Comparison of Healos/bone marrow to INFUSE(rhBMP-2/ACS) with a collagen-ceramic sponge bulking agent as graft substitutes for lumbar spine fusion

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.

Enhanced osteogenic differentiation and mineralization of human dental pulp stem cells using Prunus amygdalus amara (bitter almond) incorporated nanofibrous scaffold

Polyphenol extracts derived from plants are expected to have enhanced osteoblast proliferation and differentiation ability, which has gained much attention in tissue engineering applications. Herein, for the first time, we investigate the effects of Prunus amygdalus amara (bitter almond) (BA) extract loaded on poly (ε-caprolactone) (PCL)/gelatin (Gt) nanofibrous scaffolds on the osteoblast differentiation of human dental pulp stem cells (DPSCs). In this regard, BA (0, 5, 10, and 15% wt)-loaded PCL/Gt nanofibrous scaffolds were prepared by electrospinning with fiber diameters in the range of around 237-276 nm. Morphology, composition, porosity, hydrophilicity, and mechanical properties of the scaffolds were examined by FESEM, ATR-FTIR spectroscopy, BET, contact angle, and tensile tests, respectively. It was found that the addition of BA improved the tensile strength (up to 6.1 times), Young's modulus (up to 3 times), and strain at break (up to 3.2 times) compared to the neat PCL/Gt nanofibers. Evaluations of cell attachment, spreading, and proliferation were done by FESEM observation and MTT assay. Cytocompatibility studies support the biocompatible nature of BA loaded PCL/Gt scaffolds and free BA by demonstrating cell viability of more than 100% in all groups. The results of alkaline phosphatase activity and Alizarin Red assay revealed that osteogenic activity levels of BA loaded PCL/Gt scaffolds and free BA were significantly increased compared to the control group (p < 0.05, p < 0.01, p < 0.001). QRT-PCR results demonstrated that BA loaded PCL/Gt scaffolds and free BA led to a significant increase in osteoblast differentiation of DPSCs through the upregulation of osteogenic related genes compared to the control group (p < 0.05). Based on results, incorporation of BA extract in PCL/Gt scaffolds exhibited synergistic effects on the adhesion, proliferation, and osteogenesis differentiation of hDPSCs and was therefore assumed to be a favorable scaffold for bone tissue engineering applications.

Growth Factors, Carrier Materials, and Bone Repair

This chapter provides an overview of the growth factors active in bone regeneration and healing. Both normal and impaired bone healing are discussed, with a focus on the spatiotemporal activity of the various growth factors known to be involved in the healing response. The review highlights the activities of most important growth factors impacting bone regeneration, with a particular emphasis on those being pursued for clinical translation or which have already been marketed as components of bone regenerative materials. Current approaches the use of bone grafts in clinical settings of bone repair (including bone grafts) are summarized, and carrier systems (scaffolds) for bone tissue engineering via localized growth factor delivery are reviewed. The chapter concludes with a consideration of how bone repair might be improved in the future.

Supramolecular self-assembling peptides to deliver bone morphogenetic proteins for skeletal regeneration

Recombinant human bone morphogenetic proteins (BMPs) have shown clinical success in promoting bone healing, but they are also associated with unwanted side effects. The development of improved BMP carriers that can retain BMP at the defect site and maximize its efficacy would decrease the therapeutic BMP dose and thus improve its safety profile. In this review, we discuss the advantages of using self-assembling peptides, a class of synthetic supramolecular biomaterials, to deliver recombinant BMPs. Peptide amphiphiles (PAs) are a broad class of self-assembling peptides, and the use of PAs for BMP delivery and bone regeneration has been explored extensively over the past decade. Like many self-assembling peptide systems, PAs can be designed to form nanofibrous supramolecular biomaterials in which molecules are held together by non-covalent bonds. Chemical and biological functionality can be added to PA nanofibers, through conjugation of chemical moieties or biological epitopes to PA molecules. For example, PA nanofibers have been designed to bind heparan sulfate, a natural polysaccharide that is known to bind BMPs and potentiate their signal. Alternatively, PA nanofibers have been designed to synthetically mimic the structure and function of heparan sulfate, or to directly bind BMP specifically. In small animal models, these bio-inspired PA materials have shown the capacity to promote bone regeneration using BMP at doses 10-100 times lower than established therapeutic doses. These promising results have motivated further evaluation of PAs in large animal models, where their safety and efficacy must be established before clinical translation. We conclude with a discussion on the possiblity of combining PAs with other materials used in orthopaedic surgery to maximize their utility for clinical translation.

Anterior cervical discectomy and fusion with recombinant human bone morphogenetic protein-2-adsorbed β-tricalcium phosphate granules: a preliminary report

Background

Anterior cervical discectomy and fusion (ACDF) is an alternative to conservative therapy in the treatment of cervical spondylopathy. This study evaluated the clinical outcome of ACDF with BMP-2-adsorbed β-tricalcium phosphate granules.

Methods

Thirty-two patients with cervical spondylopathy received treatment of ACDF with BMP-2-adsorbed β-tricalcium phosphate granules. The clinical outcomes were evaluated with the Japanese Orthopedic Association (JOA) scores and Neck Disability Index (NDI). Meanwhile, the cervical curvature and intervertebral heights were obtained through lateral cervical X-ray films pre- and postoperatively at each interval, and the precision of cervical fusion was assessed by three-dimensional computed tomography scan.

Results

The follow-up averaged 15.2 months (range 13–18). Average JOA scores significantly increased from a preoperative point (7.4 ± 1.2) to each interval after surgery (P < 0.05). NDI decreased from preoperative point (43.1 ± 9.0) to each interval after surgery (P < 0.05). The angles of cervical curvature and intervertebral heights were improved postoperatively and kept throughout the follow-up period. CT scan demonstrated a fusion rate of 82.9% at 6 months postoperatively and was improved to 100% at 12 months postoperatively. In all cases, no complications appeared and reported due to any lapse in surgical procedure skills throughout the follow-up period.

Conclusions

Our preliminary findings suggest that BMP-2-adsorbed β-tricalcium phosphate granules will be an effective alternative to autogenous bone grafting for cervical fusion in treating cervical spondylopathy. Our surgical procedure usingβ-tricalcium phosphate granules could improve neurological function, recover intervertebral height and cervical curvature, and could be potentially exploitable in the clinical setting.

Efficacy and safety of bone substitutes in lumbar spinal fusion: a systematic review and network meta-analysis of randomized controlled trials

PURPOSE

A variety of alternative grafts to autologous iliac crest bone (ICBG) have been developed for lumbar spondylodesis, due to frequent complications following ICBG harvest. The optimal alternative graft to ICBG, however, remains elusive till now. The purpose of this study was to compare the efficacy and safety of fusion materials in lumbar degeneration diseases and to provide a ranking spectrum of the grafts.

METHODS

Randomized controlled trials (RCTs) comparing different bone grafts in lumbar arthrodesis were eligible for inclusion. A network meta-analysis was performed for endpoints including fusion rate and incidence of adverse events.

RESULTS

Twenty-seven RCTs involving 2488 patients and 13 available interventions were included. rhBMP-2 provided the highest fusion rate, being significantly superior to that of ICBG (OR = 0.21, p < 0.001), autograft local bone (ALB) (OR = 0.18, p = 0.022), rhBMP-7 (OR = 0.15, p < 0.001), allograft (OR = 0.13, p = 0.009), and DBM + ALB (OR = 0.07, p = 0.048). The treatment efficacy of allograft could be significantly enhanced by bone marrow concentrate (BMC) supplying (OR = 0.16, p = 0.010). ICBG ranks second on the frequency of complications, which is significantly higher than that of allograft (OR = 0.14, p = 0.041) and ALB (OR = 0.14, p = 0.030). All of the other comparisons showed similar efficacy and safety profiles between groups.

CONCLUSION

Ranking spectrums of the efficacy and safety for various bone grafts were provided graphically. Though rhBMP-2 was of the highest success rate, the application should be taken with proper caution because of the widely proposed life-threatening adverse events. ALB, ALB plus synthetic ceramic materials and allograft mixed with BMC were also proved to be potentially effective alternative graft to ICBG. These slides can be retrieved under Electronic Supplementary Material.

Autologous bone marrow clot as an alternative to autograft for bone defect healing

Objectives

Long bone defects often require surgical intervention for functional restoration. The ‘gold standard’ treatment is autologous bone graft (ABG), usually from the patient’s iliac crest. However, autograft is plagued by complications including limited supply, donor site morbidity, and the need for an additional surgery. Thus, alternative therapies are being actively investigated. Autologous bone marrow (BM) is considered as a candidate due to the presence of both endogenous reparative cells and growth factors. We aimed to compare the therapeutic potentials of autologous bone marrow aspirate (BMA) and ABG, which has not previously been done.

Methods

We compared the efficacy of coagulated autologous BMA and ABG for the repair of ulnar defects in New Zealand White rabbits. Segmental defects (14 mm) were filled with autologous clotted BM or morcellized autograft, and healing was assessed four and 12 weeks postoperatively. Harvested ulnas were subjected to radiological, micro-CT, histological, and mechanical analyses.

Results

Comparable results were obtained with autologous BMA clot and ABG, except for the quantification of new bone by micro-CT. Significantly more bone was found in the ABG-treated ulnar defects than in those treated with autologous BMA clot. This is possibly due to the remnants of necrotic autograft fragments that persisted within the healing defects at week 12 post-surgery.

Conclusion

As similar treatment outcomes were achieved by the two strategies, the preferred treatment would be one that is associated with a lower risk of complications. Hence, these results demonstrate that coagulated BMA can be considered as an alternative autogenous therapy for long bone healing.

Cite this article: Z. X. H. Lim, B. Rai, T. C. Tan, A. K. Ramruttun, J. H. Hui, V. Nurcombe, S. H. Teoh, S. M. Cool. Autologous bone marrow clot as an alternative to autograft for bone defect healing. Bone Joint Res 2019;8:107–117. DOI: 10.1302/2046-3758.83.BJR-2018-0096.R1.

Injectable and compression-resistant low-viscosity polymer/ceramic composite carriers for rhBMP-2 in a rabbit model of posterolateral fusion: a pilot study

Background

The challenging biological and mechanical environment of posterolateral fusion (PLF) requires a carrier that spans the transverse processes and resists the compressive forces of the posterior musculature. The less traumatic posterolateral approach enabled by minimally invasive surgical techniques has prompted investigations into alternative rhBMP-2 carriers that are injectable, settable, and compression-resistant. In this pilot study, we investigated injectable low-viscosity (LV) polymer/composite bone grafts as compression-resistant carriers for rhBMP-2 in a single-level rabbit PLF model.

Methods

LV grafts were augmented with ceramic microparticles: (1) hydrolytically degradable bioactive glass (BG), or (2) cell-degradable 85% β-tricalcium phosphate/15% hydroxyapatite (CM). Material properties, such as pore size, viscosity, working time, and bulk modulus upon curing, were measured for each LV polymer/ceramic material. An in vivo model of posterolateral fusion in a rabbit was used to assess the grafts’ capability to encourage spinal fusion.

Results

These materials maintained a working time between 9.6 and 10.3 min, with a final bulk modulus between 1.2 and 3.1 MPa. The LV polymer/composite bone grafts released 55% of their rhBMP-2 over a 14-day period. As assessed by manual palpation in vivo, fusion was achieved in all (n = 3) animals treated with LV/BG or LV/CM carriers incorporating 430 μg rhBMP-2/ml. Images of μCT and histological sections revealed evidence of bone fusion near the transverse processes.

Conclusion

This study highlights the potential of LV grafts as injectable and compression-resistant rhBMP-2 carriers for posterolateral spinal fusion.

LIPUS promotes spinal fusion coupling proliferation of type H microvessels in bone

Low-intensity pulsed ultrasound (LIPUS) has been found to accelerate spinal fusion. Type H microvessels are found in close relation with bone development. We analyzed the role of type H vessels in rat spinal fusion model intervened by LIPUS. It was found LIPUS could significantly accelerate bone fusion rate and enlarge bone callus. Osteoblasts were specifically located on the bone meshwork of the allograft, and were surrounded by type H microvessels. LIPUS could significantly increase the quantity of osteoblasts during spine fusion, which process was coupled with elevated angiogenesis of type H microvessels. Our results suggest that LIPUS may be a noninvasive adjuvant treatment modality in spinal fusion for clinical use. The treatment is recommended for usage for at least one month.

Collagen nanofibril self-assembly on a natural polymeric material for the osteoinduction of stem cells in vitro and biocompatibility in vivo

This manuscript reports the characterization of molecularly self-assembled collagen nanofibers on a natural polymeric microporous structure and their ability to support stem cell differentiation in vitro and host tissue response in vivo.

Promoting spinal fusions by biomineralized silk fibroin films seeded with bone marrow stromal cells: An in vivo animal study

OBJECTIVES

To prepare a biomineralized nano silk fibroin film seeded with bone marrow stromal cells (BMSCs), and to evaluate its performance in spinal fusion.

METHODS

The silk fibroin film was mineralized in a modified, simulated body fluid, seeded with BMSCs, and evaluated in a rat model of posterolateral lumbar fusion, compared with pure silk fibroin, silk fibroin/bone marrow stromal cells, mineralized silk fibroin, mineralized silk fibroin/bone marrow stromal cells, iliac crest bone, and no graft. After 12 weeks, all rats were sacrificed and underwent manual palpation, micro-CT scanning, biomechanical testing, and histology.

RESULTS

The infrared spectrum, X-ray diffraction, and scanning electron microscopy demonstrated deposition of mineral layers on the silk fibroin film surface. The fusion rate, bone volume, relative strength and stiffness, and histological score of the mineralized silk fibroin/bone marrow stromal cells were slightly lower than the autograft, but without any significant difference (p > 0.05). In addition, the mineralized silk fibroin was significantly greater in most parameters than the silk fibroin/bone marrow stromal cells (p < 0.05).

CONCLUSION

The mineralized silk fibroin resembles natural bone structurally, and the cellular and mineral layers of silk fibroin are both critical to bone regeneration. The ability to promote spinal fusion is enhanced when the mineralized silk fibroin is seeded with bone marrow stromal cells.

Design of biocomposite materials for bone tissue regeneration

Several synthetic scaffolds are being developed using polymers, ceramics and their composites to overcome the limitations of auto- and allografts. Polymer-ceramic composites appear to be the most promising bone graft substitute since the natural bone itself is a composite of collagen and hydroxyapatite. Ceramics provide strength and osteoconductivity to the scaffold while polymers impart flexibility and resorbability. Natural polymers have an edge over synthetic polymers because of their biocompatibility and biological recognition property. But, very few natural polymer-ceramic composites are available as commercial products, and those few are predominantly based on type I collagen. Disadvantages of using collagen include allergic reactions and pathogen transmission. The commercial products also lack sufficient mechanical properties. This review summarizes the recent developments of biocomposite materials as bone scaffolds to overcome these drawbacks. Their characteristics, in vitro and in vivo performance are discussed with emphasis on their mechanical properties and ways to improve their performance.

Salicylic Acid-Based Polymers for Guided Bone Regeneration Using Bone Morphogenetic Protein-2

Bone morphogenetic protein-2 (BMP-2) is used clinically to promote spinal fusion, treat complex tibia fractures, and to promote bone formation in craniomaxillofacial surgery. Excessive bone formation at sites where BMP-2 has been applied is an established complication and one that could be corrected by guided tissue regeneration methods. In this study, anti-inflammatory polymers containing salicylic acid [salicylic acid-based poly(anhydride-ester), SAPAE] were electrospun with polycaprolactone (PCL) to create thin flexible matrices for use as guided bone regeneration membranes. SAPAE polymers hydrolyze to release salicylic acid, which is a nonsteroidal anti-inflammatory drug. PCL was used to enhance the mechanical integrity of the matrices. Two different SAPAE-containing membranes were produced and compared: fast-degrading (FD-SAPAE) and slow-degrading (SD-SAPAE) membranes that release salicylic acid at a faster and slower rate, respectively. Rat femur defects were treated with BMP-2 and wrapped with FD-SAPAE, SD-SAPAE, or PCL membrane or were left unwrapped. The effects of different membranes on bone formation within and outside of the femur defects were measured by histomorphometry and microcomputed tomography. Bone formation within the defect was not affected by membrane wrapping at BMP-2 doses of 12 μg or more. In contrast, the FD-SAPAE membrane significantly reduced bone formation outside the defect compared with all other treatments. The rapid release of salicylic acid from the FD-SAPAE membrane suggests that localized salicylic acid treatment during the first few days of BMP-2 treatment can limit ectopic bone formation. The data support development of SAPAE polymer membranes for guided bone regeneration applications as well as barriers to excessive bone formation.

Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers

Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration.

Initial Experience With rhBMP-2 Delivered in a Compressive Resistant Matrix for Mandibular Reconstruction in 5 Dogs

OBJECTIVE

To document cumulative initial experience and long-term follow-up of the use of rhBMP-2/CRM for reconstruction of large mandibular defects (≥5 cm) in dogs.

STUDY DESIGN

Retrospective case series.

ANIMALS

Dogs (n = 5).

METHODS

Medical records (October 1999-April 2011) of dogs that had mandibular reconstruction for defects/resections of ≥5 cm using rhBMP-2/CRM were reviewed. Signalment, preoperative assessment/rationale for mandibular reconstruction, surgical methods, postoperative assessment of the reconstruction (evaluation of occlusion), and complications were recorded. A definitive histologic diagnosis was obtained in dogs that had mandibular resection for mass removal. Long-term complications were determined. A minimum time frame of 2-year in-hospital follow-up was required for case inclusion.

RESULTS

Mandibular reconstruction was successfully performed in all dogs' defects where gaps of 5-9 cm were bridged. Surgical reconstruction rapidly restored cosmetic appearance and function. All dogs healed with new bone formation across the gap. New bone formation was present within the defects as early as 2 weeks after surgery based on palpation, and new bone formation bridging the gap was documented radiographically by 16 weeks. Minor complications occurred in all dogs in the early postoperative period, and included early firm swelling and gingival dehiscence in 1 dog; late plate exposure in 3 dogs; and exuberant/cystic bone formation in 2 dogs (related to concentration/formulation of rhBMP-2/CRM). Two dogs had minor long-term complications of late plate exposure and a non-vital canine tooth; the plates and the affected canine tooth were removed. Long-term in-hospital follow-up was 5.3 years (range, 2-12.5 years); further long-term telephone follow-up was 6.3 years (range, 2-12.5 years). All owners were pleased with the outcome and would repeat the surgery again under similar circumstances.

CONCLUSION

The efficacy and success of this mandibular reconstruction technique, using rhBMP-2/CRM with plate fixation, was demonstrated with bridging of large mandibular defects regardless of the underlying cause, and with excellent cosmetic and functional results. Complications were common, but considered minor and easily treated. The complications encountered revealed the importance of tailoring the use of BMPs and fixation methods to this specific anatomic location and indication.

Evaluation of rhBMP-2 and bone marrow derived stromal cell mediated bone regeneration using transgenic fluorescent protein reporter mice

The aim of the study is use of transgenic fluorescent protein reporter mouse models to understand the cellular processes in recombinant human bone morphogenetic protein-2 (rhBMP-2) mediated bone formation. Bilateral parietal calvarial bone defects in Col3.6Topaz transgenic fluorescent osteoblast reporter mouse were used to understand the bone formation in the presence and absence of rhBMP2 and/or Col3.6Cyan bone marrow derived stromal cells (BMSCs), using collagen-hydroxyapatite matrix (Healos) as a biomaterial. The bone regeneration was not confined to the site of BMP-2 implantation and significant bone formation was observed in the neighboring defect site. Osteogenic cellular activity with overlying alizarin complexone staining was observed in both the defects indicating host cell induced mineralization. However, implantation of BMSCs along with rhBMP-2 demonstrated a donor cell derived bone formation. The presence of rhBMP-2 did not support host cell recruitment in the presence of donor cells. This study demonstrates the potential of multiple fluorescent reporters to understand the cellular processes involved in the bone regeneration process using biomaterials, growth factors, and/or stem cells.

Complications with the use of bone morphogenetic protein 2 (BMP-2) in spine surgery

BACKGROUND CONTEXT

Recombinant human bone morphogenetic protein 2 (rhBMP-2) is a very potent osteogenic growth factor that has been used successfully in various spine fusions, obviating the need for autologous iliac crest bone graft harvest and therefore avoiding the associated morbidities.

PURPOSE

In the past few years, a tremendous increase in rhBMP-2 usage was noted, and concerns regarding costs, benefits, and safety issues were raised by many. The goal of this work was to provide a comprehensive review of the adverse events and complications associated with use of rhBMP-2.

STUDY DESIGN

Literature review.

METHODS

This is a review of the current literature on the reported adverse events, complications, and concerns associated with rhBMP-2 use.

RESULTS

This article discusses the wide spectrum of adverse outcomes related to rhBMP-2 use in the lumbar and the cervical spine; retrograde ejaculation, antibodies formation, postoperative radiculitis, postoperative nerve root injury, ectopic bone formation, vertebral osteolysis/edema, dysphagia and neck swelling, hematoma formation, interbody graft lucency, and wound healing complications are reviewed. Cost-related concerns, dosage considerations, carrier types, and theoretical carcinogenesis concerns were also presented.

CONCLUSIONS

Despite the excellent spinal fusion rates promoted by this powerful molecule, the increasingly reported adverse outcomes associated with bone morphogenetic protein usage have created real concerns. This article will provide the reader with a good understanding of the reported complications associated with rhBMP-2 use and ultimately help recognize its safety spectrum and limits for better clinical application.

Regenerating Mandibular Bone Using rhBMP-2: Part 1-Immediate Reconstruction of Segmental Mandibulectomies

OBJECTIVE

To describe a surgical technique using a regenerative approach and internal fixation for immediate reconstruction of critical size bone defects after segmental mandibulectomy in dogs.

STUDY DESIGN

Prospective case series.

ANIMALS

Dogs (n = 4) that had reconstruction after segmental mandibulectomy for treatment of malignant or benign tumors.

METHODS

Using a combination of extraoral and intraoral approaches, a locking titanium plate was contoured to match the native mandible. After segmental mandibulectomy, the plate was secured and a compression resistant matrix (CRM) infused with rhBMP-2, implanted in the defect. The implant was then covered with a soft tissue envelope followed by intraoral and extraoral closure.

RESULTS

All dogs that had mandibular reconstruction healed with intact gingival covering over the mandibular defect and had immediate return to normal function and occlusion. Mineralized tissue formation was observed clinically within 2 weeks and solid cortical bone formation within 3 months. CT findings at 3 months showed that the newly regenerated mandibular bone had ∼50% of the bone density and porosity compared to the contralateral side. No significant complications occurred.

CONCLUSION

Mandibular reconstruction using internal fixation and CRM infused with rhBMP-2 is an excellent solution for immediate reconstruction of segmental mandibulectomy defects in dogs.

Regenerating Mandibular Bone Using rhBMP--2: Part 2-Treatment of Chronic, Defect Non-Union Fractures

OBJECTIVE

To describe a surgical technique using a regenerative approach and internal fixation for reconstruction of critical size bone defect non-union mandibular fractures.

STUDY DESIGN

Case series.

ANIMALS

Dogs (n = 6) that had internal fixation of defect non-union mandibular fracture.

METHODS

In 5 dogs, the repair was staged and extraction of teeth performed during the initial procedure. After 21-98 days (mean, 27 days) pharyngotomy intubation and temporary maxillomandibular fixation were performed. Using an extraoral approach, a locking titanium miniplate was contoured and secured to the mandible. A compression resistant matrix (CRM) infused with rhBMP-2 was implanted in the defect. The implant was then covered with a soft tissue envelope followed by surgical wound closure.

RESULTS

All dogs healed with intact gingival covering over the mandibular fracture site defect and had immediate return to normal function and correct occlusion. Hard-tissue formation was observed clinically within 2 weeks and solid cortical bone formation within 3 months. CT findings in 1 dog at 3 months postoperatively demonstrated that the newly regenerated mandibular bone had 92% of the bone density and porosity compared to the contralateral side. Long-term follow-up revealed excellent outcome.

CONCLUSION

Mandibular reconstruction using internal fixation and CRM infused with rhBMP-2 is an excellent solution for the treatment of critical size defect non-union fractures in dogs.

Tissue engineering strategies in spinal arthrodesis: the clinical imperative and challenges to clinical translation

Skeletal disorders requiring the regeneration or de novo production of bone present considerable reconstructive challenges and are one of the main driving forces for the development of skeletal tissue engineering strategies. The skeletal or mesenchymal stem cell is a fundamental requirement for osteogenesis and plays a pivotal role in the design and application of these strategies. Research activity has focused on incorporating the biological role of the mesenchymal stem cell with the developing fields of material science and gene therapy in order to create a construct that is not only capable of inducing host osteoblasts to produce bone, but is also osteogenic in its own right. This review explores the clinical need for reparative approaches in spinal arthrodesis, identifying recent tissue engineering strategies employed to promote spinal fusion, and considers the ongoing challenges to successful clinical translation.

BMP2 induces osteoblast apoptosis in a maturation state and noggin-dependent manner

Large doses of bone morphogenetic protein 2 (BMP2) are used clinically to induce bone formation in challenging bone defects. However, complications after treatment include swelling, ectopic bone formation, and adjacent bone resorption. While BMP2 can be effective, it is important to characterize the mechanism of the deleterious effects to optimize its use. The aim of this study was to determine the effect of BMP2 on apoptosis in osteoblast lineage cells and to determine the role of the BMP inhibitor Noggin in this process. Human mesenchymal stem cells (MSCs), immature osteoblast-like MG63 cells, and mature normal human osteoblasts (NHOst) were treated with BMP2. A model system of increased endogenous BMP signaling was created by silencing Noggin (shNOG-MG63). Finally, the BMP pathway regulating apoptosis in NHOst was examined using BMP signaling inhibitors (5Z-7-oxozeaenol, dorsomorphin, H-8). Apoptosis was characterized by caspase-3, BAX/BCL2, p53, and DNA fragmentation. BMP2 induced apoptosis in a cell-type dependent manner. While the effect was minor in MSCs, MG63 cells had modest increases and NHOst cells had robust increases apoptosis after BMP2 treatment. Apoptosis was significantly higher in shNOG-MG63 than MG63 cells. 5Z-7-oxozeaenol and dorsomorphin eliminated the BMP2-induced increase in DNA fragmentation in NHOst, suggesting roles for TAB/TAK1 and Smad signaling. These results indicate that the apoptotic effect of BMP2 is dependent on cell maturation state, inducing apoptosis in committed osteoblasts through Smad and TAB/TAK1 signaling, and is regulated by Noggin. Dose and delivery must be optimized in therapeutic applications of BMP2 to minimize complications.

Review: development of clinically relevant scaffolds for vascularised bone tissue engineering

Clinical translation of scaffold-based bone tissue engineering (BTE) therapy still faces many challenges despite intense investigations and advancement over the years. To address these clinical barriers, it is important to analyse the current technical challenges in constructing a clinically relevant scaffold and subsequent clinical issues relating to bone repair. This review highlights the key challenges hampering widespread clinical translation of scaffold-based vascularised BTE, with a focus on the repair of large non-union defects. The main limitations of current scaffolds include the lack of sufficient vascularisation, insufficient mechanical strength as well as issues relating to the osseointegration of the bioresorbable scaffold and bone infection management. Critical insights on the current trends of scaffold technologies and future directions for advancing next-generation BTE scaffolds into the clinical realm are discussed. Considerations concerning regulatory approval and the route towards commercialisation of the scaffolds for widespread clinical utility will also be introduced.

Bone graft substitutes

Replacement of missing bone stock is a reconstructive challenge to upper extremity surgeons and decision-making with regards to available choices remains difficult. Preference is often given to autograft in the form of cancellous, cortical, or corticocancellous grafts from donor sites. However, the available volume from such donor sites is limited and fraught with potential complications. Advances in surgical management and medical research have produced a wide array of potential substances that can be used for bone graft substitute. Considerations in selecting bone grafts and substitutes include characteristic capabilities, availability, patient morbidity, immunogenicity, potential disease transmission, and cost variability.

Volumetric bone regenerative efficacy of biphasic calcium phosphate-collagen composite block loaded with rhBMP-2 in vertical bone augmentation model of a rabbit calvarium

Block-type biphasic calcium phosphate (BCP) carriers are more effective at delivering recombinant human bone morphogenetic protein-2 (rhBMP-2) in various clinical situations than are particle-type carriers, due to their potential for highly successful three-dimensional bone regeneration. The aim of this study was to confirm the bone-regenerative capabilities of three-dimensional BCP blocks with a low hydroxyapatite/β-tricalcium phosphate ratio (20/80) combined with collagen (10% wt) as an rhBMP-2 delivery system in a craniofacial vertical bone augmentation model. BCP blocks and BCP-collagen blocks (with average macropore sizes of 296 and 390 μm, respectively) with or without rhBMP-2 were fixed with osteosynthesis screws to the calvarial surface of rabbits. After 8 weeks, histologic and histomorphometric analyses were performed to evaluate the resulting new bone area, augmented area, bone density, and degree of integration. The area of new bone was significantly greater in specimens containing rhBMP-2 than in the control group (p < 0.05). Moreover, the area fractions of newly formed bone within the augmented area and a degree of integration between the regenerative bone and the calvarium were both significantly greater in the BCP-collagen/rhBMP-2 group than in the BCP/rhBMP-2 group (p < 0.05), whereas the two carrier systems exhibited similar rhBMP-2 release profiles, with sustained and linear release. The BCP and BCP/rhBMP-2 blocks exhibited excellent structural integrity, with large fragments of residual ceramic. In conclusion, the BCP-collagen composite block exhibited enhanced osteoinductive potential and could be a good candidate as a carrier of rhBMP-2 due to its characteristics of favorable volumetric stability, ease of handling, and excellent remodeling properties.

Assessment of MASTERGRAFT PUTTY as a graft extender in a rabbit posterolateral fusion model

STUDY DESIGN

Randomized, controlled study in a laboratory setting. Blinded observations/assessment of study outcomes.

OBJECTIVE

The purpose of this study was to determine the performance characteristics of MASTERGRAFT PUTTY as a bone graft extender in a rabbit posterolateral spine fusion model.

SUMMARY OF BACKGROUND DATA

The rabbit posterolateral fusion model is an established environment for testing of fusion concepts. It offers the opportunity to obtain radiographical, histological, and biomechanical data on novel fusion materials.

METHODS

Thirty-six rabbits were entered into the study with 30 used for analysis. Bilateral posterolateral lumbar intertransverse fusions were performed at L5-L6. The lateral two-thirds of the transverse processes were decorticated and covered with graft material: autograft only (2.5-3.0 cc per side), 25% MASTERGRAFT PUTTY/75% autograft (3.0 cc total per side), or 50% MASTERGRAFT PUTTY and 50% autograft (3.0 cc total per side). Animals were humanely killed at 8 weeks postsurgery.

RESULTS

The autograft group had a 63% radiographical fusion rate (5 of 8) and correlated with manual palpation results (63%). The 25% MASTERGRAFT PUTTY group had a 73% radiographical fusion rate (8 of 11) and a manual palpation fusion rate of 64%. The 50% MASTERGRAFT PUTTY group demonstrated a 91% (10 of 11) radiographical fusion rate and 73% manual palpation fusion rate. Histologically, no inflammatory reactions were evident regardless of implant. The 2 MASTERGRAFT PUTTY groups had new bone in direct apposition to the MASTERGRAFT ceramic granules.

CONCLUSION

In this commonly used rabbit posterolateral fusion model, MASTERGRAFT PUTTY in an autograft extender mode produces clinically and radiographically similar results to autograft fusion alone.

Osteoblasts exhibit a more differentiated phenotype and increased bone morphogenetic protein production on titanium alloy substrates than on poly-ether-ether-ketone

BACKGROUND CONTEXT

Multiple biomaterials are clinically available to spine surgeons for performing interbody fusion. Poly-ether-ether-ketone (PEEK) is used frequently for lumbar spine interbody fusion, but alternative materials are also used, including titanium (Ti) alloys. Previously, we showed that osteoblasts exhibit a more differentiated phenotype when grown on machined or grit-blasted titanium aluminum vanadium (Ti6Al4V) alloys with micron-scale roughened surfaces than when grown on smoother Ti6Al4V surfaces or on tissue culture polystyrene (TCPS). We hypothesized that osteoblasts cultured on rough Ti alloy substrates would present a more mature osteoblast phenotype than cells cultured on PEEK, suggesting that textured Ti6Al4V implants may provide a more osteogenic surface for interbody fusion devices.

PURPOSE

The aim of the present study was to compare osteoblast response to smooth Ti6Al4V (sTiAlV) and roughened Ti6Al4V (rTiAlV) with their response to PEEK with respect to differentiation and production of factors associated with osteogenesis.

STUDY DESIGN

This in vitro study compared the phenotype of human MG63 osteoblast-like cells cultured on PEEK, sTiAlV, or rTiAlV surfaces and their production of bone morphogenetic proteins (BMPs).

METHODS

Surface properties of PEEK, sTiAlV, and rTiAlV discs were determined. Human MG63 cells were grown on TCPS and the discs. Confluent cultures were harvested, and cell number, alkaline phosphatase-specific activity, and osteocalcin were measured as indicators of osteoblast maturation. Expression of messenger RNA (mRNA) for BMP2 and BMP4 was measured by real-time polymerase chain reaction. Levels of BMP2, BMP4, and BMP7 proteins were also measured in the conditioned media of the cell cultures.

RESULTS

Although roughness measurements for sTiAlV (S(a)=0.09±0.01), PEEK (S(a)=0.43±0.07), and rTiAlV (S(a)=1.81±0.51) varied, substrates had similar contact angles, indicating comparable wettability. Cell morphology differed depending on the surface. Cells cultured on Ti6Al4V had lower cell number and increased alkaline phosphatase specific activity, osteocalcin, BMP2, BMP4, and BMP7 levels in comparison to PEEK. In particular, roughness significantly increased the mRNA levels of BMP2 and BMP4 and secreted levels of BMP4.

CONCLUSIONS

These data demonstrate that rTiAlV substrates increase osteoblast maturation and produce an osteogenic environment that contains BMP2, BMP4, and BMP7. The results show that modifying surface structure is sufficient to create an osteogenic environment without addition of exogenous factors, which may induce better and faster bone during interbody fusion.

The efficacy of porous hydroxyapatite bone chip as an extender of local bone graft in posterior lumbar interbody fusion

OBJECTIVE

To evaluate whether a synthetic bone chip made of porous hydroxyapatite can effectively extend local decompressed bone graft in instrumented posterior lumbar interbody fusion (PLIF).

METHODS

130 patients, 165 segments, who had undergone PLIF with cages and instrumentation for single or double level due to degenerative conditions, were investigated retrospectively by independent blinded observer. According to the material of graft, patients were divided into three groups. HA group (19 patients, 25 segments): with hydroxyapatite bone chip in addition to autologous local decompressed bone, IBG group (25 patients, 28 segments): with autologous iliac crest bone graft in addition to local decompressed bone and LB group (86 patients, 112 segments): with local decompressed bone only. Radiologic and clinical outcome were compared among groups and postoperative complications, transfusion, time and cost of operation and duration of hospitalization were also investigated.

RESULTS

Radiologic fusion rate and clinical outcome were not different. Economic cost, transfusion and hospital stay were also similar. But operation time was significantly longer in IBG group than in other groups. There were no lasting complications associated with HA and LB group with contrast to five cases with persisting donor site pain in IBG group.

CONCLUSION

Porous hydroxyapatite bone chip is a useful bone graft extender in PLIF when used in conjunction with local decompressed bone.

Positive effect on bone fusion by the combination of platelet-rich plasma and a gelatin β-tricalcium phosphate sponge: a study using a posterolateral fusion model of lumbar vertebrae in rats

We developed a novel method for bone fusion by combining platelet-rich plasma (PRP) and a gelatin β-tricalcium phosphate (β-TCP) sponge. The PRP is an autologous concentration of platelets that includes several growth factors. The gelatin β-TCP sponge comprises gelatin and β-TCP, thus enabling the sustained release of growth factors and osteoconduction. To evaluate this method, we generated a posterolateral fusion model of lumbar vertebrae in rats and divided it into five groups by implanting the following materials between transverse processes of vertebrae, (1) the gelatin β-TCP sponge with PRP (PRP sponge), (2) the gelatin β-TCP sponge with platelet-poor plasma, (3) gelatin hydrogel with PRP, (4) autologous iliac bone (autograft), and (5) no material was implanted as a control. The assessment of bone fusion by a radiographic assessment, a biomechanical test, microcomputed tomography, and histological evaluations demonstrated that there were no significant differences between the PRP sponge and the autograft groups regarding the osteogenic effect. Subsequent examinations revealed that no significant differences existed between the PRP sponge and the autograft groups in either biomechanical stiffness or the bone volume over time; whereas the radiographic and histological composition underwent similar changes in the fusion process. These results indicate that the PRP sponge could, therefore, be potentially useful as an attractive and less invasive method for bone fusion.

Bone morphogenetic protein-2 and spinal arthrodesis: the basic science perspective on protein interaction with the nervous system

The use and "off-label" indications for recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal arthrodesis have been significantly expanded over the last decade. New surgical approaches and pathologies treated often place the exogenous protein near the spinal cord or peripheral nerves, yet little data exist to the potential interaction between rhBMP-2 and the nervous system. The current review was undertaken to provide a basic science perspective on the wide-ranging effects that rhBMP-2, a potent growth factor, has on the injured spinal cord and the local dorsal root ganglia (DRG). Results from the early animal studies on neural safety of rhBMP-2 were compared with the more recent in vivo work characterizing protein impact on the injured spinal cord. Potential mechanism of the rhBMP-2-induced radiculitis after lumbar arthrodesis is also discussed. The original pre-FDA approval animal study did not uncover any interaction between rhBMP-2 and the spinal cord or the nerve rootlets comprising the cauda equina. Recent in vivo work indicated, however, that in a penetrating injury model, rhBMP-2 triggers direct signaling in all spinal cord cells. In the rat, this interaction was deleterious to spontaneous recovery by exacerbating the inflammatory response to injury, increasing the glial scar, and making it more inhibitory to axonal regeneration. With respect to posterolateral lumbar arthrodesis in a noninjury model, rhBMP-2 use contributed to a transient postoperative mechanical hyperalgesia. Potential mechanism of this allodynia is through an observed inflammatory response within and around the local DRG. In summary, contrary to the original beliefs in the clinical community, rhBMP-2 does elicit a profound signaling response within the spinal cord and the peripheral ganglia. Recent preclinical studies indicate that rhBMP-2, if provided direct access to the spinal cord parenchyma or the DRG, can trigger significant inflammation and morphologic changes within these tissues that could be deleterious to neurologic recovery.

Evaluation and treatment of spinal injuries in the obese patient

Given the increasing incidence and severity of obesity in the adult population, orthopaedic surgeons are evaluating and treating more acutely injured obese patients. Management of obese patients is complicated given their body habitus and associated medical comorbidities. Although evaluation and treatment are almost the same as for nonobese patients, some special considerations are necessary to prevent errors in diagnosis and treatment of obese trauma patients. This article focuses on spine injuries in obese patients. Predisposition to spinal injury, effective evaluation and early management, principles of treatment planning, operative technical pearls, and postoperative management are discussed.

Bone grafting options for lumbar spine surgery: a review examining clinical efficacy and complications

Background

Iliac crest harvest has been considered the “gold standard” at producing successful arthrodesis of the lumbar spine but is also associated with many donor-site morbidities. Many alternatives have been used to avoid iliac crest harvest, including autologous bone from other donor sites, allogeneic bone, ceramics, and recombinant human bone morphogenetic proteins (rhBMPs). This review will highlight the properties and preparations of these graft types and their potential complications and reported clinical efficacy.

Methods

A Medline search was conducted via PubMed by use of the following terms in various combinations: lumbar fusion, freeze-dried allograft, fresh-frozen allograft, autograft, iliac crest, demineralized bone matrix, rhBMP-2, rhBMP-7, scoliosis, bone marrow aspirate, HEALOS, coralline hydroxyapatite, beta tricalcium phosphate, synthetic, ceramics, spinal fusion, PLF, PLIF, ALIF, and TLIF. Only articles written in English were assessed for appropriate material. Related articles were also assessed depending on the content of articles found in the original literature search.

Conclusions

Although iliac crest remains the gold standard, reported success with alternative approaches, especially in combination, has shown promise. Stronger evidence with limited sources of potential bias is necessary to provide a clear picture of their clinical efficacy.

Bone grafting options in children

STUDY DESIGN

Retrospective review of the literature.

OBJECTIVE

To review the current literature as well as recent trends in bone grafting techniques available for children.

SUMMARY OF BACKGROUND DATA

The currently accepted gold standard in bone grafting for adolescent idiopathic scoliosis (AIS) is autogenous iliac crest. Due to questions concerning complications such as donor site pain, other options have been explored, including various allograft sources, demineralized bone matrix, and bone morphogenetic protein.

METHODS

A review of the current medical literature was completed and additional case examples are presented.

RESULTS

A review of the literature reveals that up to 31% of patients have persistent pain at 2 years post surgery when autogenous iliac crest bone graft is harvested. Allograft supplementation of local autograft has been demonstrated in the literature to be as effective as autogenous iliac crest bone grafting in contributing to a successful posterior spinal fusion in patients with AIS. Modern demineralized bone matrix formulations have been found in both animal models as well as in a recent retrospective clinical review to contribute to a successful posterior spinal fusion in AIS. Bone morphogenetic protein has been shown to contribute to a successful posterior spinal fusion in complex pediatric spinal deformity patients. At 2 years follow-up, patients who underwent a posterior instrumented spinal fusion that was not augmented with any bone graft appear to have successful spinal fusions.

CONCLUSION

Although autogenous iliac bone graft remains the benchmark to which bone grafting materials are compared, other options including the placement of no bone graft at all provides similar fusion rates in patients with AIS.

Bone morphogenetic protein-2 and bone marrow aspirate with allograft as alternatives to autograft in instrumented revision posterolateral lumbar spinal fusion: a minimum two-year follow-up study

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

Compare the efficacy of rhBMP-2 and bone marrow aspirate with allograft (BMAA) as alternatives to autograft in instrumented revision posterolateral lumbar fusion (PLF).

SUMMARY OF BACKGROUND DATA

The use of autogenous bone graft is the current gold standard in revision PLF; however, this practice is associated with significant donor-site morbidity. Revision PLF pose the additional challenges of a less than ideal fusion environment and a limited quantity of autogenous bone graft. rhBMP-2 and BMAA have been shown to be acceptable bone graft substitutes in several primary orthopedic procedures. The role of these bone graft substitutes in instrumented revision PLF has yet to be determined.

METHODS

Sixty-two patients (125 levels) who underwent instrumented revision PLF with a minimum 2-year follow-up were included. Group 1 contained 24 patients (13 single- [group 1A] and 11 multilevel [group 1B]) who underwent instrumented revision PLF using rhBMP-2 on an absorbable collagen sponge. Group 2 included 18 patients (7 single- [group 2A] and 11 multilevel [group 2B]) with procedures using BMAA. Group 3 consisted of 20 patients (10 single- [group 3A] and 10 multilevel [group 3B]) with procedures using autograft. Demographic, surgical, and clinical data were collected from medical records. Time to solid fusion mass formation, fusion rate, complications, and clinical outcomes were evaluated. The progression of the fusion mass was evaluated by reviewing radiographs. A diagnosis of nonunion was based on exploration during an additional revision surgery or evidence of nonunion on dynamic radiographs or computerized tomography. Clinical outcomes were assessed using a visual analog scale (VAS) before surgery and at 6-week, 6-, 12-, and 24-month follow-ups.

RESULTS

Overall fusion rate was 93.5% (58/62). All single-level revision PLF achieved solid fusion. Groups 1B and 3B achieved 100% fusion, (11/11) and (10/10), respectively;whereas group 2B had a fusion rate of 63.6% (7/11). Group 1 also developed a solid fusion mass earlier than the other groups. There was a significant decrease between preoperative and 2-year postoperative VAS scores in all groups, but no significant difference among groups. Three patients in group 2 required an additional revision surgery.

CONCLUSION

rhBMP-2 may be an appropriate alternative to autogenous bone graft in both single- and multilevel revision PLF, whereas BMAA may be appropriate as a substitute in single-level revision PLF. The use of BMAA in single-level revisions may be a more cost-effective option than rhBMP-2.

The design and use of animal models for translational research in bone tissue engineering and regenerative medicine

This review provides an overview of animal models for the evaluation, comparison, and systematic optimization of tissue engineering and regenerative medicine strategies related to bone tissue. This review includes an overview of major factors that influence the rational design and selection of an animal model. A comparison is provided of the 10 mammalian species that are most commonly used in bone research, and existing guidelines and standards are discussed. This review also identifies gaps in the availability of animal models: (1) the need for assessment of the predictive value of preclinical models for relative clinical efficacy, (2) the need for models that more effectively mimic the wound healing environment and mass transport conditions in the most challenging clinical settings (e.g., bone repair involving large bone and soft tissue defects and sites of prior surgery), and (3) the need for models that allow more effective measurement and detection of cell trafficking events and ultimate cell fate during the processes of bone modeling, remodeling, and regeneration. The ongoing need for both continued innovation and refinement in animal model systems, and the need and value of more effective standardization are reinforced.

Cultured autologous bone marrow stem cells inhibit bony fusion in a rabbit model of posterolateral lumbar fusion with autologous bone graft

Mesenchymal stem cells (MSCs) have been isolated from various tissues and expanded in culture. MSCs add osteogenic potential to ceramic scaffolds when used together. A spinal fusion rabbit model was used to evaluate whether a pellet of cultured, autologous bone marrow MSCs (BMSCs) with osteogenic differentiation could increase the fusion rate when co-grafted with an autologous bone graft compared to autograft alone. Thirty rabbits were randomly assigned to two groups. Group 1 received bone autograft alone and Group 2 received bone autograft plus a pellet of cultured and differentiated BMSCs. Group 2 rabbits had a bone marrow puncture, after which the BMSC were cultured and osteoblastic differentiation was induced. BMSC cultures were obtained from 12 of 15 rabbits. The 27 rabbits underwent a bilateral, L4-L5 intertransverse fusion with an autograft and in Group 2 rabbits a pellet of differentiated BMSCs was added to the autograft. In Group 1, the fusion rate was 53% (8 of 15 rabbits) and in Group 2 the fusion rate was 0% (p<0.05). Adding differentiated BMSCs in a pellet without a scaffold not only failed to increase fusion rate, but completely inhibited bony growth.

A prospective consecutive study of instrumented posterolateral lumbar fusion using synthetic hydroxyapatite (Bongros-HA) as a bone graft extender

A prospective, single institution, clinical case-matched, radiographic study was undertaken. Thirty-two patients underwent posterior lumbar interbody fusion with cages containing laminectomized bone chips and posterolateral lumbar fusion with pedicle screws. Autogenous bone graft (3 mL) plus 3 mL of hydroxyapatite was placed in one side of a posterolateral gutter, and 6 mL of autogenous iliac bone graft was placed on the other side. Bony union, volumes of fusion mass, and bone absorption rates were postoperatively evaluated using simple radiographs and 3D-CT scans. Average postoperative Lenke scores at 3 and 6 months in the hydroxyapatite group were statistically higher than in the autograft group, but at 12 months no difference was found between the hydroxyapatite and autograft groups in terms of fusion rate. Complete fusion rates by 3D-CT were 86.7% in the hydroxyapatite group and 88.9% in the autograft group, which are not significantly different. Volumes of fusion mass and bone absorption rates at 12 months were 2.35 mL in the hydroxyapatite group and 1.31 mL in the autograft group. The mean fusion mass volume was greater in the hydroxyapatite group than in the autograft group. Lumbar posterolateral fusion using a mixture of hydroxyapatite artificial bone and autogenous bone graft showed good bony union similar to that shown with autogenous bone only. This study suggests that hydroxyapatite bone chips could be used usefully as a bone-graft extender in short-segment posterolateral spinal fusion.

Posterolateral spinal fusion in a rabbit model using a collagen-mineral composite bone graft substitute

Choosing the appropriate graft material to participate in the healing process in posterolateral spinal fusion continues to be a challenge. Combining synthetic graft materials with bone marrow aspirate (BMA) and autograft is a reasonable treatment option for surgeons to potentially reduce or replace the need for autograft. FormaGraft, a bone graft material comprising 12% bovine-derived collagen and 88% ceramic in the form of hydroxyapatite (HAp) and beta tricalcium phosphate (beta-TCP) was evaluated in three possible treatment modalities for posterior spinal fusion in a standard rabbit model. These three treatment groups were FormaGraft alone, FormaGraft soaked in autogenous BMA, and FormaGraft with BMA and iliac crest autograft. No statistically demonstrable benefits or adverse effects of the addition of BMA were found in the current study based on macroscopic, radiology or mechanical data. This may reflect, in part, the good to excellent results of the collagen HA/TCP composite material alone in a well healing bony bed. Histology did, however, reveal a benefit with the use of BMA. Combining FormaGraft with autograft and BMA achieved results equivalent to autograft alone. The mineral and organic nature of the material provided a material that facilitated fusion between the transverse processes in a standard preclinical posterolateral fusion model.

Mesenchymal stem cell and gene therapies for spinal fusion

THE IDEAL GRAFT material to promote spinal fusion should possess osteoconductive, osteoinductive, and osteogenic properties. Although autogenous bone graft has all three qualities and is the standard for comparison, research has focused on finding alternatives that have similar efficacy but not the morbidities associated with graft donor sites. Efforts have focused on various osteoconductive scaffolds and introduction of osteoinductive proteins, including bone morphogenetic protein. Recently, interest in using osteoprogenitor cells, or osteogenesis, for spinal fusion has increased. Bone marrow aspiration allows the introduction of mesenchymal stem cells and ultimately osteoblasts to promote fusion. Preclinical studies suggest that the addition of osteoprogenitor cells to various osteoconductive materials results in a fusion rate similar to that of autograft. There is growing recognition that local gene therapy has the benefit of delivering therapeutic genes that encode novel osteoinductive proteins. Gene delivery offers an alternative to local implantation of recombinant protein, which typically requires high doses of the protein to result in a sufficient osteoinductive response. The findings of animal studies demonstrate that gene therapy results in sustained and regulated production of desired osteoinductive proteins and is efficacious in promoting spinal fusion; however, before treatment in humans can be undertaken, obstacles such as the safety profile, host immune response, transfection rates with insufficient transgene expression, and imprecise control of the timing of transgene expression must be overcome. In this review, the authors summarize the latest research efforts under way to promote spinal fusion with osteoprogenitor cells and gene therapy and discuss the clinical implications of these treatments.

Use of bone morphogenetic proteins for augmentation of bone regeneration

A large body of preclinical and clinical data now documents that recombinant BMPs can be used for skeletal regeneration in humans and animals. Recombinant human BMP-2 and BMP-7 have been approved for use in human patients with long-bone fractures and nonunions and in patients undergoing lumbar fusion or various maxillofacial and dental regenerative procedures. These products have also been made available for veterinary use.

An overview of the histology of skeletal substitute materials

CONTEXT

Orthopedic and spine surgeons are in frequent need of bone for skeletal reconstruction. The amount of autograft is limited, and conventional allograft has some disadvantages, so surgeons are now using increasing amounts of demineralized allograft and a variety of synthetic materials to replace or "extend" autograft.

OBJECTIVE

To provide an overview of the composition and histology of the materials most likely to be seen by pathologists today.

DATA SOURCES

The review is based on published literature and the author's experience with preclinical studies and human biopsies.

CONCLUSIONS

Pathologists are likely to find these skeletal substitute materials in biopsy and resection specimens from patients who have undergone prior treatment, and recognizing a synthetic bone substitute can help explain an otherwise confusing specimen. Pathologists also play an important role in helping define the safety and efficacy of new bioactive materials.

Influence of recovering collagen with bioactive glass on osteoblast behavior

Bioactive ceramics have interesting properties from the biological standpoint, but their effects on cellular events remain partially unknown. In the current work, we investigated cellular viability, proliferation, and metabolic activity of rat primary osteoblasts in contact with four different samples: type I collagen, bioactive glass-coated collagen (GC), and both samples submitted to immersion for 5 days in a simulated body fluid. The bioactive glass coating was obtained from a sol-gel process. The cell viability, the alkaline phosphate, the collagen secretion, and the nitric oxide production by osteoblast were measured after 72 h of incubation in the presence of the samples. The GC that was immersed for 5 days in a simulated body fluid solution showed an increase in osteoblast viability and proliferation when it was compared with control and the other samples.

Biomimetic nanocomposites for bone graft applications

Allograft bone, dematerialized bone matrix and calcium-based synthetic materials have long been used as bone graft substitutes. First-generation bone graft substitutes as stand-alone graft substitutes have not developed as hoped. It remains a great challenge to design an ideal bone graft that emulates nature’s own structures or functions. To further improve the performance of such bone graft substitutes, scientists are investigating biomimetic processes to incorporate the desirable nano-features into the next generation of biomaterials. In this regard, nanostructured biomaterials less than 100 nm in at least one dimension, in particular nanocomposites, are perceived to be beneficial and potentially ideal for bone applications, owing to their nanoscale functional characteristics that facilitate bone cell growth and subsequent tissue formation. In fact, bone itself is a nanocomposite system with a complex hierarchical structure. This review reports the impact of biomimetically derived nanocomposite biomaterials for use in bone applications and provides possible suggestions for future research and development.

Instrumented fusion of thoracolumbar fracture with type I mineralized collagen matrix combined with autogenous bone marrow as a bone graft substitute: a four-case report

In order to avoid the morbidity from autogenous bone harvesting, bone graft substitutes are being used more frequently in spinal surgery. There is indirect radiological evidence that bone graft substitutes are efficacious in humans. The purpose of this four-case study was to visually, manually, and histologically assess the quality of a fusion mass produced by a collagen hydroxyapatite scaffold impregnated with autologous bone marrow aspirate for posterolateral fusion. Four patients sustained an acute thoracolumbar fracture and were treated by short posterior segment fusion using the AO fixateur interne. Autologous bone marrow (iliac crest) impregnated hydroxyapatite-collagen scaffold was laid on the decorticated posterior elements. Routine implant removal was performed after a mean of 15.3 months (12–20). During this second surgery, fusion mass was assessed visually and manually. A bone biopsy was sent for histological analysis of all four cases. Fusion was confirmed in all four patients intraoperatively and sagittal stress testing confirmed mechanical adequacy of the fusion mass. Three out of the four (cases 2–4) had their implants removed between 12 and 15 months after the index surgery. All their histological cuts showed evidence of newly formed bone and presence of active membranous and/or enchondral ossification foci. The last patient (case 1) underwent implant removal at 20 months and his histological cuts showed mature bone, but no active ossification foci. This four-case report suggests that the fusion mass produced by a mineralized collagen matrix graft soaked in aspirated bone marrow is histologically and mechanically adequate in a thoracolumbar fracture model. A larger patient series and/or randomized controlled studies are warranted to confirm these initial results.