The Effect of Gamma Radiation Sterilization on the Fatigue Crack Propagation Resistance of Human
Cortical Bone
Erika J. MITCHELL1, Allison M. STAWARZ2, Ramazan KAYACAN*3, Clare M. RIMNAC2
1
Department of Orthopaedics, University Hospitals of Cleveland, Cleveland, OH 44106, USA
2
Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH
44106, USA
3
Department of Mechanical Engineering, Suleyman Demirel University, 32260 Isparta, Turkey
Keywords
Gamma Radiation
Sterilization
Cortical Bone
Crack Propagation
Fatigue
Abstract: 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 postyield 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.
1. Introduction
Large cortical allografts have been used for many years in the reconstruction of large osseous defects
secondary to trauma, tumor resection, or joint reconstruction. Patients treated because of trauma or tumors
are often young, and the reconstructions are generally in weight-bearing bones. The goal is to restore the
patient to his or her prior functional status, and so the allograft must eventually be able to withstand the loads
that occur during the activities of daily living of an active individual. Complete incorporation of allograft
bone may take several years, during which time the patient has resumed weight-bearing activities (Stevenson
et al., 1996). It is thus important that the graft material, in conjunction with an appropriate fixation device, be
able to sustain substantial loads as it becomes incorporated into the host skeleton.
Allograft fractures often occur under normal loading conditions and have been found to occur in 12% to 20%
of all large allografts (Manking et al., 1983; Lietman et al., 2000; Berrey et al., 1990; Thompson et al., 1993).
The addition of stress-risers in allograft bone by way of screw-holes, intraoperative scratches or cracks, and
postoperative physiologic resorption may predispose the allograft to fracture. Fracture is one of the most
frequent complications in the use of large cortical allografts in orthopaedic reconstructive surgery and carries
substantial morbidity, often requiring additional surgery and in some cases even amputation (Lietman et al.,
2000; Berrey et al., 1990; Thompson et al., 1993).
2. Materials and Methods
Four pairs of human femora with no known skeletal abnormality were obtained from the Musculoskeletal
Transplant Foundation (Edison, New Jersey) and the Anatomical Donations Program at the University of
Michigan Medical School (Ann Arbor, Michigan). Femora were obtained from one younger (fifteen-yearold) female, one younger (eighteen year-old) male, one older (sixty-one-year-old) male, and one older
(seventy-five-year-old) female donor (Table 1).
Table 1 Fatigue Crack Propagation Resistance of the Test Groups Assessed with the Pooled Regression*
*
Corresponding author: ramazankayacan@sdu.edu.tr
Each femur was stripped of soft tissue, and the mid-portion of the diaphysis was sectioned into rings
approximately 30 mm in length with use of an autopsy saw (Stryker, Rutherford, New Jersey). Each ring was
then wet-machined with use of a tabletop micromill (Micromill 2000; Denford, Medina, Ohio) that was
numerically controlled by a computer to produce notched compact tension specimens that were 17.5 mm
wide, 16.8 mm high, and 3.0 mm thick from the medial and lateral cortices (Figs. 1-A and 1-B) (American
Society for Testing and Materials, 1996).
Figure 1a Schema of a compact tension specimen as machined from the femoral diaphyseal cortex.
Figure 1b Schema of a compact tension specimen with dimensions.
3. Results
Seven specimens were lost during testing because of machine problems. For the forty-three other specimens,
stable fatigue crack propagation was achieved for all age-gender groups in both the control and the radiationsterilized condition. The fatigue crack propagation resistance of human cortical bone was significantly
reduced by gamma radiation sterilization in all four test groups (p < 0.05; Figs. 3a through 3d) as determined
by a significant increase in the constant (C) (Table 1). The percentage difference of the means of the constant
between different treatment groups demonstrated that the loss in fatigue crack propagation resistance
between control and irradiated specimens was greatest in the younger male group, followed by the younger
female group, then the older male group (Table 2).
2
Table 2 Percentage Difference of the Means of the Constants for the Irradiated Specimens Compared with
the Control Specimens for Each Age-Gender Group*
4. Discussion and Conclusion
This investigation is one of the first studies to examine how human cortical bone tissue resists fatigue crack
growth. In addition, this study examined the relative fatigue crack growth behavior of macrocracks rather
than of microcracks. The growth of macrocracks is clinically relevant in terms of the development of stress
fractures. This study demonstrates that cracks can be grown experimentally in human cortical bone in a
stable manner under cyclic loading conditions. It was found that gamma radiation sterilization led to a
significant decrease in fatigue crack propagation resistance. In addition, it was observed that there was less
crack branching and less fibril bridging behind the crack tip in the gamma-irradiated bone groups compared
with the nonirradiated bone groups.
Acknowledgements
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.
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