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.     

Opioids delay healing of spinal fusion: a rabbit posterolateral lumbar fusion model

Background Context

Opioid use is prevalent in the management of pre- and postoperative pain in patients undergoing spinal fusion. There is evidence that opioids downregulate osteoblasts in vitro, and a previous study found that morphine delays the maturation and remodeling of callus in a rat femur fracture model. However, the effect of opioids on healing of spinal fusion has not been investigated before. Isolating the effect of opioid exposure in humans would be limited by the numerous confounding factors that affect fusion healing. Therefore, we have used a well-established rabbit model to study the process of spinal fusion healing that closely mimics humans.

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.     

Effect of Hydroxyapatite porous characteristics on healing outcomes in rabbit posterolateral spinal fusion model

Hydroxyapatite (HA) has been commonly used as a bone graft substitute in various kinds of clinical fields. To improve the healing capability of HA, many studies have been performed to reveal its optimal structural characteristics for better healing outcomes. In spinal reconstruction surgery, non-interconnected porous HAs have already been applied as a bone graft extender in order to avoid autogenous bone harvesting. However, there have been few experimental studies regarding the effects of the structural characteristics of HA in posterolateral lumbar intertransverse process spine fusion (PLF). The aims of this study were to investigate the effect of HA porous characteristics on healing outcomes in a rabbit PLF model in order to elucidate appropriate structural characteristics of HA as a bone graft extender. Thirty-six adult female Japanese White rabbits underwent bilateral intertransverse process fusion at the level of L5–6 without internal fixation. We prepared three types of HA with different porosities: HA with 15% porosity (HA15%), HA with 50% porosity (HA50%), and HA with 85% porosity (HA85%), all of which were clinically available materials. The HA15% and HA50% had few interconnecting pores, whereas the HA85%, which was a recently developed material, had abundant interconnecting pores. All rabbits were randomly divided into the following four groups according to the grafted materials: (1) HA15% + autogenous bone, (2) HA50% + autogenous bone, (3) HA85% + autogenous bone, (4) pure autogenous bone graft. The animals were euthanized at 5 weeks after surgery, and post-mortem analyses including biomechanical testing, radiographical and histological evaluations were performed. There was no statistically significant difference in either fusion rate and/or bending stiffness among the three HA groups. However, in histological and radiological analyses, both bone ingrowth rate and direct bone bonding rate in the HA85% group were significantly higher than those in the HA15% and HA50% groups, despite the similar value of bone volume rate in fusion mass among the three HA groups. In the HA85% group, bone ingrowth was achieved throughout the implanted HAs via interconnecting pores and there was excellent unification between the HA granules and the newly mineralized bone. On the other hand, in the non-interconnected porous HA groups, only a little bone ingrowth could be seen at the peripheral pores of the implanted HA, and its surface was mostly covered with fibrous tissue or empty space. The current study demonstrated that the HA porous characteristics had an effect on the histological outcomes in a rabbit PLF model. We would like to conclude that the interconnected high porous structure seems to be promising for the environment of PLF in the point of producing fusion mass with higher cellular viability. This is because the HA85% is superior in terms of integration with the newly formed bone in fusion mass compared to the non-interconnected porous HAs. However, the porous modifications of HA have little influence on fusion rate and mechanical strength because primary stabilization of the fusion segment is mainly achieved by bridging bone between the adjacent transverse processes outside the implanted materials, rather than the degree of integration between the newly formed bone and the HA granules in PLF.     

rhBMP-2/异体骨复合骨应用于兔腰椎植骨融合的实验研究

目的评价rhBMP-2/异体骨复合骨在兔腰椎后路横突间植骨融合中的效果,探讨此复合骨替代自体骨用于腰椎后路横突间植骨融合的可能性。方法30只新西兰大白兔随机分为三组,行后路腰椎横突间植骨融合术,分别植入自体髂骨条、rhBMP-2/异体骨复合骨及单纯异体髂骨条。术后喂养6周,处死动物,取出标本,分别采取盲法进行手工测试,影像学、组织学观察及单向拉伸的生物力学测试,并用图像分析系统定量分析植骨区内成骨量,取得数据后进行综合评价。结果手工测试显示rhBMP-2/异体骨复合骨组融合率(90%)明显优于自体骨(40%)及异体骨组(20%)(P＜0．05)。影像学及组织学显示rhBMP-2/异体骨复合骨组成骨速度及骨成熟程度均优于其它两组。单向拉伸生物力学测试结果表明复合骨组和自体骨组两组间无明显差别(P＞0．05),但均明显优于异体骨组(P＜0．05)。定量分析显示植骨区内新骨形成面积复合骨组和自体骨组两组间无明显差别(P＞0．05),但均明显优于异体骨组(P＜0．05)。结论在兔腰椎后路横突间植骨融合术中,rhBMP-2/异体骨复合骨可促进骨形成并提高融合率,可作为替代自体骨的理想材料。     

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.     

The effect of alendronate sodium on spinal fusion: a rabbit model.

BACKGROUND CONTEXT: Bisphosphonates affect bone remodeling and increase bone mass through the inhibition of osteoclasts. Their effect on osteoblasts, and the balance between osteoblastic and osteoclastic activity on bone turnover and healing, is not completely understood. Specifically, the effect of bisphosphonates on spinal fusion has yet to be determined. With the increasing use of bisphosphonates in the elderly population, this effect needs to be delineated. PURPOSE: To evaluate the effect of alendronate sodium after an intertransverse process spinal fusion in a rabbit model. STUDY DESIGN/SETTING: Randomized double-blinded in vivo study of the effect of alendronate sodium in a spinal fusion model. METHODS: Fifty New Zealand white rabbits underwent a posterolateral L5-L6 intertransverse process arthrodesis with autogenous iliac crest bone graft. The rabbits were then randomly divided into two groups. Group I received 3 cc of saline placebo per oral gavage, and Group II received 200 micrograms (approximately 0.05 mg/kg/day) of alendronate sodium dissolved in 3 cc of saline per day for 8 weeks. Upon completion, the rabbits were sacrificed and the lumbar spines harvested, radiographed and graded for motion across the fusion site with manual palpation. Two independent pathologists then prepared and sectioned each left and right fusion mass. Three random x10 fields were examined and graded for both the cephalad and caudad ends of each section (516 fields). Fusion quality was graded using an established histological scoring scale (score 0 to 7 based on fibrous and bone content of the fusion mass). RESULTS: Two rabbits died on the day of operation, and 48 rabbits survived the operation. Five additional rabbits died within the first 2 postoperative weeks. Thus, 43 rabbits (21 in Group I, 22 in Group II) completed the 8-week course of treatment. Grading each side separately, 26 of 42 fusion masses (62%) in Group I and 24 of 44 fusion masses (55%) in Group II had radiographic evidence of fusion (p=.76). With gross palpation, 11 of 21 motion segments (52%) in Group I versus 13 of 22 motion segments (59%) in Group II were determined to have a solid fusion (p=.76). Histologically, Group I had a higher median score (6.0; range, 0 to 7 vs. 1.0; range, 0 to 7; p<.0001) and a higher fusion rate (76% vs. 45%; p=.004) than Group II. CONCLUSIONS: Alendronate sodium appears to inhibit or delay bone fusion in a rabbit model. Presumably, this occurs as a result of uncoupling the balanced osteoclastic and osteoblastic activity inherent to bone healing. These findings suggest that a discontinuance of alendronate sodium postoperatively during the acute fusion period may be warranted.     

The effect of hyperbaric oxygen therapy on spinal fusion: using the model of posterolateral intertransverse fusion in rabbits

BACKGROUND: The purpose of this study is to evaluate the facilitating effect of hyperbaric oxygen (HBO) on posterolateral intertransverse fusion using a validated rabbit model. METHODS: Twenty-four male New Zealand rabbits underwent posterolateral intertransverse fusion at L5-L6 with autogenous iliac bone graft. They were evenly divided into two groups: the HBO group and the normal room air (RA) group. Each group had six rabbits killed at 4 weeks and 8 weeks, respectively. The rabbits in the HBO groups were treated with 100% oxygen at 2.5 atm for 2 hours a day. After being killed, all rabbits were subjected to radiographic examination, manual testing, and torsional loading to evaluate the results of spinal fusion. RESULT: Radiographic union of intertransverse fusion areas at 4-week RA, 4-week HBO, 8-week RA, and 8-week HBO were 2 of 12, 7 of 12, 7 of 12, and 10 of 12, respectively. Solid union proven by manual palpation was found to be zero of six, three of six, four of six, and five of six of the cases, respectively. The average peak torsional momentums were 2120.2, 2576.5, 2661.6, and 3079.8 N-mm, respectively. Spinal fusion was significantly improved in the HBO groups at both 4 weeks and 8 weeks. CONCLUSION: The results of this study suggest that intermittent hyperbaric oxygen therapy will hasten the bone healing process and improve the fusion rate as compared with the non-HBO group.     

rhBMP-2 enhancement of posterolateral spinal fusion in a rabbit model in the presence of concurrently administered doxorubicin.

BACKGROUND CONTEXT: Spinal fusions can be necessary in patients undergoing chemotherapy with doxorubicin. In a previous study, doxorubicin was shown to decrease spinal fusion rates in a rabbit model of lumbar intertransverse process spinal fusion with autograft iliac crest bone. In the current study, we determine whether spinal fusion with recombinant human bone morphogenetic protein-2 (rhBMP-2) can overcome the inhibitory effect of doxorubicin in spinal fusion. PURPOSE: To determine if rhBMP-2 can overcome the inhibitory effects of doxorubicin (adriamycin) in an animal model of posterolateral spinal fusion. STUDY DESIGN/SETTING: Prospective, controlled, rabbit model of posterolateral lumbar fusion. OUTCOME MEASURES: Spine fusion was assessed by manual palpation (by observers blinded to the treatment group) at the level of arthrodesis. Fusion was graded according to a five-tiered classification (0-4). Posteroanterior radiographs of the excised spines were also graded in a blinded fashion using a six-point scoring system (0-5) devised to describe the amount of bone observed between the L5-L6 transverse processes. METHODS: Thirty-two New Zealand White rabbits underwent posterolateral fusion at L5-L6 with either autograft (iliac crest autograft bone) or rhBMP-2 (rhBMP-2/absorbable collagen sponge (0.86 mg/level). All animals received a dose of doxorubicin (2.5 mg/kg) known to inhibit spine fusion via the central vein of the ear immediately postoperatively. Five weeks postoperatively the rabbits were euthanized. Spine fusion was assessed by manual palpation, and graft quality was assessed with posteroanterior radiographs. RESULTS: Four of the 16 spines (25%) in the autograft group and 16 of the 16 spines (100%) in the rhBMP-2 group fused in the presence of doxorubicin administration (p<.05). There was significantly increased bone formation in the rhBMP-2 group (p<.05). One unilateral, subclinical wound infection was observed in each group at the time of euthanization (autograft [n=1, 6%] and rhBMP-2 [n=1, 6%]). CONCLUSIONS: We confirm that when autograft is used, doxorubicin decreases spinal fusion rate (25%) compared with historical controls (60-75%). More importantly, using rhBMP-2 overcomes the inhibitory effect of doxorubicin, resulting in 100% fusion in our animal model. This study suggests that rhBMP-2 has the potential to improve fusion rates in human patients undergoing chemotherapy with doxorubicin.     

Effect of a single dose of pamidronate administered at the time of surgery in a rabbit posterolateral spinal fusion model

Spinal fusion is usually performed on patients who receive bisphosphonates (BP); however, limited data on their action on spinal fusion are available. Previous studies in animal models have shown that chronic administrations of BP reduced spinal fusion rates, and only one study has shown that a single dose administration of zolendronic acid increased fusion rate. The objective of the present study was to evaluate if pamidronate (PA), which was previously demonstrated to reduce spinal fusion rate when administered continuously for 8 weeks, would increase the spinal fusion rate if administered in a single dose at the time of surgery in a rabbit model. Thirty-two New Zealand rabbits underwent an L5–L6 posterolateral intertransverse fusion with iliac crest autograft. Animals were randomized to receive either PA 3 mg/kg in a single dose immediately after surgery, or normal saline. Animals were killed 8 weeks after surgery and fusion was determined by manual palpation and radiographic analysis. Fusion healing was obtained in eight rabbits (50%) in the PA group and in four animals (25%) in the control group, p = 0.137. In a rabbit model, a single dose of PA did not decrease lumbar spinal arthrodesis consolidation rates, but it obtained a nonsignificant higher spinal fusion rate.     

Stopping nicotine exposure before surgery. The effect on spinal fusion in a rabbit model

STUDY DESIGN: A double-blind, prospective, randomized study using a validated rabbit model of intertransverse process fusion. OBJECTIVES: To determine the effect of stopping prolonged nicotine exposure on autogenous bone graft incorporation in a rabbit lumbar spinal fusion model. SUMMARY OF BACKGROUND DATA: There is a growing body of evidence that systemic nicotine impairs healing of spinal fusions and fractures. However, it remains to be determined whether, if nicotine increases the nonunion rate of spinal fusion surgery, stopping nicotine exposure before surgery will negate this inhibitory effect. METHODS: Forty-seven rabbits were divided into two experimental groups and one control group. The two experimental groups were exposed to systemic nicotine for 8 weeks. Nicotine exposure was stopped in one group 1 week before surgery; nicotine exposure was continued in the other group throughout the study. All rabbits underwent an L5-L6 intertransverse process fusion with autogenous iliac crest bone graft. All rabbits were killed 35 days after surgery. Forty rabbits completed the study and underwent radiographic, biomechanical, and histologic testing. RESULTS: Fusion, as determined by a blinded examiner palpating the spine, occurred in 7 of 13 control rabbits, 4 of 13 rabbits that "quit" nicotine, and none of the 14 rabbits exposed to continuous nicotine. There was a statistically significant difference between the control and continuous nicotine (P = 0.0015) and between the discontinued nicotine and continuous nicotine groups (P = 0.025). Biomechanical testing showed no significant differences between groups (P = 0.11). A blinded musculoskeletal pathologist was unable to detect a difference between groups based on histologic analysis. CONCLUSIONS: Chronic nicotine exposure was shown to decrease spinal fusion rates. Discontinuing nicotine before surgery improved fusion rates.     

The effect of ketoprophen on lumbar spinal fusion healing in a rabbit model. Laboratory investigation

OBJECT: Several reports have shown that nonsteroidal antiinflammatory drugs (NSAIDs) have an inhibitory effect in osteogenesis and reduce heterotopic ossification in humans. A deleterious effect of NSAIDs in posterolateral intertransverse process fusion has also been suggested. The authors used a validated rabbit model to try to determine the influence of the NSAID ketoprophen on the fusion rate in lumbar spinal arthrodesis. METHODS: Thirty New Zealand male rabbits underwent posterolateral (intertransverse process) bilateral spinal fusions at a single level, using autologous bone graft obtained from both iliac crests. The animals were randomized after the operation, so that 15 rabbits received ketoprophen as a postoperative analgesic and the other 15 received the postoperative analgesic tramadol. The animals were killed 8 weeks after surgery, and fusion status was determined by inspection, palpation, anteroposterior radiographs, and histological analysis. RESULTS: A solid fusion was obtained in eight rabbits (53%), and pseudarthrosis in seven rabbits (47%) in each group. CONCLUSIONS: These findings suggest that the use of ketoprophen after intertransverse spinal fusion at a single level does not decrease the fusion rate, compared with tramadol.     

Engineered periosteum-bone biomimetic bone graft enhances posterolateral spine fusion in a rabbit model

BACKGROUND CONTEXT

Bone marrow derived mesenchymal stem cells (BMSCs) and periosteum-derived cells (PDCs) have shown great viability in terms of osteogenic potential and have been considered the major cellular source for skeletal tissue engineering. Using a PDCs-impregnated cell sheet to surround a BMSCs-impregnated tricalcium phosphate (TCP) scaffold might create a periosteum-bone biomimetic bone graft substitute to enhance spine fusion.

Acquired spondylolysis after posterolateral spinal fusion

A case of spondylolysis occurring immediately above a posterolateral lumbar spinal fusion in a 12-year-old girl is described. This case illustrates a potential problem of stress concentration at the pars interarticularis, previously only described after posterior interlaminar fusion.