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

• Published in: Clinical orthopaedics and related research 2022-02, Vol.480 (2), p.407-418
• Main Authors: Yang Harmony, Tan Chern, Yusof, Norimah, Ramalingam, Saravana, Baharin, Ruzalina, Syahrom, Ardiyansyah, Mansor, Azura
• Format: Article
• Language: English
• Subjects: Adult; Allografts; Basic Research; Biomechanics; Bone grafts; Cadaver; Cadavers; Collagen (type I); Compression; Compressive Strength - radiation effects; Cortical bone; Cortical Bone - radiation effects; Deep freezing; Disease transmission; Femur - radiation effects; Free radicals; Freezing; Gamma Rays; Humans; Immobilization; Infectious diseases; Long bone; Male; Mechanical loading; Mechanical properties; Radiation; Radiolysis; Sterility; Sterilization; Sterilization - methods; Stress, Mechanical; Temperature; Yield stress; γ Radiation
• ISSN: 0009-921X; 1528-1132
• DOI: 10.1097/CORR.0000000000001968

Gamma 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. Does a controlled deep-freezing temperature during irradiation help preserve the compressive mechanical properties of human femoral cortical bone allografts? Cortical 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. The 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