Bone marrow lesions in knee osteoarthritis change in 6-12 weeks.

Objectives: Knee osteoarthritis (OA) is thought to be a slowly evolving disease with glacial changes in cartilage morphology necessitating trials of potential treatments lasting 1-2 years with evidence that over 6 months change in cartilage is not detectable. In contrast to cartilage, bone has the capacity to adapt rapidly, such as after fracture. We tested whether bone marrow lesions (BMLs) change in volume in 6 and 12 weeks, suggesting they may provide evidence of short term fluctuations of joint damage.

Methods: In 62 patients with patellofemoral knee OA (mean age 55.7 years, 59.7% women, mean BMI 31.0), we obtained baseline, 6 and 12 week knee MRIs with contrast enhancement. Of those with BMLs at baseline, we assessed BML volume on the axial proton density fat saturated (FS) images and postcontrast sagittal T1 weighted FS images. We manually segmented BML volumes, testing repeatability of BML volumes in knees remeasured. Using the standard deviation of the difference between repeated measurements to calculate Bland-Altman Limits of Agreement, we determined how much BML volume change represented a change greater than due to chance.

Results: Fifty-two patients had BMLs at baseline. Test-retest reliability for BML volume was high (ICC 0.89, 95% CI 0.80-0.97). All knees showed at least some change in BML volume by 6 and 12 weeks. On the axial view at 6 weeks, 20/49 (40.8%) knees showed BML volume changes greater than the limits of agreement with similar results at 12 weeks. BML changes were evenly divided among knees with enlarging and shrinking BMLs. 63.3% of the knees had more than 50% change in BML volume at either 6 or 12 weeks on the axial view and 48.7% on the sagittal view.

Conclusions: Knee BML volumes change in several weeks in many persons with knee OA. To the extent that they could be regarded as treatment targets, trials testing BML effects could avoid the usual prolonged structure modification trials.