Objectives

To evaluate bone marrow changes on knee magnetic resonance imaging (MRI) in patients with 3- to 6-week-long period of unloading.

Methods

MRI knee examinations were performed in 30 patients (14 men, 16 women; aged 20-53 years) at baseline and 5-10 weeks after immobilisation of the ipsilateral lower extremity; subsets of patients were examined at additional time-points. Ten volunteers (4 men, 6 women; aged 20-50 years) were studied as control cohort at two time-points. Bone marrow signal abnormalities were analysed 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's 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 1 year (P < 0.001). High scores of severity were associated with confluent and patchy patterns of bone marrow (SCR = 0.923, P < 0.001 and KT = 0.877, P <0.001).

Conclusions

Signal abnormalities of the bone marrow related to unloading are consistent findings and most prominent 10-25 weeks following immobilisation when both confluent and patchy hyperintense patterns are present.