Bone Robusticity Values - Non Weight Bearing Vs Weight Bearing Bones: The Iowa Bone Development Study

Abstract

Adolescence is a key time for bone development with 25% of adult bone accrued in these years. Evidence also indicates that robusticity (bone width relative to length) may account for a 30%-80% difference in bone strength with slender bones being weaker and prone to stress fracture. Few studies have investigated robustness and bone strength in children. PURPOSE: To determine the variability in robusticity and bone strength pre puberty and at maturity of weight bearing and non-weight bearing bones. METHODS: Secondary analysis of data from the Iowa Bone Development Study (IBDS) was used. https://clinicaltrials.gov/ct2/show/NCT03547128 Using peripheral Quantitative Computed Tomography (pQCT) measures of bone strength from the tibia and radius from 11-25 years of age were obtained. Robusticity (total bone area/ bone length) was calculated and the variability of each measure was determined by calculating the Coefficient of Variation (CV) (mean/standard deviation). CV’s were compared for bone strength variables, bone mineral density, moment of inertia, cortical area, robusicity, total area and bone length between the non weight bearing radius and weight bearing tibia. RESULTS: At both 11 and 23 years of age, robusticity values in the radius were approximately 25-30% more variable compared to the tibia (Pre-puberty CV: Tibia 17.15%, Radius 24.52%. Post-puberty CV: Tibia 19.21%, Radius 25.69%) Similar CV’s were found in total area (Pre-puberty CV: Tibia: 22.91%, Radius 29.04%. Post-puberty CV: Tibia 26.18%, Radius 32.90%) but not in bone length (Pre-puberty CV: Tibia 9.57%, Radius 9.18%. Post-puberty CV: Tibia 10.14%, Radius 10.59%). CONCLUSIONS: Robusticity varied less in the tibia pre and post puberty. The increase in variability measured by the CV for the radius may be due to more variety in loading of the upper limb compared to the lower limb. Most ambulatory individuals consistently apply at least 1x body weight loading to their lower limb bones while walking. Normative data indicates healthy adults typically take between 4,000 and 18,000 steps/day. Also the variability in robusticity is from the changes in total area of the bone suggesting different osteoblast and osteoclast activity for the upper and lower limbs.