Longitudinal Evaluation of the Occurrence of MRI-Detectable Bone Marrow Edema in Osteoarthritis of the Knee

Background: Bone marrow edema (BME) is a condition detectable with magnetic resonance imaging (MRI) and is present in different stages of osteoarthritis (OA). Its pathogenesis is still not completely known. Purpose: To evaluate the longitudinal occurrence and persistence of BME in early OA of the knee. Material and Methods: Twenty-three patients (eight females, 15 males; mean age 55.5 +/- 10.3 years) were scanned with a 1.5T MR imaging unit (sagittal fat-suppressed intermediate-weighted fast spin echo; 4-mm section thickness, 1-mm intersection gap, 256x192 matrix, 120-mm field of view). Images were obtained in all 23 patients at two time points (TPs) and in 12 patients at three TPs. Images were evaluated by two readers independently; discrepancies in image grading were reviewed and evaluated in consensus. A four-point image-grading scale was used (absence of BME to severe BME). Four main anatomical regions were evaluated (medial femur, lateral femur, medial tibia, lateral tibia), which were subcategorized into anterior, central, and posterior regions. Results: One hundred five areas of BME in the 23 patients were found at all three TPs. In 16 areas, the BME was consistent at the same location over time, in seven locations the BME became larger, in six areas the BME became smaller, and in 16 locations it could not be detected in follow-up MRIs. In one case, the BME was smaller at TP2 but increased at TP3. In eight cases, only at the last time point could a BME be detected. Conclusion: BME is not a static phenomenon but changes over time. Correlation to physical activity and local inflammatory reaction should be evaluated.