3D MRI Quantification of Femoral Head Deformity in Legg-Calvé-Perthes Disease

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Abstract

The purpose of this study was to quantify femoral head deformity in patients with Legg–Calvé–Perthes disease (LCPD) using a novel three dimensional (3D) magnetic resonance imaging (MRI) reconstruction and volume based analysis. Bilateral femoral heads of 17 patients (mean age 9.9 ± 2.0 years; 12 boys, 5 girls) with LCPD were scanned 1–2 times (n = 33 LCPD heads, 20 normal heads) using a 1.5T MRI scanner. Fourteen patients had unilateral and three had bilateral LCPD with five hips in the Waldenström initial stage, 9 in the fragmentation stage, 14 in the reossification stage, and 5 in the healed stage. 3D digital reconstructions of femoral heads were created using MIMICS software. Deformity was quantified using a 3D volume ratio method based on reference hemisphere volume as well as two surface geometry methods. Intra-observer analysis showed that 97% of the LCPD femoral heads were within 10% of the original value and test shapes had 99.6% accuracy. For normal femoral heads, the volume ratios of all except one were between 95 and 98% (n = 20) of a perfect hemisphere volume. For femoral heads affected with LCPD, the volume ratios ranged from 43% to 96% of a perfect hemisphere (n = 33). The volume ratio method and the two surface geometry comparison methods had high correlation (r = 0.89 and 0.96). In summary, the 3D MRI volume ratio method allowed accurate quantification and demonstrated small changes (<10%) of the femoral head deformity in LCPD. This method may serve as a useful tool to evaluate the effects of treatment on femoral head shape. Published by Wiley Periodicals, Inc. J Orthop Res

Bilateral femoral heads of LCPD patients were scanned 1–2 times (n = 53 femoral heads). 3D digital reconstructions were created and deformity was quantified using a volume ratio method based on a reference hemisphere. Two surface geometry methods, geometric test shapes and an intra-observer test were used for validation. Femoral head volume ratios were between 93% and 98% for normals hips and 43–96% for LCPD hips. Our 3D MRI method allowed accurate quantification of femoral head deformity and can be used to detect small changes over time.

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