Abstract
The biomechanical consequences of an isolated overload to the vertebral body may play a role in the etiology of vertebral fracture. In this context, we quantified residual strains and reductions in stiffness and ultimate load when vertebral bodies were loaded to various levels beyond the elastic regimen and related these properties to the externally applied strain and bone density. Twentyβthree vertebral bodies (T11βL4, from 23 cadavers aged 20β90 years) were loaded once in compression to a randomized nominal strain level between 0.37 and 4.5%, unloaded, and then reloaded to 10% strain. Residual strains of up to 1.36% developed on unloading and depended on the applied strain (r^2^ = 0.85) but not on density (p = 0.25). Percentage reductions in stiffness and ultimate load of up to 83.7 and 52.5%, respectively, depended on both applied strain (r^2^ = 0.90 and r^2^ = 0.32, respectively) and density (r^2^ = 0.23 and r^2^ = 0.22, respectively). Development of residual strains is indicative of permanent deformations, whereas percentage reductions in stiffness are direct measures of effective mechanical damage. These results therefore demonstrate that substantial mechanical damageβwhich is not visible from radiographsβcan develop in the vertebral body after isolated overloads, as well as subtle but significant permanent deformations. This behavior is similar to that observed previously for cylindrical cores of trabecular bone. Taken together, these findings indicate that the damage behavior of the lumbar and lower thoracic vertebral body is dominated by the trabecular bone and may be an important factor in the etiology of vertebral fracture.