Regional analysis of subtrochanteric femoral cortical bone microstructure in healthy adults using double-echo ultrashort echo time magnetic resonance imaging.

Abstract

The subtrochanteric region of the femur is a common site for atypical femoral fracture (AFF), and the research of its cortical bone microstructure is important but currently lacking. Conventional whole-bone analysis may mask regional heterogeneities of cortical bone characteristics. This study aimed to utilize double-echo ultrashort echo time (UTE) MRI for in vivo regional investigation of subtrochanteric femoral cortical bone microstructure in healthy adults, exploring regional differences in microstructure at this site and the effects of various factors, thereby providing references for subsequent related research. Healthy adults without osteoporosis risk factors (n = 124) were enrolled and underwent double-echo UTE MRI of the non-dominant proximal femur. The delineation of the subtrochanteric femoral cortical bone region of interest (ROI) and the division of regions (anterior, medial, posterior, and lateral) were performed manually by two radiologists independently, and then the porosity index (PI) and cortical bone thickness (CbTh) were obtained using image processing software. The repeatability of regional measurements was evaluated using intra-class correlation coefficient (ICC) analysis. We used one-way repeated measures analysis of variance (RM-ANOVA) and Bonferroni post-hoc contrast tests to verify regional variations, analysis of covariance (ANCOVA) to verify global and regional sex differences, and finally a general linear model with repeated measures to investigate effects of various factors on cortical bone microstructure. A total of 110 healthy subjects (44 females, 66 males) aged 18-50 years were finally included, with no significant difference in age between sexes (p = 0.240) but males having a higher BMI than females (p < 0.001). The repeatability of regional measurements was good to excellent (ICC: 0.866 to 0.964). There were statistically significant regional differences in PI and CbTh in the subtrochanteric femoral cortex, regardless of sex (all p < 0.001), with the lateral region exhibiting the highest PI (+28.61 % from the global mean in all subjects) and the medial region exhibiting the largest CbTh (+11.09 % from the global mean in all subjects). Apart from CbTh in the lateral region (p = 0.930), both global and regional cortical bone microstructures showed statistically significant sex differences (all p < 0.01), with the most pronounced sex difference in PI in anterior region (-10.97 % in females compared to males) and CbTh in posterior region (-14.68 % in females compared to males). Cortical PI was affected by region (p = 0.003) and sex (p < 0.001), with sex being the most significant factor (η² = 13.8 %); CbTh was affected similarly by sex (p = 0.003) and BMI (p = 0.002), and also affected by interactions of region × sex (p = 0.003) and region × age (p = 0.037). This study provides a potentially feasible tool for in vivo assessment of subtrochanteric femoral cortical bone microstructure, and discovers the regional heterogeneity of cortical bone in healthy adults and the effects of potential related factors, suggesting that regional differences should be considered when evaluating cortical bone, and offers references for subsequent further research.