Bone marrow changes in osteoarthritis.

Magnetic resonance imaging (MRI) is gaining increasing significance to study disease burden and progression in osteoarthritis. Bone marrow edema pattern has been identified as a typical MR finding associated with osteoarthritis. Histologically, bone marrow edema pattern is characterized by a mix of different pathologies, including bone marrow necrosis, fibrosis, microfractures, and bone remodeling as well as fibrovascular ingrowth. On MR imaging, bone marrow edema pattern is typically associated with subchondral cysts, cartilage defects, and meniscal degeneration; prevalence and size correlates with disease severity. Bone marrow edema pattern may be found in association with other abnormalities such as subchondral insufficiency fractures. Clinically the significance of bone marrow edema is controversially discussed with some studies showing evidence of associated pain. In summary, bone marrow signal abnormalities are frequent MRI signs of osteoarthritis with different histological findings, typical associated abnormalities, and also clinical significance.