Bone Marrow Lesions and Knee Pain
Osteoarthritis is most commonly associated with pain and cartilage damage. However, cartilage has no nerve endings, so the degradation of cartilage cannot be the cause of the pain. We do know that OA is a disease of the entire joint, including the bones, ligaments joint capsule and synovium. So the pain must be originating from one of those sources.
What Problem Was Studied?
If all these different structures are affected by osteoarthritis, what is the main cause of pain and how can that pain be stopped? This was the question on the minds of past Arthritis Foundation grant recipient David T. Felson, MD, MPH, of Boston University School of Medicine, and a team of researchers from various institutions. Bone is highly innervated and previous studies have indicated that perhaps bone marrow lesions – commonly called bone bruises – are linked to knee pain. Armed with this knowledge, and looking to clarify results of some contradictory study results regarding bone marrow lesions (BMLs), Dr. Felson and team undertook a prospective study of the relationship between knee pain and BMLs in the knee.
Prospective study: A study in which the subjects are identified and then followed forward in time.
Retrospective study: A study that looks backward in time, usually using medical records and interviews with patients who already are known to have a disease.
Epidemiologic study: Studies on human populations that attempt to link human health effects (e.g., cancer) to a cause (e.g., exposure to a specific chemical).
What Was Done in the Study?
Dr. Felson and colleagues used a subsample of the Multicenter Osteoarthritis Study, a large epidemiologic study. At the beginning of the study and again one month later, all participants were asked the following question, “During the past 30 days, have you had pain, aching, or stiffness in your knee on most days?” If the participant answered “no” at both time points, he or she was considered eligible for analysis. After 15 months, the same question was posed again, and again one month later. If the person answered “yes” at both of these time points, the knee with new pain was included as a “case knee.” All participants had magnetic resonance images (MRIs) taken at the beginning and end of the study. Control knees were selected randomly among the people who had no knee pain at the beginning or end of the trial. Bone bruises, or BMLs, cannot be seen on a regular X-ray; they can only be seen on MRI. BMLs probably represent areas of bone damage, with accompanying swelling and fluid collection below the bone surface within the marrow. A typical bone bruise appears on MRI as an area of signal loss within the marrow as a result of the water content of the injured marrow. BMLs were noted and measured for all case and control knees at baseline and after 15 months. The difference in BML score (combined total volume of all lesions found at followup minus total volume at baseline) was compared with the presence of pain.
What Were the Study Results?
The research team found that 54 of 110 (49.1 percent) case knees had an increase in BML score, whereas only 59 of 220
(26.8 percent) control knees showed an increase in BML score. New knee pain was strongly associated with a two-unit or more increase in BML score. Through further analysis, the team was able to determine that more than half of the BML increases reflected the development of single large lesions rather than the development of several small lesions.
What Does This Mean for People with OA?
Dr. Felson concludes, “our observations provide strong evidence the BMLs are one source of pain in knees with or without OA.” However, he notes that the findings do not identify BMLs as being the only source of pain in OA, as evidenced by the fact that less than half of the participants who developed frequent knee pain had an increase in BML score and more than one-quarter of those without frequent knee pain also had increasing BML scores. Dr. Felson sees future research as focused on trying to make bone marrow lesions go away to see if this makes pain better.
Felson DT, Niu J, Guermazi A, et al. Correlation of the development of knee pain with enlarging bone marrow lesions on magnetic resonance imaging. Arthritis Rheum 2007;56:2986–92.