Bone Marrow Lesions are Associated with Pain in Knee Osteoarthritis
In a cross-sectional observational study, Felson, et al (Ann Intern Med 134:541, 2001) evaluated 401 persons with knee osteoarthritis to determine whether bone marrow lesions were associated with pain in knee osteoarthritis (OA). The size of bone marrow lesions was determined by MRI using coronal T2-weighted fat-saturated images. Participants were asked to complete a visual analogue scale for pain and to fill out the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). These scores were used to assess severity of knee pain and disability.
77.5% (272 of 351) of patients with knee pain had MRI evidence of bone marrow lesions compared with only 30% (15 of 50) of patients without knee pain (P<0.001). Large bone marrow lesions were found in 35.9% of patients having knee pain compared to only 2% of patients without knee pain. No correlation was found between the severity of knee pain and the presence of these lesions. The association of knee pain with bone marrow lesions remained significant even after adjustment for age, gender, and severity of radiographic disease.
These data indicate that bone marrow edema is found in most patients with painful osteoarthritis of the knee. Therefore, edematous changes in the subcortical bone marrow can be a source of pain in OA patients.
Editorial Comment: The source of pain in knee OA is not well understood but is likely to be multifactorial. Cartilage degradation is a primary manifestation of OA but is unlikely to be the source of pain since cartilage has no innervation. The frequency of bone marrow lesions, and their association with pain, in knee OA advances our understanding of the cause of pain in this disease.