HR-pQCT measurements are carried out in clinical research protocols to analyse separately cortical bone and trabecular bone. Micro-computed tomography (micro-CT) is a standard tool for ex vivo examination of bone in 3D. The aim of this work was to evaluate cortical measurements derived from HR-pQCT images compared to micro-CT (Skyscan 1172® device (voxel size=7.5 μm)) in a distal position with a sufficient amount of cortical bone (4.2 cm from the distal pilon). Sixteen tibia specimens were scanned with HR-pQCT using protocols provided by the manufacturer. The standard measured outcomes included volumetric bone density of the cortical region (Dcomp, mgHA/cm3), and the cortical thickness (Ct.Th,mm). An auto-contouring process measured cortical porosity (Ct.Po,%), pore volume (Ct.PoV,mm3), mean pore diameter (Ct.Po.Dm,mm2),cortical thickness (Ct.ThautoC) and cortical Bone Mineral Density (Ct.BMD, mgHA/cm3). All tibias were harvested in four quadrants at the same position of HR-pQCT measurements (9 mm height) for the micro-CT analyses. Pore volume (PoV), porosity (PoV/TV), pore size (Po.Si), pore spacing (Po.Sp), pore number (Po.N) were measured. micro-CT was compared to HR-pQCT images in site matched areas after averaging the parameters of the 4 quadrants. The correlation coefficients of Ct.Thmicro-CT versus Ct.Th or Ct.ThautoC were high: r=0.93 p<0.001 and r=0.89, p<0.01, respectively. The other main Pearson correlation (spearman correlation in italic) results are in the following Table (*p<0.05, **p< 0.01, ***p<10−3, £ p=0.06)
|HR-pQCT vs micro-CT standard method||PoV||PoV/TV||PoS/PoV||Po.Si||Po.N|
Conclusion: Distal tibia is a reliable region to study cortical bone with HR-pQCT measurements with Dcomp as the best parameter because it reflects both the micro-porosity (Havers canals) and macro-porosity (resorption lacunae) of the cortical bone.