Enhanced spinal fusion using a biodegradable porous mesh container in a rat posterolateral spinal fusion model

Background contextPosterolateral fusion (PLF) with an autogenous iliac bone graft is the most common procedure for treating various lumbar spinal diseases. However, the limited success and associated morbidity from an iliac crest graft demands new biologically competent graft enhancers or substitutes.PurposeTo investigate the feasibility of tubular mesh container made of bioabsorbable sutures (poly-1,4-dioxane-2-one, PDO) for spinal fusion.Study designExperimental animal study.MethodsA biodegradable PDO tubular mesh container was used to contain small pieces of bone grafts. Twenty Sprague-Dawley male rats underwent PLF between L4 and L5 transverse processes with bilateral iliac grafts. Experimental animals were assigned into two different groups: autograft-only group (N=10) that underwent PLF with autograft-only or mesh container group (N=10) that underwent PLF with tubular mesh container filled with autogenous bone grafts. The rats were sacrificed at 8 weeks postoperatively, and the lumbar spines were removed. Spinal fusion was evaluated by manual palpation, microcomputed tomography, three-point bending test, and histological examination.ResultsSolid fusion was achieved in all cases of the mesh container group, whereas the autograft-only group showed 60% of solid fusion. New bone mass was higher and more solidly fused in the mesh container group than the autograft-only group (p<.01). Volume of fusion mass and density of bone were significantly higher in the mesh container group (p<.05). In all cases, inflammatory response was minimal.ConclusionsThis study demonstrated that a tubular mesh container made of bioabsorbable suture is useful to hold small pieces of bone grafts and to enhance spinal fusion.     

Erythropoietin augments bone formation in a rabbit posterolateral spinal fusion model

We tested the hypothesis that erythropoietin (EPO) enhances bone formation after posterolateral spinal fusion (PLF) in a rabbit model. Thirty-four adult rabbits underwent posterolateral intertransverse arthrodesis at the L5-L6 level using 2.0 g autograft per side. The animals were randomly divided into two groups receiving subcutaneous daily injections of either EPO or saline for 20 days. Treatment commenced 2 days preoperatively. Hemoglobin was monitored at baseline and 2, 4, and 6 weeks after fusion surgery. After euthanasia 6 weeks postoperatively, manual palpation, radiographic, and histomorphometric examinations were performed. Bone volume of the fusion mass was estimated by CT after 6 weeks. EPO increased bone fusion volume to 3.85 ccm (3.66-4.05) compared with 3.26 ccm (2.97-3.55) in the control group (p<0.01). EPO treatment improved vascularization of the fusion mass and increased hemoglobin levels (p<0.01). Fusion rate tended to be higher in the EPO group based on manual palpation, CT, and radiographic examinations. For the first time EPO has shown to augment bone formation after autograft PLF in a rabbit model. Increased vascularization provides a partial explanation for the efficacy of EPO as a bone autograft enhancer.     

Novel approach to calvarial bone transport using a rabbit model

Calvarial defects sometimes require cranioplasty to protect the brain. Alloplastic materials, such as acrylic resin, hydroxyapatite ceramics, and titanium, involve various problems, such as vulnerability, infection, deformity resulting from growth, and high cost. We devised a new bone transport model in the rabbit based on the distraction osteogenesis theory of Ilizarov. Twelve Japan white rabbits with a mean body weight of 2.5 kg aged 12 weeks were used. Craniectomy (7 x 14 mm) was performed in 12 rabbits. Trapezoid bone osteotomy was performed anterior to the calvarial defect in 10 rabbits. The distraction device (Extension-plates) was fixed between the trapezoid bone island and the skull. Distraction was initiated 5 days postoperatively. The device was activated once every other day, with approximately 0.75 mm or 0.5 mm per activation. Bone distraction was continued until the rod could not be moved. The lengths of distraction were 4 mm in two cases, 5 mm in one case, 6 mm in one case, and 7 mm in two cases, with a mean of 5.5 +/- 0.56 mm. Both radiographic and histological findings showed osteogenesis by intramembranous ossification and trans-chondroid bone formation. Distraction osteogenesis has potential clinical applications in cranioplasty, especially in children because usage of autogenous bone is difficult if not impossible in most cases.     

Response of bone marrow stroma cells to demineralized cortical bone matrix in experimental spinal fusion in rabbits

The effect of autogeneic bone marrow (BM) cells and allogeneic demineralized bone matrix (DBM), alone or combined, as transplantation materials was studied in an experimental posterior thoracic spinal fusion model in rabbits. Transplantation of composite grafts composed of BM and DBM showed the first signs of fusion between two spinal segments after four weeks, reaching 86% after 20 weeks. Late fusion results achieved with DBM alone were similar. The capacity of BM per se to build up a spinal fusion was insignificant. Calcified tissue, documented roentgenographically, was shown to develop locally with time, and the earliest bridging of an interspace was noted after four weeks. Histologically, formation of new bone and cartilage was observed after two weeks, showing mature lamellar bone formation between thoracic segments after 20 weeks. Furthermore, increased 45Ca activity was still observed in the fused tissues after 20 weeks. Although, with grafting materials used, this model for experimental spinal fusion gave promising results, further investigations with other fusion techniques could give still better effects.     

An update on bone substitutes for spinal fusion

With the current advances in spinal surgery, an understanding of the precise biological mechanism of each bone substitute is necessary for inducing successful spinal fusion. In this review, the categories of bone substitutes include allografts, ceramics, demineralized bone matrix, osteoinductive factors, autogenous platelet concentrate, mesenchymal stem cells, and gene therapy. Further, clinical studies have been evaluated by their levels of evidence in order to elucidate the precise effect of the bone substitute employed and to establish clinical guidance. This article will review both clinical studies based on evidence and basic research in current advances in order to avoid as far as possible any chances of failure in the future and to understand cellular biology in novel technologies.     

Locally applied simvastatin promotes bone formation in a rat model of spinal fusion

Simvastatin, an inexpensive lipid‐lowering drug widely used to prevent cardiovascular disorders, is known to increase osteoblastic activity, inhibit osteoclastic activity, and stimulate osteoblastic production of bone morphogenetic protein 2. Furthermore, local simvastatin application increased bone formation in animal models of fracture or bone defects. We investigated the effect of locally applied simvastatin in a rat model of spinal fusion. We performed posterolateral lumbar fusion surgery with iliac crest autograft in 36 rats divided into group I (n = 17; implanted with a gelatin scaffold) and group II (n = 19; implanted with a gelatin scaffold infused with 0.5 mg simvastatin). The rats were euthanized at 6 or 12 weeks postoperatively, and the spines were explanted and assessed. The fusion rates in group II (16.7%: 6 weeks, 30%: 12 weeks) were considerably higher than those in groups I (0%: 6 weeks, 0%: 12 weeks). The 6‐ and 12‐week radiographic scores were significantly higher in group II than in group I. High‐resolution micro‐computerized tomography revealed that the tissue and bone volumes of the callus tended to be higher in group II than in group I. Histologic analysis of the spines explanted after 12 weeks demonstrated new bone formation between the transverse processes in group II, but thicker and wider individual trabeculae with fibrotic tissue and muscle fiber between the transverse processes in group I. Locally applied simvastatin was efficacious in accelerating bone formation in our rat model of spinal fusion, supporting its potential clinical application as a promoter of bone morphogenesis in spinal fusion. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1942–1948, 2017.

     

A porous bioactive titanium implant for spinal interbody fusion: an experimental study using a canine model

OBJECT: Porous biomaterials with adequate pore structure and appropriate mechanical properties are expected to provide a new generation of devices for spinal interbody fusion because of their potential to eliminate bone grafting. The purpose of this study was to evaluate the fusion characteristics of porous bioactive titanium implants using a canine anterior interbody fusion model. METHODS: Porous titanium implants sintered with volatile spacer particles (porosity 50%, average pore size 303 microm, compressive strength 116.3 MPa) were subjected to chemical and thermal treatments that give a bioactive microporous titania layer on the titanium surface (BT implant). Ten adult female beagle dogs underwent anterior lumbar interbody fusion at L6-7 using either BT implants or nontreated (NT) implants, followed by posterior spinous process wiring and facet screw fixation. Radiographic evaluations were performed at 1, 2, and 3 months postoperatively using X-ray fluoroscopy. Animals were killed 3 months postoperatively, and fusion status was evaluated by manual palpation and histological examination. RESULTS: Interbody fusion was confirmed in all five dogs in the BT group and three of five dogs in the NT group. Histological examination demonstrated a large amount of new bone formation with marrowlike tissue in the BT implants and primarily fibrous tissue formation in the NT implants. CONCLUSIONS: Bioactive treatment effectively enhanced the fusion ability of the porous titanium implants. These findings, coupled with the appropriate mechanical properties in load-bearing conditions, indicate that these porous bioactive titanium implants represent a new generation of biomaterial for spinal interbody fusion.     

Intervertebral disc degeneration adjacent to a lumbar fusion. An experimental rabbit model

Our study establishes a rabbit model of disc degeneration which requires neither a chemical nor physical injury to the disc. Disc degeneration similar to that seen in man was created at levels proximal (L4-L5) and caudal (L7-S1) to a simulated lumbar fusion and was studied for up to nine months after arthrodesis. Loss of the normal parallel arrangement of collagen bundles within the annular lamellae was observed in intervertebral discs adjacent to the fusion at three months. By six months there was further disorganisation as well as loss of distinction between the lamellae themselves. By nine months the structure of the disc had been replaced by disorganised fibrous tissue, and annular tears were seen. There was an initial cellular proliferative response followed by loss of chondrocytes and notochordal cells in the nucleus pulposus. Degeneration was accompanied by a decrease in the monomer size of proteoglycans. Narrowing of the disc space, endplate sclerosis and the formation of osteophytes at adjacent disc spaces were observed radiologically.     

Experimental anterior spine fusion using bovine bone morphogenetic protein: a study in rabbits

We developed an experimental model to study the merit of bovine bone morphogenic protein (bBMP) injection into the intervertebral disc to induce anterior interbody fusion. A total of 24 rabbits, divided into three groups of 8 animals each, were used. One hundred and fifty μg of partially purified bBMP was employed in the first group and 10 μg bBMP in the second group. In the control group, a sham operation was performed. The animals were followed radiographically at weekly intervals and animals were killed 3, 6, and 12 weeks postoperatively. After sacrifice, a mechanical and histologic evaluation of fusion was performed. Results of radiographic and histologic evaluation showed bone formation, which had resulted in the bridging of adjacent endplates, in the 150-μg group. In the 10-μg group, new bone formation was less extensive. In the control group, intradiscal bone formation was seen in only 1 animal. Range of motion measurements on flexion/extension films showed significantly decreased motion in segments that were fused with 150-μg of BMP. This study demonstrated the utility of an experimental model which allowed investigation of how anterior spine fusion may be further studied. Intradiscal injection of BMP could ultimately play a role in the development of minimally invasive techniques for anterior spinal fusion. Received for publication on Jan. 6, 1999; accepted on Aug. 18, 1999     

Middle East respiratory syndrome coronavirus experimental transmission using a pig model

Dromedary camels are the main reservoir of Middle East respiratory syndrome coronavirus (MERS‐CoV), but other livestock species (i.e., alpacas, llamas, and pigs) are also susceptible to infection with MERS‐CoV. Animal‐to‐animal transmission in alpacas was reported, but evidence for transmission in other species has not been proved. This study explored pig‐to‐pig MERS‐CoV transmission experimentally. Virus was present in nasal swabs of infected animals, and limited amounts of viral RNA, but no infectious virus were detected in the direct contact pigs. No virus was detected in the indirect contact group. Furthermore, direct and indirect contact pigs did not develop specific antibodies against MERS‐CoV. Therefore, the role of pigs as reservoir is probably negligible, although it deserves further confirmation.     

大鼠脊柱融合模型中BBP增强BMP-2的骨诱导作用

[目的]验证在大鼠脊柱融合模型中BBP对于rhBMP-2骨诱导作用的影响。[方法]采取Lewis大鼠的脊柱后外侧横突间融合模型,在胶原海绵为载体的rhBMP-2中加入BBP并减少rhBMP-2的用量,测试两种不同剂量的BBP(500 ug和1 000 ug)有或无低剂量的rhBMP2(1 ug)时的骨融合效果,并与单纯的低剂量rhBMP-2(1 ug)组相对比。融合效果采用手工评估,影像学评分,Micro-CT评估和组织学评估4种方法。[结果]BBP本身不管是低剂量还是高剂量均不能诱导骨融合。BBP复合低剂量BMP-2不能完全取得与高剂量BMP-2完全相同的效果,但可以减少BMP-2的用量。加入BBP的低剂量BMP-2组显然较低剂量BMP-2组融合率高,而且与高剂量BMP-2组的融合率相近,而且BBP的低剂量BMP-2组显然较低剂量BMP-2组融合的要早。[结论]在大鼠的脊柱融合模型中,BBP本身不管是低剂量还是高剂量均不能诱导骨融合。BBP可以增强BMP-2的骨形成作用,提高融合率,降低BMP-2的使用剂量以及减少了剂量相关性副作用的发生率,但不能取得与高剂量BMP-2完全相同的效果。BBP可以减少脊柱融合所需的时间和提高形成骨的质量。进一步的研究可以优化BBP和BMP-2的剂量,从而为以后的临床手术应用中取得更好的融合效果。     

First experience with laparoscopic spine fusion in an experimental model in the pig

Background: We elucidated whether anterior lumbar spine fusion with interbody implants (BAK) can be performed in an experimental model in the pig using a transperitoneal laporoscopic approach. Methods: In seven animals, a pneumoperitoneum with an intraabdominal pressure of 12 mmHg was induced, and five trocars were placed in the middle, as well as in the left and right lateral aspect of the abdomen. With the use of specially designed instruments, the bifurcations of the aorta and vena cava were prepared. The sacral artery, overlying the anterior aspect of the L5/S1 disc space, was retracted, allowing the exposure of the disc space. A working trocar was then fixed to the spine bodies above (L6) and below (S1) the disc, and instrumentation was completed by destruction of the disc, insertion of distraction plug, and implantation of the BAK cage. X-ray control allowed exact positioning of the cage. Results: There were no major complications during the operative procedure, in particular no bleeding from major blood vessels and no injury to intraperitoneal organs. Cages were implanted in all animals in correct position, as indicated by postoperative X-ray control. Conclusions: We conclude from our experiments that in the pig model implants for anterior interbody lumbar spine fusion can be inserted successfully using the laparoscopic approach. We propose that the pig model represents an ideal tool for training before applying this operative procedure in men.     

An experimental model of detrusor instability in the obstructed pig

Bladder outflow obstruction was produced in 18 young male pigs using either a silver ring or a silk ligature placed around the proximal urethra. Normal growth of the animals resulted in progressive obstruction. This was monitored by urodynamic studies in conscious animals, using either long-term indwelling bladder cannulae or by intermittent suprapubic catheterisation. At urodynamic assessment 3 to 5 months later, the obstructed pigs voided at an elevated pressure and with a diminished flow rate compared with control animals. Sixty-four per cent of the obstructed pigs developed detrusor instability, with spontaneous contractions exceeding 15 cm H2O during bladder filling; another 14% had decreased bladder compliance. In control animals the filling cystometrogram was stable, with little pressure rise during filling and no spontaneous contractions. This animal model provides the opportunity to study the physiological changes responsible for the development of detrusor instability in the obstructed bladder. It may also be useful for evaluating new treatment regimes for detrusor instability.