Introduction Bone size, shape, and micro-architecture vary point by point around and along the length of a bone, especially at metaphyses, irregularly designed ends of long bones. Image acquisition using HR-pQCT is achieved by scanning fixed region of interest (ROI) without considering bone length. Given the heterogeneity in structure, sex and racial differences may be a consequence of measuring different regions rather than true differences in bone. To quantify sexual and racial differences in bone microarchitecture we examined effects of placement of the ROI to ensure anatomical identity was maintained by sex and race.
Methods In 77 women (40 Asian and 37 Caucasian) and 85 men (37Asian and 48 Caucasian), age range 22-52 years, the distal part of non-dominant radius was scanned using HR-pQCT . Images were analysed slice by slice using StrAx 1.0. Total vBMD and porosity of total and compact cortex were assessed using the standard-fixed method (110 slices) versus a region of 4.3-6.2% of the radius length before and after adjustment for total cross sectional area (TCSA) of the ROIs.
Results The standard-fixed method produced either no differences in porosity or higher porosity in males than females . After adjusting for bone length to ensure the same anatomical location, differences in porosity either disappeared or reversed . However, when the standard-fixed or adjusted ROI was adjusted by total CSA, the same result was found; females had higher porosity than males in both races and there is no racial differences in men and women.
Conclusion Differences in the relative to position of the ROI has biologically significant effects on cortical porosity which may result in erroneous reporting of age, sex and racial differences in this trait. Adjustment for Total CSA is sufficient to correct for anatomical variation in the ROI in persons with differences in radius length.