Deep-Freezing Temperatures During Irradiation Preserves the Compressive Strength of Human Cortical Bone Allografts: A Cadaver Study

Abstract

BackgroundGamma irradiation, which minimizes the risk of infectious disease transmission when human bone allograft is used, has been found to negatively affect its biomechanical properties. However, in those studies, the deep-freezing temperature during irradiation was not necessarily maintained during transportation and sterilization, which may have affected the findings. Prior reports have also suggested that controlled deep freezing may mitigate the detrimental effects of irradiation on the mechanical properties of bone allograft.Question/purposeDoes a controlled deep-freezing temperature during irradiation help preserve the compressive mechanical properties of human femoral cortical bone allografts?MethodsCortical bone cube samples, each measuring 64 mm3, were cut from the mid-diaphyseal midshaft of five fresh-frozen cadaver femurs (four male donors, mean [range] age at procurement 42 years [42 to 43]) and were allocated via block randomization into one of three experimental groups (with equal numbers of samples from each donor allocated into each group). Each experimental group consisted of 20 bone cube samples. Samples irradiated in dry ice were subjected to irradiation doses ranging from 26.7 kGy to 27.1 kGy (mean 26.9 kGy) at a deep-freezing temperature below -40°C (the recommended long-term storage temperature for allografts). Samples irradiated in gel ice underwent irradiation doses ranging from 26.2 kGy and 26.4 kGy (mean 26.3 kGy) in a freezing temperature range between -40°C and 0°C. Acting as controls, samples in a third group were not subjected to gamma irradiation. The mechanical properties (0.2% offset yield stress, ultimate compression stress, toughness, and the Young modulus) of samples from each group were subsequently evaluated via axial compression loading to failure along the long axis of the bone. The investigators were blinded to sample group during compression testing.ResultsThe mean ultimate compression stress (84 ± 27 MPa versus 119 ± 31 MPa, mean difference 35 [95% CI 9 to 60]; p = 0.005) and toughness (3622 ± 1720 kJ/m3 versus 5854 ± 2900 kJ/m3, mean difference 2232 [95% CI 70 to 4394]; p = 0.009) of samples irradiated at a higher temperature range (-40°C to 0°C) were lower than in those irradiated at deep-freezing temperatures (below -40°C). The mean 0.2% offset yield stress (73 ± 28 MPa versus 109 ± 38 MPa, mean difference 36 [95% CI 11 to 60]; p = 0.002) and ultimate compression stress (84 ± 27 MPa versus 128 ± 40 MPa, mean difference 44 [95% CI 17 to 69]; p < 0.001) of samples irradiated at a higher temperature range (-40°C to 0°C) were lower than the nonirradiated control group samples. The mean 0.2% offset yield stress (73 ± 28 MPa versus 101 ± 28 MPa, mean difference 28 [95% CI 3 to 52]; p = 0.02; effect size = 1.0 [95% CI 0.8 to 1.2]) of samples irradiated at higher temperature range (-40°C to 0°C) were no different with the numbers available to those irradiated at deep-freezing temperature. The mean toughness (3622 ± 1720 kJ/m3 versus 6231 ± 3410 kJ/m3, mean differenc...

CORR Insights®: Deep-freezing Temperatures During Irradiation Preserves the Compressive Strength of Human Cortical Bone Allografts: A Cadaver Study

“…We are still learning about the factors affecting structural bone allograft quality. In the current study by Yang Harmony et al [13], the authors found that gamma irradiation of cortical bone specimens below -40°C preserved the mechanical properties of bone compared with higher temperatures. This study calls to attention the importance of bone-processing considerations in affecting structural allograft quality.…”

“…One of the greatest challenges in utilization of structural allograft bone is donor heterogeneity. Therefore, it is critical to study bone-processing practices, which are within our control, and, as demonstrated by Yang Harmony et al [13], can have a major impact on structural integrity and, likely, clinical outcomes.…”

CORR Insights®: The High-cycle Fatigue Life of Cortical Bone Allografts Is Radiation Sterilization Dose-dependent: An In Vitro Study

“…The current study by Ina et al [6] on the fatigue properties of cortical bone and radiation sterilization dose builds on previous work highlighting the importance of improving our understanding of the relationship between radiation sterilization and mechanical properties [1, 2, 5, 7, 9-12], as well as the chemical composition of cortical bone [4]. Ina et al [6] reported a dose-dependent decrease in fatigue life and a sixfold decrease in the mean cycles to failure of cortical bone between 17.5 kGy and 25 kGy.…”

Applied use of biomechanical measurements from human tissues for the development of medical skills trainers: a scoping review

“…Five studies compared different preservation methods of cadavers and assessed how the biomechanical properties changed. 92,166,188,202,206 The consensus was that cadaveric tissues preserved in formalin tend to have different properties to freshfrozen tissues. 92,166,206 Additionally, biomechanical properties of extracted tissues do not seem to be affected by the length of freezing time.…”

“…92,166,206 Additionally, biomechanical properties of extracted tissues do not seem to be affected by the length of freezing time. 188,202 It should be noted that only 1 study 92 included fresh tissues for comparison, which further demonstrates the need for studies using fresh tissues as a control. This study 92 also found that the viscoelastic properties of embalmed and fresh-frozen tissues were different.…”