BONE PERFUSION AND ADIPOSITY BEYOND THE NECROTIC ZONE IN FEMORAL HEAD OSTEONECROSIS: A QUANTITATIVE MRI STUDY

Purpose: To describe bone perfusion and adiposity beyond the necrotic zone with quantitative MRI techniques in osteonecrosis of the femoral head (ONFH). Method: In this cross-sectional multicentre study, we recruited patients suffering from late-stage ONFH or hip osteoarthritis. Hip MRI included quantitative MRI sequences: chemical-shift imaging and dynamic contrastenhanced MRI. We drew regions of interest inside the necrotic zone (inner necrosis and its border) and outside (femoral head, neck and greater trochanter) in ONFH. In the control group, regions of interest were drawn in the femoral head, femoral neck and the greater trochanter. For each region of interest, we measured fat fraction, and calculated semi-quantitative (area under the curve, initial slope) and pharmacokinetic perfusion parameters (K-trans and K-ep). Results: Thirty-two male adults (mean age 58 +/- 9 years, range 38-74 years) were included. Sixteen patients formed the ONFH group and fifteen the control group; one was excluded. In the normal-appearing non-necrotic part of the femoral head, fat fraction was not significantly different in comparison with controls (p = 1), but Ktrans was significantly lower than in controls (0.012 +/- 0.018 vs. 0.027 +/- 0.045; p = 0.05). This perfusion parameter reflects exchanges between blood microvessels and bone marrow. Conclusions: Our results question the concept of adipose toxicity on the macroscopic scale, and bring up the concept of regional ischemic penumbra that goes beyond the visible necrotic zone. Further studies are required to test these hypotheses in larger populations and earlier disease states.