Fracture tolerance related to skeletal development and aging throughout life: 3-point bending of human femurs

This study investigated the mechanical factors contributing to changes in fracture tolerance of the femur throughout skeletal development, maturity and advanced age. A database was compiled from the literature describing dynamic three-point bending tolerances of cadaver femurs. This database was augmented with 23 new tests targeting pediatric and young adult ages (median age of new tests: 27 years). For a subset of specimens an analytical model was developed to decompose the observed changes with age into contributing geometric and material factors. The resulting aggregated dataset included tests on 83 specimens, with an age range of 16 months to 83 years. The fracture moments ranged from 20 Nm (for a pediatric specimen) to 630 Nm (for an adult male). The data showed a rapid increase in fracture moment during skeletal development with a plateau or peak during adulthood (approximately 25-45 years). This was followed by a general decrease in fracture moment in advanced age. Decomposition of these trends suggests that the increase in strength through skeletal development was attributable to geometric changes. The decrease in fracture moment in advanced age was likely due to decreases in cortical thickness combined with other factors, possibly including a decrease in cortical bone ultimate stress.