Biomechanical issues in bone transplantation

Polydopamine-Coated Poly(l-lactide) Nanofibers with Controlled Release of VEGF and BMP-2 as a Regenerative Periosteum

The periosteum plays an important role in vascularization and ossification during bone repair. However, in most studies, an artificial periosteum cannot restore both functions of the periosteum concurrently. In this study, a novel nanofiber that can sustain the release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) was fabricated to enhance the durability of angiogenesis and osteogenesis during bone regeneration. A cell-free tissue engineered periosteum based on an electrospinning poly-l-lactic acid (PLLA) nanofiber was fabricated, on which VEGF and BMP-2 were immobilized through a polydopamine (PDA) coating conveniently and safely (BVP@PLLA membrane). The results indicated a significantly improved loading rate as well as a slow and sustained release of VEGF and BMP-2 with the help of the PDA coating. BMP-2 immobilized on nanofibers successfully induced the osteogenic differentiation of human bone marrow mesenchymal stem cells (BMSCs) in vitro with high expression of runt-related transcription factor 2 (Runx2), osteopontin (OPN), and alkaline phosphatase (ALP). Similarly, angiogenic differentiation of BMSCs with the expression of fetal liver kinase-1 (Flk-1) and vascular endothelial cadherin (VE-cadherin) was observed under the environment of VEGF sustained release. Moreover, an in vivo study revealed that the BVP@PLLA membrane could enhance vascular formation and new bone formation, which accelerates bone regeneration in rat femoral defects along with a massive periosteum defect. Therefore, our study suggests that the novel artificial periosteum with dual growth factor controlled release is a promising system to improve bone regeneration in bone defects along with a massive periosteum defect.

Autograft, Allograft, and Bone Graft Substitutes: Clinical Evidence and Indications for Use in the Setting of Orthopaedic Trauma Surgery

Bone grafts are the second most common tissue transplanted in the United States, and they are an essential treatment tool in the field of acute and reconstructive traumatic orthopaedic surgery. Available in cancellous, cortical, or bone marrow aspirate form, autogenous bone graft is regarded as the gold standard in the treatment of posttraumatic conditions such as fracture, delayed union, and nonunion. However, drawbacks including donor-site morbidity and limited quantity of graft available for harvest make autograft a less-than-ideal option for certain patient populations. Advancements in allograft and bone graft substitutes in the past decade have created viable alternatives that circumvent some of the weak points of autografts. Allograft is a favorable alternative for its convenience, abundance, and lack of procurement-related patient morbidity. Options include structural, particulate, and demineralized bone matrix form. Commonly used bone graft substitutes include calcium phosphate and calcium sulfate synthetics-these grafts provide their own benefits in structural support and availability. In addition, different growth factors including bone morphogenic proteins can augment the healing process of bony defects treated with grafts. Autograft, allograft, and bone graft substitutes all possess their own varying degrees of osteogenic, osteoconductive, and osteoinductive properties that make them better suited for different procedures. It is the purpose of this review to characterize these properties and present clinical evidence supporting their indications for use in the hopes of better elucidating treatment options for patients requiring bone grafting in an orthopaedic trauma setting.

Periosteum tissue engineering-a review

As always, the clinical therapy of critical size bone defects caused by trauma, tumor removal surgery or congenital malformation is facing great challenges. Currently, various approaches including autograft, allograft and cell-biomaterial composite based tissue-engineering strategies have been implemented to reconstruct injured bone. However, due to damage during the transplantation processes or design negligence of the bionic scaffolds, these methods expose vulnerabilities without the assistance of periosteum, a bilayer membrane on the outer surface of the bone. Periosteum plays a significant role in bone formation and regeneration as a store for progenitor cells, a source of local growth factors and a scaffold to recruit cells and growth factors, and more and more researchers have recognized its great value in tissue engineering application. Besides direct transplantation, periosteum-derived cells can be cultured on various scaffolds for osteogenesis or chondrogenesis application due to their availability. Research studies also provide a biomimetic methodology to synthesize artificial periosteum which mimic native periosteum in structure or function. According to the studies, these tissue-engineered periostea did obviously enhance the therapeutic effects of bone graft and scaffold engineering while they could be directly used as substitutes of native periosteum. Periosteum tissue engineering, whose related research studies have provided new opportunities for the development of bone tissue engineering and therapy, has gradually become a hot spot and there are still lots to consummate. In this review, tissue-engineered periostea were classified into four kinds and discussed, which might help subsequent researchers get a more systematic view of pseudo-periosteum.

Potential of autogenous or fresh-frozen allogeneic bone block grafts for bone remodelling: a histological, histometrical, and immunohistochemical analysis in rabbits

Our aim was to compare the wound healing of autogenous bone grafts with that of fresh-frozen allogeneic block bone in rabbits. We used 25 animals. One was killed before the experiment to provide the allogeneic bone, and the remainder were killed at four time points (n=6 in each group). On histometrical analysis there was a significant difference between the two groups only at 45days and between 15 and 45days in the intergroup analysis. However, there was significantly more revascularisation (p<0.05), resorption (p<0.05), and bony replacement (p<0.05) in the autogenous group in the immunohistochemical analysis. In later periods, the autogenous bone was replaced by newly-formed bone in all samples, whereas it was always possible to find regions of devitalised bone in the fresh-frozen allogeneic bone grafts. Autogenous grafts were completely replaced whereas, in the fresh- frozen allogeneic grafts, we found acellular tissue that had been incorporated into the receptor bed interface during the later evaluation times.

Biomimetic Approaches for Bone Tissue Engineering

Although autologous bone grafts are considered a gold standard for the treatment of bone defects, they are limited by donor site morbidities and geometric requirements. We propose that tissue engineering technology can overcome such limitations by recreating fully viable and biological bone grafts. Specifically, we will discuss the use of bone scaffolds and autologous cells with bioreactor culture systems as a tissue engineering paradigm to grow bone in vitro. We will also discuss emergent vascularization strategies to promote graft survival in vivo, as well as the role of inflammation during bone repair. Finally, we will highlight some recent advances and discuss new solutions to bone repair inspired by endochondral ossification.

Osteogenic Capacity of Human Adipose-Derived Stem Cells is Preserved Following Triggering of Shape Memory Scaffolds

Recent advances in shape memory polymers have enabled the study of programmable, shape-changing, cytocompatible tissue engineering scaffolds. For treatment of bone defects, scaffolds with shape memory functionality have been studied for their potential for minimally invasive delivery, conformal fitting to defect margins, and defect stabilization. However, the extent to which the osteogenic differentiation capacity of stem cells resident in shape memory scaffolds is preserved following programmed shape change has not yet been determined. As a result, the feasibility of shape memory polymer scaffolds being employed in stem cell-based treatment strategies remains unclear. To test the hypothesis that stem cell osteogenic differentiation can be preserved during and following triggering of programmed architectural changes in shape memory polymer scaffolds, human adipose-derived stem cells were seeded in shape memory polymer foam scaffolds or in shape memory polymer fibrous scaffolds programmed to expand or contract, respectively, when warmed to body temperature. Osteogenic differentiation in shape-changing and control scaffolds was compared using mineral deposition, protein production, and gene expression assays. For both shape-changing and control scaffolds, qualitatively and quantitatively comparable amounts of mineral deposition were observed; comparable levels of alkaline phosphatase activity were measured; and no significant differences in the expression of genetic markers of osteogenesis were detected. These findings support the feasibility of employing shape memory in scaffolds for stem cell-based therapies for bone repair.

Selection of animal models for pre-clinical strategies in evaluating the fracture healing, bone graft substitutes and bone tissue regeneration and engineering

In vitro assays can be useful in determining biological mechanism and optimizing scaffold parameters, however translation of the in vitro results to clinics is generally hard. Animal experimentation is a better approximation than in vitro tests, and usage of animal models is often essential in extrapolating the experimental results and translating the information in a human clinical setting. In addition, usage of animal models to study fracture healing is useful to answer questions related to the most effective method to treat humans. There are several factors that should be considered when selecting an animal model. These include availability of the animal, cost, ease of handling and care, size of the animal, acceptability to society, resistance to surgery, infection and disease, biological properties analogous to humans, bone structure and composition, as well as bone modeling and remodeling characteristics. Animal experiments on bone healing have been conducted on small and large animals, including mice, rats, rabbits, dogs, pigs, goats and sheep. This review also describes the molecular events during various steps of fracture healing and explains different means of fracture healing evaluation including biomechanical, histopathological and radiological assessments.

Surgical revascularization in structural orthotopic bone allograft increases bone remodeling

BACKGROUND

Osseous defects reconstructed with cryopreserved structural allografts are poorly revascularized and therefore are prone to nonunion, infection, deterioration of mechanical properties, and fracture. Whether this can be mitigated by specific interventions such as intramedullary surgical revascularization has been incompletely evaluated.

QUESTIONS/PURPOSES

We aimed to study surgical revascularization as a means to improve bone remodeling in cryopreserved allograft. Second, we questioned whether spatial histomorphometric differences occur in cortical bone areas after intramedullary surgical revascularization. Third, biomechanical properties of the graft-recipient construct in surgically revascularized allograft were compared with those of conventional allografts.

METHODS

Allografts were harvested from 10 Brown Norway rats, cryopreserved, and transplanted orthotopically in a 10-mm defect in two groups of 10 Lewis rats each (major histocompatibility mismatch). In the control group, no surgical revascularization was performed, whereas in the experimental group, a saphenous arteriovenous bundle was transposed in the bone marrow cavity. Bone remodeling was measured with histomorphometry, histology, and microcomputed tomography at 16 weeks. Spatial differences were analyzed with histomorphometry. To determine biomechanical properties, load at failure and structural stiffness in bending were evaluated by the three-point bend testing. In both groups, normal values of the contralateral femur also were analyzed.

RESULTS

Surgically revascularized allografts had increased bone remodeling (bone formation rate to bone surface ratio: 130 ± 47 µm(3)/µm(2)/year versus 44 ± 43 µm(3)/µm(2)/year, p = 0.006) and higher cortical osteocyte counts (18.6% ± 12.7% versus 3.1% ± 2.8%, p = 0.002) than nonrevascularized grafts. In nonrevascularized grafts, the bone formation rate to bone surface ratio was 35% of the contralateral normal values, whereas in surgically revascularized grafts, the bone formation rate to bone surface ratio in the grafts exceeded the contralateral values (110%). Microcomputed tomography did not show differences in bone volume between groups, however in both groups, bone volume was less in grafts compared with the contralateral femurs. Inner cortical bone formation rate to bone surface ratio was greater in surgically revascularized grafts (65 ± 30 µm(3)/µm(2)/year versus 13 ± 16 µm(3)/µm(2)/year in the control group, p = 0.012). Outer cortical bone formation rate to bone surface ratio also increased in surgically revascularized grafts (49 ± 31 µm(3)/µm(2)/year versus 19 ± 21 µm(3)/µm(2)/year, p = 0.032). No differences were found in load at failure and structural stiffness between both groups. In the control group, load at failure and structural stiffness were lower in grafts than in the contralateral femurs (p = 0.004 and p = 0.02, respectively). In the experimental group, surgically revascularized grafts also had lower load at failure and structural stiffness than the contralateral femurs (p = 0.008 and p = 0.02, respectively).

CONCLUSIONS

Surgical revascularization of large segmental allografts improved bone remodeling and viability without an adverse effect on total bone volume or bending strength and stiffness in this short-term analysis.

CLINICAL RELEVANCE

Cryopreserved allografts remain largely necrotic and are associated with a high rate of complications. Surgical revascularization increases graft healing which could contribute to graft survival with time.

Comparative biomechanical and microstructural analysis of native versus peracetic acid-ethanol treated cancellous bone graft

Bone transplantation is frequently used for the treatment of large osseous defects. The availability of autologous bone grafts as the current biological gold standard is limited and there is a risk of donor site morbidity. Allogenic bone grafts are an appealing alternative, but disinfection should be considered to reduce transmission of infection disorders. Peracetic acid-ethanol (PE) treatment has been proven reliable and effective for disinfection of human bone allografts. The purpose of this study was to evaluate the effects of PE treatment on the biomechanical properties and microstructure of cancellous bone grafts (CBG). Forty-eight human CBG cylinders were either treated by PE or frozen at −20°C and subjected to compression testing and histological and scanning electron microscopy (SEM) analysis. The levels of compressive strength, stiffness (Young's modulus), and fracture energy were significantly decreased upon PE treatment by 54%, 59%, and 36%, respectively. Furthermore, PE-treated CBG demonstrated a 42% increase in ultimate strain. SEM revealed a modified microstructure of CBG with an exposed collagen fiber network after PE treatment. We conclude that the observed reduced compressive strength and reduced stiffness may be beneficial during tissue remodeling thereby explaining the excellent clinical performance of PE-treated CBG.

Cell lineage in vascularized bone transplantation

BACKGROUND

The biology behind vascularized bone allotransplantation remains largely unknown. We aim to study cell traffic between donor and recipient following bone auto-, and allografting.

METHODS

Vascularized femoral transplantation was performed with arteriovenous bundle implantation and short-term immunosuppression. Twenty male Piebald Virol Glaxo (PVG; RT1(c) ) rats received isotransplants from female PVG (RT1(c) ) rats and 22 male PVG rats received allografts from female Dark Agouti rats (DA, RT1(a) ), representing a major histocompatibility mismatch. Both groups were randomly analyzed at 4 or 18 weeks. Bone remodeling areas (inner and outer cortical samples) were labeled and laser capture microdissected. Analysis of sex-mismatch genes by real-time reverse transcription-polymerase chain reaction provided the relative Expression Ratio (rER) of donor (female) to recipient (male) cells.

RESULTS

The rER was 0.456 ± 0.266 at 4 weeks and 0.749 ± 0.387 at 18 weeks (p = 0.09) in allotransplants. In isotransplants, the rER was 0.412 ± 0.239 and 0.467 ± 0.252 at 4 and 18 weeks, respectively (p = 0.21). At 4 weeks, the rER at the outer cortical area of isotransplants was significantly lower in isotransplants as compared with allotransplants (0.247 ± 0.181 vs. 0.549 ± 0.184, p = 0.007). Cells in the inner and outer cortical bone remodeling areas in isotransplants were mainly donor derived (rER < 0.5) at 18 weeks, whereas allotransplants contained mainly recipient-derived cells (rER > 0.5) at 18 weeks.

CONCLUSIONS

Applying novel methodology, we describe detailed cell traffic in vascularized bone transplants, elaborating our comprehension on bone transplantation.

Induction of angiogenesis and osteogenesis in surgically revascularized frozen bone allografts by sustained delivery of FGF-2 and VEGF

Large conventional bone allografts are susceptible to fracture and nonunion due to incomplete revascularization and insufficient bone remodeling. We aim to improve bone blood flow and bone remodeling using surgical angiogenesis combined with delivery of fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF). Frozen femoral allografts were heterotopically transplanted in a rat model. The saphenous arteriovenous bundle was implanted within the graft medullary canal. Simultaneously, biodegradable microspheres containing phosphate buffered saline (control), FGF-2, VEGF, or FGF-2 + VEGF were placed within the graft. Rats were sacrificed at 4 and 18 weeks. Angiogenesis was determined by quantifying bone capillary density and measuring cortical bone blood flow. Bone remodeling was assessed by histology, histomorphometry, and alkaline phosphatase activity. VEGF significantly increased angiogenesis and bone remodeling at 4 and 18 weeks. FGF-2 did not elicit a strong angiogenic or osteogenic response. No synergistic effect of FGF-2 + VEGF was observed. VEGF delivered in microspheres had superior long-term effect on angiogenesis and osteogenesis in surgically revascularized frozen bone structural allografts as compared to FGF-2 or FGF-2 + VEGF. Continuous and localized delivery of VEGF by microencapsulation has promising clinical potential by inducing a durable angiogenic and osteogenic response in frozen allografts.

Surgical revascularization induces angiogenesis in orthotopic bone allograft

BACKGROUND

Remodeling of structural bone allografts relies on adequate revascularization, which can theoretically be induced by surgical revascularization. We developed a new orthotopic animal model to determine the technical feasibility of axial arteriovenous bundle implantation and resultant angiogenesis.

QUESTIONS/PURPOSES

We asked whether arteriovenous bundles implanted in segmental allografts would increase cortical blood flow and angiogenesis compared to nonrevascularized frozen bone allografts and contralateral femoral controls.

METHODS

We performed segmental femoral allotransplantation orthotopically from 10 Brown Norway rats to 20 Lewis rats. Ten rats each received either bone allograft reconstruction alone (Group I) or allograft combined with an intramedullary saphenous arteriovenous flap (Group II). At 16 weeks, we measured cortical blood flow with the hydrogen washout method. We then quantified angiogenesis using capillary density and micro-CT vessel volume measurements.

RESULTS

All arteriovenous bundles were patent. Group II had higher mean blood flow (0.12 mL/minute/100 g versus 0.05 mL/minute/100 g), mean capillary density (23.6% versus 2.8%), and micro-CT vessel volume (0.37 mm(3) versus 0.07 mm(3)) than Group I. Revascularized allografts had higher capillary density than untreated contralateral femora, while vessel volume did not differ and blood flow was lower.

CONCLUSIONS

Axial surgical revascularization in orthotopic allotransplants can achieve strong angiogenesis and increases cortical bone blood flow.

Concise review: personalized human bone grafts for reconstructing head and face

Regeneration of normal shape, architecture, and function of craniofacial tissues following congenital abnormality, trauma, or surgical treatment presents special problems to tissue engineering. Because of the great variations in properties of these tissues, currently available treatment options fall short of adequate care. We propose that the engineering of personalized bone graft customized to the patient and the specific clinical condition would revolutionize the way we currently treat craniofacial defects and discuss some of the current and emerging treatment modalities.

Revascularization and bone remodeling of frozen allografts stimulated by intramedullary sustained delivery of FGF-2 and VEGF

Frozen bone allografts are susceptible to nonunion and fracture due to limited revascularization and incomplete bone remodeling. We aim to revascularize bone allografts by combining angiogenesis from implanted arteriovenous (AV) bundles with delivery of fibroblast growth factor (FGF-2) and/or vascular endothelial growth factor (VEGF) via biodegradable microspheres. Rat femoral diaphyseal allografts were frozen at -80°C, and heterotopically transplanted over a major histocompatibility mismatch. A saphenous AV bundle was inserted into the intramedullary canal. Growth factor was encapsulated into microspheres and inserted into the graft, providing localized and sustained drug release. Forty rats were included in four groups: (I) phosphate-buffered saline, (II) FGF-2, (III) VEGF, and (IV) FGF-2 + VEGF. At 4 weeks, angiogenesis was measured by the hydrogen washout method and microangiography. Bone remodeling was evaluated by quantitative histomorphometry and histology. Bone blood flow was significantly higher in groups III and IV compared to control (p < 0.05). Similarly, bone remodeling was higher in VEGF groups. FGF-2 had little effect on allograft revascularization. No synergistic effect was observed with use of both cytokines. Delivered in microspheres, VEGF proved to be a potent angiogenic cytokine, increasing cortical bone blood flow and new bone formation in frozen allografts revascularized with an implanted AV bundle.

Variability in tissue bank practices regarding donor and tissue screening of structural allograft bone

STUDY DESIGN

A standardized questionnaire was directed to medical directors of US structural allograft bone providers regarding their practices in screening potential donors and allograft bone itself for parameters potentially affecting mechanical strength.

OBJECTIVE

To determine the uniformity of practices within the US allograft bone industry regarding parameters related to structural allograft bone mechanical strength.

SUMMARY OF BACKGROUND DATA

Despite oversight with respect to disease transmission and contamination, few guidelines exist regarding donor eligibility and bone itself for issues potentially affecting the mechanical integrity of structural allograft bone.

METHODS

A survey regarding donor and tissue screening practices impacting mechanical strength of structural allograft bone was administered to medical directors of American Association of Tissue Banks-accredited structural allograft bone providers. Results are reported as the percentage of all tissue banks using a given donor or tissue screening method and the percentage of the total US supply of structural allograft bone affected.

RESULTS

Eighty-one percent (14 of 16) of bone-processing banks completed the survey, accounting for 98% of the US supply of structural allograft bone. Approximately 76% (18,712 of 24,671) of all tissue donors are used as a source of structural bone allograft. Thirty-nine percent (6 of 14) of tissue banks have no upper age limit or accept structural allograft bone donors up to age 80. Fifty percent (7 of 14) of banks exclude donors with a diagnosis of osteoporosis. Sixty-four percent (9 of 14) of banks require a minimum cortical dimension of structural bone allograft, representing 81% (15,110 of 18,712) of the US supply. No tissue bank performs dual energy x-ray absorptiometry scans of potential bone donors.

CONCLUSION

Substantial variability exists in screening practices of US tissue banks regarding mechanical strength of structural allograft bone. Reported variations may reflect the lack of regulatory standards regarding these issues. Further data regarding these variables' impacts on allograft strength and clinical outcomes would be helpful in developing appropriate standards.

Fresh-frozen vs. irradiated allograft bone in orthopaedic reconstructive surgery

The use of allograft bone is increasingly common in orthopaedic reconstruction procedures. The optimal method of preparation of allograft bone is subject of great debate. Proponents of fresh-frozen graft cite improved biological and biomechanical characteristics relative to irradiated material, whereas fear of bacterial or viral transmission warrants some to favour irradiated graft. Careful review of the literature is necessary to appreciate the influence of processing techniques on bone quality. Whereas limited clinical trials are available to govern the selection of appropriate bone graft, this review presents the argument favouring the use of fresh-frozen bone allograft as compared to irradiated bone.

Effects of 20% demineralization on surface physical properties of compact bone scaffold and bone remodeling response at interface after orthotopic implantation

To enhance osteointegration with preservation of mechanical strength, a surface modification technique using 20% surface demineralization in a controlled manner was applied to custom-built cylindrical bio-derived compact bones (20% surface-demineralized cylindrical compact bio-derived bone scaffold: SDCBS); an undemineralized version was the control. The micro-surface topography of the two types of bone scaffolds was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). 20% demineralization led to significant increases in surface roughness (38.19%, P=0.001) and surface area (15.1%, P=0.030), compared with the control group's, while the decrease in mechanical properties was not statistically significant. Results of orthotopic implantation for 9 months demonstrated that 20% surface demineralization caused significantly rapid and homogeneous bone remodeling at the interface compared to control and led to a significantly rapid osteointegration of SDCBS with the host bone at the early and intermediate stages of osteointegration. The study indicates the potential of SDCBS in repairing clinical bone defects, and would help direct the use of various processes of biomaterials to support defect repairs within osseous sites.

Optimal handling of fresh cancellous bone graftDifferent peroperative storing techniques evaluated by in vitro osteoblast-like cell metabolism

We investigated the influence of three peroperative handling techniques on the quality of autogenous bone graft by means of osteoblast-like cell metabolism in vitro. Cancellous bone was harvested from the iliac crest of 12 4-month-old female pigs. Osteoblast-like cell cultures were established, using the tissue-explant method: (1) immediately after harvest of bone, (2) after storage of bone in saline at room temperature for 2 hours and (3) after "dry" storage of bone at room temperature for 2 hours. Proliferation was assessed by 3H-thymidine incorporation. Differentiation was assessed by alkaline phosphatase activity and procollagen I production (PICP). We found that osteoblast-like-cell proliferation was higher, when cultures were started shortly after harvesting of bone, or else stored in saline for 2 hours, as compared to bone left "to dry" for 2 hours. Basal alkaline phosphatase and PICP production did not differ in the three groups. These in vitro results suggest the superiority of harvest of autogenous bone graft shortly before the grafting procedure, or else temporary storage of the graft in saline for up to 2 hours.

Subsidence of the stem after impaction bone grafting for revision hip replacement using irradiated bone

Loss of bone stock is a major problem in revision surgery of the hip. Impaction bone grafting of the femur is frequently used when dealing with deficient bone stock. In this retrospective study a consecutive series of 68 patients (69 hips) who had revision of a hip replacement with femoral impaction grafting were reviewed. Irradiated bone allograft was used in all hips. Radiological measurement of subsidence of the stem, incorporation of the graft and remodelling was carried out and showed incorporation of the graft in 26 of 69 hips (38%). However, there was no evidence of trabecular remodelling. Moderate subsidence of 5 mm to 10 mm occurred in ten hips (14.5%), and massive subsidence of > 10 mm in five (7.2%). The results of this study are less favourable than those of others describing studies of revision of the femoral stem using impaction bone grafting. The absence of the characteristic changes of graft remodelling noted in other series raises the question as to whether irradiated bone graft may be a significant factor influencing the post-operative outcome.

How to store autologous bone graft perioperatively: an in vitro study

INTRODUCTION

Autologous bone graft is the golden standard for bone grafting, but little is known about the influence of various preservation techniques used during surgery immediately following harvest on the osseous structures and graft vitality. Several studies focussed on the optimal treatment of the bone during harvest and implantation, but only few examined the intraoperative storage conditions on the back table. The aim of our study was to examine the influence of various intraoperative preservation techniques on human cancellous bone at different points to optimize the storage during surgery.

MATERIALS AND METHODS

Cancellous bone was harvested during hip arthroplasty and stored for 2 and 4 h under dry conditions, inside a swab moistened with saline solution or in saline solution, 5% glucose solution or culture medium. After the storage period, the bone was cultured and examined 7 days after the first cells grew out in one of these groups. Following the identification of the cells as osteoblast-like cells, the cultures were analysed by fluorescence staining, cell count and the XTT-test.

RESULTS

Fluorescence staining revealed no avital cells in all groups. Dry storage of the bone led to significantly lower cell metabolism after 2 h compared to saline solution and 5% glucose solution. The same was true after 4 h dry storage compared to the moistened swab, and glucose and culture medium. Cell count was significantly lower after 2 h of dry storage compared to saline solution and culture medium.

CONCLUSIONS

Perioperative storage of cancellous bone under dry conditions should be avoided. The bone graft should be stored in saline or 5% glucose solution or a moistened swab.

A perspective: engineering periosteum for structural bone graft healing

Autograft is superior to both allograft and synthetic bone graft in repair of large structural bone defect largely due to the presence of multipotent mesenchymal stem cells in periosteum. Recent studies have provided further evidence that activation, expansion and differentiation of the donor periosteal progenitor cells are essential for the initiation of osteogenesis and angiogenesis of donor bone graft healing. The formation of donor cell-derived periosteal callus enables efficient host-dependent graft repair and remodeling at the later stage of healing. Removal of periosteum from bone autograft markedly impairs healing whereas engraftment of multipotent mesenchymal stem cells on bone allograft improves healing and graft incorporation. These studies provide rationale for fabrication of a biomimetic periosteum substitute that could fit bone of any size and shape for enhanced allograft healing and repair. The success of such an approach will depend on further understanding of the molecular signals that control inflammation, cellular recruitment as well as mesenchymal stem cell differentiation and expansion during the early phase of the repair process. It will also depend on multidisciplinary collaborations between biologists, material scientists and bioengineers to address issues of material selection and modification, biological and biomechanical parameters for functional evaluation of bone allograft healing.

Structural bone allograft combined with genetically engineered mesenchymal stem cells as a novel platform for bone tissue engineering

The presence of live periosteal progenitor cells on the surface of bone autografts confers better healing than devitalized allograft. We have previously demonstrated in a murine 4 mm segmental femoral bone-grafting model that live periosteum produces robust endochondral and intramembraneous bone formation that is essential for effective healing and neovascularization of structural bone grafts. To the end of engineering a live pseudo-periosteum that could induce a similar response onto devitalized bone allograft, we seeded a mesenchymal stem cell line stably transfected with human bone morphogenic protein-2/beta-galactosidase (C9) onto devitalized bone allografts or onto a membranous small intestinal submucosa scaffold that was wrapped around the allograft. Histology showed that C9-coated allografts displayed early cartilaginous tissue formation at day 7. By 6 and 9 weeks, a new cortical shell was found bridging the segmental defect that united the host bones. Biomechanical testing showed that C9-coated allografts displayed torsional strength and stiffness equivalent to intact femurs at 6 weeks and superior to live isografts at 9 weeks. Volumetric and histomorphometric micro-computed tomography analyses demonstrated a 2-fold increase in new bone formation around C9-coated allografts, which resulted in a substantial increase in polar moment of inertia (pMOI) due to the formation of new cortical shell around the allografts. Positive correlations between biomechanics and new bone volume and pMOI were found, suggesting that the biomechanical function of the grafted femur relates to both morphological parameters. C9-coated allograft also exhibited slower resorption of the graft cortex at 9 weeks than live isograft. Both new bone formation and the persistent allograft likely contributed to the improved biomechanics of C9-coated allograft. Taken together, we propose a novel strategy to combine structural bone allograft with genetically engineered mesenchymal stem cells as a novel platform for bone tissue engineering.

Sterilization of allograft bone: effects of gamma irradiation on allograft biology and biomechanics

Gamma irradiation from Cobalt 60 sources has been used to terminally sterilize bone allografts for many years. Gamma radiation adversely affects the mechanical and biological properties of bone allografts by degrading the collagen in bone matrix. Specifically, gamma rays split polypeptide chains. In wet specimens irradiation causes release of free radicals via radiolysis of water molecules that induces cross-linking reactions in collagen molecules. These effects are dose dependent and give rise to a dose-dependent decrease in mechanical properties of allograft bone when gamma dose is increased above 25 kGy for cortical bone or 60 kGy for cancellous bone. But at doses between 0 and 25 kGy (standard dose), a clear relationship between gamma dose and mechanical properties has yet to be established. In addition, the effects of gamma radiation on graft remodelling have not been intensively investigated. There is evidence that the activity of osteoclasts is reduced when they are cultured onto irradiated bone slices, that peroxidation of marrow fat increases apoptosis of osteoblasts; and that bacterial products remain after irradiation and induce inflammatory bone resorption following macrophage activation. These effects need considerably more investigation to establish their relevance to clinical outcomes. International consensus on an optimum dose of radiation has not been achieved due to a wide range of confounding variables and individual decisions by tissue banks. This has resulted in the application of doses ranging from 15 to 35 kGy. Here, we provide a critical review on the effects of gamma irradiation on the mechanical and biological properties of allograft bone.

Allograft and alloplastic bone substitutes: a review of science and technology for the craniomaxillofacial surgeon

Bone healing is a complex and multifactorial process. As such, there are numerous steps in the process to which intervention can be directed. This has given rise to many bone graft technologies that have been used to regenerate bone, creating, perhaps, a bewildering array of options. The options that surgeons have the most familiarity with are the ones that have been available the longest (i.e., autograft and allograft). Although useful for the widest spectrum of clinical applications, limitations of these grafts has prompted the development of new materials. Demineralized bone matrix formulations and synthetic ceramic materials are now being used with greater frequency. These biomaterials have demonstrated their usefulness in facial plastic and reconstructive surgery with their ability to augment and replace portions of the craniofacial skeleton. The purpose of this article is to describe and discuss the allograft and alloplastic bone grafting technologies so that the reader can consider each in the context of the others and gain a better appreciation for how each fits into the universe of existing and emerging treatments for bone regeneration.

Periosteal progenitor cell fate in segmental cortical bone graft transplantations: implications for functional tissue engineering

A murine segmental femoral bone graft model was used to show the essential role of donor periosteal progenitor cells in bone graft healing. Transplantation of live bone graft harvested from Rosa 26A mice showed that approximately 70% of osteogenesis on the graft was attributed to the expansion and differentiation of donor periosteal progenitor cells. Furthermore, engraftment of BMP-2-producing bone marrow stromal cells on nonvital allografts showed marked increases in cortical graft incorporation and neovascularization, suggesting that gene-enhanced, tissue engineered functional periosteum may improve allograft incorporation and repair.

INTRODUCTION

The loss of cellular activity in a structural bone allograft markedly reduces its healing potential compared with a live autograft. To further understand the cellular mechanisms for structural bone graft healing and repair and to devise a therapeutic strategy aimed at enhancing the performance of allograft, we established a segmental femoral structural bone graft model in mice that permits qualitative and quantitative analyses of graft healing and neovascularization.

MATERIALS AND METHODS

Using this segmental femoral bone graft model, we transplanted live isografts harvested from Rosa 26A mice that constitutively express beta-galactosidase into their wildtype control mice. In an attempt to emulate the osteogenic and angiogenic properties of periosteum, we applied a cell-based, adenovirus-mediated gene therapy approach to engraft BMP-2-producing bone marrow stromal cells onto devitalized allografts.

RESULTS

X-gal staining for donor cells allowed monitoring the progression of periosteal progenitor cell fate and showed that 70% of osteogenesis was attributed to cellular proliferation and differentiation of donor progenitor cells on the surface of the live bone graft. Quantitative muCT analyses showed a 3-fold increase in new bone callus formation and a 6.8-fold increase in neovascularization for BMP-2/stromal cell-treated allograft compared with control acellular allografts. Histologic analyses showed the key features of autograft healing in the BMP-2/stromal cell-treated allografts, including the formation of a mineralized bone callus completely bridging the segmental defects, abundant neovascularization, and extensive resorption of bone graft.

CONCLUSIONS

The marked improvement of healing in these cellularized allografts suggests a clinical strategy for engineering a functional periosteum to improve the osteogenic and angiogenic properties of processed allografts.

Bone quality and healing in a swine vascularized bone allotransplantation model using cyclosporine-based immunosuppression therapy

Although vascularized bone and joint allotransplantation is a promising new treatment option for reconstructing large bone defects, the need for immunosuppressive agents to prevent rejection in these procedures poses a major problem. This problem stems from the fact that several of these agents can cause harmful side effects, such as alterations in bone quality and healing. Therefore, the purpose of this study was to determine what effect the commonly used immunosuppressant regimen cyclosporine A-based combination therapy has on bone quality and healing. In 10 pigs, vascularized bone allografts with skin and muscle components (osteomyocutaneous free flaps) were transplanted from size-matched donor animals. Recipient animals received oral cyclosporine A/mycophenolate mofetil/prednisone therapy for 90 days. Bone quality was studied before and after transplantation by measuring the bone's acoustic velocity and density and calculating the bone's elastic coefficient. Bone healing was assessed using radiographic analysis. Four animals were lost as a result of graft rejection or immunosuppression-related complications before the 90-day endpoint of the study. Although bone specimens taken from the six animals that completed the 90-day protocol had histological signs of rejection, they all seemed to have normal bone healing. Posttransplant bone density values were significantly decreased (p < 0.05) (1544.7 +/- 47.5 kg/m3) as compared with pretransplant values (1722.7 +/- 44.1 kg/m3). Results of the acoustic velocity and elastic coefficients measurements showed a significant decrease (p < 0.05) in posttransplant values (from 3503.0 +/- 165.1 meters/sec to 2963.0 +/- 54.6 meters/sec and from 21.6 +/- 2.2 GPa to 13.6 +/- 0.5 GPa, respectively), indicating diminished bone quality. The findings indicate that cyclosporine A/mycophenolate mofetil/prednisone combination therapy is ineffective in preventing bone rejection, that it decreases bone quality, and that it is associated with systemic toxicity, suggesting that this immunosuppressive regimen at the doses used in this study is not ideal for vascularized bone allotransplantation procedures.

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.

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.

Biological and biophysical principles in extracorporal bone tissue engineering. Part III

Over the last decade extracorporal bone tissue engineering has moved from laboratory to clinical application. The restoration of maxillofacial bones from cell harvesting through product manufacture and end-use has benefited from innovations in the fields of biomechanical engineering, product marketing and transplant research. Cell/scaffold bone substitutes face a variety of unique clinical challenges which must be addressed. This overview summarises the recent state of the art and future anticipations in the transplantation of extracorporally fabricated bone tissues.

A novel murine segmental femoral graft model

To further understand the cellular and molecular mechanisms underlying cortical bone graft healing, we have developed a novel mouse femur model that permits quantitative and molecular analysis of structural bone graft healing. A 4 mm mid-diaphyseal femoral segment was removed and replaced by either immediate implantation of a fresh autograft, a frozen, genetically identical isograft or a frozen allograft from a different strain of mouse, which was secured with a 22-gauge metal intramedullary pin. Healing was evaluated by radiology, histomorphometry, and in situ hybridization. Autograft repair occurred by endochondral bone formation at the host-graft junction and by intramembranous bone formation along the length of the graft bed at 2 weeks, with maturation and remodeling apparent by 4 weeks. Bone repair in allografts and isografts completely relied on endochondral bone formation at the host-graft cortical junction, with absence of periosteal bone formation along the length of the graft, suggesting that live periosteal cells from the donor tissue are necessary for this response. This small animal model of structural bone grafting can be used to evaluate tissue-engineered allografts and novel bone graft substitutes using quantitative and molecularly defined outcome measures.

Propriétés mécaniques de greffons humains provenant de têtes fémorales et traitées par un procédé d’épuration physico-chimique (Ostéopure™)

PURPOSE OF THE STUDY

Bone grafts and bone substitutes must be biocompatible osteoconductors with satisfactory mechanical properties similar to native bone. When the bone treatment is conducted under specific conditions, the elasticity module under infra-maximal loading can be optimized to achieve reproducible values. The purpose of this work was to determine the effect of the cleaning and sterilization process using Osteopure on the biomechanical properties of trabecular bone harvested from human femoral heads.

MATERIAL AND METHOD

Seventy trabecular bone samples were tested: group 1F (fresh samples); group 1N (after application of Osteopure cleaning); group 1S (after Osteopure cleaning and sterilization). Non-destructive and destructive tests (group 1D) were performed. Two fresh femoral heads were used as controls for the destructive test (group 2). The first non-destructive test was applied directly after section (group 1F). Other samples were then purified with Osteopure treatment and a second non-destructive test was conducted (group 1N). A third non-destructive test was conducted after sterilization with 25 kgray radiation (group 1S). Treatments 1 and 2 were performed by OST Developpement SA (Clermont-Ferrand). Finally a destruction test was applied along the directional axis (group 1D). For the 31 samples in group 2 (control) the destructive test was applied along the directional axis immediately after section. Compression tests were performed at a deformation speed of 3 mm/min for 0.3% deformation.

RESULTS

The Young module did not exhibit any significant difference between the three steps of the testing in the three orthogonal directions. The Young module was not significantly different between group 1F and group 2 (controls). Maximal force of compression was significantly different (P<0.01). There was a linear relationship between maximal force at rupture and the Young module obtained during destructive tests, for groups 1D and 2 respectively. The compression curves obtained from sterilized samples (group 1D) were not significantly different from those observed for fresh trabecular bone in group 2 (controls).

DISCUSSION

The Young module values measured from 70-673 MPa. For non-destructive tests, the module values were to the order of 64% of those obtained for destructive tests. Decreased maximal force of rupture observed for treated samples in comparison with fresh samples can be explained by the extraction of most of the lipids.

CONCLUSION

The Osteopure method does not alter stiffness of bone allografts. The elasticity module observed in treated bones is close to that observed in fresh bones. Mechanical resistance to compression is however only half the force of compression observed in the hip joint for daily activities. The linear relationship between the elasticity mode and loading required for rupture is not affected by treatment with Osteopure. The advantages related to elimination of prions or viral contamination appear by far to be more important than the minor changes observed in the mechanical characteristics of allografts.

ANTERIOR CERVICAL FUSION USING DENSE CANCELLOUS ALLOGRAFTS AND DYNAMIC PLATING

OBJECTIVE

Dense cancellous grafts provide an open matrix for vascular and cellular penetration for early osseous integration. Thus, they provide a better biological fusion substrate than cortical or corticocancellous grafts. The aim of this study is to evaluate the efficacy of the dense cancellous allografts as a substrate for anterior cervical fusion along with instrumentation.

METHODS

This is a retrospective study of 98 patients who underwent anterior cervical discectomy, fusion with dense cancellous allograft bone, and instrumentation using dynamic plating between January 2001 and March 2002. Of these procedures, 60 involved single-level and 38 involved two-level fusions. Subsidence was assessed by plain x-rays at 1, 3, 6, and 12 months and fusion at 3, 6, and 12 months after surgery. Fusion was defined as the appearance of bridging trabecular bone and absence of motion in flexion-extension films.

RESULTS

The mean follow-up period was 15 months (range, 12-25 mo). Successful fusion was observed in 70, 84, and 96% of the patients at 3, 6, and 12 months, respectively. The average subsidences for single-level and two-level fusions were 2.0 and 3.2 mm, respectively. No allograft- or hardware-related complications were encountered in our series.

CONCLUSION

Dense cancellous allografts are very effective as bone graft substitutes for achieving anterior cervical fusion along with instrumentation. Successful fusion was observed in 70% of our patients at 3 months, with a fusion rate of 96% at 1 year. These allografts provide an effective replacement for autologous grafts in cervical interbody fusion.

In vitro osteoblast-like cell metabolism in spondylodesis--a tool that may predict fusion capacity: a prospective study in 50 patients with a 1-year follow-up

In vitro cultures of human primary osteoblast-like cells provide a model for studying cellular mechanisms associated with human bone biology. We investigated in vitro osteoblast-like cell metabolism as a method for predicting the occurrence of spinal fusion in the individual patient. A bone biopsy was taken from the iliac crest of 50 patients, median age 49 (23-77) years, who were undergoing lumbar spine fusion. First-passage osteoblast-like cells were established by the bone-tissue-explant method. We then estimated 3H-thymidine incorporation, alkaline phosphatase activity and procollagen I production. Fusion rates were evaluated at the 1-year follow-up. Primary human osteoblast-like cell cultures showed an age-dependent decline in their capacity for cellular outgrowth and expression of alkaline phosphatase, which suggested a useful biological response pattern of the osteoblast culture. However, such cultures were unsatisfactory as an in vitro tool for predicting fusion capacity.

Threaded cortical bone dowels in lumbosacral arthrodesis: a review

Lumbar fusion is a common spinal surgery, for which numerous devices have been developed to aid in segment stabilization. A threaded cortical bone dowel is a machined and processed bone allograft which is one such development. Threaded cortical bone dowels are attractive because of their osteoconductive nature and the opportunity to load them with osteogenic morselized bone autograft or osteoinductive growth factors, such as bone morphogenetic proteins. Although threaded cortical bone dowels have been in clinical use for more than 5 years, they have not been the subject of a comprehensive review. The current article covers the history, preparation, uses, safety, and efficacy of threaded cortical bone dowels in lumbosacral interbody fusion.

Bone graft substitutes

A better understanding of the biology of fracture healing and an increasing awareness of the limitations and potential complications of autogenous bone graft harvest have combined to foster a burgeoning interest in the development of bone graft substitutes. A few of these materials have been available for more than a decade, and many more should become available in the near future. The characteristics of the ideal bone graft substitute may vary considerably depending on the intended site of application and the clinical setting in which it is used. Knowledge of the available alternatives is a necessary prerequisite to informed decision making.

Bone transplantation

Bony deficiency, particularly loss of bone stock associated with failed joint replacements or tumours, is a challenging problem in orthopaedic surgery. Bone transplantation techniques provide solutions that can be tailored to the clinical problem. However, the risks of bone transplantation are well documented and the biology of allograft incorporation remains unpredictable and poorly understood.

Complications of iliac crest graft and bone grafting alternatives in foot and ankle surgery

The ability to harvest iliac crest bone is a well-established skill in the surgical armamentarium of the orthopedic surgeon. As with any surgical procedure, this operation has its own set of complications. The surgeon must be aware of these potential problems in an effort to avoid them when possible. Other autologous sites for bone harvest are available to the surgeon, and s/he should be aware of these in terms of location, limitations of use, harvest technique, and potential pitfalls. The foot and ankle surgeon almost always needs less bone graft than our colleagues in spine surgery or joint revision surgery, so these other sites may be more suitable than the iliac crest for obtaining bone graft. Nonautogenous alternatives are becoming increasingly available to the orthopedist as a way to decrease morbidity and operating times. Scranton recently published an article about his success with several different bone substitute products that are used in foot and ankle reconstructive cases. As these options become more varied, it becomes more difficult to know which product to select. Understanding the biology of bone grafting with respect to osteoconduction, osteoinduction, and osteogenesis provides the surgeon with the knowledge that is needed to make an informed choice when selecting a bone grafting option. Before choosing an alternative graft material, the surgeon should also investigate how the graft material has performed in cases similar to his or her patient's needs. In the future, with continued research, the fields of tissue engineering and gene therapy will provide even better options for nonautogenous bone graft material.

Modern issues in bone graft substitutes and advances in bone tissue technology

Autogenous bone grafting is the gold standard in repair of bony defects, fracture nonunion, and promoting arthrodesis. The complications related to obtaining autogenous grafts can be significant, and numerous materials are now available for augmentation or substitution. Allograft materials are highly effective for most applications; however, the surgeon needs to be acutely aware of the source of the tissue, for some tissue banks still use unacceptable processing techniques that destroy the structural and osteoinductive capacities of the graft. DBM products are unregulated and serious concerns exist as to the distribution of inactive products as commercially available to the practicing surgeon. Pressure from the orthopedic community has caused some manufacturers to test their products for activity before distribution. Calcium-based ceramic materials are effective as osteoconductive agents and work well alone as bone void fillers; however, augmentation of these implants with osteoinductive materials should be considered for use in nonunions and arthrodesis. Composite materials that incorporate osteoinductive materials in osteoconductive scaffolds are promising. New technology in isolation and creation of recombinant human bone morphogenic proteins and growth factors, and in the application of autogenous stem cells are emerging as the future of bone grafting procedures.

The effects of bone chips dehydrated with solvent on healing bone defects

The effect of bone chips dehydrated with solvent on the healing of bone defects was evaluated. Solvent-dehydrated spongiose bone chips were placed in experimentally formed cavities in the right back tibia of rabbits. After 10, 20 and 30 days, histopathological cross-sections from the bone grafts were examined microscopically for bone healing and formation of spongiose bone, cortex and bone marrow. Spongiose bone chips had a positive and accelerating influence on the healing of bone defects in the 10-day period after transplantation, but no significant differences were observed between the treated and control groups 20 and 30 days after transplantation.

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.