Bone marrow changes related to disuse

OBJECTIVE: To evaluate bone marrow changes on knee MRI in patients with 3-to-6 week long period of unloading. MATERIALS AND METHODS: MRI knee examinations were performed in 30 patients (14 men, 16 women, aged 20–53 years) at baseline and 5–10 weeks after immobilization of the ipsilateral lower extremity; subsets of patients were examined at additional time points. Ten volunteers (4 men, 6 women; aged 20–50) were studied as control cohort at 2 time points. Bone marrow signal abnormalities were analyzed according to 1) severity, 2) signal alteration relative to hyaline cartilage, 3) morphology, 4) increased vascularity in the knee joint and 5) T1-signal alteration. Spearman rank correlation test (SRC) and Kendall’s tau (KT) were used to compare individual scores. RESULTS: All 30 patients presented abnormal bone marrow findings after unloading, which reached a peak at 10–25 weeks (P <0.001). These findings decreased within one year (P <0.001). High scores of severity were associated with confluent and patchy patterns of bone marrow (SCR=0.923, P <0.01 and KT= 0.877 P <0.01). CONCLUSION: Signal abnormalities of the bone marrow related to unloading are consistent findings and most prominent 10–25 weeks following immobilization when both confluent and patchy hyperintense patterns are present