Microstructurally based model analysis of gamma-irradiated tendon allografts.

A mathematical model of the collagenous microstructure of tendon was used to analyze the mechanical responses of gamma-irradiated patellar tendon allografts and nonirradiated controls. The model was fit to tensile test response curves from 10 pairs of allografts. Donors ranged in age from 16-64 years (six males, four females). The model indicated a decrease in elastic modulus of irradiated tendon collagen. It also suggested a significant increase in the degree and range of collagen fiber crimping following gamma irradiation. The model results agree with the literature and histological observations. The model fit the experimental response curves well and provided a structurally based, objective method of quantitatively studying the mechanical response of tendons and the consequences of irradiation sterilization.     

Osteon pullout in the equine third metacarpal bone: effects of ex vivo fatigue.

An important concept in bone mechanics is that osteons influence mechanical properties in several ways, including contributing to toughness and fatigue strength by debonding from the interstitial matrix so as to "bridge" developing cracks. Observations of "pulled out" osteons on fracture surfaces are thought to be indicative of such behavior. We tested the hypothesis that osteon pullout varies with mode of loading (fatigue vs. monotonic), cortical region, elastic modulus, and fatigue life. Mid-diaphseal beams from the dorsal, medial, and lateral regions of the equine third metacarpal bone were fractured in four point bending by monotonic loading to failure under deflection control, with or without 10(5) cycles of previous fatigue loading producing 5000 microstrain (15-20% of the expected failure strain) on the first cycle; or sinusoidal fatigue loading to failure, under load or deflection control, with the initial cycle producing 10,000 microstrain (30-40% of the expected failure strain). Using scanning electron microscopy, percent fracture surface area exhibiting osteon pullout (%OP.Ar) was measured. Monotonically loaded specimens and the compression side of fatigue fracture surfaces exhibited no osteon pullout. In load-controlled fatigue, pullout was present on the tension side of fracture surfaces, was regionally dependent (occurring to a greater amount dorsally), and was correlated negatively with elastic modulus and positively with fatigue life. Regional variation in %OP.Ar was also significant for the pooled (load and deflection controlled) fatigue specimens. %OP.Ar was nearly significantly greater in deflection controlled fatigue specimens than in load-controlled specimens (p=0.059). The data suggest that tensile fatigue loading of cortical bone eventually introduces damage that results in osteonal debonding and pullout, which is also associated with increased fatigue life via mechanisms that are not yet clear.     

The effect of gamma radiation sterilization on the fatigue crack propagation resistance of human cortical bone

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.     

High-dose gamma irradiation for soft tissue allografts: High margin of safety with biomechanical integrity.

Screening and processing methods currently in place have made the risk of bacterial and viral infections from allograft tissues extremely low. However, the development of a terminal sterilization method that does not adversely affect tissue function would provide an added safety to tissues for transplantation. We assessed whether high-dose gamma irradiation could be used as an effective terminal sterilization method for allografts without impairing the preimplantation mechanical integrity of the tissues. Semitendinosus tendons were pretreated with a radioprotectant solution and then irradiated to 50 kGy under well-defined conditions that included a tight dose range and maintained low temperatures. Maximum force, strain, stress, modulus, and strain energy density for tendons irradiated to 50 kGy were compared to nonirradiated control tendons and tendons irradiated to 18 kGy by a commercial tissue bank using their existing method. The preimplantation biomechanical properties of the 50-kGy group compared favorably to the nonirradiated and 18 kGy groups. A study to evaluate the postimplantation mechanical and biological performance of grafts irradiated to 50 kGy is ongoing. Pathogen inactivation was also quantified following 50 kGy of irradiation, with > or =4.5 logs of Sindbis virus and 4.9 logs of parvovirus kill achieved. Analysis of Clostridium sordellii inactivation kinetics indicated that a 16 log10 reduction is predicted with 50 kGy of irradiation. A high dose of gamma irradiation using the described conditions can reduce infectious risks associated with soft tissue allografts while maintaining the preimplantation biomechanical performance of the tissues.     

Fracture resistance of gamma radiation sterilized cortical bone allografts.

Gamma radiation is widely used for sterilization of human cortical bone allografts. Previous studies have reported that cortical bone becomes brittle due to gamma radiation sterilization. This embrittlement raises concern about the performance of a radiation sterilized allograft in the presence of a stress concentration that might be surgically introduced or biologically induced. The purpose of this study was to investigate the effect of gamma radiation sterilization on the fracture resistance of human femoral cortical bone in the presence of a stress concentration. Fracture toughness tests of specimens sterilized at a dose of 27.5 kGy and control specimens were conducted transverse and longitudinal to the osteonal orientation of the bone tissue. The formation of damage was monitored with acoustic emission (AE) during testing and was histologically observed following testing. There was a significant decrease in fracture toughness due to irradiation in both crack growth directions. The work-to-fracture was also significantly reduced. It was observed that the ability of bone tissue to undergo damage in the form of microcracks and diffuse damage was significantly impaired due to radiation sterilization as evidenced by decreased AE activity and histological observations. The results of this study suggest that, for cortical bone irradiated at 27.5 kGy, it is easier to initiate and propagate a macrocrack from a stress concentration due to the inhibition of damage formation at and near the crack tip.     

Irradiation has no effect on the incorporation of impacted morselized bone: a bone chamber study in goats

Background Gamma irradiation has been widely used for sterilization of bone allografts. However, gamma irradiation alters proteins. This is favorable when it reduces immunogenicity, but is undesirable when osteoinductive proteins are damaged. Although the effect of gamma irradiation on BMPs has been studied, the effect of irradiation on the process of incorporation of morselized bone chips remains unclear. We studied the effects of sterilization by gamma irradiation on the incorporation of impacted morselized allografts.

Methods Bone chambers with impacted allografts, rinsed impacted allografts, allografts that were rinsed and subsequently irradiated, and an empty control were implanted in proximal medial tibiae of goats. Incorporation was evaluated using histology and histomorphometry.

Results Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in unprocessed, rinsed, and both rinsed and irradiated bone grafts. After 12 weeks, no difference in bone and tissue ingrowth was found between the unprocessed, the rinsed, and the rinsed and subsequently irradiated allografts. The amount of unresorbed graft remnant was highest in the unprocessed bone grafts.

Interpretation We conclude that sterilization with gamma irradiation does not influence the incorporation of impacted rinsed bone allografts.     

Free radical scavenging alleviates the biomechanical impairment of gamma radiation sterilized bone tissue.

Terminal sterilization of bone allografts by gamma radiation is often essential prior to their clinical use to minimize the risk of infection and disease transmission. While gamma radiation has efficacy superior to other sterilization methods it also impairs the material properties of bone allografts, which may result in premature clinical failure of the allograft. The mechanisms by which gamma radiation sterilization damages bone tissue are not well known although there is evidence that the damage is induced via free radical attack on the collagen. In the light of the existing literature, it was hypothesized that gamma radiation induced biochemical damage to bone's collagen that can be reduced by scavenging for the free radicals generated during the ionizing radiation. It was also hypothesized that this lessening of the extent of biochemical degradation of collagen will be accompanied by alleviation in the extent of biomechanical impairment secondary to gamma radiation sterilization. Standardized tensile test specimens machined from human femoral cortical bone and specimens were assigned to four treatment groups: control, scavenger treated-control, irradiated and scavenger treated-irradiated. Thiourea was selected as the free radical scavenger and it was applied in aqueous form at the concentration of 1.5 M. Monotonic and cyclic mechanical tests were conducted to evaluate the mechanical performance of the treatment groups and the biochemical integrity of collagen molecules were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native mechanical properties of bone tissue did not change by thiourea treatment only. The effect of thiourea treatment on mechanical properties of irradiated specimens were such that the post-yield energy, the fracture energy and the fatigue life of thiourea treated-irradiated treatment group were 1.9-fold, 3.3-fold and 4.7-fold greater than those of the irradiated treatment group, respectively. However, the mechanical function of thiourea treated and irradiated specimens was not to the level of unirradiated controls. The damage occurred through the cleavage of the collagen backbone as revealed by SDS PAGE analysis. Irradiated specimens did not exhibit a noteworthy amount of intact alpha-chains whereas those irradiated in the presence of thiourea demonstrated intact alpha-chains. Results demonstrated that free radical damage is an important pathway of damage, caused by cleaving the collagen backbone. Blocking the activity of free radicals using the scavenger thiourea reduces the extent of damage to collagen, helping to maintain the mechanical strength of sterilized tissue. Therefore, free radical scavenger thiourea has the potential to improve the functional life-time of the allograft component following transplantation.     

Fabric-mechanical property relationships of trabecular bone allografts are altered by supercritical CO₂ treatment and gamma sterilization

Tissue grafts are implanted in orthopedic surgery every day. In order to minimize infection risk, bone allografts are often delipidated with supercritical CO₂ and sterilized prior to implantation. This treatment may, however, impair the mechanical behavior of the bone graft tissue. The goal of this study was to determine clinically relevant mechanical properties of treated/sterilized human trabecular bone grafts, e.g. the apparent modulus, strength, and the ability to absorb energy during compaction. They were compared with results of identical experiments performed previously on untreated/fresh frozen human trabecular bone from the same anatomical site (Charlebois, 2008). We tested the hypothesis that the morphology–mechanical property relationships of treated cancellous allografts are similar to those of fresh untreated bone. The morphology of the allografts was determined by μCT. Subsequently, cylindrical samples were tested in unconfined and confined compression. To account for various morphologies, the experimental data was fitted to phenomenological mechanical models for elasticity, strength, and dissipated energy density based on bone volume fraction (BV/TV) and the fabric tensor determined by MIL. The treatment/sterilization process does not appear to influence bone graft stiffness. However, strength and energy dissipation of the bone grafts were found to be significantly reduced by 36% to 47% and 66% to 81%, respectively, for a broad range of volume fraction (0.14 < BV/TV < 0.39) and degree of anisotropy (1.24 < DA < 2.18). Since the latter properties are strongly dominated by BV/TV, the clinical consequences of this reduction can be compensated by using grafts with lower porosity. The data of this study suggests that an increase of 5–10% in BV/TV is sufficient to compensate for the reduced post-yield mechanical properties of treated/sterilized bone in monotonic compression. In applications where graft stiffness needs to be matched and strength is not a concern, treated allograft with the same BV/TV as an appropriate fresh bone graft may be used.     

Effect of a supercritical CO2 based treatment on mechanical properties of human cancellous bone

Bone allografts can be treated by various techniques before implantation. Recently, treatments based on supercritical carbon dioxide (CO₂) were developed. The goal of this study was to evaluate the influence of such a treatment on the biomechanical properties of bone allografts. Thirteen human femoral heads obtained from patients who had undergone hip arthroplasty were cut along the frontal plane yielding to two slices with similar mechanical properties. For each femoral head, one of the two slices (randomly chosen) was fresh-frozen, whereas the other one underwent all steps of a supercritical CO₂ based treatment in order to clean and secure bone tissue. Nine specimens (7 mm×9 mm×10 mm) per slice were then cut and loaded under compression in a physiologic saline solution maintained at 37°C. For the maximal compressive strength a mean value (SD) of 9.6 (2.4) MPa for fresh bone and 10.2 (5.2) MPa for treated one was found. Regarding the Young’s modulus a mean value of 417 (85) MPa was obtained for fresh specimens and 412 (149) MPa for the treated ones. No statistical difference was found between the bone specimens treated with supercritical CO₂ and the fresh-frozen paired specimens when considering maximal compressive strength, Young’s modulus and work to failure.     

Effect of gamma irradiation on remodeling process of tendon allograft

Freeze-dried tendon allograft sterilized with gamma irradiation could be a reasonable option for ligament substitute. In the current study, the effects of freezing or freeze-drying followed by gamma irradiation on remodeling were analyzed biomechanically in a rat patellar tendon transplantation model at the time of harvest and during a 24-week healing period. The grafts were divided into four groups: fresh-freezing, freeze-drying, fresh-freezing followed by gamma irradiation, and freeze-drying followed by gamma irradiation. Before transplantation, the fresh-frozen grafts and the freeze-dried grafts showed significantly greater tensile strength than the gamma-irradiated grafts. However, at 4 weeks, the tensile strength of each group decreased to the equivalent level, which was approximately 20% of the tensile strength at Time 0, then increased gradually with time. At 24 weeks, the mean tensile strength of each transplanted graft achieved as much as 50% of the tensile strength at Time 0. The change in the tangent modulus with time followed a similar pattern as changes in the tensile strength. This study assumed that the extraarticular tendon transfer model was suitable for evaluating anterior cruciate ligament graft healing. These data suggest that the freeze-dried tendon allografts sterilized by gamma radiation could be a suitable substitute for anterior cruciate ligament reconstruction, if care is taken to protect the graft during the early stage after transplantation (< 4 weeks).     

Biomechanical analysis of allograft bone treated with a novel tissue sterilization process.

BACKGROUND CONTEXT: Several methods to sterilize allograft bone exist, including gamma irradiation and freeze-drying, which can alter the mechanical properties of the graft. Efforts are under way to develop a method for processing osseous allograft that maintains structural integrity. Herein is presented one such method. PURPOSE: To analyze the mechanical properties, compared with nontreated controls, of a novel sterilization process for allograft cortical bone. STUDY DESIGN/SETTING: A controlled biomechanical evaluation of allograft bone under various types of loading after a novel sterilization treatment. PATIENT SAMPLE: Not applicable; basic science. OUTCOME MEASURES: The load to failure was recorded for both the study and control groups, and statistical analysis of these results was performed. Significance level (alpha) and power (beta) were set to 0.05 and 0.90, respectively. Single-factor analysis of variance (ANOVA) was used to detect significant differences between the treated and untreated groups. A post-experimental power analysis was performed for each of the response variables. METHODS: Cortical tibia and femur samples from seven cadaveric donors (mean age 68.7 years) were treated with Biocleanse and compared with untreated samples with regard to density and strength. All samples were loaded to failure under diametral and biaxial compression, shear, and three-point bending. RESULTS: Statistical analysis was done on the density and failure stress for all modes of loading. ANOVA did not indicate a significant (p>.05) effect of treatment on the density except for the axial and biaxial specimens (p<.05). ANOVA analysis of failure stress demonstrated no significant differences (p>.05) between cortical bone treated with Biocleanse and untreated specimens under all four types of mechanical loading. Post-experimental power analysis revealed power to be greater than 0.9 for each test. CONCLUSIONS: Sterilization of allograft bone with Biocleanse does not significantly alter the mechanical properties when compared with untreated samples. The effect of this sterilization process on the osteoconductive and osteoinductive properties of allograft bone must be determined.     

Determining the elastic modulus of mouse cortical bone using electronic speckle pattern interferometry (ESPI) and micro computed tomography: A new approach for characterizing small-bone material properties

Mice phenotypes are invaluable for understanding bone formation and function, as well as bone disease. The elastic modulus is an important property of bones that can provide insights into bone quality. The determination of the elastic modulus of mouse cortical bone is complicated by the small dimensions of the bones. Whole bone bending tests are known to under estimate the elastic modulus compared to nanoindentation tests. The latter however provides information on extremely localized areas that do not necessarily correspond to the bulk elastic modulus under compression.This study presents a novel method for determining the bulk or effective elastic modulus of mouse cortical bone using the femur. We use Electronic Speckle Pattern Interferometry (ESPI), an optical method that enables the measurement of displacements on the bone surface, as it is compressed under water. This data is combined with geometric information obtained from micro-CT to calculate the elastic modulus. Roughly tubular cortical bone segments (2 mm) were cut from the diaphyses of femora of four week old C57BL/6 (B6) female mice and compressed axially using a mechanical tension–compression device. Displacements in the loading direction were mapped on the bone surface after loading the specimen. A linear regression of the displacement vs. axial-position enabled the calculation of the effective strain. Effective stress was calculated using force (N) data from the system's load cell and the mean cross-sectional area of the sample as determined by micro-CT. The effective elastic modulus (E) was calculated from the stress to strain ratio. The method was shown to be accurate and precise using a standard material machined to similar dimensions as those of the mouse femoral segments.Diaphyses of mouse femora were shown to have mean elastic moduli of 10.4 ± 0.9 GPa for femora frozen for eight months, 8.6 ± 1.4 GPa for femora frozen for two weeks and 8.9 ± 1.1 GPa for the fresh femora. These values are much higher than those measured using three-point bending, and lower than values reported in the literature based on nanoindentation tests from mice bones of the same age. We show that this method can be used to accurately and precisely measure the effective elastic modulus of mouse cortical bone.     

Sterilization by gamma radiation impairs the tensile fatigue life of cortical bone by two orders of magnitude.

Cortical bone grafts are utilized frequently for skeletal reconstruction, spinal fusion and tumor surgery. Due to its efficacy and convenience terminal sterilization by gamma radiation is often essential to minimize disease transmission and infection. However, the impairment in the material properties of bone tissue secondary to gamma radiation sterilization is a concern since the mechanical functionality of a bone graft is of primary importance. While the extent of this impairment is well investigated for monotonic loading conditions, there does not seem to exist any information on the effects of gamma radiation sterilization on cortical bone's fatigue properties, the physiologically relevant mode of loading. In this study we investigated the degradation in the high-cycle and low-cycle tensile fatigue lives of cortical bone tissue secondary to gamma radiation sterilization at a dose of 36.4 kGy which approximately falls in the higher end of the standard dose range used in tissue banking. The high-cycle and the low-cycle fatigue tests were conducted under load control at initial strain levels of 0.2% and 0.4%, respectively. Monotonic tensile tests were also conducted to compare the impairment of fatigue properties with the impairment of monotonic properties. Results demonstrated that the impairment in both the high-cycle and the low-cycle fatigue lives were two orders of magnitude following sterilization, a change much more pronounced than that observed for monotonic loading. In conclusion, the results suggest that the impairment of the mechanical function of gamma radiation sterilized allografts is even worse in fatigue than monotonically. Therefore, grafts should be designed to minimize functional strains and avoid stress raisers to prevent premature fatigue failures.     

Effects of solvent preservation with or without gamma irradiation on the material properties of canine tendon allografts

We studied the effects of solvent preservation with and without gamma irradiation on the material properties and morphology of canine tendons. Twenty-four paired tendons were harvested from both hind limbs of eight dogs. The tendons from the right legs were divided into three treatment groups of eight tendons each. In the first group, the tendons were subjected to solvent preservation for sterilization and drying (solvent group). In the second group, the tendons were treated in the same manner and then were sterlized by gamma irradiation (solvent/gamma group). The same treatments were applied to the tendons in the third group but in reverse order (gamma/solvent group). Tendons from the contralateral left legs were frozen immediately for use as controls for each corresponding treatment group. Histologically, the tendons treated with solvent, with or without gamma irradiation, had a more prominent wavy pattern in the collagen fibers than the control tendons. Mechanically, the tangent moduli for the solvent, solvent/gamma, and gamma/solvent groups were 58.53, and 99%, respectively, of each contralateral control. The respective tensile strengths were 85, 39, and 86% of that of the contralateral control. The tendons in the solvent/gamma group underwent the most severe changes in material properties: the tendons in the gamma/solvent group changed the least. This suggests that gamma irradiation followed by solvent drying is the procedure of choice for the preservation of tendon allografts.     

In vitro study of the role of various preservation methods on mechanical properties of allografts of the patellar tendon]

Tendon allografts are presently used for surgical reconstruction of the anterior cruciate ligament. The aim of this study was the in vitro evaluation of the modification of the mechanical properties of conserved human patellar tendons, deep-frozen or freeze-dried and sterilized with gamma rays. Thirty pairs of patellar tendons (central third) with their bony attachments were removed from fresh corpses, frozen in liquid nitrogen, then conserved at -80 degrees C. Out of each pair, one tendon was submitted to an additional treatment and the other was used as a control. Three types of treatment were studied: 2.5 Mrad irradiation (groupe I), freeze-drying with 1% residual humidity (groupe II), consecutive freeze-drying and irradiation (group III). After warming up (controls and group I treated tendons), the specimens were submitted to mechanical tests on the pulling machine with a suitable arrangement. Two types of tests were performed: a creep test (80 cycles at 1 Hz between 0 and 50 N) then an ultimate tensile strength test (0.25 mm/s). Freeze-drying causes macroscopic morphological alterations, which are even more marked if irradiation is applied in addition. The three types of treatment induce an increase in creep and a decrease in the ultimate, tensile strength and in Young's module, all being statistically significant. The three types of treatment alter the mechanical properties of the allograft. Freeze-drying maintains a better resistance of the graft. The combination of freeze-drying and irradiation is the most damaging method, and freeze-drying even seems to potentialize the harmful effects of irradiation resistance (group II freeze-dried grafts), the treated allografts present with changes in their viscoelastic properties that are incompatible with their clinical use. This study has also shown that some parameters influence the extent of the damaging effects of these three treatments, and experiments are being continued to optimize the conservation and sterilization procedure.     

Removal of the surface layers of human cortical bone allografts restores in vitro osteoclast function reduced by processing and frozen storage

A major complication of cortical bone grafting is nonunion at the host-graft junction. Many factors are thought to be involved in successful engraftment including the quality of the graft and the host response to it. In particular, the recipient osteoclasts (OCs) play a critical role by resorbing the engrafted bone. Thus, effective engraftment may depend on the inherent biological properties of the bone graft, which subsequently correlates with early and effective OC resorption. Normally, bone grafts are stored and processed by freezing, freeze-drying, irradiation, and lipid extraction. We sought to determine whether processing and storage affected bone quality, as evaluated by OC bone resorption. Cortical bone specimens from six human donors were either fresh, frozen at -75 degrees C, or had undergone combinations of freezing at -75 degrees C, freeze-drying, lipid extraction, irradiation, and treatment with hydrogen peroxide. Bone slices of 0.5-mm thickness taken from the surface, beneath the surface, and at a depth of 7.5 mm were incubated with isolated rabbit OCs and resorption lacunae were measured. We observed highest OC activity with fresh bone followed by frozen, partially processed, and fully processed bone. When allografts were stored at -75 degrees C for 12 months, there was up to a 4.2-fold reduction in OC activity on the surface layer. Additionally, we found reduced OC activity upon the outer surface bone compared to the inner layers. Removal of more than 0.5 mm of frozen and processed bone significantly improved OC activity. These results imply that inner bone layers of stored and processed bone allografts are protected against degradation of bone matrix components, except when frozen for extended periods of time. Taken together, these data suggest that bone allografts should be stored for less than 1 year and require the removal of at least 0.5 mm from their surface prior to transplantation.     

The fate of cancellous and cortical bone after transplantation of fresh and frozen tissue-antigen-matched and mismatched osteochondral allografts in dogs

After implantation, a massive osteochondral allograft cannot be completely protected from the stresses that are produced by weight-bearing, and it is susceptible to collapse during incorporation, revascularization, and substitution. How these processes are affected by disparities between the tissue antigens of the host and the graft remain unclear. To clarify the role of histocompatibility antigen-matching in the incorporation of cancellous and cortical bone, we orthotopically implanted both fresh and cryopreserved dog leukocyte-antigen-matched and mismatched proximal osteochondral radial allografts in beagles. Four groups of beagle dogs were used; they received (1) a dog leukocyte-antigen-mismatched frozen allograft, (2) a dog leukocyte-antigen-mismatched fresh allograft, (3) a dog leukocyte-antigen-matched fresh allograft, or (4) a dog leukocyte-antigen-matched frozen allograft. In twelve dogs, a sham operation was done in the contralateral limb (the first living donor had a sham operation), and in the remaining ten dogs, the proximal part of the contralateral radius was removed and then replaced as an autogenous (control) graft. The animals were given fluorochromes periodically, and they were killed eleven months after the operation. The osseous portion of the grafts was evaluated radiographically, biomechanically, and histomorphometrically. No dog had grossly obvious clinical abnormalities, all host-graft interfaces healed, and no joints dislocated. Radiographic examination of the allografts frequently showed deformation of the radial head and variable peripheral resorption. No significant difference in the modulus of elasticity at the host-graft interface was found among the groups. The repair process of the cortical bone was similar for all grafted segments. New periosteal and endosteal bone formed, and the cortical bone became porotic as vessels penetrated it. The uptake of fluorochrome was the most active in the autogenous grafts and the least active in the fresh antigen-mismatched grafts. The volume of cancellous bone was significantly greater and the trabeculae were thicker in all allografts compared with the bones on which a sham operation had been done and compared with the autogenous grafts. The volume of intertrabecular fibrous connective tissue was directly proportional to the immunogenicity of the allografts, and the percentage of the surface on which bone was forming tended to be inversely proportional to the immunogenicity of the allografts. The grafts were revascularized by the ingrowth of vessels into the intertrabecular spaces; necrotic trabeculae were not penetrated by vessels. This pattern was particularly pronounced in the antigen-mismatched grafts, regardless of whether they were fresh or frozen.(ABSTRACT TRUNCATED AT 400 WORDS)     

Compressive mechanical properties of human cancellous bone after gamma irradiation.

The effect of gamma irradiation on the mechanical properties of human bone was examined. Specimens of cancellous bone were cut from the proximal epiphyseal region of fresh-frozen tibiae and divided into control and irradiated groups according to anatomical region. The irradiated groups were exposed to 10,000, 31,000, 51,000, or 60,000 gray (1.0, 3.1, 5.1, or 6.0 megarad). The specimens were tested in compression to failure to determine failure stress, strain to failure, and elastic modulus. Failure stress and elastic modulus were found to be proportional to the square of the density and were normalized with respect to this property. Significant differences in normalized failure stress (p less than 0.001) and normalized elastic modulus (p = 0.003), when compared with the values for matched control specimens, were found only for the specimens that had been irradiated with 60,000 gray (6.0 megarad).     

11 kGy gamma irradiated demineralized bone matrix enhances osteoclast activity

Background

Demineralized bone matrix (DBM) allografts are widely used in orthopaedic clinics. However, the biological impact on its osteoinductivity after its sterilization process by gamma irradiation is not well studied. Furthermore, little is known about the relationship between residual calcium levels on osteoinductivity.

Hypothesis

We hypothesize that low-dose gamma irradiation retains the osteoinducitivity properties of DBM and causes ectopic bone formation.

Materials and methods

A randomised animal trial was performed to compare tissue and molecular responses of low-dose (11 kGy) gamma irradiated and non-irradiated human DBM at 6 weeks post-intramuscular implantation using an athymic rat model. In addition, we correlated residual calcium levels and bone formation in gamma irradiated DBM.

Results

A modified haematoxylin and eosin stain identified ectopic bony capsules at all implanted sites with no significant difference on the amount of new bone formed between the groups. Statistically significantly lower ratio of alkaline phosphatase expression over tartrate-resistant acid phosphatase and/or cathepsin K expressions was found between the groups.

Discussion

This study found that low-dose gamma irradiated DBM, which provides a sterility assurance level of 10^?6 for bone allografts, retained osteoinductivity but exhibited significantly enhanced osteoclastic activity. Furthermore, this is the first study to find a positive correlation between residual calcium levels and bone formation in gamma irradiated DBM.     

冷冻干燥同种骨临床应用的初步报告

目的：建立现代骨组织库，观察系列冷冻干燥同种骨移植的临床效果。方法：采用深度冷冻、真空冷冻干燥和辐照灭菌等现代技术处理人类骨组织，临床应用系列冻干骨94例，包括骨缺损填充、骨不连植骨、脊柱和关节融合、人工关节翻修、髋臼造盖等，观察近期临床结果。结果：冻干同种骨的理化性能、无菌检测和生物性能完全符合体内植入物的相关国家标准，常温下可保存2年。94例中的90例无明显的免疫排斥反应，优良率为95．76％，成功率为97．87％。结论：冷冻干燥同种骨使用安全，保存和运输方便，可替代临床自体骨移植。