T1-weighted MRI images accurately represent the volume and surface of architectural mineral damage of osteonecrosis of the femoral head: Comparison with high-resolution computed tomography.

The potency of magnetic resonance imaging (MRI) to measure the exact extent of osteonecrosis of the femoral head (ONFH) remains uncertain. The objective of this study was to determine if the volume of necrosis assessed with MRI accurately reflects the volume of architectural mineral alterations in osteonecrosis of the femoral head by comparison with high-resolution microfocus X-ray computed tomography (HR-μCT). Fourteen male patients aged 53 years [46.2;59.0] suffering from ONFH were prospectively enrolled to undergo preoperative MRI and ex vivo analysis using HR-μCT. The necrotic zone on T1-weighted MRI scans was defined as total necrosis (delimited by the low-signal peripheral band) or dark necrosis (low-signal lesions only). The HR-μCT scans delimited outer necrosis and inner necrosis by including or excluding the sclerotic zone. The intra-class correlation coefficient (ICC) was calculated to compare the agreement of surface areas and volumes of necrosis measurements with the two techniques. There was an overall excellent agreement between MRI dark necrosis volume and HR-μCT outer necrosis volume (ICC=0.91[0.54;0.98]) while the MRI total necrosis volume showed poor agreement with both HR-μCT delimitations of necrosis volume. For surface area, agreement between MRI dark necrosis and HR-μCT delimitations was good for inner necrosis (ICC=0.70[0.21;0.9]) and moderate for outer necrosis (ICC=0.58[0.07;0.85]). This study demonstrates that measurement of the MRI lesions provides a reliable assessment of the extent of ONFH-related architectural damage.