Retroviral transmission by the transplantation of connective-tissue allografts. An experimental study

Using a developed co-culture device to evaluate the proliferation of bone marrow stem cells by stimulation with platelet-rich plasma and electromagnetic field

BACKGROUNDS

Bone marrow stem cell can differentiate to osteoblast by growth factors, pulsed low-intensity ultrasound and electric magnetic field. In the research, bone marrow stem cells were cultured; bone marrow stem cells in culture can be stimulated by platelet-rich plasma and electric field.

METHODS

The culture well of the co-cultivation device has a radius of 7.5 mm and a depth of 7 mm. It is divided into two sub-chambers separated by a 3 mm high and 1 mm wide barrier. The bone marrow stem cells were seeded at a density of 2 × 104 cells and the medium volume was 120μl. Platelet-rich plasma (PRP) or platelet-poor plasma (PPP) was added to the other sub-chamber at a volume of 10μl. The bone marrow stem cells were subjected to different electric fields (0 ~ 1 V/cm) at a frequency of 70 kHz for 60 min.

RESULTS

The highest osteogenic capacity of bone marrow stem cells was achieved by addition of PRP to electric field stimulation (0.25 V/cm) resulted in a proliferation rate of 599.78%. In electric field stimulation (0.75 V/cm) with PPP, the proliferation rate was only 10.46%.

CONCLUSIONS

Bone marrow stem cell with PRP in the co-culture device combined with electric field at 0.25 V/cm strength significantly promoted the growth of bone marrow stem cells.

Native tissue-based strategies for meniscus repair and regeneration

Meniscus injuries appear to be becoming increasingly common and pose a challenge for orthopedic surgeons. However, there is no curative approach for dealing with defects in the inner meniscus region due to its avascular nature. Numerous strategies have been applied to regenerate and repair meniscus defects and native tissue-based strategies have received much attention. Native tissue usually has good biocompatibility, excellent mechanical properties and a suitable microenvironment for cellular growth, adhesion, redifferentiation, extracellular matrix deposition and remodeling. Classically, native tissue-based strategies for meniscus repair and regeneration are divided into autogenous and heterogeneous tissue transplantation. Autogenous tissue transplantation is performed more widely than heterogeneous tissue transplantation because there is no immunological rejection and the success rates are higher. This review first discusses the native meniscus structure and function and then focuses on the use of the autogenous tissue for meniscus repair and regeneration. Finally, it summarizes the advantages and disadvantages of heterogeneous tissue transplantation. We hope that this review provides some suggestions for the future design of meniscus repair and regeneration strategies.

Superior return to sports rate after patellar tendon autograft over patellar tendon allograft in revision anterior cruciate ligament reconstruction

PURPOSE

After revision anterior cruciate ligament reconstruction (ACLR), the rate of return to the pre-injury type of sport (RTS type) is low and graft choice might be an important factor. The aim of this study was to determine whether there is a difference in outcome after revision ACLR using a patellar tendon allograft compared to an ipsilateral patellar tendon autograft. It was hypothesized that the rate of RTS type using an ipsilateral patellar tendon autograft will be superior to using patellar tendon allograft.

METHODS

The design is a retrospective cohort study. Inclusion criteria were patients who underwent revision ACLR with a minimum follow-up of 1 year after revision using a patellar allograft or ipsilateral autograft. Primary study parameter was rate of RTS type. Secondary study parameters were RTS level, subscores of the KOOS, the IKDC_subjective, the Tegner score and reasons for no RTS.

RESULTS

Eighty-two patients participated in this study (36 allografts and 46 autografts). In patients with a minimum follow-up of 1 year, rate of RTS type was 51.4% for the patellar tendon allograft and 62.8% for the patellar tendon autograft group (n.s.). In patients with a minimum follow-up rate of 2 years, rate of RTS type was 43.3 versus 75.0%, respectively (p = 0.027). No differences in secondary study parameters were found. In patients with a minimum follow-up of 1 year, rate of RTS type was significantly higher (p = 0.025) for patients without anxiety compared to patients who were anxious to perform certain movements.

CONCLUSION

After a minimum follow-up of 2 years, rate of RTS type is in favour of using an ipsilateral patellar tendon autograft when compared to using a patellar tendon allograft in patients undergoing revision ACLR; after a minimum follow-up of 1 year, no significant difference was found. In revision ACLR, the results of this study might influence graft choice in favour of autologous graft when the use of an allograft or autograft patellar tendon is considered.

LEVEL OF EVIDENCE

III.

Bone Marrow Mesenchymal Stem Cells Expressing Baculovirus-Engineered Bone Morphogenetic Protein-7 Enhance Rabbit Posterolateral Fusion

Previous studies have suggested that bone marrow-derived mesenchymal stem cells (BMDMSCs) genetically modified with baculoviral bone morphogenetic protein-2 (Bac-BMP-2) vectors could achieve successful fusion in a femur defect model or in a spinal fusion model. In this study, BMDMSCs expressing BMP-7 (Bac-BMP-7-BMDMSCs) were generated. We hypothesized that Bac-BMP-7-BMDMSCs could secrete more BMP-7 than untransduced BMDMSCs in vitro and achieve spinal posterolateral fusion in a rabbit model. Eighteen rabbits underwent posterolateral fusion at L4-5. Group I (n = 6) was implanted with collagen-β-tricalcium phosphate (TCP)-hydroxyapatite (HA), Group II (n = 6) was implanted with collagen-β-TCP-HA plus BMDMSCs, and Group III (n = 6) was implanted with collagen-β-TCP-HA plus Bac-BMP-7-BMDMSCs. In vitro production of BMP-7 was quantified with an enzyme-linked immunosorbent assay (ELISA). Spinal fusion was examined using computed tomography (CT), manual palpation, and histological analysis. ELISA demonstrated that Bac-BMP-7-BMDMSCs produced four-fold to five-fold more BMP-7 than did BMDMSCs. In the CT results, 6 fused segments were observed in Group I (50%, 6/12), 8 in Group II (67%, 8/12), and 12 in Group III (100%, 12/12). The fusion rate, determined by manual palpation, was 0% (0/6) in Group I, 0% (0/6) in Group II, and 83% (5/6) in Group III. Histology showed that Group III had more new bone and matured marrow formation. In conclusion, BMDMSCs genetically transduced with the Bac-BMP-7 vector could express more BMP-7 than untransduced BMDMSCs. These Bac-BMP-7-BMDMSCs on collagen-β-TCP-HA scaffolds were able to induce successful spinal fusion in rabbits.

Decellularized Versus Fresh-Frozen Allografts in Anterior Cruciate Ligament Reconstruction: An In Vitro Study in a Rabbit Model

BACKGROUND

The common fresh-frozen allografts that are used for anterior cruciate ligament (ACL) reconstructions behave slower during the remodeling process and produce weaker tendon-bone integrations than do autografts. Decellularization of allogenic tendons results in a clean and porous collagen scaffold with low antigenicity and high compatibility, which may be more suitable for ACL reconstructions.

HYPOTHESIS

Allograft decellularization will result in a tissue structure with suitable mechanical characteristics for ACL reconstruction, thereby promoting graft remodeling and enhancing tendon-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Decellularized allograft tissues were prepared with a pH-modified decellularization process and evaluated for their biocompatibility and biomechanical character in vitro. Eighty New Zealand White rabbits were divided into 2 groups, with 40 in each group, to receive ACL reconstruction with either fresh-frozen (common) allografts or decellularized allografts on both knees. At 2, 4, 8, and 12 weeks postoperatively, the rabbits were euthanized for biomechanical testing, micro-computed tomography analysis, and histologic analysis.

RESULTS

The pH-modified decellularized allograft tissues kept excellent biocompatibility and biomechanical character during the in vitro study. Biomechanical testing indicated that the decellularized allograft had significantly higher ultimate load (P = .02) and stiffness (P = .01) levels than the common allograft at 12 weeks, and there was no significant difference between the 2 groups at any other time point. The micro-CT evaluation determined significantly higher bone mineral density (P < .01) in the decellularized allograft group than that in the common allograft group at 12 weeks, but no difference between the 2 groups was observed at any other time point. Regarding bone volume/total volume, there was no difference between the 2 groups at any time point. Fibroblast ingrowths, vascular formation, and connective tissue formation in the tendon-bone interface were better in the decellularized group within 8 weeks. New bone formation was more common in the decellularized allograft group. The collagen birefringence was restored more quickly in the decellularized allograft group than in the common allograft group at all time points.

CONCLUSION

The use of pH-modified decellularized allografts compared with the common allografts resulted in better cellularity, vascularity, collagen matrix remolding, new bone formation around the graft, enhanced tendon-bone healing, and higher ultimate failure load and stiffness of the graft after ACL reconstruction in the rabbit model.

CLINICAL RELEVANCE

The pH-modified decellularized allograft may be a better graft option than the common fresh-frozen allograft for knee ligament reconstructions.

Periprosthetic fractures: bespoke solutions

We are currently facing an epidemic of periprosthetic fractures around the hip. They may occur either during surgery or post-operatively. Although the acetabulum may be involved, the femur is most commonly affected. We are being presented with new, difficult fracture patterns around cemented and cementless implants, and we face the challenge of an elderly population who may have grossly deficient bone and may struggle to rehabilitate after such injuries. The correct surgical management of these fractures is challenging. This article will review the current choices of implants and techniques available to deal with periprosthetic fractures of the femur.

The management of type B1 periprosthetic femoral fractures: when to fix and when to revise

The incidence of periprosthetic fractures around total hip arthroplasty is increasing as patient longevity rises and the number of patients with hip implants continues to grow. Type B1 periprosthetic femoral fractures are associated with a well-fixed stem and have traditionally been treated with internal fixation. However, there are a subset of these fractures which fare badly when internal fixation is undertaken, and revision of the femoral component to a long-stemmed implant may be more appropriate. We look at the traditional methods of fixation, and the evidence and indications for revision of these fractures.

Allografts in soft tissue reconstructive procedures: important considerations

CONTEXT

Allografts offer several important advantages over autografts in musculoskeletal reconstructive procedures, such as anterior cruciate ligament reconstruction. Despite growing widespread use of allograft tissue, serious concerns regarding safety and functionality remain. We discuss the latest knowledge of the potential benefits and risks of allograft use and offer a critical review of allograft tissue regulation, management, and sterilization to enable the surgeon to better inform athletes considering reconstructive surgery options.

EVIDENCE ACQUISITION

A review of sources published in the past 10 years is the primary basis of this research.

STUDY DESIGN

Observational analysis (cohort study).

LEVEL OF EVIDENCE

Level 3.

RESULTS

Comparable outcome data for autografts and allografts do not support universal standards for anterior cruciate ligament reconstruction, and physician recommendation and bias appear to significantly influence patient preference and satisfaction. Sterilization by gamma and electron-beam irradiation diminishes the biomechanical integrity of allograft tissue, but radioprotective agents such as collagen cross-linking and free radical scavengers appear to have potential in mitigating the deleterious effects of irradiation and preserving tissue strength and stability.

CONCLUSION

Allografts offer greater graft availability and reduced morbidity in orthopaedic reconstructive procedures, but greater expansion of their use by surgeons is challenged by the need to maintain tissue sterility and biomechanical functionality. Advances in the radioprotection of irradiated tissue may lessen concerns regarding allograft safety and structural stability.

Effects of gamma radiation sterilization and strain rate on compressive behavior of equine cortical bone

OBJECTIVES

Gamma radiation has been widely used for sterilization of bone allograft. However, sterilization by gamma radiation damages the material properties of bone which is a major clinical concern since bone allograft is used in load bearing applications. While the degree of this damage is well investigated for quasi-static and cyclic loading conditions, there does not appear any information on mechanical behavior of gamma-irradiated cortical bone at high speed loading conditions. In this study, the effects of gamma irradiation on high strain rate compressive behavior of equine cortical bone were investigated using a Split Hopkinson Pressure Bar (SHPB). Quasi-static compression testing was also performed.

METHODS

Equine cortical bone tissue from 8year old retired racehorses was divided into two groups: non-irradiated and gamma-irradiated at 30kGy. Quasi-static and high strain rate compression tests were performed at average strain rates of 0.0045/s and 725/s, respectively.

RESULTS

Agreeing with previous results on the embrittlement of cortical bone when gamma-irradiated, the quasi-static results showed that gamma-irradiation significantly decreased ultimate strength (9%), ultimate strain (27%) and toughness (41%), while not having significant effect on modulus of elasticity, yield strain and resilience. More importantly, contrary to what is typically observed in quasi-static loading, the gamma-irradiated bone under high speed loading showed significantly higher modulus of elasticity (45%), ultimate strength (24%) and toughness (26%) than those of non-irradiated bone, although the failure was at a similar strain.

SIGNIFICANCE

Under high speed loading, the mechanical properties of bone allografts were not degraded by irradiation, in contrast to the degradation measured in this and prior studies under quasi-static loading. This result calls into question the assumption that bone allograft is always degraded by gamma irradiation, regardless of loading conditions. However, it needs further investigation to be translated positively in a clinical setting.

Infectious feline herpesvirus detected in distant bone and tendon following mucosal inoculation of specific pathogen-free cats

Emerging evidence suggests that cats infected with feline herpesvirus-1 (FHV-1) may experience a brief viremic phase. The objective of this study was to determine whether natural routes of FHV-1 inoculation could result in viremic transmission of infectious virus to connective tissues (cortical bone, tendon). Three specific pathogen-free cats were experimentally inoculated with FHV-1 via a combined mucosal (oronasal, ocular) route. Cats were euthanized at the peak of clinical signs to aseptically harvest tissues (cortical bone, tendon, trachea/tongue) for co-culture with a susceptible cell line to promote spread of infectious virus. Viral infection of Crandall-Rees feline kidney cells was microscopically visualized by cytopathic effect (CPE). Additionally, co-culture DNA was extracted either at the point of CPE or 16 days of culture without evidence of CPE, to amplify FHV-1 glycoprotein B gene using real-time PCR. Infectious virus was detected in distant cortical bone (two cats, moderate to severe clinical signs) and tendon (one cat, severe clinical signs). Direct infection of mucosal (trachea, tongue) tissues also was confirmed in these two cats. In contrast, all co-cultured tissues from the third cat (mild clinical signs) were negative for FHV-1 by CPE and PCR. Results of this study demonstrated that early primary FHV-1 viremia may be distributed to distant connective tissues.

Sterilization with electron beam irradiation influences the biomechanical properties and the early remodeling of tendon allografts for reconstruction of the anterior cruciate ligament (ACL)

Although allografts for anterior cruciate ligament (ACL) replacement have shown advantages compared to autografts, their use is limited due to the risk of disease transmission and the limitations of available sterilization methods. Gamma sterilization has shown detrimental effects on graft properties at the high doses required for sufficient pathogen inactivation. In our previous in vitro study on human patellar tendon allografts, Electron beam (Ebeam) irradiation showed less detrimental effects compared to gamma sterilization (Hoburg et al. in Am J Sports Med 38(6):1134-1140, 2010). To investigate the biological healing and restoration of the mechanical properties of a 34 kGy Ebeam treated tendon allograft twenty-four sheep underwent ACL replacement with either a 34 kGy Ebeam treated allograft or a non-sterilized fresh frozen allograft. Biomechanical testing of stiffness, ultimate failure load and AP-laxity as well as histological analysis to investigate cell, vessel and myofibroblast-density were performed after 6 and 12 weeks. Native sheep ACL and hamstring tendons (HAT, each n = 9) served as controls. The results of a previous study analyzing the remodeling of fresh frozen allografts (n = 12) and autografts (Auto, n = 18) with the same study design were also included in the analysis. Statistics were performed using Mann-Whitney U test followed by Bonferroni-Holm correction. Results showed significantly decreased biomechanical properties during the early remodeling period in Ebeam treated grafts and this was accompanied with an increased remodeling activity. There was no recovery of biomechanical function from 6 to 12 weeks in this group in contrast to the results observed in fresh frozen allografts and autografts. Therefore, high dose Ebeam irradiation investigated in this paper cannot be recommended for soft tissue allograft sterilization.

Fractionation of high-dose electron beam irradiation of BPTB grafts provides significantly improved viscoelastic and structural properties compared to standard gamma irradiation

PURPOSE

Irradiation >30 kGy is required to achieve sterility against bacterial and viral pathogens in ACL allograft sterilization. However, doses >20 kGy substantially reduce the structural properties of soft-tissue grafts. Fractionation of irradiation doses is a standard procedure in oncology to reduce tissue damage but has not been applied in tissue graft sterilization.

METHODS

Forty-four human 10-mm wide bone-patellar-tendon-bone grafts were randomized into four groups of sterilization with (1) 34 kGy of ebeam (2) 34 kGy gamma (3) 34 kGy fractionated ebeam, and (4) non sterilized controls. Graft´s biomechanical properties were evaluated at time zero. Biomechanical properties were analyzed during cyclic and load-to-failure testing.

RESULTS

Fractionation of ebeam irradiation resulted in significantly higher failure loads (1,327 ± 305) than with one-time ebeam irradiation (1,024 ± 204; P = 0.008). Compared to gamma irradiation, significantly lower strain (2.9 ± 1.5 vs. 4.6 ± 2.0; P = 0.008) and smaller cyclic elongation response (0.3 ± 0.2 vs. 0.6 ± 0.4; P = 0.05), as well as higher failure loads (1,327 ± 305 vs. 827 ± 209; P = 0.001), were found. Compared to non-irradiated BPTB grafts, no significant differences were found for any of the biomechanical parameters. Non-irradiated controls had significantly lower cyclic elongation response and higher failure loads than ebeam and gamma irradiation.

CONCLUSIONS

In this study, it was found that fractionation of high-dose electron beam irradiation facilitated a significant improvement of viscoelastic and structural properties of BPTB grafts compared to ebeam and gamma irradiation alone, while maintaining levels of non-irradiated controls. Therefore, this technique might pose an important alternative to common methods for sterilization of soft-tissue allografts.

Investigation of the regenerative capacity of an acellular porcine medial meniscus for tissue engineering applications

Previously, we have described the development of an acellular porcine meniscal scaffold. The aims of this study were to determine the immunocompatibility of the scaffold and capacity for cellular attachment and infiltration to gain insight into its potential for meniscal repair and replacement. Porcine menisci were decellularized by exposing the tissue to freeze-thaw cycles, incubation in hypotonic tris buffer, 0.1% (w/v) sodium dodecyl sulfate in hypotonic buffer plus protease inhibitors, nucleases, hypertonic buffer followed by disinfection using 0.1% (v/v) peracetic, and final washing in phosphate-buffered saline. In vivo immunocompatibility was assessed after implantation of the acellular meniscal scaffold subcutaneously into galactosyltransferase knockout mice for 3 months in comparison to fresh and acellular tissue treated with α-galactosidase (negative control). The cellular infiltrates in the explants were assessed by histology and characterized using monoclonal antibodies against: CD3, CD4, CD34, F4/80, and C3c. Static culture was used to assess the potential of acellular porcine meniscal scaffold to support the attachment and infiltration of primary human dermal fibroblasts and primary porcine meniscal cells in vitro. The explants were surrounded by capsules that were more pronounced for the fresh meniscal tissue compared to the acellular tissues. Cellular infiltrates compromised mononuclear phagocytes, CD34-positive cells, and nonlabeled fibroblastic cells. T-lymphocytes were sparse in all explanted tissue types and there was no evidence of C3c deposition. The analysis revealed an absence of a specific immune response to all of the implanted tissues. Acellular porcine meniscus was shown to be capable of supporting the attachment and infiltration of primary human fibroblasts and primary porcine meniscal cells. In conclusion, acellular porcine meniscal tissue exhibits excellent immunocompatibility and potential for cellular regeneration in the longer term.

Effect of electron beam irradiation on biomechanical properties of patellar tendon allografts in anterior cruciate ligament reconstruction

BACKGROUND

Sterilization of anterior cruciate ligament (ACL) allografts is an important prerequisite to prevent disease transmission. However, mechanical tissue properties are compromised by most current sterilization procedures, so that uncompromised sterilization of allografts is difficult to achieve. Hypothesis/

PURPOSE

The aim of this study was to evaluate the effect of the novel electron beam sterilization procedure on the biomechanical properties of human patellar tendon allografts at various irradiation dosages. Electron beam sterilization may be an appropriate alternative to gamma sterilization.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-two human 10-mm wide bone-patellar tendon-bone grafts were randomized into 4 groups of sterilization with 15, 25, or 34 kGy of electron beam irradiation, respectively. The grafts' biomechanical properties were evaluated at time zero. Unsterilized grafts functioned as controls. Biomechanical properties were analyzed during cyclic and load-to-failure testing.

RESULTS

Strain and cyclic elongation response showed no significant differences between the groups. Electron beam irradiation had no significant effect on stiffness and failure load with the exception of 34 kGy, which resulted in a significant decrease in failure load (1300.6 +/- 229.2 N) compared with unsterilized grafts (1630.5 +/- 331.1 N).

CONCLUSION

This study showed that electron beam might be an appropriate alternative in sterilization of patellar tendon allografts with minimal effect on mechanical properties of tendon grafts in vitro. Future studies will have to evaluate the effect of the process on the biological properties of allografts in vitro and in vivo.

CLINICAL RELEVANCE

Terminal sterilization of patellar tendon allografts with electron beam irradiation can ensure higher safety of transplanted grafts and hence improve patient safety and acceptance.

Follow-up of collagen meniscus implant patients: clinical, radiological, and magnetic resonance imaging results at 5 years

This study investigated at medium term follow-up the clinical outcomes and any progression of knee osteoarthritis in a population of patients that underwent arthroscopic placement of a collagen meniscus implant. Thirty-four patients underwent arthroscopic placement of a collagen meniscus implant for a symptomatic deficiency of medial meniscal tissue. Follow-up evaluation included Lysholm II score and Tegner activity scores and MR arthrography of the knee at 2 and 5 years after surgery. Plain radiographs were also obtained at 5 years. Six patients were excluded. In eight cases arthroscopic second look evaluation was performed. Lysholm and Tegner activity scores at 2 and 5 years after surgery improved significantly compared to the preoperative score. These patients showed good to excellent clinical results after 5 years from a CMI placement. The chondral surfaces of the medial compartment had not degenerated further since placement of the CMI. MR signal had continued to mature between 2 and 5 years after implant, progressively decreasing signal intensity but in any case comparable to the low signal of a normal meniscus. In most of cases the CMI-new tissue complex had a slight reduction in size, compared to a normal medial meniscus, but the new tissue had no apparent negative effects.

Synthetic alginate is a carrier of OP-1 for bone induction

Bone morphogenetic proteins (BMPs) can induce bone formation in vivo when combined with appropriate carriers. Several materials, including animal collagens and synthetic polymers, have been evaluated as carriers for BMPs. We examined alginate, an approved biomaterial for human use, as a carrier for BMP-7. In a mouse model of ectopic bone formation, the following four carriers for recombinant human OP-1 (BMP-7) were tested: alginate crosslinked by divalent cations (DC alginate), alginate crosslinked by covalent bonds (CB alginate), Type I atelocollagen, and poly-D,L-lactic acid-polyethyleneglycol block copolymer (PLA-PEG). Discs of carrier materials (5-mm diameter) containing OP-1 (3-30 microg) were implanted beneath the fascia of the back muscles in six mice per group. These discs were recovered 3 weeks after implantation and subjected to radiographic and histologic studies. Ectopic bone formation occurred in a dose-dependent manner after the implantation of DC alginate, atelocollagen, and PLA-PEG, but occurred only at the highest dose implanted with CB alginate. Bone formation with DC alginate/OP-1 composites was equivalent to that with atelocollagen/OP-1 composites. Our data suggest DC alginate, a material free of animal products that is already approved by the FDA and other authorities, is a safe and potent carrier for OP-1. This carrier may also be applicable to various other situations in the orthopaedic field.

Feline leukemia virus immunity induced by whole inactivated virus vaccination

A fraction of cats exposed to feline leukemia virus (FeLV) effectively contain virus and resist persistent antigenemia/viremia. Using real-time PCR (qPCR) to quantitate circulating viral DNA levels, previously we detected persistent FeLV DNA in blood cells of non-antigenemic cats considered to have resisted FeLV challenge. In addition, previously we used RNA qPCR to quantitate circulating viral RNA levels and determined that the vast majority of viral DNA is transcriptionally active, even in the absence of antigenemia. A single comparison of all USDA-licensed commercially available FeLV vaccines using these modern sensitive methods has not been reported. To determine whether FeLV vaccination would prevent nucleic acid persistence, we assayed circulating viral DNA, RNA, antigen, infectious virus, and virus neutralizing (VN) antibody in vaccinated and unvaccinated cats challenged with infectious FeLV. We identified challenged vaccinates with undetectable antigenemia and viremia concomitant with persistent FeLV DNA and/or RNA. Moreover, these studies demonstrated that two whole inactivated virus (WIV) adjuvanted FeLV vaccines (Fort Dodge Animal Health's Fel-O-Vax Lv-K) and Schering-Plough Animal Health's FEVAXYN FeLV) provided effective protection against FeLV challenge. In nearly every recipient of these vaccines, neither viral DNA, RNA, antigen, nor infectious virus could be detected in blood after FeLV challenge. Interestingly, this effective viral containment occurred despite a weak to undetectable VN antibody response. The above findings reinforce the precept of FeLV infection as a unique model of effective retroviral immunity elicited by WIV vaccination, and as such holds valuable insights into retroviral immunoprevention and therapy.

Scaffold stiffness influences cell behavior: opportunities for skeletal tissue engineering

Skeletal defects resulting from trauma, tumors, or abnormal development frequently require surgical treatment to restore normal tissue function. To overcome the limitations associated with conventional surgical treatments, several tissue engineering approaches have been developed. In particular, the use of scaffolds enriched with stem cells appears to be a very promising strategy. A crucial issue in this approach is how to control stem cell behavior. In this respect, the effects of growth factors, scaffold surface characteristics, and external ‘active’ loading conditions on stem cell behavior have been investigated. Recently, it has become clear that the stiffness of a scaffold is a highly potent regulator of stem cell differentiation. In addition, the stiffness of a scaffold affects cell migration, which is important for the infiltration of host tissue cells. This review summarizes current knowledge on the role of the scaffold stiffness in the regulation of cell behavior. Furthermore, we discuss how this knowledge can be incorporated in scaffold design which may provide new opportunities in the context of orthopedic tissue engineering.

Allograft update: the current status of tissue regulation, procurement, processing, and sterilization

Allografts are commonly used during sports medicine surgical procedures in the United States, and their frequency of use is increasing. Based on surgeon reports, it is estimated that more than 60 000 allografts were used in knee surgeries by members of the American Orthopaedic Society for Sports Medicine in 2005. In the United States, there are governmental agencies and other regulatory bodies involved in the oversight of tissue banks. In 2005, the Food and Drug Administration finalized its requirements for current good tissue practice and has mandated new rules regarding the "manufacture" of allogenic tissue. In response to well-publicized infections associated with the implantation of allograft tissue, some tissue banks have developed methods to sterilize allograft tissue. Although many surgeons have significant concerns about the safety of allografts, the majority believe that sterilized allografts are safe but that the sterilization process negatively affects tissue biology and biomechanics. However, most know very little about the principles of sterilization and the proprietary processes currently used in tissue banking. This article will review the current status of allograft tissue regulation, procurement, processing, and sterilization in the United States.

Meniscus allograft transplantation: a current concepts review

Meniscus allotransplantation represents the biological solution for the symptomatic, meniscus-deficient patient who has not developed advanced osteoarthritis. A growing body of evidence suggests that pain relief and functional improvement may reliably be achieved at short- and medium-term follow-up, and even, in some cases, at long-term (>10 years) follow-up. Future research must address the issue of optimal timing of the procedure and whether meniscal transplantation results in demonstrable long-term benefits, especially with regard to protection of articular cartilage.

Development of a useful technique to discriminate anterior cruciate ligament cells and mesenchymal stem cells—The application of cell electrophoresis

Mesenchymal stem cells (MSCs) can differentiate into multiple nonhematopoietic cell lineages, including osteoblasts, chondrocytes, and ligament cells. The purpose of this study is to identify the difference between MSCs and anterior cruciate ligament (ACL) cells for the application of distinguishing these two cells during the process of MSCs differentiating into ACL cells. Although culture of MSCs and ACL cells have been studied extensively, it was found that these two cells could not be distinguished from their appearance, expression of surface antigens (including CD105, CD34, CD45, CD29, CD44, and CD71), alpha-smooth muscle actin, and mRNAs for type I collagen, type III collagen, and tenascin-C, based on a series of traditional methods for cell identification. Cell electrophoresis, measuring the electrophoretic mobility (EPM) of cells, was proposed to investigate the discrepancy in surface charge properties of MSCs and ACL cells. Surprisingly, the EPM value of MSCs is significantly greater than that of ACL cells (p < 0.001). Although cell electrophoresis cannot determine the specific surface protein, it can reflect the net surface charge density of cell membrane, which can be influenced by the dissociation of functional groups of peripheral membrane proteins. Therefore, it is suggested that cell electrophoresis, while simple and cheap in manipulation, can serve as a useful research tool to assist in identification of MSCs differentiating into ACL cells.

The differentiation of mesenchymal stem cells by mechanical stress or/and co-culture system

Differentiation of mesenchymal stem cells (MSCs) into anterior cruciate ligament (ACL) cells is regulated by many factors. Mechanical stress affects the healing and remodeling process of ACL after surgery in important ways. Besides, co-culture system had also showed the promise to induce MSCs toward different kinds of cells on current research. The purpose of this study was to investigate the gene expression of ACL cells' major extracellular matrix (ECM) component molecules of MSCs under three induction groups. In addition, to follow our previous study, cell electrophoresis technique and mRNA level gene expression of MSC protein were also used to analyze the differentiation of MSCs. The results reveal that specific regulatory signals which released from ACL cells appear to be responsible for supporting the selective differentiation toward ligament cells in co-culture system and mechanical stress promotes the secretion of key ligament ECM components. Therefore, the combined regulation could assist the development of healing and remolding of ACL tissue engineering. Furthermore, this study also verifies that cell electrophoresis could be used in investigation of cell differentiation. Importantly, analysis of the data suggests the feasibility of utilizing MSCs in clinical applications for repairing or regenerating ACL tissue.

Fibroblast Growth Factor-2 Augments Recombinant Human Bone Morphogenetic Protein-2-Induced Osteoinductive Activity

The osteoinductive activity induced by recombinant human BMP-2 (rhBMP-2) blunts proportionately as the recipient ages. In order to compensate for this bluntness administration of fibroblast growth factor-2 (FGF-2) has been considered. The aim of this study was to determine whether FGF-2 administration augments osteoinductive activity caused by rhBMP-2 and to evaluate the effect of aging on bone formation induced by coadministration of rhBMP-2 and FGF-2. Sixty-four Wistar strain male rats of 8-week-old (prepubertal) and 16-week-old (postpubertal) received bone defects bilaterally in the parietal bone and the defects were filled by a polylactic acid polyglycolic acid copolymer/gelatin sponge (PGS) impregnated with rhBMP-2 plus 0 ng, 25 ng, and 250 ng FGF-2 (n=10 in each). At 2 weeks after grafting, the new bone volume seemed to be larger in the rhBMP-2+FGF-2 groups than in the rhBMP-2 alone group. At 4 weeks, the new bone formation was linked to the adjacent original bone. In the prepubertal rats, all newly formed bone was similarly calcified. In the postpubertal rats, only the rhBMP-2+25 ng FGF-2 group showed this higher degree of calcification. At 2 weeks, alkaline phosphatase (ALP) activity in the rhBMP-2+25 ng FGF-2 group was significantly (p<0.05) larger than that in the rhBMP-2 group in both prepubertal and postpubertal rats. This result shows that low-dose administration of FGF-2 enhanced the degree of calcification and ALP activity in the rhBMP-2 grafting site especially in the postpubertal rats. Therefore, FGF-2 would be a candidate to compensate for the reduction of osteoinductive activity of rhBMP-2 with aging.

The indications and technique for meniscal transplant

Meniscal allograft transplantation (MAT) has moved into mainstream orthopedics. With proper patient selection, and recognition and treatment of comorbid conditions, MAT offers a solution that can at least temporarily decrease pain and increase function. This article reviews the basic science of meniscal mechanics, the pathomechanics of meniscal injury, and MAT indications and techniques. A brief description of treatment of comorbid conditions and the outcomes of MAT is also provided.

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.

The current status of treatment for large meniscal defects

Meniscal pathology causing loss of function is a common problem that requires treatment in a large number of individuals each year. A patient with a meniscal-deficient knee is doomed to the development of osteoarthritis, pain, and knee dysfunction. The amount, shape, and composition of meniscal tissue influence its function and, therefore, influence the health of the knee joint. When preservation of healthy meniscal tissue cannot be accomplished, methods for replacement or regeneration of meniscal tissue are necessary. This review article will discuss current methods of meniscal tissue replacement and regeneration and potential future modes of therapy.

Tissue-engineered collagen meniscus implants: 5- to 6-year feasibility study results

PURPOSE

In this feasibility study, a 5- to 6-year clinical follow-up evaluation was conducted on 8 patients who had undergone reconstruction of 1 injured medial meniscus with a tissue-engineered collagen meniscus implant. The hypothesis was that these patients would show significant clinical improvement over their preoperative status and would have maintained their status determined at the 2-year follow-up evaluation.

TYPE OF STUDY

Prospective longitudinal feasibility study follow-up evaluation.

METHODS

Eight patients underwent arthroscopic placement of a collagen meniscus implant by a single surgeon to reconstruct and restore the irreparably damaged medial meniscus of 1 knee. All patients returned for clinical, radiographic, magnetic resonance imaging, and arthroscopic examinations an average of 5.8 years (range, 5.5-6.3 y) after collagen meniscus implant placement.

RESULTS

Lysholm scores improved significantly (P = .045) from 75 preoperatively to 88 at most recent follow-up evaluation. Average Tegner activity scores improved significantly (P = .001) from 3 to 6. Patient self-assessment improved significantly (P = .046) from 2.4 to 1.9 (1 = normal, 4 = severely abnormal). Pain scores improved from 23 to 11 (0 = no pain, 100 = worst pain). Imaging studies confirmed that the chondral surfaces of the medial compartment had not degenerated further since the placement of the implant 5.8 years earlier. Relook arthroscopy with direct measurement of the newly generated tissue revealed 69% defect filling. Histologic assessment of tissue biopsy specimens from 3 patients showed the presence of fibrocartilage with a uniform extracellular matrix.

CONCLUSIONS

The meniscus-like tissue that developed after collagen meniscus implant placement has maintained its structure and functioned without negative effects for more than 5 years. The hypothesis was affirmed that these patients were improved significantly compared with their preoperative status and unchanged compared with 2-year evaluations.

LEVEL OF EVIDENCE

Level IV.

Re-examination of feline leukemia virus: host relationships using real-time PCR

The mechanisms responsible for effective vs. ineffective viral containment are central to immunoprevention and therapies of retroviral infections. Feline leukemia virus (FeLV) infection is unique as a naturally occurring, diametric example of effective vs. ineffective retroviral containment by the host. We developed a sensitive quantitative real-time DNA PCR assay specific for exogenous FeLV to further explore the FeLV-host relationship. By assaying p27 capsid antigen in blood and FeLV DNA in blood and tissues of successfully vaccinated, unsuccessfully vaccinated, and unvaccinated pathogen-free cats, we defined four statistically separable classes of FeLV infection, provisionally designated as abortive, regressive, latent, and progressive. These host-virus relationships were established by 8 weeks post-challenge and could be maintained for years. Real-time PCR methods offer promise in gaining deeper insight into the mechanisms of FeLV infection and immunity.

Viruses adsorbed on musculoskeletal allografts are inactivated by terminal ethylene oxide disinfection

In 1987 it was anticipated that unsterilized tissues would transmit virus diseases such as hepatitis and HIV-1 from infected donors so a freeze-drying process for musculoskeletal tissue was developed to include terminal ethylene oxide (EO) exposure for 14 h. We found no studies of EO efficacy when viruses were associated with human allografts so we studied the antiviral effect of terminal EO disinfection using all but the final freeze-drying phase of this clinical processing protocol (CPP). Specifically we looked at EO inactivation of HIV-1, a human hepatitis B surrogate and test viruses known to be highly resistant to disinfecting agents, including irradiation. Freeze-drying, ordinarily required after EO disinfection and part of the CPP, was not done. Suspensions of HIV-1, Bovine viral diarrhea, Reovirus type 3, Duck hepatitis B, Poliomyelitis and Canine parvovirus were adsorbed on glass, demineralized bone powder, and preprocessed strips of femoral cortex, iliac wedges, cancellous blocks and patellar bone-tendon-bone preparations and subjected to EO disinfection. Test viruses were inactivated at the end of 7 h of EO disinfection, providing a safety factor in the CPP of at least 100%. Because allografts can transmit viruses, terminal EO disinfection should provide safer musculoskeletal allografts than non-disinfected tissues or those irradiated with a standard irradiation dose. New spontaneously appearing viruses would probably be inactivated with this terminal EO disinfection but they and viral bioweapons will require individual validation to assure viral inactivation.

Revision of total hip arthroplasty using an anterior cortical window, extensive strut allografts, and an impaction graft: follow-up study

PURPOSE

To report the outcome of revised total hip arthroplasty procedures involving an anterior cortical window, extensive strut allografts, and an Exeter impaction graft.

METHOD

Eight patients (9 hips) with a mean age of 58 years underwent revision of total hip arthroplasty using the Exeter hip impaction graft system and strut allografts between 1995 and 1998. An extensile anterior approach was used, and an anterior cortical window was created in the femur, to remove the old implant. External strut allografts were attached by wires to provide cortical support. The mean follow-up duration was 74 months. Indications for surgery were aseptic loosening of previous implants in 8 hips and infection of one hip that had previously undergone total arthroplasty.

RESULTS

19 Dall Miles cables, 4 ordinary cerclage wires, and 8 cerclage wires tightened with the clincher knot technique were used to secure the allograft to the host bone. The strut grafts were found to be incorporated in all cases. No wires became loose. One patient developed 20 degrees of angulation at the allograft-host bone junction. Using the method of Fowler and Gie, we found that one femoral implant had subsided 2 mm within the cement mantle. Two other implants had 1 mm of subsidence at the cement bone interface, and one patient had a major subsidence of 15 mm that required revision.

CONCLUSION

Using an anterior cortical window in the femur to remove the old implant does not predispose to failure of the allograft to incorporate into the host bone.

Antiretroviral efficacy of a 98% solution of glycerol or ethylene oxide for inactivation of feline leukemia virus in bone

OBJECTIVE

To determine whether infectious retrovirus was inactivated in bones from FeLV-infected cats after ethylene oxide (ETO) sterilization or preservation in a 98% solution of glycerol in an in vitro cell culture system.

SAMPLE POPULATION

Metatarsal bones obtained from 5 FeLV-infected cats and cultured with feline fibroblast cells.

PROCEDURE

Metatarsal bones were treated with 100% ETO, a 98% solution of glycerol, or left untreated. Twenty-five flasks of feline fibroblast cells were assigned to 5 groups: negative control, positive control, ETO-treated bone, glycerol-treated bone, and untreated bone with 5 replicates/group for 4 passages. Media and cell samples were harvested from every flask at each passage to measure FeLV p27 antigen and the number of copies of provirus per 100 ng of DNA, respectively.

RESULTS

All negative control and ETO-treated group replicates were negative for FeLV p27 antigen and provirus throughout the study. All positive control group replicates were positive for FeLV p27 antigen and provirus at passages 1 to 4. Untreated bone group replicates were positive for FeLV p27 antigen at passages 3 and 4 and provirus beginning at passage 2. Glycerol-treated group replicates had delayed cell replication and were negative for FeLV p27 antigen and provirus at passages 1 to 4 and 2 to 4, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Ethylene oxide sterilization of bone from FeLV-infected cats appeared to abrogate transmission of infectious retrovirus and effectively sterilized bone allografts. Impact for Human Medicine-Additional studies to confirm effectiveness of ETO treatment of allograft tissues for prevention of pathogen transmission via transplantation are warranted.

Lyophilization does not inactivate infectious retrovirus in systemically infected bone and tendon allografts

BACKGROUND

A review of multiple transplantations of human immunodeficiency virus-infected musculoskeletal allografts found that recipients of lyophilized (freeze-dried) bone or tendon from an infected donor all tested negative for human immunodeficiency virus. The finding that 75% of the recipients of fresh-frozen bone from the same donor contracted human immunodeficiency virus has led to speculation that freeze-drying may render retroviral-infected musculoskeletal allografts noninfectious.

HYPOTHESIS

Lyophilization does not inactivate retrovirus in systemically infected bone and tendon.

STUDY DESIGN

Controlled laboratory study.

METHODS

Tendons and cortical bone segments from cats systemically infected with feline leukemia virus were used in this study. Feline embryonic fibroblast cells were cultured in the presence of fresh-frozen or freeze-dried cortical bone or tendon segments. At each passage, feline leukemia virus p27 antigen was measured in media by enzyme-linked immunosorbent assay, and feline leukemia virus (pro)viral nucleic acids were quantified by real-time quantitative polymerase chain reaction in the DNA extracted from cells.

RESULTS

Enzyme-linked immunosorbent assay results and quantitative polymerase chain reaction results demonstrated retroviral antigen and proviral DNA in all cultured cell replicates after exposure to fresh-frozen or freeze-dried bones or tendons.

CONCLUSION

Freeze-drying (lyophilization) of retroviral-infected cortical bone and tendon does not inactivate retrovirus.

CLINICAL RELEVANCE

These results conclusively demonstrate that freeze-drying should not be relied on to inactivate infectious retrovirus in systemically infected musculoskeletal allografts.

Anterior cruciate ligament injury in the skeletally immature

Although ACL injuries in truly skeletally immature patients are relatively uncommon events, they are experienced more frequently than initially reported--especially in the adolescent population. Natural history data is limited but appears to mirror the natural history in adults with this injury if return to high-risk activity is allowed. Treatment of this injury presents unique challenges because of the substantial growth that occurs through the distal femoral and proximal tibial physes. The physiologic skeletal maturity of the patient must be determined prior to deciding treatment. Techniques of reconstruction include physeal sparing, partial transphyseal, and transphyseal methods. Reconstruction is recommended for any patient with an "ACL +" knee (a complete ACL tear and concomitant meniscal injury) or one who is non-compliant with a nonoperative treatment program and develops symptoms of persistent instability. Short-term outcomes of functional return postreconstruction appear promising, but study numbers are small and follow-up times relatively brief in truly immature patients. Long-term outcome studies are still needed.

Demineralization for inactivation of infectious retrovirus in systemically infected cortical bone: in vitro and in vivo experimental studies

BACKGROUND

Clinical and experimental studies have demonstrated viral transmission through the transplantation of fresh-frozen infected bone. While sterilization methods sufficient to inactivate the human immunodeficiency virus (HIV) have been shown to markedly alter osteoconductive and osteoinductive properties of bone allografts, the ability of a process for creating demineralized bone matrix to abrogate transmission of a retrovirus has not been investigated, to our knowledge. We hypothesized that a clinically accepted demineralization procedure would alter the nucleic acids of the feline leukemia virus (FeLV, a retrovirus with a structure and replication cycle similar to those of HIV), inactivating the virus in infected bone and rendering it noninfectious.

METHODS

Bone infected with FeLV was demineralized with a method employed for creating demineralized bone matrix powder. The effects of demineralization on cellular and (pro)viral nucleic acids were examined with use of gel electrophoresis and quantitative polymerase chain reaction, respectively. To compare the infectivity of the demineralized bone matrix with that of mineralized bone particles in cell cultures and in animals in which they had been implanted, we measured FeLV p27 antigen and (pro)viral nucleic acids as well as antiviral antibodies.

RESULTS

Demineralization of FeLV-infected bone appeared to inactivate the virus by degradation and fragmentation of the DNA, rendering it noninfectious in both in vitro and in vivo test systems. In contrast, untreated mineralized FeLV-infected bone contained intact nucleic acids and readily transmitted the virus in both test systems.

CONCLUSIONS

The demineralization process inactivated infectious retrovirus in infected cortical bone, thereby preventing disease transmission.

Intact genetic material is present in commercially processed cadaver allografts used for pubovaginal slings

PURPOSE

We determined the presence, quantitated the concentration and assessed the length of DNA present in 4 commercially available human cadaver allografts.

MATERIALS AND METHODS

We evaluated 10 tissue samples from each of 4 commercial sources of human allograft (Mentor Corp., Santa Barbara, California; Musculoskeletal Transplant Foundation, Edison, New Jersey; Regeneration Technologies, Inc., Alachua, Florida; and Life Cell Corp., Woodlands, Texas) for intact DNA segments. All allograft samples underwent a standard extraction technique (proteinase K/sodium dodecyl sulfate/phenol) to isolate genetic material. Spectrophotometry evaluation was done to quantify DNA concentrations. Polymerase chain reaction was performed to amplify the retrieved DNA material. Agarose gel electrophoresis was performed to determine the size of DNA fragments.

RESULTS

Of the 49 samples tested from all 4 commercial sources of human allograft fascia 39 (97.5%) contained DNA of 400 to 2,000 bp segments. A 400 bp DNA segment was present in 9 Mentor, 10 Musculoskeletal Transplant Foundation, 10 Regeneration Technologies and 10 Life Cell samples. A 700 bp DNA segment was present in 10 Musculoskeletal Transplant Foundation, 10 Regeneration Technologies and 10 Life Cell allografts. A 2,000 bp DNA segment was present in 10 Life Cell tissues.

CONCLUSIONS

Intact genetic material was present in all 4 commercially processed human allografts. Tissue processing did not completely eliminate intact DNA segments. The size of the intact DNA and the concentration of DNA varied widely based on tissue processing methods.

Composition options for tissue-engineered bone

The logical assembly of tissue-engineered bone is ultimately directed by the clinical status of the patient. The basic elements for tissue-engineered bone should include signaling molecules, cells, and extracellular matrix. The assembly of these basic elements may need to be modified by tissue engineers to account for patient variables of age, gender, health, systemic conditions, habits, and anatomical implant. Moreover, different regions of the body will have different functional loads and vascularity. This review discusses several basic options that may be necessary to engineer bone, including spatial and temporal assembly of signaling factors, cells, and biomimetic extracellular matrices. Moreover, the importance of the health care status of the patient who may be receiving the tissue-engineered composition is emphasized.

Effect of cisplatin on bone transport osteogenesis in dogs

OBJECTIVE

To document effects of cisplatin on regenerate bone formation during the distraction and consolidation phases of bone transport osteogenesis.

ANIMALS

10 skeletally mature hounds.

PROCEDURES

Bone transport osteogenesis was performed to reconstruct a 3-cm defect in the radius of each dog. Five dogs were randomly selected to receive cisplatin (70 mg/m2, IV, q 21 d for 4 cycles), and 5 were administered saline (0.9% NaCl) solution. Bone mineral density was measured by use of dual-energy x-ray absorptiometry (DEXA) on days 24, 55, and 90 after surgery. Dogs were euthanatized 90 days after surgery. Histomorphometry was performed on nondecalcified sections of regenerate bone. Bone mineral density and histomorphometric indices of newly formed bone were compared between groups.

RESULTS

Densitometric differences in regenerate bone mineral density were not detected between groups at any time period. Cisplatin-treated dogs had decreased mineralized bone volume, decreased percentage of woven bone volume, decreased percentage of osteoblast-covered bone, increased porosity, and increased percentage of osteoblast-covered surfaces, compared with values for control dogs. Lamellar bone volume and osteoid volume did not differ significantly between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Regenerate bone will form and remodel during administration of cisplatin. Results of histomorphometric analysis suggest that bone formation and resorption may be uncoupled in cisplatin-treated regenerate bone as a result of increased osteoclast activity or delayed secondary bone formation during remodeling. These histomorphometric differences were modest in magnitude and did not result in clinically observable complications or decreased bone mineral density as measured by use of DEXA.

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.

Radiomorphometry and biomechanical assessment of recombinant human bone morphogenetic protein 2 and polymer in rabbit radius ostectomy model

The study objective was to determine the mechanical integrity and radiopacity of regenerated bone within critical-sized defects (CSDs) in radii of rabbits using recombinant human bone morphogenetic protein 2 (rhBMP-2) with a porous, biodegradable poly(D,L-lactic acid) (PDLLA) carrier (designated PLA). Twenty millimeter, unilateral radial ostectomies were created in 96 skeletally mature New Zealand white rabbits. The rabbits were randomly assigned to six treatment groups with two euthanasia periods. Treatment groups included unfilled defect (n = 8), segmental autograft (n = 8), PLA + 0 microg rhBMP-2 (n = 8), PLA + 17 microg rhBMP-2 (n = 8), PLA + 35 microg rhBMP-2 (n = 8), and PLA + 70 microg rhBMP-2 (n = 8). The radiopacity was significantly greater for the 35- and 70-microg rhBMP-2 groups at 4 weeks compared to unfilled controls, PLA only, and 17-microg rhBMP-2 groups and equivalent to the autograft. At 8 weeks all groups receiving rhBMP-2 were equivalent to the autograft and significantly greater than unfilled defects and PLA alone. Similarly, the biomechanical analysis indicated significantly greater torque at failure for the 35-microg rhBMP-2 group compared to all other groups at 4 weeks. By 8 weeks all groups receiving rhBMP-2 and autograft had significantly greater torque than unfilled controls and PLA alone. These radiomorphometric and biomechanical results indicate PLA may be a suitable carrier for rhBMP-2 used for skeletal regeneration.

Effects of a 98% solution of glycerol or sterilization with ethylene oxide on FeLV in bone allografts and effects on bone incorporation of allografts in cats

OBJECTIVES

To compare virucidal effects and bone incorporation properties of cortical bone allografts transplanted into specific-pathogen-free (SPF) cats. Allografts consisted of untreated bone from a SPF cat (negative-control group) and bone from 5 FeLV-infected cats that was subjected to sterilization with ethylene oxide (ETO), preservation with glycerol, or no treatment (positive-control group).

SAMPLE POPULATION

Bones from the aforementioned groups and twenty 8-week-old SPF cats (5 cats/group) implanted with an allograft from 1 of the aforementioned groups.

PROCEDURE

After implantation, blood samples were collected weekly to monitor FeLV p27 antigen and antibody titers. Quantification of FeLV provirus was performed on blood samples at weeks 0, 4, and 8 and donor bone samples at time of implantation. Cats were euthanatized 8 weeks after transplantation, and graft sites were evaluated.

RESULTS

All results for negative-control cats were negative. All ETO group cats had negative results for antigen and provirus in blood, whereas 1 cat had a low antibody titer. Although 3 ETO-treated allografts were positive for provirus, the DNA appeared denatured. One cat in the glycerol group had positive results for all tests in blood samples. All glycerol-preserved allografts were positive when tested for provirus. All results for positive-control group cats were positive. Differences in incorporation of bone grafts were not observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Glycerol preservation of FeLV-infected bone allografts did not eliminate transmission of retrovirus to recipients. In contrast, ETO sterilization appeared to denature DNA and prevent infection. Treatments did not affect incorporation of bone grafts in young cats.

Circumferential allograft replacement of the proximal femur. A critical analysis

The use of proximal femoral structural allografts in revision hip arthroplasty remains controversial. The current study constitutes the mean 8.8 years followup (range, 3-12.5 years) of a consecutive series of 55 proximal femoral allografts in 51 patients. In 46 patients the implant was cemented into the allograft and the distal femur, and the host proximal femur was resected at the time of reconstruction in all but seven patients. Five patients underwent revision surgery for acetabular failure, and six additional patients underwent revision surgery for failure of the proximal femoral allograft. Three patients underwent successful revision surgery and had additional proximal femoral allografts. Failure was caused by graft fracture in one patient, by deep infection in two patients, and by junctional nonunion in three patients. Junctional nonunion was seen in five patients (9%), two of whom were treated successfully with bone grafting and bone grafting and plating, respectively. Instability was observed in six patients (11%). Trochanteric nonunion was seen in 22 patients (43%) and trochanteric escape was seen in 14 patients (27%). The mean Harris hip score improved from 39 to 79 points. Resorption involving the full thickness of the allograft in at least one zone was seen in seven patients. This progressed rapidly and silently within the first 3 years but has yet to lead to the failure of any of the reconstructions. Infection was ruled out in every case. Allograft resorption was seen in seven patients and may be related to a combination of factors. It is most likely that this is an immunologic problem of slow rejection, but it is possible that the distal cement fixation led to stress shielding and resorption attributable to mechanical disuse. The possible protective role of retaining the bivalved host bone as a vascularized onlay autograft remains to be clarified. Although these results justify the continued use of structural allografts for selected patients, continued followup is warranted.

Bone formation with use of rhBMP-2 (recombinant human bone morphogenetic protein-2)

We examined the effect of rhBMP-2 (recombinant human bone morphogenetic protein-2), delivered in a porous poly(DL-lactic acid) implant, on bone formation in a critical-sized defect in the radial diaphysis in rabbits. A unilateral segmental defect, twenty millimeters long, was created in the radius in ninety-six skeletally mature New Zealand White rabbits. Forty-eight rabbits were evaluated at four weeks and forty-eight, at eight weeks. Six groups were studied at each time-period. The defect was left empty in one group (control), the defect was filled with an autogenous corticocancellous bone graft in one group, and the defect was filled with a porous poly(DL-lactic acid) implant containing zero, seventeen, thirty-five, or seventy micrograms of rhBMP-2 (one group each). Radiographs of the defects were made every two weeks. The percentage of the total area of the defect that was radiopaque was determined with use of computerized radiomorphometry, and this percentage was used as a quantitative measure of the extent of new-bone formation in the defect. There were time and dose-dependent responses to rhBMP-2 for as long as four weeks; thereafter, the effects of seventeen, thirty-five, and seventy micrograms of rhBMP-2 were independent of dose and time (p < or = 0.05). The defects that had been treated with either thirty-five or seventy micrograms of rhBMP-2 had a significantly greater (p < or = 0.05) area of radiopacity than the defects that had been treated with either zero or seventeen micrograms of rhBMP-2. No significant difference could be found between the defects treated with thirty-five or seventy micrograms of rhBMP-2 and the defects filled with an autogenous graft. Healing and bone formation were examined histologically and histomorphometrically as well. At four weeks, polarized light microscopy revealed remnants of poly(DL-lactic acid) only in the defects that had been filled with an implant containing zero micrograms of rhBMP-2. At eight weeks, regardless of the dose of rhBMP-2, poly(DL-lactic acid) was not visible on histological examination. The presence of multinucleated giant cells was the hallmark of the inflammatory response elicited by poly(DL-lactic acid). At four and eight weeks, macrophages and lymphocytes were also present. The intensity of the cellular response at four weeks suggested an inverse relationship between these cells and the dose of rhBMP-2 -- that is, there appeared to be more multinucleated giant cells in defects treated with zero micrograms of rhBMP-2 than in defects treated with seventy micrograms of rhBMP-2. At eight weeks, multinucleated giant cells were rare in the defects treated with seventeen, thirty-five, or seventy micrograms of rhBMP-2. Histomorphometric data at four and eight weeks indicated that the amount of bone formation in the defects treated with seventeen, thirty-five, or seventy micrograms of rhBMP-2 was equivalent to the amount in the defects treated with an autogenous graft and was significantly less (p < or = 0.05) in the untreated defects and the defects treated with zero micrograms of rhBMP-2 (p < or = 0.05). By eight weeks, only thirty-five and seventy micrograms of rhBMP-2 had restored cortices and marrow elements.