Bone Mineral Density Distribution in the Foot Bones and Correlation with Hindfoot Alignment

Abstract

Category: Basic Sciences/Biologics; Hindfoot Introduction/Purpose: Weight-bearing CT (WBCT) enables accurate 3D hindfoot alignment (HA) measurements such as the Foot Ankle Offset (FAO). However, this uses anatomical landmarks and oversimplifies anatomy. Stress distribution influences bone mineral density (BMD). Hounsfield units (HU) are the tomographic measurement unit for BMD. We aim to analyze the distribution of BMD in the foot bones, relative to the long axis of the second metatarsal (M2), an accepted landmark for foot orientation, and its correlation with HA. Methods: In this retrospective study, 81 feet (27 per HA group : normal, valgus or varus) were included from our database after ethics approval. After 3D segmentation, a HU-weighted map (HUM) of the foot was projected on the ground plane with orientation defined by the longitudinal axis of the 2nd metatarsal. A HU Curve (HUC) was drawn, corresponding to the center of mass of the HUM in the coronal plane. We studied the HU angle (HUA) formed by HU Line (HUL) (linear regression of the HUC) and M2 longitudinal axis. Results: The groups were comparable by age, sex and BMI. A positive correlation between FAO and HU angle was found (r =0.75, p< 0.001). HUA were -0.4° ± 5.5° in varus, 3.5° ± 6.8° in normals, 13.4° ± 5.1° in valgus (F=39.7 and p< 0.001). HUA differences were significant between normals and varus (p < 0.05), and between normals and valgus (p < 0.001). FAO and HUA were significantly correlated in valgus (rho=0.437, p=0.002) and varus (rho=0.540, p=0.004). Conclusion: We found altered distributions in misaligned cases, and BMD was correlated with HA. The HUL could be an interesting new tool to analyse the topography of bone distribution in WBCT.