Effect of recovery time and loading modes on mechanical properties measures in damaged human cortical bone

Skeletal fragility is an important orthopedic concern. In this study, the effect of the recovery period after damage under different mode of damage loading on the human cortical bone was investigated. Human cortical bone samples were damaged with one of three different loading modes (tension, compression and torsion) and the change of mechanical properties (stiffness, viscous relaxation and energy dissipation) before and after the damage with respect to different recovery time (1, 10, 30, 60 and 100 minutes) were measured. Results showed that measures of mechanical properties after damage varied significantly with recovery time and load modes. Typically, significant changes in property ratios occurred in the first 10 minutes for loading modulus measures in all loading modes. In addition, results showed that, with respect to loading mode effects, all torsional modulus changes were largest followed by tensile and then compressive modulus changes. We concluded that a minimum 10 minutes recovery period is required for all three loading modes while tension and torsion would require 30 minutes recovery time to obtain an accurate measure of the damage state and recovery effect because more than 90% of strain recovery and modulus recovery were observed during this period.