The effects of torsional loading conditions and damage on bovine cortical bone strength

Loading conditions have dramatic effects on bone strength, and torsion is a common mode of loading for bone in the physiologic setting. The relationship between loading conditions, particularly loading rate and damage accumulation was investigated. How rate dependent damage effects bone strength was also examined. Bovine cortical bone specimens were tested with three loading protocols to: (1) establish the rate dependence of bovine bone strength in torsion, (2) determine the rate dependent nature of damage accumulation, and (3) characterize damage accumulation in relation to time. A statistically significant rate dependent reduction in torsional strength was noted. When specimens were loaded to the same twist level at three different loading rates, the authors found a significant rate dependent reduction in bone strength. These results confirmed prior assumptions that rate dependent reductions in strength are due to time dependent damage accumulation. The authors also presented data in which they further explored this time dependent damage accumulation more specifically. Initial results suggested that damage accumulates nonlinearly with time, and the authors believe this nonlinear behavior may be important for understanding the mechanical response to torsional loading.