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The Journal of Bone and Joint Surgery (American). 2004;86:2648-2657
© 2004 The Journal of Bone and Joint Surgery, Inc.

The Effect of Gamma Radiation Sterilization on the Fatigue Crack Propagation Resistance of Human Cortical Bone

Erika J. Mitchell, MD1, Allison M. Stawarz, MS2, Ramazan Kayacan, PHD3 and Clare M. Rimnac, PHD2

1 Department of Orthopaedics, University Hospitals of Cleveland, 11100 Euclid Avenue, Cleveland, OH 44106-7222. E-mail address for E.J. Mitchell: erikajas{at}aol.com
2 Musculoskeletal Mechanics and Materials Laboratories, Department of Mechanical and Aerospace Engineering, Case Western Reserve University, 10900 Euclid Avenue, 620 Glennan Building, Cleveland, OH 44106
3 Department of Mechanical Engineering, Suleyman Demirel University, 32260 Isparta, Turkey

Investigation performed at the Department of Orthopaedics, University Hospitals of Cleveland, Cleveland, and the Musculoskeletal Mechanics and Materials Laboratories, Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, Ohio

In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from National Institutes of Health Grant AG17171, the Allen Scholarship Foundation, and a National Science Foundation Graduate Fellowship. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: Clinical evidence has suggested that the rate of fracture in allografts sterilized with gamma radiation may be higher than that in controls. Gamma radiation sterilization has been shown to affect the post-yield properties of bone but not the elastic modulus. Since most allograft fractures occur with subcritical loads during activities of daily living, it may be that the fatigue properties of irradiated allografts are diminished. In this study, the fatigue crack propagation behavior of cortical bone sterilized with gamma radiation was compared with that of gender and age-matched controls. We hypothesized that gamma radiation significantly reduces the resistance of cortical bone to fatigue crack growth.

Methods: Specimens for fatigue crack propagation testing were machined from four pairs of fresh-frozen human femora obtained from four individuals (a younger male, younger female, older male, and older female donor). Half of the specimens were sterilized with 31.7 kGy of gamma radiation. The specimens were cyclically loaded to failure in a servohydraulic testing system, and crack growth was monitored. The cyclic stress intensity factor and the fatigue crack growth rate were calculated to examine the kinetics of fatigue crack growth. Following testing, the damage zone around the fracture plane was analyzed histologically.

Results: The morphology and kinetics of crack growth in irradiated specimens differed from the control data. Overall, the irradiated bone was significantly less resistant to fatigue crack growth than was control tissue (p < 0.05). There was less microdamage associated with fracture in the irradiated specimens than in the control specimens, with the exception of the bone from the older female donor.

Conclusions: Gamma radiation sterilization significantly reduces the fatigue crack propagation resistance of cortical bone. Irradiated specimens also demonstrate a smaller amount of microdamage along the fracture plane. These findings may be due to ultrastructural alterations in the collagen matrix caused by radiation.

Clinical Relevance: This study suggests that, despite having pre-yield mechanical properties that are similar to those of nonirradiated bone, gamma-radiation-sterilized allograft may be more predisposed to fracture even under the subcritical loads that occur during the activities of daily living.


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