Mechanical strength of bone allografts subjected to chemical sterilization and other terminal processing methods

Fatigue crack propagation and fracture toughness of cortical bone are radiation dose-dependent

Cortical bone allograft sterilized with a standard γ-radiation dose of 25-35kGy has demonstrated reduced static and cyclic fracture resistance compared with unirradiated bone. To mitigate radiation damage, we recently observed a dose-dependent response of high-cycle fatigue behavior of human cortical bone from 0 to 25 kGy, with lower doses exhibiting logarithmically longer fatigue lives. The objectives of this study were as follows: (1) to determine whether fracture toughness, work-to-fracture, and fatigue crack propagation resistance of human cortical bone are also radiation dose-dependent, and (2) to determine the associations of radiation dose and a Raman biomarker for collagen disorder with fracture properties. Compact tension specimens were machined from two donor femoral pairs and allocated to four treatment groups: 0 (unirradiated control), 10, 17.5, and 25 kGy. Fracture toughness specimens were monotonically loaded to failure and the critical stress intensity factor (KC ) was determined. Work-to-fracture was calculated from the load versus displacement integral up to fracture. Fatigue crack propagation specimens were cyclically loaded under constant room-temperature irrigation and fatigue crack growth rate (da/dN) and cyclic stress intensity (∆K) were calculated. Fracture toughness, work-to-fracture, and fatigue crack propagation resistance decreased 18%, 33%, and 15-fold from 0 to 25 kGy, respectively (p < 0.05). Radiation dose was more predictive of fracture properties than collagen disorder. These findings support that quasi-static and fatigue fracture properties of cortical bone are radiation dose-dependent within this dose range. The structural alterations arising from irradiation that cause these losses in fracture resistance remain to be elucidated.

Biocomponentes à base de hidroxiapatita: Influência da esterilização na resistência mecânica

Objetivo O objetivo deste estudo foi avaliar a influência da esterilização na resistência mecânica à compressão e flexão de biocomponentes à base de hidroxiapatita obtida a partir de osso bovino liofilizado e sua associação com quitosana.

Métodos O osso bovino liofilizado foi processado em partículas de 100 μm e misturado à quitosana em proporção de 50% de seu peso. A mistura foi acondicionada em moldes metálicos para preparo dos espécimes e esterilizada a 127°C em autoclave para posterior experimentação. Os espécimes foram submetidos a ensaios de compressão e flexão seguindo a norma 5833 da International Organization for Standardization (ISO); os espécimes eram blocos cilíndricos de 6 × 12 mm (para ensaios de compressão) e placas de 75 × 10 × 3,3 mm (para ensaios de flexão). As amostras foram divididas em quatro grupos de 20 espécimes cada, sendo 10 para ensaios de compressão e 10 para ensaios de flexão. Três grupos foram esterilizados (por autoclavagem, raios gama e óxido de etileno), enquanto o quarto grupo (controle) não foi. Os testes mecânicos obtidos nos diferentes processos de esterilização foram comparados por análise de variância (ANOVA, p < 0,05) seguido pelo teste de comparação múltipla de médias de Tukey, com intervalo de confiança de 95%.

Resultados Os espécimes apresentaram resistências médias à compressão de 10,25 MPa para o grupo de controle e 3,67 MPa, 9,65 MPa e 9,16 MPa após esterilização com óxido de etileno, raios gama e autoclavagem, respectivamente. Os resultados do teste de flexão mostraram uma resistência média de 0,40 MPa no grupo de controle, e 0,15 MPa, 0,17 MPa e 0,30 MPa após esterilização com óxido de etileno, raios gama e autoclavagem, respectivamente. A compressão máxima observada no grupo esterilizado com óxido de etileno foi estatisticamente diferente à obtida no grupo de controle (p = 0,0002), esterilizado com raios gama (p = 0,0003) e autoclavado (p = 0,0006). A flexão máxima dos espécimes esterilizados com raios gama foi estatisticamente diferente à observada no grupo de controle (p = 0,0245). No entanto, a resistência à flexão foi baixa em todos os espécimes.

Conclusão A esterilização em autoclave não foi associada a diferenças estatisticamente significativas nos testes de compressão ou flexão. Assim, a autoclave foi a melhor opção de esterilização para os biocomponentes à base de hidroxiapatita neste estudo.

Effect of High Hydrostatic Pressure on Human Trabecular Bone Regarding Cell Death and Matrix Integrity

The reconstruction of critical size bone defects is still clinically challenging. Even though the transplantation of autologous bone is used as gold standard, this therapy is accompanied by donor site morbidities as well as tissue limitations. The alternatively used allografts, which are devitalized due to thermal, chemical or physical processing, often lose their matrix integrity and have diminished biomechanical properties. High Hydrostatic Pressure (HHP) may represent a gentle alternative to already existing methods since HHP treated human osteoblasts undergo cell death and HHP treated bone cylinders maintain their mechanical properties. The aim of this study was to determine the biological effects caused by HHP treatment regarding protein/matrix integrity and type of cell death in trabecular bone cylinders. Therefore, different pressure protocols (250 and 300 MPa for 10, 20 and 30 min) and end point analysis such as quantification of DNA-fragmentation, gene expression, SDS-PAGE, FESEM analysis and histological staining were performed. While both protein and matrix integrity was preserved, molecular biological methods showed an apoptotic differentiation of cell death for lower pressures and shorter applications (250 MPa for 10 and 20 min) and necrotic differentiation for higher pressures and longer applications (300 MPa for 30 min). This study serves as a basis for further investigation as it shows that HHP successfully devitalizes trabecular bone cylinders.

Mechanical Characterization of Human Trabecular and Formed Granulate Bone Cylinders Processed by High Hydrostatic Pressure

One main disadvantage of commercially available allogenic bone substitute materials is the altered mechanical behavior due to applied material processing, including sterilization methods like thermal processing or gamma irradiation. The use of high hydrostatic pressure (HHP) might be a gentle alternative to avoid mechanical alteration. Therefore, we compressed ground trabecular human bone to granules and, afterwards, treated them with 250 and 300 MPa for 20 and 30 min respectively. We characterized the formed bone granule cylinders (BGC) with respect to their biomechanical properties by evaluating stiffness and stress at 15% strain. Furthermore, the stiffness and yield strength of HHP-treated and native human trabecular bone cylinders (TBC) as control were evaluated. The mechanical properties of native vs. HHP-treated TBCs as well as HHP-treated vs. untreated BGCs did not differ, independent of the applied HHP magnitude and duration. Our study suggests HHP treatment as a suitable alternative to current processing techniques for allogenic bone substitutes since no negative effects on mechanical properties occurred.

Tantalum: the next biomaterial in spine surgery?

Tantalum is a porous metal, whose elastic modulus, high frictional properties and biocompatibility make it an ideal construct to facilitate adequate bony fusion in spine surgery. Since 2015, the published literature on clinical outcomes of tantalum in spine surgery has more than doubled. A review of the literature was performed on the PubMed (MEDLINE) database on January 27, 2019, for papers pertinent to the use of tantalum metal in spine surgery. Thirteen studies were included in this review. For cervical spine, we found increased fusion rates in autograft alone compared to tantalum standalone (92.8% vs. 89.0%, P=0.001) and tantalum cages plus autograft (92.8% vs. 64.8%, P<0.0001). Complication rates in cervical fusion were lower in patients treated with tantalum standalone versus those treated with autograft (7.4% vs. 13.7%, P<0.0001), and autograft and anterior plate (7.4% vs. 33%, P=0.001). Autograft patients had higher rates of revision surgery compared to tantalum standalone (12.8% vs. 2.8%, P<0.0001) and tantalum ring with autograft (12.8% vs. 7.7%, P<0.001). For lumbar spine, we found autograft had lower fusion rate compared to tantalum standalone (80.0% vs. 93.4%, P<0.0001). Use of tantalum metal in spine fusion surgery shows promising results in fusion, complication and revision rates, and clinical outcomes compared to autograft. Although, fusion rates in short-term studies evaluating tantalum in the cervical spine are conflicting, long-term series beyond 2 years show excellent results. This early finding may be related difficulties in radiographic evaluation of fusion in the setting of tantalum cage use. Further studies are needed to further delineate the timing of fusion with the implementation of tantalum in the cervical and lumbar spine.

Radioprotection and cross-linking of allograft bone in the presence of vitamin E

Bone allografts are the preferred method for bone augmentation in over 500,000 orthopedic surgical procedures in the US. Sterilization by ionizing radiation is the most effective method of minimizing the bioburden of bone allografts; however, radiation causes chain scission of collagen, resulting in the reduction of the allografts' mechanical strength. In this study, we doped bone allografts with vitamin E as radioprotectant using a novel two-step process to protect the collagen architecture against radiation damage and to preserve the mechanical strength of the construct. In addition, combining the radioprotectant with a cross-linking agent further minimized collagen degradation and further preserved the mechanical strength of the allografts. Both vitamin E and combined vitamin E/genipin-treated allograft were less cytotoxic to both osteoblasts and osteoclasts when compared to irradiated-only allografts. Host bone-allograft unionization was faster in a rat calvaria defect model with vitamin E-treated and combined vitamin E and genipin-treated allograft when compare to irradiated-only allografts. This method can enable the efficient and uniform radioprotective treatment of bone allograft of desired shapes for sterilization with improved mechanical strength and biointegration.

Dual functional approaches for osteogenesis coupled angiogenesis in bone tissue engineering

Bone fracture healing is a multistep and overlapping process of inflammation, angiogenesis and osteogenesis. It is initiated by inflammation, causing the release of various cytokines and growth factors. It leads to the recruitment of stem cells and formation of vasculature resulting in the functional bone formation. This combined phenomenon is used by bone tissue engineers from past few years to address the problem of vasculature and osteogenic differentiation during bone regeneration. In this review, we have discussed all major studies reporting the dual functioning approach to promote osteogenesis coupled angiogenesis using various scaffolds. These scaffolds are broadly classified into four types based on the nature of their structural and functional components. The functionality of the scaffold is either due to the structural components or the loaded cargo which conducts or induces the coupled functionality. Dual delivery system for osteoinductive and angioinductive factors ensures the co-delivery of two different types of molecules to induce osteogenesis and angiogenesis. Single delivery scaffold for angioinductive and osteoinductive molecule releases single type of molecules which could induce both angiogenesis and osteogenesis. Osteoconductive scaffold consisted of bone constituents releases angioinductive factors. Osteoconductive and angioconductive scaffold composed of components which provide the native substrate features for osteogenesis and angiogenesis. This review article also discusses the studies highlighting the synergism of physico-chemical stimuli as dual functioning feature to enhance angiogenesis and osteogenesis simultaneously. In addition, this article covers one of the least discussed area of the bone regeneration i.e. 'cartilage formation as a median between angiogenesis and osteogenesis'.

A Decellularized Porcine Xenograft-Derived Bone Scaffold for Clinical Use as a Bone Graft Substitute: A Critical Evaluation of Processing and Structure

BACKGROUND

Bone grafts are used in approximately one half of all musculoskeletal surgeries. Autograft bone is the historic gold standard but is limited in supply and its harvest imparts significant morbidity to the patient. Alternative sources of bone graft include allografts, synthetics and, less commonly, xenografts which are taken from animal species. Xenografts are available in unlimited supply from healthy animal donors with controlled biology, avoiding the risk of human disease transmission, and may satisfy current demand for bone graft products.

METHODS

In the current study, cancellous bone was harvested from porcine femurs and subjected to a novel decellularization protocol to derive a bone scaffold.

RESULTS

The scaffold was devoid of donor cellular material on histology and DNA sampling (p < 0.01). Microarchitectural properties important for osteoconductive potential were preserved after decellularization as shown by high resolution imaging modalities. Proteomics data demonstrated similar profiles when comparing the porcine bone scaffold against commercially available human demineralized bone matrix approved for clinical use.

CONCLUSION

We are unaware of any porcine-derived bone graft products currently used in orthopaedic surgery practice. Results from the current study suggest that porcine-derived bone scaffolds warrant further consideration to serve as a potential bone graft substitute.

"Proprietary Processed" Allografts: Clinical Outcomes and Biomechanical Properties in Anterior Cruciate Ligament Reconstruction

BACKGROUND

The processing of allograft tissues in anterior cruciate ligament (ACL) reconstruction continues to be controversial. While high-dose irradiation of grafts has received scrutiny for high failure rates, lower dose irradiation and "proprietary-based" nonirradiated sterilization techniques have become increasingly popular, with little in the literature to evaluate their outcomes. Recent studies have suggested that the specifics of allograft processing techniques may be a risk factor for higher failure rates.

PURPOSE

To assess these proprietary processes and their clinical outcomes and biomechanical properties.

STUDY DESIGN

Systematic review.

METHODS

A systematic review was performed using searches of PubMed, EMBASE, Google Scholar, and Cochrane databases. English-language studies were identified with the following search terms: "allograft ACL reconstruction" (title/abstract), "novel allograft processing" (title/abstract), "allograft anterior cruciate ligament" (title/abstract), "anterior cruciate ligament allograft processing" (title/abstract), or "biomechanical properties anterior cruciate ligament allograft" (title/abstract). Duplicate studies, studies not providing the allograft processing technique, and those not containing the outcomes of interest were excluded. Outcomes of interest included outcome scores, complication and failure rates, and biomechanical properties of the processed allografts.

RESULTS

Twenty-four studies (13 clinical, 11 biomechanical) met inclusion criteria for review. No demonstrable difference in patient-reported outcomes was appreciated between the processing techniques, with the exception of the Tutoplast process. The clinical failure rate of the Tutoplast process was unacceptably high (45% at 6 years), but no other difference was found between other processing techniques (BioCleanse: 5.4%; AlloTrue: 5.7%; MTF: 6.7%). Several studies did show an increased failure rate, but these studies either combined processing techniques or failed to delineate enough detail to allow a specific comparison for this study. The biomechanical studies showed overall maintenance of satisfactory biomechanical properties throughout multiple testing modes with normalization to the percentage of control specimens.

CONCLUSION

A comparison of proprietary allograft processing techniques is difficult because of the variability and lack of specificity of reporting in the current literature. Among the available literature, except for the Tutoplast process, no notable differences were found in the clinical outcomes or biomechanical properties. Future study with a longer follow-up is necessary to determine the role and limitations of these grafts in the clinical setting.

Elastic modulus in the selection of interbody implants

BACKGROUND

The modulus of elasticity of an assortment of materials used in spinal surgery, as well as cortical and cancellous bones, is determined by direct measurements and plotting of the appropriate curves. When utilized in spine surgery, the stiffness of a surgical implant can affect its material characteristics. The modulus of elasticity, or Young's modulus, measures the stiffness of a material by calculating the slope of the material's stress-strain curve. While many papers and presentations refer to the modulus of elasticity as a reason for the choice of a particular spinal implant, no peer-reviewed surgical journal article has previously been published where the Young's modulus values of interbody implants have been measured.

METHODS

Materials were tested under pure compression at the rate of 2 mm/min. A maximum of 45 kilonewtons (kN) compressive force was applied. Stress-strain characteristics under compressive force were plotted and this plot was used to calculate the elastic modulus.

RESULTS

The elastic modulus calculated for metals was more than 50 Gigapascals (GPa) and had significantly higher modulus values compared to poly-ether-ether-ketone (PEEK) materials and allograft bone.

CONCLUSIONS

The data generated in this paper may facilitate surgeons to make informed decisions on their choices of interbody implants with specific attention to the stiffness of the implant chosen.

Dual growth factor delivery from biofunctionalized allografts: Sequential VEGF and BMP-2 release to stimulate allograft remodeling

Autografts have been shown to stimulate osteogenesis, osteoclastogenesis, and angiogenesis, and subsequent rapid graft incorporation. Large structural allografts, however, suffer from limited new bone formation and remodeling, both of which are directly associated with clinical failure due to non-unions, late graft fractures, and infections, making it a priority to improve large structural allograft healing. We have previously shown the osteogenic ability of a polymer-coated allograft that delivers bone morphogenetic protein-2 both in vitro and in vivo through both burst release and sustained release kinetics. In this study, we have demonstrated largely sequential delivery of bone morphogenetic protein-2 and vascular endothelial growth factor from the same coated allograft. Release data showed that loading both growth factors onto a polymeric coating with two different techniques resulted in short-term (95% release within 2 weeks) and long-term (95% release within 5 weeks) delivery kinetics. We have also demonstrated how released VEGF, traditionally associated with angiogenesis, can also provide a stimulus for allograft remodeling via resorption. Bone marrow derived mononuclear cells were co-cultured with VEGF released from the coated allograft and showed a statistically significant (p < 0.05) and dose dependent increase in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclasts. Functionality of these osteoclasts was assessed quantitatively and qualitatively by evaluating resorption pit area from both osteo-assay plates and harvested bone. Data indicated a statistically significant higher resorption area from the cells exposed to VEGF released from the allografts over controls (p < 0.05). These results indicate that by using different loading protocols temporal control can be achieved when delivering multiple growth factors from a polymer-coated allograft. Further, released VEGF can also stimulate osteoclastogenesis that may enhance allograft incorporation, and thus mitigate long-term clinical complications. © 2017 Orthopedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1086-1095, 2017.

Disinfection of human musculoskeletal allografts in tissue banking: a systematic review

Musculoskeletal allografts are typically disinfected using antibiotics, irradiation or chemical methods but protocols vary significantly between tissue banks. It is likely that different disinfection protocols will not have the same level of microorganism kill; they may also have varying effects on the structural integrity of the tissue, which could lead to significant differences in terms of clinical outcome in recipients. Ideally, a disinfection protocol should achieve the greatest bioburden reduction with the lowest possible impact on tissue integrity. A systematic review of three databases found 68 laboratory and clinical studies that analyzed the microbial bioburden or contamination rates of musculoskeletal allografts. The use of peracetic acid–ethanol or ionizing radiation was found to be most effective for disinfection of tissues. The use of irradiation is the most frequently published method for the terminal sterilization of musculoskeletal allografts; it is widely used and its efficacy is well documented in the literature. However, effective disinfection results were still observed using the BioCleanse™ Tissue Sterilization process, pulsatile lavage with antibiotics, ethylene oxide, and chlorhexidine. The variety of effective methods to reduce contamination rate or bioburden, in conjunction with limited high quality evidence provides little support for the recommendation of a single bioburden reduction method.

Safety of nanosuspensions in drug delivery

Nanosuspension technology is currently undergoing dramatic expansion in pharmaceutical science research and development. However, most of the research efforts generally focus on formulation and potential beneficial description, while the research into potential toxicological effects and implications (i.e., in vivo safety and health effects) is lacking. This review identifies some of the key factors for studying nanosuspension safety and the potential undesired effects related to nanosuspension exposure. The key factors for discussion herein include particle characterization, preparation approach, composition, and excipients of the formulation and sterilization methods. A few comments on the primary and required safety aspects of each administration route are also reviewed.

Allograft tissue irradiation and failure rate after anterior cruciate ligament reconstruction: A systematic review

AIM: To evaluate whether anterior cruciate ligament (ACL) allograft irradiation is effective for sterility without compromising graft integrity and increasing failure rate.

METHODS: A literature search was conducted using PubMed, Cochrane, and Google. The following search terms were used: “Gamma irradiation AND anterior cruciate ligament AND allograft” with a return of 30 items. Filters used included: English language, years 1990-2015. There were 6 hits that were not reviewed, as there were only abstracts available. Another 5 hits were discarded, as they did not pertain to the topic of interest. There were 9 more articles that were excluded: Three studies were performed on animals and 6 studies were meta-analyses. Therefore, a total of 10 articles were applicable to review.

RESULTS: There is a delicate dosing crossover where gamma irradiation is both effective for sterility without catastrophically compromising the structural integrity of the graft. Of note, low dose irradiation is considered less than 2.0 Mrad, moderate dose is between 2.1-2.4 Mrad, and high dose is greater than or equal to 2.5 Mrad. Based upon the results of the literature search, the optimal threshold for sterilization was found to be sterilization at less than 2.2 Mrad of gamma irradiation with the important caveat of being performed at low temperatures. The graft selection process also must include thorough donor screening and testing as well as harvesting the tissue in a sterile fashion. Utilization of higher dose (≥ 2.5 Mrad) of irradiation causes greater allograft tissue laxity that results in greater graft failure rate clinically in patients after ACL reconstruction.

CONCLUSION: Allograft ACL graft gamma irradiated with less than 2.2 Mrad appears to be a reasonable alternative to autograft for patients above 25 years of age.

Repair of a Critical Porcine Tibial Defect by Means of Allograft Revitalization

BACKGROUND

The authors previously described the generation of vascularized bone in a pig model, using a hemimandibular allograft scaffold, adipose-derived stem cells, recombinant human bone morphogenetic protein-2, and periosteum. This study tests the hypothesis that this "allograft revitalization" technique is as effective as vascularized autograft for repairing critical bony defects.

METHODS

Three groups of pigs had 3-cm defects created in their bilateral tibial diaphyses for repair using rigid fixation and one of three modalities. Negative control tibias were repaired with allograft tibia alone. To simulate repair using vascularized autograft, the osteotomized bone in positive control animals was left in situ, with the posterior periosteum intact. Experimental animals' defects were repaired with allograft tibia packed with autologous adipose-derived stem cells and recombinant human bone morphogenetic protein-2, with native periosteum intact. After 8 weeks, unilateral midgraft osteotomies were performed to assess graft healing potential. Serial radiographs and terminal micro-computed tomography and histology enabled evaluation of healing.

RESULTS

At week 7 after ostectomy, no negative control tibias had healed (zero of six) whereas most positive control (five of six) and all experimental tibias (six of six) had healed. Unilateral midgraft osteotomies were performed at 8 weeks to assess graft ability to heal. As expected, no negative control tibias (three of three) had radiographic union 7 weeks later. However, all positive control (two of two; p = 0.05) and experimental (three of three; p = 0.01) tibias had healed their repeated osteotomies by this time.

CONCLUSION

Similar to vascularized autograft, revitalized allograft successfully repaired a critical tibial defect, including after refracture, suggesting that this technique may be an alternative to osseous free flaps.

Revision Risk After Allograft Anterior Cruciate Ligament Reconstruction: Association With Graft Processing Techniques, Patient Characteristics, and Graft Type

BACKGROUND

Allograft tissue is a common graft choice for anterior cruciate ligament reconstruction (ACLR). Allograft sterilization methods vary widely across numerous commercial tissue vendors. Multiple studies, despite being limited in sample size, have suggested a higher rate of clinical failure associated with the use of allograft tissue in ACLR when compared with autograft.

PURPOSE

To examine the association of graft processing techniques, patient characteristics, and graft type with risk of revision surgery after allograft ACLR.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A retrospective cohort study was conducted that used an integrated United States health care system's ACLR registry to identify primary unilateral cases in which allografts were used. Aseptic revision was the endpoint of the study. Allograft type, processing methods (irradiation dose, AlloWash, AlloTrue, BioCleanse), and graft donor age were assessed as potential risk factors for revision, with adjustment for patient age, sex, and body mass index (BMI) by use of survival analysis. Hazard ratios (HR) and 95% confidence intervals (CIs) were calculated.

RESULTS

A total of 5968 primary ACLR cases with allograft were included in the study, of which 3688 (61.8%) were male patients. The median age of the cohort at the time of surgery was 34.1 years (interquartile range, 24.1-42.9 years). The mean time to follow-up (±SD) was 2.1 ± 1.5 years. There were 3751 (62.9%) allograft ACLRs using soft tissue, 1188 (19.9%) with Achilles tendon, and 1029 (17.2%) with bone-patellar tendon-bone (BPTB). Graft processing groups included BioCleanse (n = 367), AlloTrue or AlloWash (n = 2278), irradiation greater than 1.8 Mrad (n = 1146), irradiation up to 1.8 Mrad (n = 3637), and no irradiation (n = 1185). There were 156 (2.6%) aseptic revisions. After adjustment for patient age, sex, and BMI, the use of BioCleanse (HR = 2.45; 95% CI, 1.36-4.40) and irradiation greater than 1.8 Mrad (HR = 1.64; 95% CI, 1.08-2.49) were associated with a higher risk of revision when compared with all other methods of processing. BPTB allografts were at higher risk of revision (HR = 1.79; 95% CI, 1.20-2.66) when compared with soft tissue allografts. Conversely, with every 5-year increase in age, the risk of revision was 0.67 (95% CI, 0.61-0.73) times lower. Male patients were found to be at higher risk of revision when compared with females (HR = 1.47; 95% CI, 1.04-2.07). The use of AlloWash or AlloTrue processing, patient BMI, and graft donor age did not affect revision rate significantly.

CONCLUSION

In the largest known study of its kind examining outcome after primary allograft ACLR, graft irradiation greater than 1.8 Mrad, BioCleanse graft processing, younger patient age, male patients, and BPTB allograft were all associated with a higher risk of clinical failure and subsequent revision surgery.

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.

Bone tissue engineering by way of allograft revitalization: mechanistic and mechanical investigations using a porcine model

PURPOSE

"Allograft revitalization" is a process in which cadaveric bone is used to generate well-vascularized living bone. We had previously found that porcine allograft hemimandibles filled with autologous adipose-derived stem cells (ASCs) and recombinant human bone morphogenetic protein-2-soaked absorbable collagen sponge (rhBMP-2/ACS) were completely replaced by vascularized bone, provided the construct had been incubated within a periosteal envelope. The present study sought to deepen our understanding of allograft revitalization by investigating the individual contributions of ASCs and rhBMP-2 in the process and the mechanical properties of the revitalized allograft.

MATERIALS AND METHODS

Porcine allograft hemimandible constructs were implanted bilaterally into rib periosteal envelopes in 8 pigs. To examine the contributions of ASCs and rhBMP-2, the following groups were assessed: group 1, periosteum alone; group 2, periosteum+ASCs; group 3, periosteum+rhBMP-2/ACS; and group 4, periosteum+ASCs+rhBMP-2/ACS. After 8 weeks, the allograft constructs were harvested for micro-computed tomography (CT) and histologic analyses and 3-point bending to assess the strength.

RESULTS

On harvesting, the constructs receiving rhBMP-2/ACS had significantly greater bone shown by micro-CT than those receiving periosteum only (51,463 vs. 34,310 mm3; P = .031). The constructs receiving ASCs had increased bone compared to group 1 (periosteum only), although not significantly (P = .087). The combination of rhBMP-2/ACS with ASCs produced bone (50,399 mm3) equivalent to that of the constructs containing rhBMP-2/ACS only. The 3-point bending tests showed no differences between the 4 groups and a nonimplanted allograft or native mandible (P = .586), suggesting the absence of decreased strength of the allograft bone when revitalized.

CONCLUSIONS

These data have shown that rhBMP-2/ACS significantly stimulates new bone formation by way of allograft revitalization and that the revitalized allograft has equivalent mechanical strength to native bone.

Comparison of structural bone autografts and allografts in pediatric foot surgery

BACKGROUND

Autogenous bone has been the gold standard as the source for structural bone-graft material due to its osteogenic potential, nonimmunogenicity, and efficiency of incorporation. However, donor-site morbidity can lead to significant problems. Allograft bone is readily available and obviates the risks associated with bone-graft harvesting. However, its use raises concerns of disease transmission, infection, slower incorporation, and immunologic reaction. Despite these concerns, allograft use has become widespread. The few comparative studies of the 2 graft types used in spine and tumor surgery are promising. We sought to compare the speed and completeness of graft incorporation and the relative safety of autograft and allograft structural bone in pediatric foot surgery.

METHODS

A retrospective analysis was performed on 161 children who underwent foot surgery requiring 182 allografts and 63 autografts from 1982 to 1994. Follow-up ranged from 2 to 146 months (mean=51.4).

RESULTS

Graft-host union, defined as radiographic evidence of healing with a clinical lack of tenderness at graft insertion site, occurred within 12 weeks in both groups. Average time to healing in both groups was just over 7 weeks. In the allograft group, there was 1 nonunion, 3 graft displacements due to technical error requiring reoperation, and 1 partial displacement that did not require reoperation. All of these complications can be attributed to technique rather than to graft type. There were no infections or instances of disease transmission. There were no reported complications in the autograft group.

CONCLUSIONS

Small, structural bone allografts provide a safe, efficient, and cost-effective alternative to iliac crest bone autograft in pediatric foot surgery.

LEVELS OF EVIDENCE

Level III, therapeutic study, retrospective comparative study.

Lateral column lengthening osteotomies

Lateral column lengthening procedures, either an Evans-type procedure or a calcaneocuboid distraction arthrodesis, clearly have a role to play in the management of a pes planovalgus foot deformity, as is evident from clinical outcome studies. Despite an abundance of literature intricately detailing the biomechanical effects of different operative procedures on the hindfoot, there is no clear consensus as to the best procedure or procedures to perform for a flexible pes planovalgus foot deformity. There is, therefore, no single solution to this problem; the surgeon must treat each patient as an individual and choose the procedure that will work best in their hands for any given foot pathology they are presented with. The surgeon must also be aware that to improve the kinematics of a planovalgus foot deformity, one may often have to perform multiple procedures and not a lateral column lengthening in isolation.

Novel approaches to bone grafting: porosity, bone morphogenetic proteins, stem cells, and the periosteum

The disadvantages involving the use of a patient's own bone as graft material have led surgeons to search for alternative materials. In this review, several characteristics of a successful bone graft material are discussed. In addition, novel synthetic materials and natural bone graft materials are being considered. Various factors can determine the success of a bone graft substitute. For example, design considerations such as porosity, pore shape, and interconnection play significant roles in determining graft performance. The effective delivery of bone morphogenetic proteins and the ability to restore vascularization also play significant roles in determining the success of a bone graft material. Among current approaches, shorter bone morphogenetic protein sequences, more efficient delivery methods, and periosteal graft supplements have shown significant promise for use in autograft substitutes or autograft extenders.

Challenges to bone formation in spinal fusion

Spinal arthrodesis continues to expand in clinical indications and surgical practice. Despite a century of study, failure of bone formation or pseudarthrosis can occur in individual patients with debilitating clinical symptoms. Here we review biological and technical aspects of spinal fusion under active investigation, describe relevant biomechanics in health and disease, and identify the possibilities and limitations of translational animal models. The purpose of this article is to foster collaborative efforts with researchers who model bone hierarchy. The induction of heterotopic osteosynthesis requires a complex balance of biologic factors and operative technique to achieve successful fusion. Anatomical considerations of each spinal region including blood supply, osteology, and biomechanics predispose a fusion site to robust or insufficient bone formation. Careful preparation of the fusion site and appropriate selection of graft materials remains critical but is sometimes guided by conflicting evidence from the long-bone literature. Modern techniques of graft site preparation and instrumentation have evolved for every segment of the vertebral column. Despite validated biomechanical studies of modern instrumentation, a correlation with superior clinical outcomes is difficult to demonstrate. In many cases, adjuvant biologic therapies with allograft and synthetic cages have been used successfully to reproduce the enhancement of fusion rates observed with cancellous and tricortical autograft. Current areas of investigation comprise materials science, stem cell therapies, recombinant growth factors, scaffolds and biologic delivery systems, and minimally invasive surgical techniques to optimize the biologic response to intervention. Diverse animal models are required to approach the breadth of spinal pathology and novel therapeutics.

Infection not associated with use of human musculoskeletal tissue allografts

The deaths of otherwise healthy patients that are attributable to contaminated allografts have heightened concerns about the screening, processing, and use of such tissues. We present one tertiary care institution's experience with musculoskeletal allografts and determine the frequency of postoperative Clostridium infection. We used an institutional microbiology database to identify all records of culture-confirmed Clostridium infection from January 1990 through July 2006. A comprehensive musculoskeletal database was cross-referenced to include all possible allograft samples surgically collected or implanted from January 1990 through July 2004 to determine the frequency of Clostridium infection associated with use of allograft musculoskeletal tissue. Musculoskeletal allografts were implanted in 16,314 patients during the study period. After a minimum follow-up of 2 years, no patient had development of a definite Clostridium infection that was attributable to the use of musculoskeletal allograft tissue. These outcomes can be achieved with established screening and processing techniques for donor tissue.

Effect of gamma sterilisation and deep-freezing on length and strength of fascia latae

PURPOSE

To compare the length and strength of fascia latae after gamma sterilisation and different durations of deep-freezing.

METHODS

50 pieces of fresh porcine fascia latae were randomly divided into 5 groups. Group 1 acted as controls, which were not gamma irradiated and deep-frozen. In groups 2 to 4, fascia latae were incubated in phosphate buffer solution for 4 hours, and then gamma irradiated at 25 kGy. They were preserved at -70 degrees Celcius for one to 3 months, respectively. In group 5, fascia latae were preserved for 3 months, and during the whole process they were fixed on a wooden board to maintain their original length. The maximum tensile strength of each fascia lata was tested at a displacement rate of 1 cm per minute until failure.

RESULTS

The maximum tensile strength was not significantly different among groups 1 to 4, but was significantly higher in group 5.

CONCLUSION

Gamma sterilisation and deep-freezing had no effect on the strength of fascia latae, but fixation on a board could increase strength.