Being able to put a finger or two - or even the palm of your hand - on the source of your knee pain may one day be able to help your doctor identify its cause and determine appropriate treatment for it, says C. Kent Kwoh, MD, who led a study to better understand the localization and patterns of pain in knee osteoarthritis (OA).

Supported in part by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), the study involved 799 participants from the University of Pittsburgh Osteoarthritis Initiative Clinical Center who had experienced knee pain in the past 12 months. Participants were interviewed and assessed by trained interviewers who recorded their responses on the Knee Pain Map, a diagram consisting of an artist's drawing of the seated participant's knees from the examiner's point of view.

"The interviewers asked first if the participants could use one or two fingers to point to the location of their pain," says Dr. Kwoh, professor of medicine and epidemiology and director of clinical research in the Division of Rheumatology and Clinical Immunology at the University of Pittsburgh Arthritis Institute. If participants could point to a painful location, their pain pattern was considered to be "localized" and the interviewer recorded it at one of seven locations on the Knee Pain Map. If the pain could not be identified with a finger or two, but the painful area could be covered by the participant's hand, their pain pattern was considered "regional" and was recorded at one of the four regions on the Knee Pain Map. If the pain source could not be covered with one hand or if the participant was unable to identify the location or region of pain, their pain pattern was considered "diffuse."

The researchers found that participants with knee pain could identify pain locations and patterns and that trained examiners could reliably record the location of knee pain using the Knee Pain Map. "To our knowledge, this is the first study that allowed patients to either point to an area or cover a region that hurt, giving the patient the responsibility of identifying their pain as being in a specific location versus a more general region," Dr. Kwoh and his colleagues wrote in the journal Arthritis & Rheumatism.

The most common locations of pain according to the researchers were the medial joint line, the lateral joint line, and the patella. The most common regions of pain were the patella region and the medial region. Given the diverse locations of pain, it is likely that there are several different causes and sources of pain, says Dr. Kwoh. While there are no nerve endings in the cartilage itself, the surrounding structures - including bone, joint lining, ligaments, etc. - do have nerve endings that may be sources of painful sensation, he says. Mapping the location of pain may eventually help doctors better understand the causes or sources of pain and how to treat them.

"Part of the idea for the Knee Pain Map came from working with one of our orthopaedic surgeons, Dr. Constance Chu, who does this on a routine basis in clinical practice," says Dr. Kwoh. "What we did was to standardize the process in a way that would allow it to be used in a reproducible manner from patient to patient. This provides a more formal, rigorous method of identifying pain location and pattern for clinical and research purposes."

The next step will be to compare findings from patients' reports on the Knee Pain Map with x-ray and MRI findings collected as part of the Osteoarthritis Initiative (OAI), a public-private partnership between the NIH and private industry that seeks to improve diagnosis and monitoring of the progression of OA and foster development of new treatments. Nearly 5,000 people who have OA or are at risk of OA are participating in the OAI at four centers in the United States. In addition to x-ray and MRI scans, participants provide biological specimens (blood, urine, and DNA) and clinical data such as dietary intake, medication use and pain, function, and general health assessments. Participants in the Knee Pain Map study were all participants in the larger OAI.

Eventually, the Knee Pain Map could become a standard part of the physical exam for OA patients, according to Dr. Kwoh. "Right now we don't have a good idea of what causes knee pain, and different people have various types of knee pain. The Knee Pain Map gives us a better way of describing different groups of people in terms of their knee pain and then getting a better understanding of what's causing it and ultimately how to cure it or help people manage it better."

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The mission of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a part of the Department of Health and Human Services' National Institutes of Health, is to support research into the causes, treatment, and prevention of arthritis and musculoskeletal and skin diseases; the training of basic and clinical scientists to carry out this research; and the dissemination of information on research progress in these diseases. For more information about NIAMS, call the information clearinghouse at 301-495-4484 or 877-22-NIAMS (free call) or visit the NIAMS Web site at

Thompson LR, Boudreau R, Hannon MJ, Newman, AB, Chu CR, Jansen M, Nevitt MC, Kwoh CK. The knee pain map: reliability of a method to identify knee pain location and pattern. Arthritis Rheum 2009 Jun 15;61(6):725-31.

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