Background: The cause of pain in osteoarthritis is unknown. Bone has pain fibers, and marrow lesions, which are thought to represent edema, have been noted in osteoarthritis.

Objective: To determine whether bone marrow lesions on magnetic resonance imaging (MRI) are associated with pain in knee osteoarthritis.

Design: Cross-sectional observational study.

Setting: Veterans Affairs Medical Center.

Patients: 401 persons (mean age, 66.8 years) with knee osteoarthritis on radiography who were drawn from clinics in the Veterans Administration health care system and from the community. Of these persons, 351 had knee pain and 50 had no knee pain.

Measurements: Knee radiography and MRI of one knee were performed in all participants. Those with knee pain quantified the severity of their pain. On MRI, coronal T(2)-weighted fat-saturated images were used to score the size of bone marrow lesions, and each knee was characterized as having any lesion or any large lesion. The prevalence of lesions and large lesions in persons with and without knee pain was compared; in participants with knee pain, the presence of lesions was correlated with severity of pain.

Results: Bone marrow lesions were found in 272 of 351 (77.5%) persons with painful knees compared with 15 of 50 (30%) persons with no knee pain (P < 0.001). Large lesions were present almost exclusively in persons with knee pain (35.9% vs. 2%; P < 0.001). After adjustment for severity of radiographic disease, effusion, age, and sex, lesions and large lesions remained associated with the occurrence of knee pain. Among persons with knee pain, bone marrow lesions were not associated with pain severity.

Conclusions: Bone marrow lesions on MRI are strongly associated with the presence of pain in knee osteoarthritis.