New sterilization methods for human bone are likely to affect the mechanical properties of human cancellous grafts. These mechanical properties dictate the short- and mid-term results of the orthopedic procedure. The aim of this study was to compare the effects on bone mechanical properties, as assessed by ultrasound velocity, of different sterilization methods used under similar conditions: bleach and sublimation, humid heat, successive baths of physiological saline with osmotic detersion, and CO(2) in the supercritical phase. Alterations in mechanical properties were small with CO(2) (velocity change: -2%) and humid heat (-2.5%). Osmotic detersion had a significant but moderate effect (-4.7%). The -9% change with the protocol involving bleach suggested a greater than 30% decrease in load to failure, based on earlier studies. Gamma irradiation of defatted trabecular allografts, in a dose of 10 or 25 KGy, produced no significant changes in ultrasound velocity. Powerful protein denaturants used in sterilization protocols substantially alter the mechanical resistance of the grafts, which may jeopardize the orthopedic procedure.
New sterilization methods for human bone allografts may lead to alterations in bone mechanical properties, which strongly influence short- and medium-term outcomes. In many sterilization procedures, bone allografts are subjected to gamma irradiation, usually with 25 KGy, after treatment and packaging. We used speed-of-sound (SOS) measurements to evaluate the effects of gamma irradiation on bone. All bone specimens were subjected to the same microbial inactivation procedure. They were then separated into three groups, of which one was treated and not irradiated and two were exposed to 10 and 25 KGy of gamma radiation, respectively. SOS was measured using high- and low-frequency ultrasound beams in each orthogonal direction. SOS and Young modulus were altered significantly in the three groups, compared to native untreated bone. Exposure to 10 or 25 KGy had no noticeable effect on the study variables. The impact of irradiation was small compared to the effects of physical or chemical defatting. Reducing the radiation dose used in everyday practice failed to improve graft mechanical properties in this study.
The aim of this study was to evaluate the mechanical consequences of different common sterilisation treatments applied to human bone before transplantation. Ultrasound velocity measurements at low (LF) and high frequency (HF) were used as surrogate markers of structural (LF) and material (HF) elastic properties and failure stress. Cubic cancellous bone specimens (N=192) were obtained from human femoral heads originated from 14 donors. The elastic properties were assessed by measuring the sound velocity along three orthogonal directions at 60 kHz and 2.25 MHz before and after treatment. The samples were divided in four groups that were exposed to different treatments: Group 1: powerful protein denaturants and gamma irradiation at 25 KGrays (TBF ® procedure). Group 2 : Physical treatment with humid heat at 125°C for 20 minutes (Toulouse bone tissue bank). Group 3:. chemical solvents for complete bone marrow cleaning and gamma irradiation of 25 KGrays (Tutogen®, Germany). Group 4: Treatment with CO 2 in supercritical phase for bone cleaning followed by chemical treatement. Samples were dried before undergoing 25 KGrays of gamma irradiation (Biobank®, France). Group 5: identical to group 4, but without irradiation. The utilisation of powerful protein denaturants (group 1, decrease in speed of sound of 8 and 10%) leads to a structural alteration of cancellous bone, probably modifying type I collagen and causing an important alteration in bone graft mechanical resistance. Prudence therefore must be taken with regards to graft choice in orthopaedic reconstructions requiring a strong graft mechanical resistance. The use of chemical solvents cleaning in group 3 causes intermediate but significant variation (2,5 to 5%). A physical treatment like heat in group 2 causes a measurable but weak alteration of 0.5 to 2%. The supercritical CO 2 in group 4 showed also limited effects on the sound velocity, at the limit of least detectable change by the protocol used. In addition, no detectable effect was observed after irradiation of dried bone when included in the final step of group 4 protocol. Measurements of sound velocity were found to be useful for the comparison of different sterilisation treatment effects on the mechanical resistance of cancellous bone.
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