Autograft versus allograft with or without demineralized bone matrix in posterolateral lumbar fusion in rabbits. Laboratory investigation

OBJECT: Posterolateral spinal fusions are performed to treat different spinal disorders. Autograft continues to be the gold standard; it is, however, associated with donor site morbidity and limited sources. Allograft has been used, but has been reported to result in lower fusion rates. Demineralized bone matrix (DBM) has also been used and reportedly increases the fusion rate in a variety of critical defect models. Different forms of DBM are available, not all have been independently studied. To evaluate the effect of a xenogenic DBM added to allograft on the fusion rate of posterolateral lumbar spine arthrodesis the authors designed an experimental study comparing posterolateral fusion rate using autograft, allograft, and allograft plus a xenogenic DBM in a validated animal model. METHODS: A bilateral, 1-level (L4-5) intertransverse process fusion was performed in 45 male New Zealand rabbits. Iliac crest bone graft was harvested bilaterally from each rabbit. The rabbits were randomly assigned to 3 groups: Group I, Autograft, 15 rabbits; Group II, Allograft, 15 rabbits; and Group III, Allograft plus DBM in a paste form (Dynagraft). The animals were killed 8 weeks after surgery. Fusion was assessed radiographically and by manual palpation by 2 independent observers. The results were analyzed using the Fisher exact test and chi-square test. RESULTS: The fusion rate was 46.6% (7 of 15 rabbits) in the autograft group, 33.3% (5 of 15 rabbits) in the allograft group, and 33.3% (5 of 15 rabbits) in the allograft plus DBM group (p > 0.05). CONCLUSIONS: Autograft produced a higher fusion rate than allograft in this spinal fusion rabbit model, but the difference was not statistically significant. Allograft plus xenogenic DBM showed the same fusion rate as allograft alone.     

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.     

Interaction of allogeneic demineralized bone matrix and porous hydroxyapatite bioceramics in lumbar interbody fusion in rabbits

Bone repair by autograft is effective in clinical practice. However, serious problems arise when a considerable volume of transplant is needed, as with spinal fusion procedures. The use of bone substitutes combined with osteoinductive agents may contribute to the solution of such problems. In this study, the effectiveness of such a procedure was tested in an experimental model of interbody fusion in rabbits in which the incorporation of a porous hydroxyapatite block (HA) was enhanced by the addition of allogeneic demineralized bone matrix (DBM). The latter was used as a delivery system for the osteoinductive activity of the bone morphogenetic protein contained in the matrix. A group implanted with combined HA + DBM showed significantly earlier stabilization of the fusion when compared to groups implanted with DBM alone, HA alone, and bone autografts. On the other hand, the general results of the fusion with HA + DBM were superimposable on those of autografts. With further research, the combination of a bone substitute and an osteoinductive agent may constitute an alternative to the use of bone autografts.     

Tissue response to bioactive glass and autogenous bone in the rabbit spine

Bioactive glass S53P4 and autogenous bone were used as bone graft materials in an experimental rabbit model for spinal fusion. The study focused on differences in bone formation using bioactive glass and autogenous bone as bone graft materials. Bioactive glass, a mixture of bioactive glass and autogenous bone or autogenous bone was implanted for 4 and 12 weeks at the thoraco-lumbar level. Undecalcified sections were prepared for histological and histomorphometric evaluation. New bone formation was seen in all implanted areas, with the bone growing from the surface of the vertebrae enclosing both glass and autogenous bone in the bone fusion mass. During the observation period, the measured amount of bone remained at the same level in the autograft group, while in the glass and the glass/autograft bone groups it increased. By ¶12 weeks, no significant difference in bone formation between the three groups was observable. The bone formation in two selected standardized areas at 12 weeks was 21 and 24% in the glass group, 23 and 28% in the glass/autograft bone group and 27 and 26% in the autograft bone group. We consider bioactive glass as a potential bone graft material in experimental spinal fusion.     

Evaluation of a new formulation of demineralized bone matrix putty in a rabbit posterolateral spinal fusion model

Background contextAlternatives to autologous bone graft (ABG) with osteoconductive, osteoinductive, and osteogenic potential continue to prove elusive. Demineralized bone matrix (DBM) however, with its osteoconductive and osteoinductive potential remains a viable option to ABG in posterolateral spine fusion.PurposeTo compare the efficacy of a new formulation of DBM putty with that of ABG in a rabbit posterolateral spinal fusion model.Study designEfficacy of a new formulation of DBM was studied in an experimental animal posterolateral spinal fusion model.MethodsTwenty-four male New Zealand White rabbits underwent bilateral posterolateral spine arthrodesis of the L5–L6 intertransverse processes, using either ABG (control group, n=12) or DBM (DBM made from rabbit bone) putty (test group, n=12). The animals were killed 12 weeks after surgery and the lumbar spines were excised. Fusion success was evaluated by manual palpation, high resolution X-rays, microcomputed tomography imaging, biomechanical four-point bending tests, and histology.ResultsTwo animals were lost because of anesthetic related issues. Manual palpation to assess fusion success in the explanted lumbar spines showed no statistical significant difference in successful fusion in 81.8% (9/11) of DBM group and 72.7% (8/11) of ABG group (p=.99). Reliability of these assessments was measured between three independent observers and found near perfect agreement (intraclass correlation cofficient: 0.92 and 0.94, respectively). Fusion using high resolution X-rays was solid in 10 of the DBM group and 9 of the ABG group (p=.59). Biomechanical testing showed no significant difference in stiffness between the control and test groups on flexion, extension, and left lateral and right lateral bends, with p values accounting for .79, .42, .75, and .52, respectively. The bone volume/total volume was greater than 85% in the DBM treated fusion masses. Histologic evaluation revealed endochondral ossification in both groups, but the fusion masses were more mature in the DBM group.ConclusionsThe DBM putty achieved comparable fusion rates to ABG in the rabbit posterolateral spinal fusion model.     

Vertebral plate regeneration induced by radiation-sterilized allogeneic bone sheets in sheep

Objective： To evaluate the effects and mechanism of radiation-sterilized allogeneic bone sheets in inducing vertebral plate regeneration after laminectomy in sheep. Methods ： Twelve adult male sheep （ aged 1.5 years and weighing 27 kg on average ） provided by China Institute for Radiation Protection underwent L3-4 and L4-5 laminectomy. Then they were randomly divided into two groups： Group A （n =6） and Group B （n =6）. The operated sites of L4-5 in Group A and L3-4 in Group B were covered by ＂ H-shaped＂ freeze-drying and radiationsterilized allogeneic bone sheets （ the experimental segments）, while the operated sites of L3-4 in Group A and L4-5 in Group B were uncovered as the self controls （ the control segments ）. The regeneration process of the vertebral plate and the adhesion degree of the dura were observed at 4,8,12,16,20 and 24 weeks after operation. X- ray and CT scan were performed in both segments of 1.34 and L4-5 at 4 and 24 weeks after operation. Results： In the experimental segments, the bone sheets were located in the anatomical site of vertebral plate, and no lumbar spinal stenosis or compression of the dura was observed. The bone sheets were absorbed gradually and fused well with the regenerated vertebral plate. While in the control segments, the regeneration of vertebral plate was not completed yet, the scar was inserted into the spinal canal, compressing the dura and the spinal cord, and the epidural area almost disappeared. Compared with the control segments, the dura adhesion degree in the experimental regenerated segments was much milder （ P 〈 0. 01 ）, the internal volume of the vertebral canal had no obvious change and the shape of the dura sack remained well without obvious compression. Conclusions： Freeze-drying and radiation-sterlilized allogeneic bone sheets are ideal materials for extradural laminoplasty due to their good biocompatibility, biomechanical characteristics and osteogenic ability. They can effectively reduce formation of post-laminectomy scars, prevent recurrence of post-lamlnectomy spinal stenosis, and induce regeneration of vertebral plates.     

Osteoinductivity of commercially available demineralized bone matrix. Preparations in a spine fusion model

BACKGROUND: Although autogenous bone is the most widely used graft material for spinal fusion, demineralized bone matrix preparations are available as alternatives or supplements to autograft. They are prepared by acid extraction of most of the mineralized component, with retention of the collagen and noncollagenous proteins, including growth factors. Differences in allograft processing methods among suppliers might yield products with different osteoinductive activities. The purpose of this study was to compare the efficacy of three different commercially available demineralized bone matrix products for inducing spinal fusion in an athymic rat model. METHODS: Sixty male athymic rats underwent spinal fusion and were divided into three groups of eighteen animals each. Group I received Grafton Putty; Group II, DBX Putty; and Group III, AlloMatrix Injectable Putty. A control group of six animals (Group IV) underwent decortication alone. Six animals from each of the three experimental groups were killed at each of three intervals (two, four, and eight weeks), and the six animals from the control group were killed at eight weeks. At each of the time-points, radiographic and histologic analysis and manual testing of the explanted spines were performed. RESULTS: The spines in Group I demonstrated higher rates of radiographically evident fusion at eight weeks than did the spines in Group III or Group IV (p < 0.05). Manual testing of the spines at four weeks revealed variable fusion rates (five of six in Group I, two of six in Group II, and none of six in Group III). At eight weeks, all six spines in Group I, three of the six in Group II, and no spine in Group III or IV had fused. Histologic analysis of the spines in Groups I, II, and III demonstrated varying amounts of residual demineralized bone matrix and new bone formation. Group-I spines demonstrated the most new bone formation. CONCLUSIONS: This study demonstrated differences in the osteoinductive potentials of commercially available demineralized bone matrices in this animal model.     

人脐血间充质干细胞修复颅骨缺损的实验研究

目的 应用人脐血间充质干细胞(umbilical cord blood derived mesenchymal stem cells,UCB-MSCs)复合脱钙骨材料构建组织工程化骨,修复裸大鼠颅骨标准缺损.方法 体外扩增培养、成骨诱导人UCB-MSCs,采用Alizarin Red染色和钙离子半定量的方法测定细胞成骨分化能力.将第2代细胞接种在脱钙骨支架材料上继续诱导培养,扫描电镜检测细胞在材料上的生长状况.制备裸大鼠双侧颅骨全层标准缺损(直径5 mm),一侧以细胞材料复合物修复作为实验侧(n=8);另一侧以单纯脱钙骨材料修复作为对照侧(n=8).术后6、12周取材,分别通过大体形态观察、显微CT(Micro-CT)、组织学方法检测颅骨缺损的修复效果.结果 UCB-MSCs体外能够诱导分化为成骨细胞,且在脱钙骨支架材料上生长良好.Micro-CT检测显示术后6周实验侧有部分新生骨组织形成,12周时骨缺损修复率达(78.19±6.45)%,脱钙骨材料降解完全;对照侧6周时无明显新骨生成,12周时材料完全降解,骨缺损未修复.组织学检测显示12周时实验侧有较多成熟骨生成,为骨性愈合;对照侧骨缺损为纤维愈合.结论 成骨诱导的人UCB.MSCs复合脱钙骨材料构建的组织工程化骨可修复裸大鼠颅骨全层标准缺损,有望成为新的组织工程骨种子细胞来源.     

Antibiotic-loaded bone graft for reduction of surgical site infection in spinal fusion

Background Context

Infections remain a leading complication associated with spinal arthrodesis, regardless of the use of prophylactic antibiotics and improved surgical techniques, with incidence of infection as high as 8.2%. Infection prolongs antibiotic usage, increases hospital time, and inevitably inflates overall treatment costs. Local antibiotics, such as vancomycin, have been used in combination with fusion materials over the past decade to decrease infection risk. An ideal graft material would serve a dual role: encouraging vertebral fusion while reducing the incidence of infection.

Anterior thoracic spinal fusion in dogs by injection of recombinant human bone morphogenetic protein-2 and a synthetic polymer

The purpose of this study was to achieve spinal fusion in the absence of bone graft material using a new, injectable, and semi-liquid synthetic polymer (polylactic acid polyethylene glycol [PLA-PEG] block copolymer) containing recombinant human bone morphogenetic protein-2 (rhBMP-2). Twenty-seven skeletally mature beagles underwent anterior thoracic spinal fusion at T9-T10. Group I (n = 9) was injected with 1 mL of PLA-PEG block copolymer carrier alone into space under the vertebral pleura and the anterior longitudinal ligament. Group II (n = 9) was injected with 1 mL of PLA-PEG carrier containing 500 microgram of rhBMP-2. Group III (n = 9) was injected with 1 mL of PLA-PEG carrier containing 1000 microgram of rhBMP-2. In the Group I animals, no evidence of new bone formation was noted at the implanted sites both radiographically and histologically. In contrast, all of the nine animals in Group III showed new bone formation in 12 weeks, and four of the nine animals in Group II showed bony mass at the injected sites. However, vertebral bony fusion was incomplete despite the significant amount of new bone formation in both groups that showed new bone formation. In addition to resulting in improvements in the surgical procedure, injection of rhBMP-2 and a synthetic polymer is useful for bone formation for spinal fusion.     

Vertebral plate regeneration induced by radiation-sterilized aliogeneic bone sheets in sheep

Objective: To evaluate the effects and mechanism of radiation-sterilized allogeneic bone sheets in inducing vertebral plate regeneration after laminectomy in sheep. Methods: Twelve adult male sheep (aged 1.5 years and weighing 27 kg on average) provided by China Institute for Radiation Protection underwent L3-4 and L4-5 laminectomy. Then they were randomly divided into two groups: Group A ( n = 6 ) and Group B ( n = 6 ). The operated sites of L4-5 in Group A and L3-4 in Group B were covered by " H-shaped" freeze-drying and radiation-sterilized allogeneic bone sheets ( the experimental segments), while the operated sites of L3-4 in Group A and L4-5 in Group B were uncovered as the self controls (the control segments ). The regeneration process of the vertebral plate and the adhesion degree of the dura were observed at 4,8,12,16,20 and 24 weeks after operation. X-ray and CT scan were performed in both segments of L3-4 and L4-5 at 4 and 24 weeks after operation. Results: In the experimental segments, the bone sheets were located in the anatomical site of vertebral plate, and no lumbar spinal stenosis or compression of the dura was observed. The bone sheets were absorbed gradually and fused well with the regenerated vertebral plate. While in the control segments, the regeneration of vertebral plate was not completed yet, the scar was inserted into the spinal canal, compressing the dura and the spinal cord, and the epidural area almost disappeared. Compared with the control segments, the dura adhesion degree in the experimental regenerated segments was much milder (P<0.01), the internal volume of the vertebral canal had no obvious change and the shape of the dura sack remained well without obvious compression. Conclusions: Freeze-drying and radiation-sterilized allogeneic bone sheets are ideal materials for extradural laminoplasty due to their good biocompatibility, biomechanical characteristics and osteogenic ability. They can effectively reduce formation of post-laminectomy scars, prevent recurrence of post-laminectomy spinal stenosis, and induce regeneration of vertebral plates.     

Demineralized bone matrix and fat autograft in a rabbit model of frontal sinus obliteration.

OBJECTIVE: In this study, we investigate the efficacy of demineralized bone matrix (DBM) as a material for frontal sinus obliteration in a rabbit model. STUDY DESIGN AND SETTING: Twenty-four New Zealand White rabbits were divided into four groups, and the study was carried out to two time periods. Twelve rabbits underwent frontal sinus obliteration with fat autograft, and 12 rabbits underwent the procedure with DBM. At 12 weeks, six control and six study rabbits were killed. The remaining 12 rabbits were killed at 36 weeks. All specimens underwent radiologic evaluation with spiral CT followed by histologic examination for evidence of bony growth. RESULTS: Sinuses obliterated with DBM showed replacement of the sinus cavity by trabecular bone. Histology demonstrated significant progressive replacement of DBM by cancellous bone from 12 weeks (53.3%) to 36 weeks (78.8%). There were no complications observed as a result of the materials used. CONCLUSION AND SIGNIFICANCE: DBM is a prospective material for frontal sinus obliteration. Long-term studies and human trials will further elucidate the role of this material.     

同种异体脂肪干细胞复合脱钙骨修复大鼠尺骨缺损

目的探讨同种异体脂肪干细胞修复管状骨缺损的可行性。方法获取SD大鼠的腹股沟处脂肪,分离培养脂肪干细胞（Adipose-Derived Stem Cells,ADSCs）;鼠第3代ADSCs与脱钙骨复合,24 h后进行成骨诱导培养。检测细胞在材料表面的生长及成骨分化能力。建立鼠两侧尺骨缺损模型,分别植入鼠ADSCs-脱钙骨复合物（实验侧）和单纯脱钙骨材料（对照侧）;8周、24周后取样,行DR和组织学检测,观察成骨情况。结果 ADSCs能在脱钙骨上很好地黏附和生长,并维持成骨分化能力。细胞-材料复合物植入24周后,DR显示实验侧有新生骨基质长成,对照侧未见骨组织生成。组织学检测显示,实验侧缺损区被典型的骨组织取代,可见新生骨小梁附着于脱钙骨表面;对照侧只有少量的骨组织和纤维组织充填。结论 ADSCs-脱钙骨材料复合物植入,能成功修复临界大小的管状骨缺损。     

Augmentation of spinal fusion with bone morphogenetic protein in dogs

Bone morphogenetic protein (BMP) induces mesenchymal cells to differentiate into cartilage and bone. To investigate the action of BMP on the growth of host bed-derived bone in experimental spinal fusions, posterior intervertebral spinal fusions of the lower thoracic spine were performed in 13 mature mongrel dogs. Four different fusion methods were used at single intervertebral levels within each dog. Three levels in each dog were used as controls for the BMP level. The spinal columns were examined by radiohistomorphometric methods at three weeks, six weeks, and 12 weeks and showed the BMP level to have two to three times more new bone than control levels. At the BMP level, an increase in the amount of new bone was observed in the interval from three to 12 weeks, in contrast to a decrease seen at the control levels. Fusion was present in five of seven of the BMP levels compared with zero of seven, one of seven, and two of seven in the control levels. The BMP level exhibited an increased number and volume of areas of de novo cartilage and woven bone formation at all time intervals compared to all control levels. The polylactic acid polymer carrier was not resorbed and partially retained in the fusion site. The preliminary observations suggest that BMP may serve as a useful adjunct in spinal fusions, but research is required to find a rapidly degradable delivery system. The objective of BMP research is to augment the host bed capacity for bone generation and regeneration and to spare children and adults the pain and complications involved in removing excessive volumes of iliac crest bone grafts.     

A comparison of commercially available demineralized bone matrix for spinal fusion

In an effort to augment the available grafting material as well as to increase spinal fusion rates, the utilization of a demineralized bone matrix (DBM) as a graft extender or replacement is common. There are several commercially available DBM substances available for use in spinal surgery, each with different amounts of DBM containing osteoinductive proteins. Each product may have different osteoinductivity potential due to different methods of preparation, storage, and donor specifications. The purpose of this study is to prospectively compare the osteoinductive potential of three different commercially available DBM substances in an athymic rodent spinal fusion model and to discuss the reasons of the variability in osteoinductivity. A posterolateral fusion was performed in 72 mature athymic nude female rats. Three groups of 18 rats were implanted with 1 of 3 DBMs (Osteofil, Grafton, and Dynagraft). A fourth group was implanted with rodent autogenous iliac crest bone graft. The rats were sacrificed at 2, 4, 6, and 8 weeks. A dose of 0.3 cm³ per side (0.6 cm³per animal) was used for each substance. Radiographs were taken at 2 weeks intervals until sacrifice. Fusion was determined by radiographs, manual palpation, and histological analysis. The Osteofil substance had the highest overall fusion rate (14/18), and the highest early 4 weeks fusion rate of (4/5). Grafton produced slightly lower fusion rates of (11/17) overall, and lower early 4 weeks fusion rate of (2/5). There was no statistically significant difference between the rate of fusion after implantation of Osteofil and Grafton. None of the sites implanted with Dynagraft fused at any time point (0/17), and there was a significantly lower fusion rate between the Dynagraft and the other two substances at the six-week-time point and for final fusion rate (P = 0.0001, Fischer’s exact test). None of the autogenous iliac crest animals fused at any time point. Non-decalcified histology confirmed the presence of a pseudarthrosis or the presence of a solid fusion, and the results were highly correlated with the manual testing. Although all products claim to have significant osteoinductive capabilities, this study demonstrates that there are significant differences between some of the tested products.     

Efficacy comparison of Accell Evo3 and Grafton demineralized bone matrix putties against autologous bone in a rat posterolateral spine fusion model

Background Context

Spinal fusion procedures are intended to stabilize the spinal column for a multitude of disorders including abnormal curvature, traumatic instability, degenerative instability, and damage from infections or tumors. As an aid in the bone healing response, bone graft materials are used to bridge joints for arthrodesis and promote unions in pseudoarthrosis. Currently, the gold standard for stabilizing fusion masses in spinal procedures involves using the osteogenic, osteoinductive, and osteoconductive properties of autologous iliac crest corticocancellous bone. However, considerable morbidity is associated with harvesting the autologous graft. Donor site complications including infection, large hematomas, and pain have been reported at rates as high as 50% (Boden and Jeffrey, 1995). Biologically, the rate of bone repair dictates the rate at which the fusion mass will unite under autologous graft conditions.

Differences in early osteogenesis and bone micro-architecture in anterior lumbar interbody fusion with rhBMP-2, equine bone protein extract,and autograft

PurposeTo investigate the microstructural differences and responsible mechanisms in early bone formation in anterior lumbar interbody fusion (ALIF) in the spine using rhBMP-2 (INFUSE), equine bone protein extract (COLLOSS E) or autograft.MethodsTwelve Danish female landrace pigs underwent a 3-level ALIF procedure at L3–6. PEEK interbody cages packed with rhBMP-2, COLLOSS E, or autograft were inserted. The animals were divided into two groups of six, and observed for four and eight weeks postoperatively. μCT was performed for evaluation of microstructure of the bone within the cage. A mathematical finite element model was developed to investigate the aqueous behavior within the cages when exposed to external compressive forces.ResultsAt 4 weeks postoperative bone surface volume fraction (BS/TV) using rhBMP-2 was higher than with use of COLLOSS E and autograft, while trabecular thickness (Tb.Th.) was lower using rhBMP-2 at this time-point. At eight weeks BS/TV and trabecular number (Tb.N.) were still higher using rhBMP-2 than autograft and COLLOSS E. Connectivity density was significantly higher using rhBMP-2 than using autograft or COLLOSS E at both time-points. Between four- and eight-week time-points BV/TV and Tb.Th. rose while Tb.N. declined using rhBMP-2. The degree of anisotropy and the calculated amount of trabeculae with main direction along the spinal axis, were higher at four weeks using COLLOSS E. rhBMP-2 had the highest amount of trabeculae directed along the spinal axis at eight weeks. A change in main direction between four and eight weeks was observed for both autograft and rhBMP-2. The numerical results from the finite element model verify that significantly different flow pattern emerges as the boundary conditions are altered. At four weeks there was an evident correlation between trabecular orientation and flow pattern using rhBMP-2.ConclusionThis study reveals large differences in microstructure in the early osteogenesis and explains important mechanisms of early bone formation using rhBMP-2, COLLOSS E or autograft treatment. These differences might explain some of the unfortunate events reported such as edema, swelling, and excessive bone formation using different bone graft substitutes in spinal fusion procedures.     

Use of demineralized bone matrix in spinal fusion

Spinal fusion remains the gold-standard treatment for several pathological spine conditions. Although, autologous Iliac Crest Bone Grafting is considered the gold-standard graft choice to promote spinal fusion; however, it is associated with significant donor site morbidity and a limited graft quantity. Therefore, several bone graft alternatives have been developed, to augment arthrodesis. The purpose of this review is to present the results of clinical studies concerning the use of demineralized bone matrix (DBM), alone or as a composite graft, in the spinal fusion. A critical review of the English-language literature was conducted on Pubmed, using key word “demineralized bone matrix”, “DBM”, “spinal fusion”, and “scoliosis”. Results had been restricted to clinical studies. The majority of clinical trials demonstrate satisfactory fusion rates when DBM is employed as a graft extender or a graft enhancer. Limited number of prospective randomized controlled trials (4 studies), have been performed comparing DBM to autologous iliac crest bone graft in spine fusion. The majority of the clinical trials demonstrate comparable efficacy of DBM when it used as a graft extender in combination with autograft, but there is no clinical evidence to support its use as a standalone graft material. Additionally, high level of evidence studies are required, in order to optimize and clarify the indications of its use and the appropriate patient population that will benefit from DBM in spine arthrodesis.     

Osteogenesis associated with bone gla protein gene expression in diffusion chambers by bone marrow cells with demineralized bone matrix.

Diffusion chambers with rat bone marrow cells and demineralized bone matrix (DBM) were implanted subcutaneously to syngeneic 8-week-old rats and were harvested every week 3-7 weeks after implantation, and histochemical examination, determination of alkaline phosphatase activity, total calcium and phosphorus, the bone-specific vitamin K-dependent gla-containing protein (BGP) content, and detection of BGP mRNA relative to mineralization were performed. Alkaline phosphatase in diffusion chamber implants reached the highest activity at 4 weeks and then decreased. Calcium and phosphorus deposits occurred at 4 weeks after implantation and were followed by marked increases until 7 weeks, which was comparable to the accumulation of BGP. The BGP gene within the diffusion chambers began to be expressed at 5 weeks, and its expression increased markedly at 7 weeks after implantation. At 4-5 weeks after implantation, new bone adjacent to the membrane filters and cartilage toward the center of the diffusion chamber were observed histochemically. Light microscopic and immunohistologic examinations of chambers with marrow cells and DBM revealed production of mineralized matrices, typical of bone characterized by the appearance of BGP and mineralized nodules. In contrast, bone marrow cells alone did not show extensive bone formation and yielded very low values for these biochemical parameters. The present experiments demonstrate the potential of bone marrow cells and DBM to produce not only cartilage formation but also membranous bone formation associated with increasing expression of BGP mRNA during the later stages of bone formation, as well as a marked accumulation of BGP.