Rabbit Posterolateral Fusion Research Articles

Physico-Chemical Characteristics and Posterolateral Fusion Performance of Biphasic Calcium Phosphate with Submicron Needle-Shaped Surface Topography Combined with a Novel Polymer Binder.

A biphasic calcium phosphate with submicron needle-shaped surface topography combined with a novel polyethylene glycol/polylactic acid triblock copolymer binder (BCP-EP) was investigated in this study. This study aims to evaluate the composition, degradation mechanism and bioactivity of BCP-EP in vitro, and its in vivo performance as an autograft bone graft (ABG) extender in a rabbit Posterolateral Fusion (PLF) model. The characterization of BCP-EP and its in vitro degradation products showed that the binder hydrolyses rapidly into lactic acid, lactide oligomers and unaltered PEG (polyethylene glycol) without altering the BCP granules and their characteristic submicron needle-shaped surface topography. The bioactivity of BCP-EP after immersion in SBF revealed a progressive surface mineralization. In vivo, BCP-EP was assessed in a rabbit PLF model by radiography, manual palpation, histology and histomorphometry up to 12 weeks post-implantation. Twenty skeletally mature New Zealand (NZ) White Rabbits underwent single-level intertransverse process PLF surgery at L4/5 using (1) autologous bone graft (ABG) alone or (2) by mixing in a 1:1 ratio with BCP-EP (BCP-EP/ABG). After 3 days of implantation, histology showed the BCP granules were in direct contact with tissues and cells. After 12 weeks, material resorption and mature bone formation were observed, which resulted in solid fusion between the two transverse processes, following all assessment methods. BCP-EP/ABG showed comparable fusion rates with ABG at 12 weeks, and no graft migration or adverse reaction were noted at the implantation site nor in distant organs.

The efficacy of a nanosynthetic bone graft substitute as a bone graft extender in rabbit posterolateral fusion

BACKGROUND CONTEXTSynthetic bone graft substitutes are commonly used in spinal fusion surgery. Preclinical data in a model of spinal fusion to support their efficacy is an important component in clinical adoption to understand how these materials provide a biological and mechanical role in spinal fusion. PURPOSETo evaluate the in vivo response of a nanosynthetic silicated calcium phosphate putty (OstP) combined with autograft compared to autograft alone or a collagen-biphasic calcium phosphate putty (MasP) combined with autograft in a rabbit spinal fusion model. STUDY DESIGNEfficacy of a nanosynthetic silicated calcium phosphate putty as an extender to autograft was studied in an experimental animal model of posterolateral spinal fusion at 6, 9, 12 and 26 weeks, compared to a predicate device. METHODSSkeletally mature female New Zealand White rabbits (70) underwent single level bilateral posterolateral intertransverse process lumbar fusion, using either autograft alone (AG), a nanosynthetic silicated calcium phosphate putty (OstP) combined with autograft (1:1), or a collagen-biphasic calcium phosphate putty (MasP) combined with autograft (1:1). Iliac crest autograft was harvested for each group, and a total of 2 cc of graft material was implanted in the posterolateral gutters per side. Fusion success was assessed at all time points by manual palpation, radiographic assessment, micro-CT and at 12 weeks only using non-destructive range of motion testing. Tissue response, bone formation and graft resorption were assessed by decalcified paraffin histology and by histomorphometry of PMMA embedded sections. RESULTSAssessment of fusion by manual palpation at the 12 week endpoint showed 7 out of 8 (87.5%) bilateral fusions in the OstP extender group, 4 out of 8 (50%) fusions in the MasP extender group, and 6 out of 8 (75%) fusions in the autograft alone group. Similar trends were observed with fusion scores of radiographic and micro-CT data. Histology showed a normal healing response in all groups, and increased bone formation in the OstP extender group at all timepoints compared to the MasP extender group. New bone formed directly on the OstP granule surface within the fusion mass while this was not a feature of the Collagen-Biphasic CaP material. After 26 weeks the OstP extender group exhibited 100% fusions (5 out of 5) by all measures, whereas the MasP extender group resulted in bilateral fusions in 3 out of 5 (60%), assessed by manual palpation, and fusion of only 20 and 0% by radiograph and micro-CT scoring, respectively. Histology at 26 weeks showed consistent bridging of bone between the transverse processes in the Ost P extender group, but this was not observed in the MasP extender group. CONCLUSIONSThe nanosynthetic bone graft substituted studied here, used as an extender to autograft, showed a progression to fusion between 6 and 12 weeks that was similar to that observed with autograft alone, and showed excellent fusion outcomes, bone formation and graft resorption at 26 weeks. CLINICAL SIGNIFICANCEThis preclinical study showed that the novel nanosynthetic silicated CaP putty, when combined with autograft, achieved equivalent fusion outcomes to autograft. The development of synthetic bone grafts that demonstrate efficacy in such models can eliminate the need for excessive autograft harvest and results from this preclinical study supports their effective use in spinal fusion surgery.

235. Evaluation of a nanosynthetic silicated calcium phosphate putty in a posterolateral rabbit spinal fusion model

BACKGROUND CONTEXT Providing surgeons with an “off the shelf” bone graft substitute to aid in bone healing is advantageous providing the materials participate in and facilitate the desired goal of fusion. Synthetic calcium phosphate-based (CaP) materials are excellent candidates considering their comparable composition to bone mineral however other factors have been shown to play a role in osteogenic behavior of these materials including surface chemistry and surface topography. The preclinical rabbit posterolateral fusion developed by Professor Boden provides a robust means to evaluate the in vivo performance of graft materials in this challenging indication. PURPOSE This study aims to evaluate the in-vivo response of a nanosynthetic silicated CaP combined with autograft compared to autograft alone or a collagen-biphasic CaP combined with autograft in a rabbit spinal fusion model. STUDY DESIGN/SETTING Preclinical animal model. PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS Following ethical approval, 70 skeletally mature female NZ white rabbits were divided into three groups: Group 1: Autograft alone (positive control); Group 2: Nanosynthetic Silicated CaP Putty + Autograft (50/50); Group 3: Collagen-Biphasic CaP Putty + Autograft (50/50). A single level posterolateral intertransverse process lumbar fusion was performed bilaterally after decortication of the transverse processes with a high-speed burr. Iliac crest autograft was harvested bilaterally in the positive control group and 2cc placed in the posterolateral gutters. The synthetic materials (1cc) were combined with autograft (1cc) and implanted. Fusion assessment at day 0 (n=2), 6, 9 weeks (n=5), 12 weeks (n=8) and 26 weeks (n=5) included harvest, manual palpation, radiographic assessment, micro-CT, non-destructive range of motion testing (12 weeks only) and decalcified paraffin and pmMA histology; no positive control group (autograft alone) was included at the 26-week time point. RESULTS The positive control group, autograft alone, performed consistent with this model in all endpoints. In the synthetic groups combined with autograft (Groups 2 and 3), radiographic incorporation was observed at the host transverse processes at 6 weeks and further into the fusion with time. Graft resorption and new bone formation was noted in the radiographs as well as the micro-computed tomography sections. Manual palpation was 7/8 at 12 weeks in the Nanosynthetic Silicated CaP Putty + Autograft group compared to 4/8 for the Collagen-Biphasic CaP Putty + Autograft. Histology showed normal healing and increased bone remodeling/formation with Nanosynthetic Silicated CaP Putty + Autograft at all timepoints compared to the Collagen-Biphasic CaP Putty + Autograft. New bone formed directly on the Nanosynthetic Silicated CaP material surface within the fusion mass while this was not a feature of the Collagen-Biphasic CaP material. By 26 weeks histology revealed consistent bridging of bone between the transverse processes in the Nanosynthetic Silicated CaP Putty + Autograft group, but this was not observed in the Collagen-Biphasic CaP group. CONCLUSIONS Developing nanosynthetic silicated CaP bone grafts that aim to mimic the size, structure and chemistry of bone mineral can eliminate the need for excessive autograft harvest and results from this preclinical study supports their effective use in spinal fusion. FDA DEVICE/DRUG STATUS Osteo 3 (the Nanosynthetic Silicated CaP Putty) (Investigational/Not approved)

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

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

Assessment of MASTERGRAFT PUTTY as a Graft Extender in a Rabbit Posterolateral Fusion Model

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

RhBMP-2 (ACS and CRM Formulations) Overcomes Pseudarthrosis in a New Zealand White Rabbit Posterolateral Fusion Model

The study design consisted of a New Zealand white rabbit model of pseudarthrosis repair. Study groups consisting of no graft, autograft, or recombinant human bone morphogenetic protein-2 (rhBMP-2) with absorbable collagen sponge (ACS) or compression resistant matrix (CRM) were evaluated. To evaluate the relative efficacy of bone graft materials (autograft, ACS, and CRM). rhBMP-2 has been shown to have a 100% fusion rate in a primary rabbit fusion model, even in the presence of nicotine, which is known to inhibit fusion. Seventy-two New Zealand white rabbits underwent posterolateral lumbar fusion with iliac crest autograft. To establish pseudarthroses, nicotine was administered to all animals. At 5 weeks, the spines were explored and all pseudarthroses were redecorticated and implanted with no graft, autograft, rhBMP-2/ACS, or rhBMP-2/CRM. At 10 weeks, fusions were assessed by manual palpation and histology. Eight rabbits (11%) were lost to complications. At 5 weeks, 66 (97%) had pseudarthroses. At 10 weeks, attempted pseudarthrosis repairs were fused in 1 of 16 of no graft rabbits (6%), 5 of 17 autograft rabbits (29%), and 31 of 31 rhBMP-2 rabbits (with ACS or CRM) (100%). Histologic analysis demonstrated more mature bone formation in the rhBMP-2 groups. The 2 rhBMP-2 formulations led to significantly higher fusion rates and histologic bone formation than no graft and autograft controls in this pseudarthrosis repair model.

Effects of Direct Current Electrical Stimulation on Gene Expression of Osteopromotive Factors in a Posterolateral Spinal Fusion Model

An in vivo model was used to determine levels of mRNA expression in response to direct current (DC) electrical stimulation in a rabbit posterolateral fusion model. This study tested the possibility that DC stimulation at the surgery site would increase expression of genes related to bone formation relative to expression in autograft alone. DC electrical stimulation as an adjunct treatment in spinal surgery has shown increased fusion rates when compared with autograft alone, yet the biology of such treatment is not fully understood. Thirty New Zealand White rabbits were entered into the study. A posterolateral, intertransverse process fusion was performed bilaterally at L4-L5, with autogenous bone graft. An implantable DC stimulator was placed across the decorticated transverse processes before placement of autograft. Animals were killed at 3, 7, 14, 21, and 28 days. mRNA levels of BMP-2, 4, 6, 7, VEGF, FGF-2, TGF-beta, ALK-2, and ALK-3 were evaluated with real-time RT-PCR. mRNA expression was significantly higher in the DC stimulated animals versus the control animals for several of the genes studied. In particular, levels of mRNA were elevated for BMP-2, BMP-6, and BMP-7. This study shows for the first time that DC stimulation results in a sustained increase of multiple osteogenic genes, suggesting that the biologic mechanism for the DC-induced increase in the rate and extent of bone formation observed clinically may be mediated by the up-regulation of these osteoinductive factors.

P78. Evaluation of the Efficacy of rhBMP-2 to Overcome Pseudoarthrosis in a New Zealand White Rabbit Posterolateral Fusion Model

P78. Evaluation of the Efficacy of rhBMP-2 to Overcome Pseudoarthrosis in a New Zealand White Rabbit Posterolateral Fusion Model

6:00 184. Rabbit posterolateral fusion is achieved with recombinant human growth differentiation factor 5

BACKGROUND CONTEXT: Growth/differentiation factor-5 (GDF-5) is a member of a divergent subgroup of the bone morphogenetic protein (BMP) family. Members in this subgroup share 40–50% protein sequence homology with the BMP-2 and BMP-7 subgroups. Expression of GDF-5 is required for proper skeletal patterning and joint development in the vertebrate limb, and null mutations result in brachydactyly syndromes in both animal and man. Type I collagen and hydroxyapatite are the predominant components of bone. Fabricated from these osteoconductive components is a mineralized collagen matrix (further referred to as matrix) comparable in composition to natural bone. This matrix, combined with bone marrow aspirate as a source of osteogenic stimuli, is used clinically as a bone grafting material to fill bony voids. In previous animal studies, this matrix combined with rhGDF-5 demonstrated osteoinductive activity and promoted new bone formation in various bony defect and spine fusion models.