Augmentation of spinal arthrodesis with autologous bone marrow in a rabbit posterolateral spine fusion model

Co-delivery of rhBMP-2 and zoledronic acid using calcium sulfate/hydroxyapatite carrier as a bioactive bone substitute to enhance and accelerate spinal fusion

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been FDA-approved for lumbar fusion, but supraphysiologic initial burst release due to suboptimal carrier and late excess bone resorption caused by osteoclast activation have limited its clinical usage. One strategy to mitigate the pro-osteoclast side effect of rhBMP-2 is to give systemic bisphosphonates, but it presents challenges with systemic side effects and low local bioavailability. The aim of this in vivo study was to analyze if posterolateral spinal fusion (PLF) could be improved by utilizing a calcium sulfate/hydroxyapatite (CaS/HA) carrier co-delivering rhBMP-2 and zoledronic acid (ZA). Six groups were allocated (CaS/HA, CaS/HA + BMP-2, CaS/HA + systemic ZA, CaS/HA + local ZA, CaS/HA + BMP-2 + systemic ZA, and CaS/HA + BMP-2 + local ZA). 10-week-old male Wistar rats, were randomly assigned to undergo L4-L5 PLF with implantation of group-dependent scaffolds. At 3 and 6 weeks, the animals were euthanized for radiography, μCT, histological staining, or biomechanical testing to evaluate spinal fusion. The results demonstrated that the CaS/HA biomaterial alone or in combination with local or systemic ZA didn't support PLF. However, the delivery of rhBMP-2 significantly promoted PLF. Combining systemic ZA with BMP-2 didn't enhance spinal fusion. Notably, the co-delivery of rhBMP-2 and ZA using the CaS/HA carrier significantly enhanced and accelerated PLF, without inhibiting systemic bone turnover, and potentially reduced the dose of rhBMP-2. Together, the treatment regimen of CaS/HA biomaterial co-delivering rhBMP-2 and ZA could potentially be a safe and cost-effective off-the-shelf bioactive bone substitute to enhance spinal fusion.

Abaloparatide Enhances Fusion and Bone Formation in a Rabbit Spinal Arthrodesis Model

STUDY DESIGN

Prospective randomized placebo controlled animal trial.

OBJECTIVE

Determine the effect of daily subcutaneous abaloparatide injection on the intervertebral fusion rate in rabbits undergoing posterolateral fusion.

STUDY OF BACKGROUND DATA

Despite the wide utilization of spine fusion, pseudarthrosis remains prevalent, and results in increased morbidity. Abaloparatide is a novel analog of parathyroid hormone-related peptide (1-34) and has shown efficacy in a rat posterolateral spine fusion model to increase fusion rates. The effect of abaloparatide on the fusion rate in a larger animal model remains unknown.

MATERIALS AND METHODS

A total of 24 skeletally mature New Zealand White male rabbits underwent bilateral posterolateral spine fusion. Following surgery, the rabbits were randomized to receive either saline as control or abaloparatide subcutaneous injection daily. Specimens underwent manual assessment of fusion, radiographic analysis with both x-ray and high-resolution peripheral quantitative computed tomography, and biomechanical assessment.

RESULTS

Rabbits that received abaloparatide had a 100% (10/10) fusion rate compared with 45% (5/11) for controls ( P <0.02) as assessed by manual palpation. Radiographic analysis determined an overall mean fusion score of 4.17±1.03 in the abaloparatide group versus 3.39±1.21 for controls ( P <0.001). The abaloparatide group also had a greater volume of bone formed with a bone volume of 1209±543 mm 3 compared with 551±152 mm 3 ( P <0.001) for controls. The abaloparatide group had significantly greater trabecular bone volume fraction and trabecular thickness and lower specific bone surface and connectivity density in the adjacent levels when compared with controls. Abaloparatide treatment did not impact trabecular number or separation. There were no differences in biomechanical testing in flexion, extension, or lateral bending ( P >0.05) between groups.

CONCLUSIONS

Abaloparatide significantly increased the fusion rate in a rabbit posterolateral fusion model as assessed by manual palpation. In addition, there were marked increases in the radiographic evaluation of fusion.

History of Bone Grafts in Spine Surgery

Bone grafting replaces damaged or missing bone with new bone and is used for surgical arthrodesis. Patients benefit from a huge variety of bone graft techniques and options for spinal fusions. This article reviews the rich history of bone grafts in surgery with particular emphasis on spinal fusion. During the early years of bone grafting in spine surgery, bone grafts were used on tuberculosis patients, and the structural support of the graft was most the important consideration. Between 1960 and 2000, many advances were made, specifically in the use of bone graft substitutes. The field of bone grafts in spine surgery has evolved rapidly since first described.

Comparing the efficacy of adipose-derived and bone marrow-derived cells in a rat model of posterolateral lumbar fusion

Although bone marrow-derived mesenchymal stem cells (BMCs) have been widely used in spinal fusion procedures, adipose-derived stem cells (ASCs) offer a number of advantages as an alternative clinical cell source. This study directly compares the efficacy of ASCs and BMCs from the same donor animals to achieve successful fusion when combined with a clinical-grade bone graft substitute in a rat lumbar fusion model. ASCs and BMCs were isolated from the same Lewis donor rats and grown to passage 2 (P2). Single-level bilateral posterolateral intertransverse process lumbar fusion surgery was performed on syngeneic rats divided into three experimental groups: clinical-grade bone graft substitute alone (CBGS); CBGS+ rat ASCs (rASC); and, CBGS+ rat BMCs (rBMC). Eight weeks postoperatively, fusion was evaluated via micro-CT, manual palpation and histology. In vitro analysis of the osteogenic capacity of rBMCs and rASCs was also performed. Results indicated that the average fusion volume in the rASC group was the largest and was significantly larger than the CBGS group. Although the rASC group displayed the highest fusion rates via micro-CT and manual palpation, this difference was not statistically significant. Cell-seeded grafts showed more histological bone formation than cell-free grafts. P2 rASCs and rBMCs displayed similar in vitro osteogenic differentiation capacities. Overall, this study showed that, when combined with a clinical-grade bone graft substitute in a rat model, rASCs cells yielded the largest fusion masses and comparable fusion results to rBMCs. These results add to growing evidence that ASCs provide an attractive alternative to BMCs for spinal fusion procedures.

Effect of Local Tranexamic Acid on the Quality of Bone Healing in a Rat Spinal Fusion Model

Introduction

The use of the antifibrinolytic agent tranexamic acid has positive effects on bleeding control, but our knowledge is still limited regarding how fibrinolysis suppression changes the process of bone formation and the quality of bone. Because of the several side effects of systemic tranexamic acid, topical usage has been established in several procedures. This study aimed to investigate the effect of local tranexamic acid on vertebral fusion by using macroscopic, radiologic, and microscopic techniques. We also attempted to determine the safe dose range in case some doses had negative effects on fusion.

Methods

Twenty-eight Wistar albino rats underwent intertransverse fusion. All rats were randomized into four groups: groups treated with local tranexamic acid doses of 1 mg/kg (D1), 10 mg/kg (D10), and 100 mg/kg (D100) and the control group with no drug (D0). At the end of the eighth week, all rats were sacrificed for evaluation in terms of palpation, mammography, and histopathologic analysis.

Results

The manual palpation results presented with lower fusion rates in D10 and D100 groups than in the control group. Radiological examination results were significantly higher in the control group. The histopathologic examination revealed no significant differences between groups in the percent of new bone formation.

Conclusions

Our results showed that local administration of tranexamic acid reduced the quality and stability of fusion without a delay in bone formation. However, doses of 1 mg/kg did not reduce the stability in the palpation test. Our findings suggest that 1 mg/kg dose is a critical threshold above which tranexamic acid reduced the bone healing process of fusion and that surgeons should consider the doses of local tranexamic acid during surgery.

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

BACKGROUND CONTEXT

Synthetic 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.

PURPOSE

To 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 DESIGN

Efficacy 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.

METHODS

Skeletally 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.

RESULTS

Assessment 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.

CONCLUSIONS

The 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 SIGNIFICANCE

This 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.

Comparison of Freshly Isolated Adipose Tissue-derived Stromal Vascular Fraction and Bone Marrow Cells in a Posterolateral Lumbar Spinal Fusion Model

STUDY DESIGN

Rat posterolateral lumbar fusion model.

OBJECTIVE

The aim of this study was to compare the efficacy of freshly isolated adipose tissue-derived stromal vascular fraction (A-SVF) and bone marrow cells (BMCs) cells in achieving spinal fusion in a rat model.

SUMMARY OF BACKGROUND DATA

Adipose tissue-derived stromal cells (ASCs) offer advantages as a clinical cell source compared to bone marrow-derived stromal cells (BMSCs), including larger available tissue volumes and reduced donor site morbidity. While pre-clinical studies have shown that ex vivo expanded ASCs can be successfully used in spinal fusion, the use of A-SVF cells better allows for clinical translation.

METHODS

A-SVF cells were isolated from the inguinal fat pads, whereas BMCs were isolated from the long bones of syngeneic 6- to 8-week-old Lewis rats and combined with Vitoss (Stryker) bone graft substitute for subsequent transplantation. Posterolateral spinal fusion surgery at L4-L5 was performed on 36 female Lewis rats divided into three experimental groups: Vitoss bone graft substitute only (VO group); Vitoss + 2.5 × 106 A-SVF cells/side; and, Vitoss + 2.5 × 106 BMCs/side. Fusion was assessed 8 weeks post-surgery via manual palpation, micro-computed tomography (μCT) imaging, and histology.

RESULTS

μCT imaging analyses revealed that fusion volumes and μCT fusion scores in the A-SVF group were significantly higher than in the VO group; however, they were not significantly different between the A-SVF group and the BMC group. The average manual palpation score was highest in the A-SVF group compared with the BMC and VO groups. Fusion masses arising from cell-seeded implants yielded better bone quality than nonseeded bone graft substitute.

CONCLUSION

In a rat model, A-SVF cells yielded a comparable fusion mass volume and radiographic rate of fusion to BMCs when combined with a clinical-grade bone graft substitute. These results suggest the feasibility of using freshly isolated A-SVF cells in spinal fusion procedures.Level of Evidence: N/A.

Local insulin application has a dose-dependent effect on lumbar fusion in a rabbit model

The purpose of this study was to determine if locally applied insulin has a dose-responsive effect on posterolateral lumbar fusion. Adult male New Zealand White rabbits underwent posterolateral intertransverse spinal fusions (PLFs) at L5-L6 using suboptimal amounts of autograft. Fusion sites were treated with collagen sponge soaked in saline (control, n = 11), or with insulin at low (5 or 10 units, n = 13), mid (20 units, n = 11), and high (40 units, n = 11) doses. Rabbits were euthanized at 6 weeks. The L5-L6 spine segment underwent manual palpation and radiographic evaluation performed by two fellowship trained spine surgeons blinded to treatment. Differences between groups were evaluated by analysis of variance on ranks followed by post-hoc Dunn's tests. Forty-three rabbits were euthanized at the planned 6 weeks endpoint, while three died or were euthanized prior to the endpoint. Radiographic evaluation found bilateral solid fusion in 10%, 31%, 60%, and 60% of the rabbits from the control and low, mid, and high-dose insulin-treated groups, respectively (p < 0.05). As per manual palpation, 7 of 10 rabbits in the mid-dose insulin group were fused as compared to 1 of 10 rabbits in the control group (p < 0.05). This study demonstrates that insulin enhanced the effectiveness of autograft to increase fusion success in the rabbit PLF model. The study indicates that insulin or insulin-mimetic compounds can be used to promote bone regeneration.

Bone marrow aspirate clot: A feasible orthobiologic

Musculoskeletal disorders are one of the major health burdens and a leading source of disability worldwide, affecting both juvenile and elderly populations either as a consequence of ageing or extrinsic factors such as physical injuries. This condition often involves a group of locomotor structures such as the bones, joints and muscles and may therefore cause significant economic and emotional impact. Some pharmacological and non-pharmacological treatments have been considered as potential solutions, however, these alternatives have provided quite limited efficacy due to the short-term effect on pain management and inability to restore damaged tissue. The emergence of novel therapeutic alternatives such as the application of orthobiologics, particularly bone marrow aspirate (BMA) clot, have bestowed medical experts with considerable optimism as evidenced by the significant results found in numerous studies addressed in this manuscript. Although other products have been proposed for the treatment of musculoskeletal injuries, the peculiar interest in BMA, fibrin clot and associated fibrinolytic mechanisms continues to expand. BMA is a rich source of various cellular and molecular components which have demonstrated positive effects on tissue regeneration in many in vitro and in vivo models of musculoskeletal injuries. In addition to being able to undergo self-renewal and differentiation, the hematopoietic and mesenchymal stem cells present in this orthobiologic elicit key immunomodulatory and paracrine roles in inflammatory responses in tissue injury and drive the coagulation cascade towards tissue repair via different mechanisms. Although promising, these complex regenerative mechanisms have not yet been fully elucidated.

A novel tissue-engineered bone graft composed of silicon-substituted calcium phosphate, autogenous fine particulate bone powder and BMSCs promotes posterolateral spinal fusion in rabbits

Background

Autogenous bone graft is the gold standard bone grafting substrate available in spinal fusion because of its osteoconductive, osteogenic, and osteoinductive properties. However, several shortcomings including bleeding, infection, chronic pain, and nerve injury are known to be associated with the procedure. Bone tissue engineering has emerged as an alternative therapeutic strategy for bone grafts. New materials have been developed and tested that can substitute for the autogenous bone grafts used in the spinal fusion. The purpose of this study is to evaluate the role of a novel tissue-engineered bone graft with silicon-substituted calcium phosphate (Si-CaP), autogenous fine particulate bone powder (AFPBP), and bone marrow mesenchymal stem cells (BMSCs) using a rabbit posterolateral lumbar fusion model based on bone tissue engineering principles. The application of this graft can represent a novel choice for autogenous bone to reduce the amount of autogenous bone and promote spinal fusion.

Methods

BMSCs from New Zealand white rabbits were isolated and cultured in vitro. Then, BMSCs were marked by the cell tracker chloromethyl-benzamidodialkylcarbocyanine (CM-Dil). A total of 96 New Zealand White rabbits were randomly divided into four groups: (a) AFPBP, (b) Si-CaP, (c) Si-CaP/AFPBP, (d) Si-CaP/AFPBP/BMSCs.The rabbits underwent bilateral posterolateral spine arthrodesis of the L5-L6 intertransverse processes using different grafts. Spinal fusion and bone formation were evaluated at 4, 8, and 12 weeks after surgery by manual palpation, radiology, micro-computed tomography (micro-CT), histology, and scanning electronic microscopy (SEM).

Results

The rate of fusion by manual palpation was higher in the Si-CaP/AFPBP/BMSCs group than the other groups at 8 weeks. The fusion rates in the Si-CaP/AFPBP/BMSCs and the AFPBP groups both reached 100%, which was higher than the Si-CaP/AFPBP group (62.5%) (P ​> ​0.05) and Si-CaP group (37.5%) (P ​< ​0.05) at 12 weeks. New bone formation was observed in all groups after implantation by radiology and micro-CT. The radiographic and CT scores increased in all groups from 4 to 12 weeks, indicating a time-dependent osteogenetic process. The Si-CaP/AFPBP/BMSCs group showed a larger amount of newly formed bone than the Si-CaP/AFPBP and Si-CaP groups at 12 weeks. Bone formation in the Si-CaP/AFPBP/BMSCs group was similar to the AFPBP group. Histology showed that new bone formation continued and increased along with the degradation and absorption of Si-CaP and AFPBP from 4 to 12 weeks in the Si-CaP, Si-CaP/AFPBP, and Si-CaP/AFPBP/BMSCs groups. At 4 weeks, a higher proportion of bone was detected in the AFPBP group (23.49%) compared with the Si-CaP/AFPBP/BMSCs group (14.66%, P ​< ​0.05). In the Si-CaP/AFPBP/BMSCs group at 8 weeks, the area percentage of new bone formation was 28.56%, which was less than the AFPBP group (33.21%, P ​< ​0.05). No difference in bone volume was observed between the Si-CaP/AFPBP/BMSCs group (44.39%) and AFPBP group (45.06%) at 12 weeks (P ​> ​0.05). At 12 weeks, new trabecular were visible in the Si-CaP/AFPBP/BMSCs group by SEM. CM-Dil-positive cells were observed at all stages. Compared with histological images, BMSCs participate in various stages of osteogenesis by transforming into osteoblasts, chondrocytes, and osteocytes.

Conclusion

This study demonstrated for the first time that Si-CaP/AFPBP/BMSCs is a novel tissue-engineered bone graft with excellent bioactivity, biocompatibility, and biodegradability. The graft could reduce the amount of autogenous bone and promote spinal fusion in a rabbit posterolateral lumbar fusion model, representing a novel alternative to autogenous bone.

The Translational potential of this article

The translational potential of this article lies in that this graft will be a novel spinal fusion graft with great potential for clinical applications.

A Comparative Evaluation of Commercially Available Cell-Based Allografts in a Rat Spinal Fusion Model

Background

To evaluate the comparative abilities of commercially available, viable, cellular bone allografts to promote posterolateral spinal fusion.

Methods

Human allografts containing live cells were implanted in the athymic rat model of posterolateral spine fusion. Three commercially available allogeneic cellular bone matrices (Trinity Evolution, Trinity ELITE and Osteocel Plus) were compared with syngeneic iliac crest bone as the control. All spines underwent radiographs, manual palpation, and micro-computed tomography (CT) analysis after excision at 6 weeks. Histological sections of randomly selected spines were subjected to semiquantitative histopathological scoring for bone formation.

Results

By manual palpation, posterolateral fusion was detected in 40% (6/15) of spines implanted with syngeneic bone, whereas spines implanted with Trinity Evolution and Trinity ELITE allografts yielded 71% (10/14) and 77% (10/13) fusion, respectively. Only 7% (1/14) of spines implanted with Osteocel Plus allografts were judged fused by manual palpation (statistically significantly less than ELITE, P < .0007, and Evolution, P < .0013). The mineralized cancellous bone component of the allografts confounded radiographic analysis, but Trinity Evolution (0.452 ± 0.064) and Trinity ELITE (0.536 ± 0.109) allografts produced statistically significantly higher bone fusion mass volumes measured by quantitative micro-CT than did syngeneic bone (0.292 ± 0.109, P < .0001 for ELITE and P < .003 for Evolution) and Osteocel Plus (0.258 ± 0.103, P < .0001). Semiquantitative histopathological scores supported these findings because the total bone and bone marrow scores reflected significantly better new bone and marrow formation in the Trinity groups than in the Osteocel Plus group.

Conclusions

The Trinity Evolution and Trinity ELITE cellular bone allografts were more effective at creating posterolateral fusion than either the Osteocel Plus allografts or syngeneic bone in this animal model.

Clinical Relevance

The superior fusion rate of Trinity cellular bone allografts may lead to better clinical outcome of spinal fusion surgeries.

Scientific, Clinical, Regulatory, and Economic Aspects of Choosing Bone Graft/Biological Options in Spine Surgery

Spinal arthrodesis is a major element of the spinal surgeon's practice. To attain successful fusion rates, attention must be paid to spinal segment immobilization and proper selection of bone graft. Autogenous bone graft (ie, ICBG), the "gold standard," with or without graft extenders and enhancers provides the foundation for most spinal fusions. ABG is the only graft option containing all 3 factors of new bone growth: osteoconductivity, osteoinductivity, and osteogenicity. While many bone graft alternatives function well as bone graft extenders, only growth factors proteins (ie, rhBMP-2 or OP-2) function as bone graft enhancers and substitutes. The search for optimal hybrid interbody cages, bone graft substitutes, autogenous or allogenic stem cells, and nanostructure scaffolds for release of growth factors continues.

Efficacy of a synthetic calcium phosphate with submicron surface topography as autograft extender in lapine posterolateral spinal fusion

Posterolateral spinal fusion (PLF) is a common procedure in orthopedic surgery that is performed to fuse adjacent vertebrae to reduce symptoms related to spinal conditions. In the current study, a novel synthetic calcium phosphate with submicron surface topography was evaluated as an autograft extender in a validated rabbit model of PLF. Fifty-nine skeletally mature New Zealand white rabbits were divided into three groups and underwent single-level intertransverse process PLF at L4-5 using (1) autologous bone graft (ABG) alone or in a 1:1 combination with (2) calcium phosphate granules (ABG/BCPgranules ), or (3) granules embedded in a fast-resorbing polymeric carrier (ABG/BCPputty ). After 6, 9, and 12 weeks, animals were sacrificed and spinal fusion was assessed by manual palpation, Radiographs, micro-CT, mechanical testing (12 weeks only), histology, and histomorphometry. Based on all endpoints, all groups showed a gradual progression in bone formation and maturation during time, leading to solid fusion masses between the transverse processes after 12 weeks. Fusion assessments by manual palpation, radiography and histology were consistent and demonstrated equivalent fusion rates between groups, with high bilateral fusion rates after 12 weeks. Mechanical tests after 12 weeks indicated substantially lower range of motion for all groups, compared to non-operated controls. By histology and histomorphometry, the gradual formation and maturation of bone in the fusion mass was confirmed for each graft type. With these results, we describe the equivalent performance between autograft and a novel calcium phosphate material as an autograft extender in a rabbit model of PLF using an extensive range of evaluation techniques. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2080-2090, 2019.

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.

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.

PURPOSE

The objective of this work was to study the effect of systemic opioids on the process of healing of spinal fusion in a rabbit posterolateral spinal fusion model.

STUDY DESIGN/SETTING

This is a preclinical animal study.

MATERIALS AND METHODS

Twenty-four adult New Zealand white rabbits were studied in two groups after approval from the Institutional Animal Care and Use Committee (IACUC). The opioid group (n=12) received 4 weeks' preoperative and 6 weeks' postoperative transdermal fentanyl. Serum fentanyl levels were measured just before surgery and 4 weeks postoperatively to ensure adequate levels. The control group (n=12) received only perioperative pain control as necessary. All animals underwent a bilateral L5-L6 posterolateral spinal fusion using iliac crest autograft. Animals were euthanized at the 6-week postoperative time point, and assessment of fusion was done by manual palpation, plain radiographs, microcomputed tomography (microCT), and histology.

RESULTS

Twelve animals in the control group and 11 animals in the opioid group were available for analysis at the end of 6 weeks. The fusion scores on manual palpation, radiographs, and microCT were not statistically different. Three-dimensional microCT morphometry found that the fusion mass in the opioid group had a lower bone volume (p=.09), a lower trabecular number (p=.02), and a higher trabecular separation (p=.02) compared with the control group. Histologic analysis found areas of incorporation of autograft and unincorporated graft fragments in both groups. In the control group, there was remodeling of de novo woven bone to lamellar organization with incorporation of osteocytes, formation of mature marrow, and relative paucity of hypertrophied osteoblasts lining new bone. Sections from the opioid group showed formation of de novo woven bone, and hypertrophied osteoblasts were seen lining the new bone. There were no sections showing lamellar organization and development of mature marrow elements in the opioid group. Less dense trabeculae on microCT correlated with histologic findings of relatively immature fusion mass in the opioid group.

CONCLUSIONS

Systemic opioids led to an inferior quality fusion mass with delay in maturation and remodeling at 6 weeks in this rabbit spinal fusion model. These preliminary results lay the foundation for further research to investigate underlying cellular mechanisms, the temporal fusion process, and the dose-duration relationship of opioids responsible for our findings.

The Effects of Topical Vancomycin on Mesenchymal Stem Cells: More May Not Be Better

BACKGROUND

The use of topical vancomycin is increasingly popular in spine surgery. Large retrospective reviews suggest that topical vancomycin provides a cost-effective decrease in post-operative infection. Currently, there is little that is known about the maximum dose that can be applied locally. When 1 gram of vancomycin is mixed into the bone graft and another 1 gram applied freely in a spine wound, the local concentration of antibiotic ranges from 260-2900 μg/mL in the immediate post-op period and 50-730 μg/mL by the second post-operative day. We hypothesized that exuberant doses of vancomycin would be toxic to mesenchymal stem cells (MSCs).

METHODS

Bone marrow was obtained from the femoral canal of patients undergoing routine elective total hip arthroplasty. Mesenchymal stem cells were isolated using plastic adhesion. Cells were exposed to a wide range of doses of vancomycin for 24 hours and then assessed for viability. Osteogenic potential was assessed with alizarin red staining.

RESULTS

There was dose-dependent cell death with vancomycin use. MSC death was 9.43% at 400 μg/mL (p=0.047), 13.79% at 1600 μg/mL (p=0.0047), 19.35% at 3200 μg/mL (p<0.0001), 24.82% at 6400 μg/mL (p<0.0001) and 51.83% at 12800 μg/mL of vancomycin (p<0.0001) in comparison to the control group containing no vancomycin.

CONCLUSIONS

Our in vitro study suggests that vancomycin has toxic effects on hMSCs, a cell population particularly important for bone formation. In the absence of any clinical evidence suggesting that "more vancomycin is better," and our data suggesting that more vancomycin is harmful in vitro, surgeons electing to use topical vancomycin in spine surgery should restrict their use to the doses currently reported in the available published studies unless specific reasons exist otherwise. This study does not establish a contraindication to the use of topical vancomycin, nor does it suggest that pseudarthroses are attributable to vancomycin use.

Variables Affecting Fusion Rates in the Rat Posterolateral Spinal Fusion Model with Autogenic/Allogenic Bone Grafts: A Meta-analysis

The rat posterolateral spinal fusion model with autogenic/allogenic bone graft (rat PFABG) has been increasingly utilized as an experimental model to assess the efficacy of novel fusion treatments. The objective of this study was to investigate the reliability of the rat PFABG model and examine the effects of different variables on spinal fusion. A web-based literature search from January, 1970 to September, 2015, yielded 26 studies, which included 40 rat PFABG control groups and 449 rats. Data regarding age, weight, sex, and strain of rats, graft volume, graft type, decorticated levels, surgical approach, institution, the number of control rats, fusion rate, methods of fusion assessment, and timing of fusion assessment were collected and analyzed. The primary outcome variable of interest was fusion rate, as evaluated by manual palpation. Fusion rates varied widely, from 0 to 96%. The calculated overall fusion rate was 46.1% with an I ² value of 62.4, which indicated moderate heterogeneity. Weight >300 g, age >14 weeks, male rat, Sprague-Dawley strain, and autogenic coccyx grafts increased fusion rates with statistical significance. Additionally, an assessment time-point ≥8 weeks had a trend towards statistical significance (p = 0.070). Multi-regression analysis demonstrated that timing of assessment and age as continuous variables, as well as sex as a categorical variable, can predict the fusion rate with R ² = 0.82. In an inter-institution reliability analysis, the pooled overall fusion rate was 50.0% [44.8, 55.3%], with statistically significant differences among fusion outcomes at different institutions (p < 0.001 and I ² of 72.2). Due to the heterogeneity of fusion outcomes, the reliability of the rat PFABG model was relatively limited. However, selection of adequate variables can optimize its use as a control group in studies evaluating the efficacy of novel fusion therapies.

Effectiveness of Posterolateral Lumbar Fusion Varies with the Physical Properties of Demineralized Bone Matrix Strip

STUDY DESIGN

A randomized, controlled animal study.

PURPOSE

To investigate the effectiveness of fusion and new bone formation induced by demineralized bone matrix (DBM) strips with jelly strengths.

OVERVIEW OF LITERATURE

The form of the DBM can make a difference to the outcome. The effect of different jelly strengths on the ability of DBM to form new bone is not known.

METHODS

Forty-eight rabbits were randomized into a control group and two experimental groups. In the control group (group 1), 1.4 g of autologous iliac crest bone was placed bilaterally. In the experimental groups, a high jelly strength DBM-hyaluronic acid (HA)-gelatin strip (group 2) and a low jelly strength DBM-HA-gelatin strip (group 3) were used. The fusion was assessed with manual manipulation and radiographs. The volume of the fusion mass was determined from computed tomographic images.

RESULTS

The fusion rates as determined by manual palpation were 37.5%, 93.8% and 50.0% in group 1, group 2, and group 3, respectively (p<0.05). By radiography, the fusion rate of High jelly strength DBM strip was statistically significantly greater than that of the other alternatives (p<0.05). The mean bone volume of the fusion mass as determined by computed tomography was 2,142.2±318.5 mm(3), 3,132.9±632.1 mm(3), and 2,741.5±380.4 mm(3) in group 1, group 2, and group 3, respectively (p<0.05).

CONCLUSIONS

These results indicate that differences in the structural and mechanical properties of gelatin that are associated with jelly strength influenced cellular responses such as cell viability and bony tissue ingrowth, facilitating greater bone fusion around high jelly strength implants.

Evaluation of posterolateral lumbar fusion in sheep using mineral scaffolds seeded with cultured bone marrow cells

The objective of this study is to investigate the efficacy of hybrid constructs in comparison to bone grafts (autograft and allograft) for posterolateral lumbar fusion (PLF) in sheep, instrumented with transpedicular screws and bars. Hybrid constructs using cultured bone marrow (BM) mesenchymal stem cells (MSCs) have shown promising results in several bone healing models. In particular, hybrid constructs made by calcium phosphate-enriched cells have had similar fusion rates to bone autografts in posterolateral lumbar fusion in sheep. In our study, four experimental spinal fusions in two animal groups were compared in sheep: autograft and allograft (reference group), hydroxyapatite scaffold, and hydroxyapatite scaffold seeded with cultured and osteoinduced bone marrow MSCs (hybrid construct). During the last three days of culture, dexamethasone (dex) and beta-glycerophosphate (β-GP) were added to potentiate osteoinduction. The two experimental situations of each group were tested in the same spinal segment (L4–L5). Spinal fusion and bone formation were studied by clinical observation, X-ray, computed tomography (CT), histology, and histomorphometry. Lumbar fusion rates assessed by CT scan and histology were higher for autograft and allograft (70%) than for mineral scaffold alone (22%) and hybrid constructs (35%). The quantity of new bone formation was also higher for the reference group, quite similar in both (autograft and allograft). Although the hybrid scaffold group had a better fusion rate than the non-hybrid scaffold group, the histological analysis revealed no significant differences between them in terms of quantity of bone formation. The histology results suggested that mineral scaffolds were partly resorbed in an early phase, and included in callus tissues. Far from the callus area the hydroxyapatite alone did not generate bone around it, but the hybrid scaffold did. In nude mice, labeled cells were induced to differentiate in vivo and monitored by bioluminescence imaging (BLI). Although the cultured MSCs had osteogenic potential, their contribution to spinal fusion when seeded in mineral scaffolds, in the conditions disclosed here, remains uncertain probably due to callus interference with the scaffolds. At present, bone autografts are better than hybrid constructs for posterolateral lumbar fusion, but we should continue to seek better conditions for efficient tissue engineering.

Cellular bone matrices: viable stem cell-containing bone graft substitutes

BACKGROUND CONTEXT

Advances in the field of stem cell technology have stimulated the development and increased use of allogenic bone grafts containing live mesenchymal stem cells (MSCs), also known as cellular bone matrices (CBMs). It is estimated that CBMs comprise greater than 17% of all bone grafts and bone graft substitutes used.

PURPOSE

To critically evaluate CBMs, specifically their technical specifications, existing published data supporting their use, US Food and Drug Administration (FDA) regulation, cost, potential pitfalls, and other aspects pertaining to their use.

STUDY DESIGN

Areview of literature.

METHODS

A series of Ovid, Medline, and Pubmed-National Library of Medicine/National Institutes of Health (www.ncbi.nlm.nih.gov) searches were performed. Only articles in English journals or published with English language translations were included. Level of evidence of the selected articles was assessed. Specific technical information on each CBM was obtained by direct communication from the companies marketing the individual products.

RESULTS

Five different CBMs are currently available for use in spinal fusion surgery. There is a wide variation between the products with regard to the average donor age at harvest, total cellular concentration, percentage of MSCs, shelf life, and cell viability after defrosting. Three retrospective studies evaluating CBMs and fusion have shown fusion rates ranging from 90.2% to 92.3%, and multiple industry-sponsored trials are underway. No independent studies evaluating spinal fusion rates with the use of CBMs exist. All the commercially available CBMs claim to meet the FDA criteria under Section 361, 21 CFR Part 1271, and are not undergoing FDA premarket review. The CBMs claim to provide viable MSCs and are offered at a premium cost. Numerous challenges exist in regard to MSCs' survival, function, osteoblastic potential, and cytokine production once implanted into the intended host.

CONCLUSIONS

Cellular bone matrices may be a promising bone augmentation technology in spinal fusion surgery. Although CBMs appear to be safe for use as bone graft substitutes, their efficacy in spinal fusion surgery remains highly inconclusive. Large, nonindustry sponsored studies evaluating the efficacy of CBMs are required. Without results from such studies, surgeons must be made aware of the potential pitfalls of CBMs in spinal fusion surgery. With the currently available data, there is insufficient evidence to support the use of CBMs as bone graft substitutes in spinal fusion surgery.

Bone marrow concentrate with allograft equivalent to autograft in lumbar fusions

STUDY DESIGN

Prospective randomized study.

OBJECTIVE

To compare autologous bone marrow concentrate mixed with allograft cancellous bone to iliac crest autograft in lumbar fusions.

SUMMARY OF BACKGROUND DATA

Bone marrow has been shown to be a rich source of osteoprogenitor cells. Osteoprogenitor cells have been shown in animals, and some human studies, to have potential in use as a bone graft substitute.

METHODS

Twenty-five patients underwent from 1- to 3-level lumbar fusions. One patient was lost to follow-up. On one half of the spine, allograft plus autologous bone marrow concentrate was used, whereas on the other half, autologous iliac crest bone was used. Cellular analysis, consisting of nucleated cell count, mononuclear cell count, CD34+ count, and colony-forming-units-fibroblast count, was done on marrow aspirates and concentrates. At 1 year postoperation, computed tomographic scans of the fusions were evaluated on a blinded basis by 2 neuroradiologists independent of each other. Radiographical fusion was the primary outcome measure.

RESULTS

There was no statistical difference in fusion scores between allograft and autograft in the lateral gutters, interbody cages, or facet joints. There was a positive trend between CD34+ counts and radiographical fusion.

CONCLUSION

The study shows equivalence between cancellous allograft mixed with bone marrow concentrate and autologous iliac crest bone for lumbar fusions.

LEVEL OF EVIDENCE

2.

The effect of noggin interference in a rabbit posterolateral spinal fusion model

STUDY DESIGN

Noggin protein levels and spinal fusion rates were compared in a rabbit model after application of siRNA against BMP antagonist noggin in paraspinal muscle.

OBJECTIVE

To test whether endogenous BMPs are sufficient to form bone in the absence of their antagonists, using noggin siRNA to interrupt the negative feedback loop on endogenous BMP within the paraspinal muscles in rabbits. Unused Posterolateral lumbar fusion is a standard surgical treatment for many spinal disorders, yet even under ideal conditions the rate of non-fusion approaches 25 %. BMPs are effective in promoting bone formation, and are inhibited by antagonists such as noggin. We have previously shown that in this model, endogenous BMPs are present and endogenous BMP antagonist noggin is strongly increased during spinal fusion. Previous studies have found that noggin siRNA enhanced spinal fusion in combination with supra-physiological amounts of exogenous BMP; however, the effect of the siRNA alone remains unknown.

METHODS

A posterolateral intertransverse rabbit lumbar fusion was utilized, as established by Boden et al. SiRNA against noggin was electroporated into paraspinal muscle to determine its effect on fusion. Outcome measures included noggin protein expression, and assessment of spinal fusion at 6 weeks.

RESULTS

SiRNAs were effective in reducing overexpressed noggin in vitro. Noggin protein was successfully knocked down in vivo for the initial 7 days in our rabbit model and returned to detectable levels by 4 weeks and to normal levels by 6 weeks. The overall fusion rate was not significantly enhanced compared to established controls from our earlier work (Tang et al.).

CONCLUSIONS

Early noggin suppression does not appear to enhance the BMP activity sufficiently to significantly affect final fusion rates in our model.

Factors influencing arthrodesis rates in a rabbit posterolateral spine model with iliac crest autograft

PURPOSE

The rabbit posterolateral intertransverse spine arthrodesis model has been widely used to evaluate spinal biologics. However, to date, the validity and reproducibility of performance of iliac crest bone graft, the most common and critical control group, has not been firmly established. We evaluated original research publications that utilized this model, identified which experimental conditions affected fusion rates, and developed an algorithm to predict fusion rates for future study designs.

METHODS

A MEDLINE search was performed for publications through December, 2011 that utilized this model to evaluate fusion rates elicited by iliac crest autograft. All study parameters were recorded, and logistic regression analyses were performed to determine the effects of these variables on fusion rates as determined by either manual palpation or radiographs.

RESULTS

Seventy studies with 959 rabbits in 102 groups met the inclusion criteria. Excluding studies that measured fusion at 4 or fewer weeks or intentionally tried to decrease the fusion rate, the overall fusion rate for autograft was 58.3 ± 16.3 % (mean ± SD) as determined by manual palpation and 66.4 ± 17.8 % by plain radiographs. Regression analysis demonstrated a difference between these outcome measures with a trend towards significance (p = 0.09). Longer time points and larger volumes of autograft resulted in significantly greater reported fusion rates (p < 0.0001 and p < 0.05, respectively). Neither strain, age, weight, nor vertebral level significantly affected fusion rates.

CONCLUSIONS

Although experimental conditions varied across studies, time point evaluation and autograft volume significantly affected fusion rates. Despite some variability demonstrated across certain studies, we demonstrated that when the time point and volume of autograft were controlled for, the iliac crest control group of the rabbit posterolateral spinal arthrodesis model is both reliable and predictably affected by different experimental conditions.

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.

Reliability of the rabbit postero-lateral spinal fusion model: A meta-analysis

The rabbit model of spinal fusion with the autogenous iliac crest bone graft (ICBG) control is widely used to evaluate bone graft substitutes and enhancers. This study examined the reliability of this model using meta-analysis. A systematic literature search from January 1995 to May 2011 identified 56 studies, involving 733 animals. The primary outcome was fusion success calculated as logit event rate. Study design, surgical technique, rabbit characteristics (gender, species, age, weight), and institution were analyzed. Overall fusion success was 52.4%. Important positive variables were time-point >4 weeks, ICBG dose >1 cm(3) , initial weight of animals ≥3 kg, level at L4-5 or L5-6, and age ≥6 months. Inter- and intra-institutional reliability was excellent. The rabbit model ICBG control group is reliable, although several factors can affect results. Fusion under normal handling occurs reliably in 5 weeks. The volume of bone graft should be >1 cm(3) but no benefits are present with >2 cm(3) . The animals should weigh a minimum of 3 kg and be at least 6 months old.

Effect of adding bone marrow to ceramic graft materials with different interconnectivities in lumbar arthrodesis : quantification of bone formation

INTRODUCTION

Combining bone marrow (BM) with graft materials can stimulate bone healing. However, bone growth is not quantified in most studies, and the influence of the rate of interconnectivity of ceramics loaded with bone marrow has not yet been quantified. Here, a rabbit model of posterolateral intertransverse arthrodesis was used to quantify the effect of adding BM to partially (PIC) or totally (TIC) interconnected ceramics.

MATERIALS AND METHODS

A single lumbar level was grafted on two sides with TIC (n = 12) or PIC (n = 18). The ceramic was loaded with 1.5 ml of BM on one side (chosen at random). The fusion rate was assessed by manual palpation test. Bone formation was quantified on scanning electron microscopy images and by dual-energy X-ray absorptiometry.

RESULTS

At week 6, bone formation with TIC was twice as high as that with PIC. When BM was added, 35.1 and 87.8 % more bone formation was observed in the TIC and PIC, respectively. In ceramics loaded with BM, the bone mineral density was significantly higher than that in ceramics alone.

CONCLUSIONS

Differences in interconnectivity within the family of biphasic ceramics should be taken into account when applying them clinically. BM increased bone formation regardless of the type of ceramic employed.

Bone graft substitutes: What are the options?

Currently, a number of bone grafting materials are available in the clinical setting to enhance bone regeneration, varying from autologous bone to several bone graft substitutes. Although autologous bone remains the "gold standard" for stimulating bone repair and regeneration, the morbidity from its harvesting and its restricted availability generated the need for the development of other materials or strategies either to substitute autologous bone graft or expand its limited supply. Bone graft substitutes can possess one or more components: an osteoconductive matrix, acting as a scaffold; osteoinductive proteins and other growth factors to induce differentiation and proliferation of bone-forming cells; and osteogenic cells for bone formation. Based on their distinct properties, all these bone grafting alternatives have specific indications, and can be used either alone or in combination. In this review, we summarise the available bone grafting materials, focussing mainly on the various bone substitutes and their characteristics, in an effort to specify the indications for their use.

Posterolateral spinal fusion with nano-hydroxyapatite-collagen/PLA composite and autologous adipose-derived mesenchymal stem cells in a rabbit model

Spinal fusion is routinely performed to treat low back pain caused by degeneration of intervertebral discs. An autologous bone graft derived from the iliac crest is the standard procedure used for spinal fusion. However, several shortcomings, including pseudarthrosis, pain and the need for blood transfusion are known to be associated with the procedure. Our study analysed the effectiveness of a new mineralized collagen matrix, nano-hydroxyapatite-collagen-polylactic acid (nHAC-PLA), combined with autologous adipose-derived mesenchymal stem cells (ADMSCs) as a graft material for posterolateral spinal fusion in a rabbit model. Forty rabbits were randomly divided into four groups: autologous iliac crest bone group (ACB), nHAC-PLA composite group (nHAC-PLA), autologous iliac crest bone mixed with nHAC-PLA composite group (ACB + nHAC-PLA), and nHAC-PLA composite combined with ADMSCs (ADMSCs + nHAC-PLA). The viability and the proliferation of the ADMSCs seeded on the scaffolds were evaluated by live/dead kit and MTT assay in vitro, respectively. Lumbar posterolateral fusions were assessed by manual palpation, radiographical and histological procedures, mechanical strength and scanning electronic microscopy (SEM) in 10 weeks of observation. The results showed that the rate of fusion was significantly higher in the ACB and ADMSCs + nHAC-PLA groups than that in the nHAC-PLA and ACB + nHAC-PLA groups. It was not significantly higher in the ACB group than in the ADMSCs + nHAC-PLA group. From microstructural analysis of the samples using histological staining methods, there was more new bone-like tissue formation in the ACB and ADMSCs + nHAC-PLA groups than that in the other two groups at the 10th postoperative week. Our study demonstrated the effective impact of nHAC-PLA combined with ADMSCs in rabbit posterolateral spinal fusion.

Alveolar ridge augmentation in irradiated rabbit mandibles

Oral carcinomas are frequently treated with a nonsegmental mandibulectomy plus radiotherapy. Improving the quality of life of these patients depends on the possibilities for dental rehabilitation. The aim of this study was to increase the alveolar ridge height. Twelve white New Zealand rabbits underwent surgery to produce a 11 x 9 x 7 mm(3) horizontal bicortical full-thickness defect at the alveolar ridge of the left mandible. Six were implanted with a composite associating resorbable collagen membrane filled with micro-macroporous biphasic calcium phosphate granules. After a daily radiation delivery schedule for 4 weeks, a total autologous bone marrow graft was injected percutaneously into the center of the implant. All animals were sacrificed at 16 weeks. Successful osseous colonization was observed in all implants. Significant ridge augmentation was observed (p = 0.0349) in the implanted group compared with the control group. This study contributed to producing an experimental model for oncological mandible defects in rabbits.

Healos graft carrier with bone marrow aspirate instead of allograft as adjunct to local autograft for posterolateral fusion in degenerative lumbar scoliosis: a minimum 2-year follow-up study

Object

The objective of this study was to examine the efficacy and safety of Healos graft carrier with bone marrow aspirate and local autograft compared with the results of allograft in patients with lumbar degenerative scoliosis undergoing posterolateral fusion.

Methods

Twenty-eight patients with degenerative scoliosis underwent posterolateral instrumented fusion and decompression. Patients were grouped according to the graft used. Group A consisted of 12 cases in which the authors used a Healos graft carrier, bone marrow aspirate, and local autograft, and Group B consisted of 16 cases in which the authors used cancellous allograft and local autograft. Patients were followed for a minimum of 2 years postoperatively in terms of pain (visual analog scale), function (Oswestry Disability Index), curve magnitude (Cobb angle), and fusion status (plain and dynamic radiographs). The 2 groups did not differ statistically significantly (p > 0.05) in age, sex, smoking habits, magnitude of preoperative visual analog scale score, Oswestry Disability Index score, Cobb angle, or number of levels requiring decompression and fusion.

Results

The groups had similar (p > 0.05) results in terms of pain, function, curve progression, and fusion rates at the 2-year follow-up examination. Radiographic fusion was achieved in all but 2 cases, 1 in each group, in which the patients were asymptomatic. Patients in the allograft group (Group B) showed evidence of fusion earlier than in the Healos group (p < 0.05). No toxicity from Healos graft was recorded.

Conclusions

The combination of Healos hydroxyapatite sponge and bone marrow aspirate plus local allograft had significantly slower fusion rates but equal clinical outcomes compared with cancellous allograft plus local autograft when used for posterolateral fusion in patients with degenerative lumbar scoliosis.

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.

Reconstruction of irradiated bone segmental defects with a biomaterial associating MBCP+(R), microstructured collagen membrane and total bone marrow grafting: an experimental study in rabbits

The bone tissue engineering models used today are still a long way from any oncologic application as immediate postimplantation irradiation would decrease their osteoinductive potential. The aim of this study was to reconstruct a segmental critical size defect in a weight-bearing bone irradiated after implantation. Six white New Zealand rabbits were immediately implanted with a biomaterial associating resorbable collagen membrane EZ(R) filled and micro-macroporous biphasic calcium phosphate granules (MBCP+(R)). After a daily schedule of radiation delivery, and within 4 weeks, a total autologous bone marrow (BM) graft was injected percutaneously into the center of the implant. All the animals were sacrificed at 16 weeks. Successful osseous colonization was found to have bridged the entire length of the defects. Identical distribution of bone ingrowth and residual ceramics at the different levels of the implant suggests that the BM graft plays an osteoinductive role in the center of the defect. Periosteum-like formation was observed at the periphery, with the collagen membrane most likely playing a role. This model succeeded in bridging a large segmental defect in weight-bearing bone with immediate postimplantation fractionated radiation delivery. This has significant implications for the bone tissue engineering approach to patients with cancer-related bone defects.

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.

Experimental posterolateral spinal fusion with beta tricalcium phosphate ceramic and bone marrow aspirate composite graft

BACKGROUND

Beta tricalcium phosphate is commonly used in metaphyseal defects but its use in posterolateral spinal fusion remains controversial. There are very few published animal studies in which use of beta tricalcium phosphate has been evaluated in the posterolateral lumbar arthrodesis model. Hence we conducted a study to evaluate the potential of composite graft of beta tricalcium phosphate and bone marrow aspirate in comparison to autologous bone graft, when used for posterolateral spinal fusion.

MATERIALS AND METHODS

Single level posterolateral lumbar fusion was performed in 40 adult male Indian rabbits, which were assigned randomly into one of the four groups based on graft materials implanted; a) 3 gm beta tricalcium phosphate plus 3 ml bone marrow aspirate (Group I); b) 3 ml bone marrow aspirate alone (Group II); c) 3 gm beta tricalcium phosphate (Group III) and d) 3 gm autologous bone graft (Group IV). Each group had 10 rabbits. Half of the rabbits were sacrificed by injecting Phenobarbitone intraperitoneally after eight weeks and the remaining after 24 weeks, and were evaluated for fusion by X-rays, computed tomography (CT) scans, manual palpation test and histology.

RESULTS

Beta tricalcium phosphate used with bone marrow aspirate produced best results when compared to other groups (P =.0001). When beta tricalcium phosphate was used alone, fusion rates were better as compared to fusion achieved with autologous iliac crest bone graft though statistically not significant (P =0.07). Autologous bone graft showed signs of new bone formation. However, the rate of new bone formation was comparatively slow.

CONCLUSION

Composite graft of beta tricalcium phosphate and bone marrow aspirate can be used as an alternative to autologous iliac crest bone graft.

Use of fluorescence labeled mesenchymal stem cells in pluronic F127 and porous hydroxyapatite as a bone substitute for posterolateral spinal fusion

Posterolateral spinal fusion is used to treat patients with degenerative spinal disorders. We investigated the effectiveness of a mesenchymal stem cell (MSC)/Pluronic F127/Interpore hybrid graft for spinal fusion in rabbits. Spinal fusion was examined using radiography, manual palpation, computed tomography (CT), torsional loading tests, and histological analysis. Using a PKH fluorescence labeling system, we also examined whether the newly formed bone was derived from the transplanted MSCs. We found that the MSCs adhered to the Interpore surface and within its pores, and differentiated into osteoblasts. Radiographs and CT images showed a continuous bone bridge and a satisfactory fusion mass incorporated into the transverse processes. The results of manual palpation and biomechanical data did not differ significantly from an autograft group. Histology from both groups revealed the presence of fibrous tissue, cartilage, and endochondral ossification in the gaps between the grafted fragments. In both groups, the degree of mature bone formation was greater at 12 weeks than at 6 weeks after grafting. Quantitative histomorphometry revealed no significant differences between the two groups at either time point. In situ tracing of the PKH 67-labeled MSCs indicated that the transplanted MSCs were partly responsible for the new bone formation in both the repaired transverse processes and the grafted fragments. Thus, the MSC/Pluronic F127/Interpore hybrid graft could be used effectively to achieve posterolateral spinal fusion.

Transpedicular aspiration of osteoprogenitor cells from the vertebral body: progenitor cell concentrations affected by serial aspiration

BACKGROUND CONTEXT

Spinal fusion is facilitated when the fusion site is augmented with autograft bone. Iliac crest, long the preferred source of autograft material, is the site of frequent complications and pain. Connective tissue progenitor cells (CTPs) aspirated from marrow provide a promising alternative to traditional autograft harvest. The vertebral body represents an even larger potential reservoir of progenitor cells than the ilium.

PURPOSE

To test the hypothesis that a suitable concentration of osteoprogenitor cells can be aspirated from different depths of the vertebral body, maintaining progenitor cell concentrations comparable to the "gold standard," the iliac crest, even after sequential aspirations along the same transpedicular axis.

STUDY DESIGN

Prospective clinical investigation quantifying CTP concentrations within the vertebral body relative to depth of sequential aspirations.

PATIENT SAMPLE

Adult men and women undergoing elective posterior lumbar fusion and pedicle screw instrumentation (six men and seven women, mean age 56 years [range 40-74 years]).

OUTCOME MEASURES

Cell count, CTP concentration (CTPs/cc marrow), and CTP prevalence (CTPs/million cells) were calculated for both individual and pooled aspirate samples.

METHODS

Thirteen patients were enrolled into an institutional review board-approved protocol studying transpedicular aspiration of marrow progenitor cells. Connective tissue progenitor cells were aspirated from four depths along the transpedicular axis of the vertebral body and quantified according to cell concentration and CTP prevalence. Histochemical analysis of alkaline phosphatase-positive colony-forming units (CFUs) provided the prevalence of vertebral CTPs relative to depth of aspiration, vertebral level, age, and gender.

RESULTS

Four 2.0cc aspirations were obtained from each pedicle of lumbar vertebrae selected for pedicle screw fixation (four 2.0cc aspirates from each of four pedicles). Aspirates of vertebral marrow demonstrated comparable or greater concentrations of CFUs compared with standards previously established for the iliac crest. Overall, the 208 aspirations from 26 vertebral bodies provided a mean CTP concentration of 741.5+/-976.2 CTPs per cubic centimeter of marrow, ranging from a mean concentration of 1316+/-1473 CTPs per cubic centimeter of marrow at superficial (30mm) aspirations to 439+/-557 CTPs per cubic centimeter marrow at deepest (45mm) aspiration depths (p<.00002). There were no significant differences relative to vertebral body level, side aspirated, or gender. An age-related decline in cellularity was suggested for vertebral body aspirates.

CONCLUSIONS

The vertebral body is a potential marrow reservoir for aspiration of autograft osteogenic CTPs that can be used to augment spinal fusion. The cancellous bone within that portion of the vertebral body routinely cannulated during pedicle screw placement allows serial aspirations with only modest depletion of progenitor cell concentrations or dilution with peripheral blood. Connective tissue progenitor cell concentrations from all depths were comparable to the mean levels previously established for the iliac crest. The ability to simultaneously harvest progenitor cells for graft augmentation while preparing the pilot hole for pedicle screw fixation will expand the potential for cell harvest techniques for fusion augmentation and reduce the need for iliac crest harvest.

Evaluation of hydroxyapatite and beta-tricalcium phosphate mixed with bone marrow aspirate as a bone graft substitute for posterolateral spinal fusion

BACKGROUND

Autologous cancellous bone is the most effective biological graft material. However, harvest of autologous bone is associated with significant morbidity. Since porous hydroxyapatite and beta-tricalcium phosphate are biodegradable materials and can be replaced by bone tissue, but it lacks osteogenic property. We conducted a study to assess their use as a scaffold and combine them with bone marrow aspirate for bone regeneration using its osteogenic property for posterolateral spinal fusion on one side and autologous bone graft on the other side and compare them radiologically in terms of graft incorporation and fusion.

MATERIALS AND METHODS

Thirty patients with unstable dorsal and lumbar spinal injuries who needed posterior stabilization and fusion were evaluated in this prospective study from October 2005 to March 2008. The posterior stabilization was done using pedicle screw and rod assembly, and fusion was done using hydroxyapatite and beta-tricalcium phosphate mixed with bone marrow aspirate as a bone graft substitute over one side of spine and autologous bone graft obtained from iliac crest over other side of spine. The patients were followed up to a minimum of 12 months. Serial radiographs were done at an interval of 3, 6, and 12 months and CT scan was done at one year follow-up. Graft incorporation and fusion were assessed at each follow-up. The study was subjected to statistical analysis using chi-square and kappa test to assess graft incorporation and fusion.

RESULTS

At the end of the study, radiological graft incorporation and fusion was evident in all the patients on the bone graft substitute side and in 29 patients on the autologous bone graft side of the spine (P > 0.05). One patient showed lucency and breakage of distal pedicle screw in autologous bone graft side. The interobserver agreement (kappa) had an average of 0.72 for graft incorporation, 0.75 for fusion on radiographs, and 0.88 for the CT scan findings.

CONCLUSION

Hydroxyapatite and beta-tricalcium phosphate mixed with bone marrow aspirate seems to be a promising alternative to conventional autologous iliac bone graft for posterolateral spinal fusion.

Radiographic analysis of fusion mass using fresh autologous bone marrow with ceramic composites as an alternative to autologous bone graft

OBJECTIVE

To determine whether a biphasic calcium phosphate (BCP) ceramic supplemented with fresh autologous bone marrow (BMA) can give rise to adequate bone to achieve a vertebral fusion mass.

MATERIALS AND METHODS

A prospective nonrandomized, radiographic study on 35 patients with posterolateral fusion using rigid transpedicular instrumentation for degenerative lumbar disease. At least 2-year follow-up. On the left side: autologous bone graft obtained from decompression. On the right side: a mixture of BCP and fresh autogenous bone marrow from the right iliac crest. Single-level fusion in 22 patients and two or more levels in 13. Patients assessed with x-rays and computed tomography by an orthopedic surgeon and an independent radiologist. Fusion mass was considered "good" when there was a continuous block of bone without radiolucent areas. No intersegmental bony bridging fusion was considered "poor" mass. McNemar, Fisher, and kappa tests were used for statistical analysis.

RESULTS

The interobserver agreement (kappa) had an average of 0.75 for the fusion masses. The interobserver average in the radiologic evaluation of ceramic resorption was 0.68. No differences between smokers and nonsmokers were found. Plain radiography findings: good left fusion masses (autologous bone) in 31 patients and poor in 4; good right masses (BMA plus BCP) in 31 patients and poor in 4 (P > 0.05). Computed tomography evaluation: good left fusion masses in 28 patients and poor in 7; good right fusion masses in 31 patients and poor in 4 (P > 0.05). One patient was reoperated, allowing biopsies to be performed: compact bone tissue was observed around hydroxyapatite in the right fusion mass.

CONCLUSIONS

The differences detected between right-side and left-side masses are not statistically significant. This indicates that, BMA and BCP, when mixed, behave like composite grafts and are able to generate sufficient bone mass for arthrodesis when a rigid instrumentation is used. However, a larger number of cases and longer follow-up are needed to generalize the indication.

rhBMP-6 stimulated osteoprogenitor cells enhance posterolateral spinal fusion in the New Zealand white rabbit

BACKGROUND CONTEXT

The nonunion rate after posterolateral spinal fusion can be as high as 35%. This has stimulated interest in the development of techniques for enhancing new bone formation, including the addition of bioactive peptides or the use of cell-based therapies, including genetically modified cells. In previous studies we have demonstrated that exposing autologous, marrow-derived osteoprogenitor cells to a recombinant human bone morphogenetic protein-6 (rhBMP-6) containing extracellular matrix induces osteoblastic differentiation, and that these cells are capable of increasing new bone formation. Growth of autologous cells on a synthetic rhBMP-6 containing matrix yields a population of stimulated osteoprogenitor cells, without the expense of adding large amounts of rhBMP-6 directly, or the risks inherent in the use of genetically altered cells.

PURPOSE

This study was performed to evaluate the potential of rhBMP-6 stimulated osteoprogenitor cells (stOPC) to enhance the rate and strength of posterolateral spinal fusion.

STUDY DESIGN

Prospective in vivo animal study

OUTCOME MEASURES

Radiographic evidence of spinal fusion, biomechanical testing of explanted spines, histological analysis of new bone formation

METHODS

Single-level posterolateral spinal arthrodeses were performed in 69 New Zealand white rabbits. Autologous marrow stem cells were concentrated and then plated on an rhBMP-6-rich extracellular matrix synthesized by genetically engineered mouse C3H10T1/2 cells. Animals in Groups I (n=18) and II (n=18) received autografts of 30M and 60M rhBMP-6 stOPCs in guanidine extracted demineralized bone matrix (gDBM), respectively, whereas those in Group III (n=13) received iliac crest bone graft (ICBG). Those in Group IV (n=10) received gDBM, and those in Group V (n=10) underwent decortication only. Assessment of fusion was made with serial radiographs, manual palpation of the explanted spines, and biomechanical testing. The fusion masses from two animals each in Groups I, II, and IV were evaluated histologically.

RESULTS

Fifty-three animals were available for analysis at the conclusion of the study. In these animals, the arthrodesis rate was significantly higher after treatment with rhBMP-6 stOPCs (77% for both Groups I and II by palpation) than ICBG, gDBM, or decortication alone (Group III=55%, IV=20% and V=0%, respectively). Similarly, the peak loads to failure of the fusion masses in Groups I and II (212.5+/-37.8 N and 234.6+/-45.7 N) were significantly greater than the corresponding values in the other groups (Group III=155.9+/-36.4N, Group IV=132.7+/-59.9N, and Group V=92.8+/-18.4N), though when only the fused specimens in Groups I, II, and III were compared, only Group II was significantly different than Group III (234.6+/-45.7N and 155.9+/-36.4N, respectively). The fusion masses in the rhBMP-6 stOPC-treated animals were typified by a thin, fusiform cortical shell, newly formed trabecular bone emanating from the decorticated transverse processes, and residual unremodeled gDBM carrier particles. The fusion masses in the gDBM treated bones were morphologically similar, though they contained less newly formed bone.

CONCLUSIONS

The use of rhBMP-6 stOPCs in a carrier of gDBM significantly enhanced the rate and strength of single-level posterolateral spinal arthrodeses in the New Zealand white rabbit, compared with ICBG, gDBM, and decortication alone. Our results confirm that the stimulation of marrow-derived osteoprogenitor cells by growing them on a rhBMP-6 containing extracellular matrix is feasible. Further investigation is warranted to determine the relative contribution of rhBMP-6 stimulation and the number of cells implanted, as well as strategies for optimizing the technique for clinical application.

Bone marrow-derived osteoblast progenitor cells in circulating blood contribute to ectopic bone formation in mice

Recent studies have suggested the existence of osteoblastic cells in the circulation, but the origin and role of these cells in vivo are not clear. Here, we examined how these cells contribute to osteogenesis in a bone morphogenetic protein (BMP)-induced model of ectopic bone formation. Following lethal dose-irradiation and subsequent green fluorescent protein-transgenic bone marrow cell-transplantation (GFP-BMT) in mice, a BMP-2-containing collagen pellet was implanted into muscle. Three weeks later, a significant number of GFP-positive osteoblastic cells were present in the newly generated ectopic bone. Moreover, peripheral blood mononuclear cells (PBMNCs) from the BMP-2-implanted mouse were then shown to include osteoblast progenitor cells (OPCs) in culture. Passive transfer of the PBMNCs isolated from the BMP-2-implanted GFP-mouse to the BMP-2-implanted nude mouse led to GFP-positive osteoblast accumulation in the ectopic bone. These data provide new insight into the mechanism of ectopic bone formation involving bone marrow-derived OPCs in circulating blood.

A bridging demineralized bone implant facilitates posterolateral lumbar fusion in New Zealand white rabbits

STUDY DESIGN

Randomized controlled animal study.

OBJECTIVE

Test the effectiveness of a single-strip demineralized bone matrix with hyaluronan and gelatin.

SUMMARY OF BACKGROUND DATA

Demineralized bone matrix is widely used to augment spinal fusion, however, the effect of changing the physical characteristic and carrier is not known.

METHODS

Demineralized bone matrix was extracted from the bones of New Zealand White rabbits, and combined with hyaluronan and gelatin to form solid strips. Forty-eight rabbits were randomized into a control and 2 experimental groups. In the control group, fusion was attempted with autograft bone. For group 2, demineralized bone matrix strips alone and for group 3, autograft and demineralized bone matrix strips were used. The fusion was assessed with manual manipulation and radiographs. The volume of the fusion mass was determined from computed tomographic images.

RESULTS

By the manual palpation test, the fusion rates were 37.5%, 93.8%, and 100%, for groups 1-3, respectively (P < 0.05). By radiography, the control group fusion rate was 68.7% compared with 100% for the experimental groups (P < 0.05). The mean bone volumes of the fusion mass were 2142.2 +/- 318.5, 3132.9 +/- 632.1, and 4181.6 +/- 609.5 mm3 for groups 1-3, respectively (P < 0.05).

CONCLUSIONS

The demineralized bone matrix-gel strip was able to function as both a bone-graft enhancer and a bone graft substitute in rabbit posterolateral spine fusion.

The use of simvastatin in rabbit posterolateral lumbar intertransverse process spine fusion

BACKGROUND CONTEXT

There has been recent enthusiasm regarding the potential positive effects of statins on bone. Statins vary in their ability to influence bone activity. Simvastatin has been shown in experimental models to stimulate bone acting growth factors and enhance bone formation.

PURPOSE

The potential efficacy of Simvastatin in enhancing spinal fusion was evaluated in a rabbit posterolateral intertransverse process fusion model.

STUDY DESIGN/SETTING

Posterior lumbar intertransverse process spinal fusion performed on New Zealand White rabbits. PATIENT/STUDY SAMPLE: 44 New Zealand White rabbits.

OUTCOME MEASURES

Spinal fusion as determined by manual palpation testing and fine detail radiography. Bone fusion mass volume and density as determined by CT scan imaging.

METHODS

Forty-four New Zealand White rabbits underwent posterolateral intertransverse process spine fusion using autogenous iliac crest bone graft. Simvastatin was administered orally in 20 animals and the serum lipid profile quantified in test and control animals. The animals were euthanized 9 weeks following index surgery and the lumbar spine was harvested. Spinal fusion was determined by manual palpation testing and fine detail radiography. The volume and density of the bone fusion mass was quantified by computed tomography.

RESULTS

Drug treatment for 9 weeks caused a reduction in serum lipid biochemical markers when compared with controls. The spinal fusion rate, as judged by manual palpation testing (13.0% control group, 16.6% Simvastatin group) and fine detail radiography, was not significantly different comparing treatment with control animals. Accordant with the assessment of spinal fusion, there was no statistically significant effect on the volume of the fusion mass (1,224.7+/-98.7 mm(3) in the control group and 1,075.9+/-66.3 mm(3) in the Simvastatin group), the density of bone in the lumbar spine or that in the formed fusion mass.

CONCLUSIONS

Systemic use of Simvastatin caused a reduction in lipid biochemical parameters in treated animals. Successful spinal fusion as judged by manual palpation testing and fine detail radiography was not significantly different in treated versus untreated animals. The bone volume density of the formed fusion mass was not significantly different in treated versus untreated animals. There did not appear to be a significant advantage or disadvantage to the use of Simvastatin rabbit posterolateral spinal fusion. The potential positive effects of statins on bone require further study.

Cell technologies for spinal fusion

For a successful spinal fusion to occur, several vital elements are necessary. They consist of the presence of the bone-forming cell (osteoblast) or its precursor, the appropriate biological signals directing bone synthesis, and a biocompatible scaffold on which the process can occur. The most critical of these components is the osteoblast or its precursor, the mesenchymal stem cell (MSC), both of which possess the ability to form bone. As a result, many current techniques attempt to maximize the benefits derived from harvesting the ready source of MSCs from bone marrow, while minimizing the associated complications. These cellular technologies seek to improve on the harvest and concentration of the MSCs or enhance their delivery and action. This review focuses on the terminology, historical underpinnings, and current research rationale and techniques and discusses the possible future of these technologies.

The use of cultured bone marrow cells in type I collagen gel and porous hydroxyapatite for posterolateral lumbar spine fusion

STUDY DESIGN

Posterolateral lumbar transverse process fusion was completed using the cultured bone marrow cells in type I collagen gel and porous hydroxyapatite.

OBJECTIVE

To compare the efficacy of cultured bone marrow cells with that of bone morphogenetic protein (BMP) as a graft alternative to autologous bone for posterolateral spine fusion.

SUMMARY OF BACKGROUND DATA

The clinical application of BMP for spinal fusion may be limited by high dose and cost. Recently, mesenchymal stem cells have been studied in various fields because of their capability to differentiate into various cells, including those in the osteogenic lineage.

METHODS

Thirty adult rabbits were used. Each underwent single-level, bilateral, posterolateral intertransverse process fusions at L4-L5. The animals were divided into 4 groups, each according to the material implanted: (1) autologous bone (autograft, n = 9); (2) porous hydroxyapatite (HA) particles and type I collagen sheet with 100 microg rhBMP-2 (BMP-HA, n = 7); (3) bone marrow cells (1 x 10(6) cells/mL, low-marrow-HA, n = 7); and (4) bone marrow cells (1 x 10(8) cells/mL, high-marrow-HA, n = 7). Before implantation for groups 3 and 4, fresh bone marrow cells from the iliac crest of each animal were cultured in a standard medium for 2 weeks. For one additional week, the marrow cells were cultured in 10(-8) M dexamethasone, type I collagen gel, and HA. Animals were euthanized 6 weeks after surgery. Spinal fusions were evaluated by radiograph, manual palpation, and histology.

RESULTS

The fusion rates were 4 of 7 in the autograft group, 7 of 7 in the BMP-HA group, 0 of 7 in the low-marrow-HA group, and 5 of 7 in the high-marrow-HA group. The histology in the BMP-HA and high-marrow-HA groups showed that grafted HA fragments were connected with mature new bone. The pores of HA fragments were filled up with bone matrix. In the low-marrow-HA group, fibrous tissue was predominant in the grafted fragments.

CONCLUSIONS

This study shows that the cultured bone marrow cells can act as a substitute for autograft or BMP in spine fusion. The current formulation may yield improved fusion success and better quality of fusion bone as compared to autograft.

Absorbable self-reinforced polylactide (SR-PLLA) rods vs rigid rods (K-wire) in spinal fusion: an experimental study in rabbits

Several clinical and experimental reports have evaluated the spinal application of bioabsorbable material for plating the anterior lumbar and cervical spine, and in anterior and posterior lumbar interbody spinal fusion. Nevertheless, the use of these materials in posterolateral interlaminar fusion has yet to be elucidated in the literature. The effects of bioabsorbable self-reinforced polylactide rod (SR-PLLA) implantation, rigid fixation (K-wire) and non-implantation with posterior interlaminar fusion were compared using a rabbit model. Twenty-four mature domestic rabbits were divided into three groups. Eight received implantation with SR-PLLA, eight with K-wire, and eight were fused without instrumentation. The animals were killed at 12 weeks and evaluated by posteroanterior radiography, manual palpation and histological examination for the presence of fusion. Successful fusion was achieved in all of the animals in both implanted groups (SR-PLLA and K-wire), whereas solid fusion was not detected in any of the specimens in the non-implanted group. Computed tomography (CT) scans were used to detect fusion mass volume. The fusion mass in the SR-PLLA implanted group had a mean volume of 1,196 mm3 +/- 167 mm3 vs 1,061 mm3 +/- 181 mm3 for the K-wire implanted group (not significant) and 711 mm3 +/- 407 mm3 (p<0.05) for the non-implanted group. The results of this study suggest that the stabilization properties of both SR-PLLA rods and K-wire seem to be sufficient for spinal fusion, but using SR-PLLA is especially advantageous, since they do not require a removal operation and do not interfere with magnetic resonance imaging (MRI).

The vertebral interbody grafting site's low concentration in osteogenic progenitors can greatly benefit from addition of iliac crest bone marrow

The ability of bone substitutes to promote bone fusion is contingent upon the presence of osteoinductive factors in the bone environment at the fusion site. Osteoblast progenitor cells are among these environmental osteoinductive factors, and one of the most abundant and available sources of osteoblastic cells is the bone marrow. As far as biological conditions are concerned, the vertebral interbody space appears as a favorable site for fusion, as it is surrounded by spongy bone, theoretically rich in osteogenic cells. This site may, however, not be as rich in osteogenic precursor cells especially at the time of grafting, because decortication of the vertebral end plates during the grafting process may modify cell content of the surrounding spongy bone. We tested this hypothesis by comparing the abundance of human osteogenic precursor cells in bone marrow derived from the iliac crest, the vertebral body, and the decorticated intervertebral body space. The number of potential osteoblast progenitors in each site was estimated by counting the alkaline phosphatase-expressing colony-forming units (CFU-AP). The results, however, demonstrate that the vertebral interbody space is actually poorer in osteoprogenitor cells than the iliac crest (P<0.001) and vertebral body (P<0.01), especially at the time of graft implantation. In light of our results, we advocate addition of iliac crest bone marrow aspirate to increase the success rate of vertebral interbody fusion.

Posterolateral intertransverse lumbar arthrodesis in the New Zealand White rabbit model: II. Operative technique

BACKGROUND CONTEXT

Although the New Zealand White (NZW) rabbit model has been increasingly used for spinal fusion research, reported complication rates have been as high as 23%. The substantial animal morbidity and mortality associated with the model makes experimentation inefficient and can lead to faulty data analysis. Operative complications are in part the result of suboptimal execution of the experimental protocol.

PURPOSE

To describe an experimental protocol for posterolateral intertransverse lumbar arthrodesis in the NZW rabbit and to analyze the effect of the protocol on the complication rate of this model.

STUDY DESIGN/SETTING

This is a descriptive analysis of the surgical technique (and related complications) used for posterolateral spinal arthrodesis in the NZW rabbit model. This study was performed at a university research facility.

METHODS

The complications of posterolateral intertransverse lumbar arthrodesis in the NZW rabbit were analyzed before and after instituting a refined experimental protocol.

RESULTS

A total of 77 NZW rabbits underwent a posterolateral lumbar arthrodesis. In the first 48 animals (Group A) complications occurred at a rate of 26% and included anesthetic demise, nerve palsies, wound infections or seromas and fusion of the wrong level. After the institution of a refined experimental protocol, there were no complications in a second group of 29 rabbits (Group B).

CONCLUSIONS

Adherence to a precise experimental protocol for posterolateral lumbar arthrodesis can minimize complications, thereby enhancing the NZW rabbit as a cost-effective and accurate animal model for spinal fusion research.