Irradiation Does Not Modify Femoral Cancellous Bone Strength or Microdamage Processes

INTRODUCTION Structurally intact cancellous bone allograft is an attractive tissue form in that it may be filled with osteoinductive agents while providing immediate structural support. Bone allograft tissue is commonly submitted to gamma radiation sterilization of 25-35 kGy to prevent disease transmission from donor to host. In cortical bone, gamma radiation sterilization has been shown to cause reductions in ultimate strength, bending strength, work to fracture, fatigue life and resistance to fatigue crack growth [4,1]. Much less is known about the effects of irradiation on cancellous bone. Previous studies of the effects of irradiation on cancellous bone have either failed to account for differences in density among specimens or studied a relatively small range in cancellous bone density. Because density greatly influences cancellous bone strength, stiffness and failure processes, the effect of irradiation may differ based on cancellous bone density. Previously we showed that irradiation of bovine cancellous bone did not modify elastic modulus or yield strength in compression but resulted in increases in microdamage in the form of cross-hatching and microfracture [3]. Here we study to human cancellous bone across a large range in density. The long-term goal of the current work is to understand the performance of structurally intact cancellous bone allograft. Specifically in the current study we: 1) determine the effects of irradiation (30 kGy) on human cancellous bone elastic modulus and yield strength and 2) determine if irradiation is associated with alterations in the amount or type of microscopic tissue damage.