A great many Americans are walking around with torn menisci in their knees, and it's not bothering them a bit. This finding, from a study done by researchers funded in part by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), encourages practitioners to take a closer look at their diagnostic and treatment options when advising their patients about knee pain.
Many people over age 50 who go to an orthopaedic physician with knee pain are diagnosed with a torn meniscus based on knee MRI readings. The menisci are two c-shaped, rubbery cushions of cartilage located in the knee where the major bones of the leg connect. They are essentially the shock absorbers of the knee and help distribute loads across the surfaces of the joint. Arthroscopic surgery on this part of the knee is the most frequent surgical procedure performed by orthopaedic surgeons in the United States.
Martin Englund, M.D., Ph.D., of Boston University Medical School and Lund University, Sweden, along with his collaborators, recently published a study in the New England Journal of Medicine that asks several questions about cartilage and knee pain. Researchers examined just how prevalent meniscal tears are in the general population between the ages of 50 and 90. They wanted to know whether, in this age group, such damage to the menisci was causing pain in all cases.
They recruited subjects from the Boston suburb of Framingham, Massachusetts, using census data and random-digit telephone dialing. People were not chosen based on whether they'd previously had joint or knee problems. They had to be at least 50 years old and ambulatory. Between October 2002 and June 2005, 991 people underwent MRIs, and to avoid bias, the readers of their scans were not made aware of any of the subjects' clinical characteristics.
Those participating in the study filled out questionnaires that included questions about the amount of pain, aching, or stiffness they had experienced in their knees in the past month. Researchers wanted to determine the presence or absence of pain with meniscal tears, as well as the co-occurrence of meniscal tears and osteoarthritis seen on plain radiographic films.
When the MRIs were read, researchers found that meniscal tears were remarkably common, that the frequency did increase with the age of the person, and that there were more often meniscal tears among those whose knee x-ray showed signs of osteoarthritis. In the group of subjects who had osteoarthritis in their knees, the prevalence of a meniscal tear was 63 percent among those with knee pain, and 60 percent among those without knee pain. In other words, both the group with pain and the group without pain had about equal numbers of people with meniscal tears.
Among the 991 who underwent MRIs—both those with and without any signs of osteoarthritis—61 percent of the meniscal tears detected were found in people who had had no pain, aching, or stiffness in the previous month. These findings are important because they suggest that meniscal tears are likely to show up frequently on MRIs in clinical practice, especially in middle-aged and older people. But, that doesn't mean that the meniscal tear is necessarily causing the patient's pain. The location of the pain and types of symptoms should be consistent with the images for diagnosis of a meniscal tear. If not, other processes related to knee osteoarthritis may be causing the pain. If that's the case, meniscal surgery will not relieve the patient's pain, and other treatments need to be considered.
This study is valuable both to patients and to clinicians who want to find out the cause of knee pain and to plan appropriate therapies.
The mission of the National Institute of Arthritis and Musculoskeletal and Skin Diseases, 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 (toll-free call) or visit the NIAMS Web site at http://www.niams.nih.gov.
Englund M, Guermazi A, Gale D, Hunter DJ, Aliabadi P, Clancy M, Felson DT. Incidental Meniscal Findings on Knee MRI in Middle-Aged and Elderly Persons. New England Journal of Medicine, 2008, 359:11; 1108-1115.