MECHANICAL-BEHAVIOR OF DAMAGED TRABECULAR BONE

The mechanical behavior of damaged trabecular bone may play a role in the etiology of age-related spine fractures since damaged bone exists in and may weaken the elderly vertebral body. To describe some charact eristics of damaged trabecular bone, we measured the changes in modulu s and strength that occur when bovine trabecular bone is loaded in com pression to various strains beyond its elastic range. Twenty-three red uced-section specimens, taken from 17 different bones, were loaded fro m 0-X-0-9% strain, where X was one of four strains: 1.0% (n = 7), 2.5% (n = 6), 4.0% (n = 5), or 5.5% (n = 5). We found that modulus was red uced for all applied strains, whereas strength was reduced only for st rain levels greater than or equal to 2.5%; the percentage changes in m odulus and strength were independent of Young's modulus but were highl y dependent on the magnitude of the applied strains; modulus was alway s reduced more than strength; and simple statistical models, using kno wledge of only the applied strains, predicted well the percentage redu ctions in modulus (r(2) = 0.97) and strength (r(2) = 0.74). The modulu s reductions reported here are in qualitative agreement with those for cortical bone in tensile loading, supporting the concept that the dam age behaviors of cortical and trabecular bone are similar for low stra ins (less than or equal to 4.0%). In addition, because modulus was alw ays reduced more than strength, damaged trabecular bone may be stress protected in vivo by redistribution of stresses to undamaged bone.