral Pain Syndrome Neuropathic? In Clinical Journal of Pain. June 2008. Vol. 24. No. 5. Pp. 384-394.
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