Bone Abstracts

Bone marrow lesions (BMLs), previously denoted bone marrow edema are detected as water signals on MR scans (low intensity on T₁ weighted images and high intensity on T₂ weighted scans). Previous histologic studies were unable to demonstrate any edematous changes at the tissue level, which led us to hypothesize that the water signal stems from increased vascularization accompanying a high turnover state in bone. To test this hypothesis we performed tetracycline labeling and MR scans of 28 patients planned for total hip replacement surgery. Among 14 femoral heads, eight revealed BMLs on MR, while six were negative. The latter acted as controls in the analysis. On the femoral heads we took out cylindrical biopsies guided by the MR scans. These biopsies were stored in 70% alcohol prior embedding in methyl methacrylate. Subsequently 7 μm sections were prepared and subjected to histomorphometric analysis of the cancellous bone envelope using a histomorphometry software (BioQuant Osteo). We chose to focus on mineralizing surface (MS/BS) and vascular area (sinusoids+blood vessels), but also evaluated mineral apposition rate (MAR), bone formation rate (BFR/BS), bone volume (BV/TV) and trabecular thickness (Tb.Th).

The analysis revealed that compared to controls bone tissue from patients with BMLs exhibited increased bone turnover: MS/BS (median (95% CI)) 8.1% (3.41–33.29) vs 0.3% (0.06–1.64) (P< 0.0007) and increased vascular area 0.29 mm² (0.17–1.14) vs 0.03 mm² (0.004–0.16) (P< 0.03). None of the other variables of interest were different between the two groups.

In conclusion, this study confirms that bone marrow lesions are characterized by increased bone turnover and increased vascularity in keeping with it being a reparatory process. Thus, the water signal, which is the hallmark of BMLs on MR, is most probably reflecting increased tissue vascularity accompanying increased remodeling activity.