Bone morphogenetic proteins for spinal fusion

A Narrative Review on Recombinant Human Bone Morphogenetic Protein 2: Where Are We Now?

Spinal fusion is a prevalent surgical intervention for degenerative spinal diseases, with increasing demand driven by ageing populations. The coexistence of multiple chronic conditions, termed multimorbidity, often complicates surgical outcomes, making advanced bone grafts crucial for successful fusions. This paper reviews the development, clinical application, and controversies surrounding the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion surgeries. A comprehensive narrative review was conducted, focusing on literature from January 1980 to January 2024, sourced from PubMed and Google Scholar. Studies included those examining rhBMP-2 specifically in spinal fusion contexts, excluding other bone morphogenetic proteins (BMPs) and non-spinal applications. This review presents an overarching synopsis of rhBMP-2, its development history and clinical efficacy, the emergence of side effects, and evolving patterns of clinical use. As discussed in this review, clinical practice has adjusted usage and dosages to mitigate adverse effects, yet the need for safer delivery mechanisms persists. rhBMP-2 remains a potent osteoinductive agent with comparable fusion success, as measured by radiographic fusion and good clinical outcomes, to autologous grafts but poses unique risks. This review sets out how further research is essential to optimise the delivery of rhBMP-2 to reduce side effects. Enhanced understanding and innovation of spatio-temporal presentation relative to endogenous BMP could significantly improve patient outcomes in spinal fusion surgeries. The review contributes to the growing body of literature on the use of rhBMP-2 in spine surgery and discusses changing patterns of clinical use over time.

Activation of the BMP2-SMAD1-CGRP pathway in dorsal root ganglia contributes to bone cancer pain in a rat model

Peripheral nerve remodeling and sensitization are involved in cancer-related bone pain. As a member of the transforming growth factor-β class, bone morphogenetic protein 2 (BMP2) is recognized to have a role in the development of the neurological and skeletal systems. Our previous work showed that BMP2 is critical for bone cancer pain (BCP) sensitization. However, the mechanism remains unknown. In the current study, we demonstrated a substantial increase in BMP2 expression in the dorsal root ganglia (DRG) in a rat model of BCP. Knockdown of BMP2 expression ameliorated BCP in rats. Furthermore, the DRG neurons of rats with BCP expressed higher levels of calcitonin gene-related peptide (CGRP), and BCP was successfully suppressed by intrathecal injection of a CGRP receptor blocker (CGRP8-37). Downregulation of BMP2 expression reduced the expression of CGRP in the DRG of rats with BCP and relieved pain behavior. Moreover, we revealed that upregulation of CGRP expression in the DRG may be induced by activation of the BMPR/Smad1 signaling pathway. These findings suggest that BMP2 contributes to BCP by upregulating CGRP in DRG neurons via activating BMPR/Smad1 signaling pathway and that therapeutic targeting of the BMP2-Smad1-CGRP pathway may ameliorate BCP in the context of advanced cancer.

Meta-Analysis on Efficacy and Complications of Bone Morphogenetic Protein-2 for Posterior Fusion of Cervical Spine

OBJECTIVE

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is effective for promoting robust fusion for long-level cervical deformity and revision surgeries. However, only a few studies have reported its efficacy and complications in posterior cervical fusion (PCF).

METHODS

Therefore we evaluated the efficacy and complications of rhBMP-2 application in PCF surgery by searching 3 electronic databases (PubMed, Cochrane Database, and EMBASE) for studies that evaluated the use of rhBMP-2 in PCF. Five studies (1 prospective and 4 retrospective) were included in the meta-analysis.

RESULTS

The quality of each study was assessed, and data on pseudarthrosis, wound infection, neurologic, and immediate medical complications were extracted and analyzed. We found that the use of rhBMP-2 in PCF showed significant benefits in terms of pseudarthrosis and no significant increases in the risk for neurologic and immediate medical complications regardless of the dose. However, high-dose (>2.1 mg/level) rhBMP-2 was a risk factor for wound infection after PCF.

CONCLUSIONS

Our meta-analysis of the currently available literature suggests that patients with PCF may benefit from BMP-2 usage without increasing the risk of complications. However, dose control and containment are important to ensure a low risk of complications.

Bone Substitute Options for Spine Fusion in Patients With Spine Trauma-Part II: The Role of rhBMP

In Part II, we focus on an important aspect of spine fusion in patients with spine trauma: the pivotal role of recombinant human bone morphogenetic protein-2 (rhBMP-2). Despite the influx of diverse techniques facilitated by technological advancements in spinal surgery, spinal fusion surgery remains widely used globally. The persistent challenge of spinal pseudarthrosis has driven extensive efforts to achieve clinically favorable fusion outcomes, with particular emphasis on the evolution of bone graft substitutes. Part II of this review aims to build upon the foundation laid out in Part I by providing a comprehensive summary of commonly utilized bone graft substitutes for spinal fusion in patients with spinal trauma. Additionally, it will delve into the latest advancements and insights regarding the application of rhBMP-2, offering an updated perspective on its role in enhancing the success of spinal fusion procedures.

Application of Escherichia coli-Derived Recombinant Human Bone Morphogenic Protein-2 to Unstable Spinal Fractures

(1) Background: Recently, Escherichia coli-derived recombinant human bone morphogenetic protein-2 (E. coli-derived rhBMP-2) has been increasingly applied to different types of spinal surgeries and reported to achieve successful fusion. This pilot study aimed to evaluate the clinical efficacy and safety of rhBMP-2 in patients undergoing posterior instrumented fusions for unstable spinal fractures. (2) Methods: This study included ten consecutive patients undergoing spinal surgery using E. coli-derived rhBMP-2 with more than one year of follow-up. Radiologic outcomes were compared, including the average fracture healing period, local kyphosis correction, and clinical outcomes between preoperative and the last follow-up. (3) Results: The average time of radiographic union was 99.9 ± 45.4 (62-192) days, with an average use of 5.2 ± 3.9 months of anabolic agents. Radiologic parameters such as anterior vertebral height and vertebral wedge angle were significantly corrected postoperatively and at the last follow-up. Clinical outcomes other than leg pain were significantly improved after the surgery. In addition, four patients with preoperative neurologic deficits showed improved neurologic status. (4) Conclusions: Combined with the anabolic agents, applying E. coli-derived rhBMP-2 to the fractured vertebral body could be an effective surgical treatment for unstable spinal fractures. Further trials are needed to validate this result.

Trends, payments, and costs associated with BMP use in Medicare beneficiaries undergoing spinal fusion

BACKGROUND CONTEXT

Bone morphogenic protein (BMP) promotes bony fusion but increases costs. Recent trends in BMP use among Medicare patients have not been well-characterized.

PURPOSE

To assess utilization trends, complication, payments, and costs associated with BMP use in spinal fusion in a Medicare-insured population.

STUDY DESIGN/SETTING

Retrospective cohort study.

PATIENT SAMPLE

Total of 316,070 patients who underwent spinal fusion in a 20% sample of Medicare-insured patients, 2006 to 2015.

OUTCOME MEASURES

Utilization trends across time and geography, complications, payments, and costs.

METHODS

Patients were stratified by fusion type and diagnosis. Multivariable logistic and linear regression were used to adjust for the effect of baseline characteristics on complications and total payments or cost, respectively.

RESULTS

BMP was used in 60,249 cases (19.1%). BMP utilization rates decreased from 23.1% in 2006 to 12.0% in 2015, most significantly in anterior cervical (7.5%-3.1%), posterior cervical (17.0%-8.3%), and posterior lumbar fusions (31.5%-15.8%). There are significant state- and region-level geographic differences in BMP utilization. Across all years, states with the highest BMP use were Indiana (28.5%), Colorado (26.6%), and Nevada (25.7%). States with the lowest BMP use were Maine (2.3%), Vermont (8.2%), and Mississippi (10.4%). After multivariate risk adjustment, BMP use was associated with decreased overall complications in thoracic (odds ratios [OR] [95% confidence intervals [CI]): 0.89 [0.81-0.99]) and anterior lumbar fusions (OR [95% CI]: 0.89 [0.84-0.95]), as well as increased reoperation rates in anterior cervical (OR [95% CI]: 1.11 [1.04-1.19]), posterior cervical (OR (95% CI): 1.14 (1.04-1.25)), thoracic (OR (95% CI): 1.32 (1.23-1.41)), and posterior lumbar fusions (OR (95% CI): 1.11 (1.06-1.16)). BMP use was also associated with greater total costs, independent of fusion type, after multivariate risk adjustment (p<.0001). Payments, however, were comparable between groups in anterior and posterior cervical fusion with or without BMP. BMP use was associated with greater total payments in thoracic, anterior lumbar, and posterior lumbar fusions. Notably, the difference in payments was smaller than the associated cost increase in all fusion types.

CONCLUSIONS

BMP use has declined across all fusion types over the last decade, after a peak in 2007. While BMP is associated with greater costs, reimbursement does not increase proportionally with BMP cost.

Mechanical Stretch Induced Osteogenesis on Human Annulus Fibrosus Cells through Upregulation of BMP-2/6 Heterodimer and Activation of P38 and SMAD1/5/8 Signaling Pathways

Degenerative disc disease (DDD) is an important cause of low back pain. Repetitive tensile stress from the daily motion of the spine predisposes it to injury of the annulus fibrosus (AF) which causes IVD degeneration. This study aims to determine the causal relationship between mechanical stretch and osteogenesis in the AF cells of IVD as affected by bone morphogenic proteins (BMPs), specifically BMP-2/6 heterodimers. Our results found that 15% tensile stress (high cyclic stretching, HCS) may induce the expression of osteogenesis-related markers (Runx2, osterix) by upregulating BMP-2/6 heterodimeric ligands and their receptors on the human AF cell line. HCS also induced transient phosphorylation of p38 mitogen-activated protein (MAP) kinase and SMAD1/5/8. Neutralizing antibodies to the BMP-2/6 receptor (ALK3) blocked the expression of Runx2 and osterix, as well as the phosphorylation of p38 and SMAD1/5/8. In addition, treatment with a p38 MAPK inhibitor (SB203580) or siRNA to neutralize the effects of SMAD1/5/8 suppressed tensile stress-induced Runx2 and osterix expression. Mechanical stretching induces activation of p38 MAP kinase and SMAD1/5/8 signaling pathways, followed by the upregulation of BMP-2/6 heterodimer expression, thereby stimulating osteogenic Runx2 and osterix expression on AF cells. HCS may accelerate the progression of IVD degeneration by promoting an osteogenic response.

The Effects of Stably Tethered BMP-2 on MC3T3-E1 Preosteoblasts Encapsulated in a PEG Hydrogel

Bone morphogenetic protein-2 (BMP-2) is a clinically used osteoinductive growth factor. With a short half-life and side effects, alternative delivery approaches are needed. This work examines thiolation of BMP-2 for chemical attachment to a poly(ethylene glycol) hydrogel using thiol-norbornene click chemistry. BMP-2 retained bioactivity post-thiolation and was successfully tethered into the hydrogel. To assess tethered BMP-2 on osteogenesis, MC3T3-E1 preosteoblasts were encapsulated in matrix metalloproteinase (MMP)-sensitive hydrogels containing RGD and either no BMP-2, soluble BMP-2 (5 nM), or tethered BMP-2 (40-200 nM) and cultured in a chemically defined medium containing dexamethasone for 7 days. The hydrogel culture supported MC3T3-E1 osteogenesis regardless of BMP-2 presentation, but tethered BMP-2 augmented the osteogenic response, leading to significant increases in osteomarkers, Bglap and Ibsp. The ratio, Ibsp-to-Dmp1, highlighted differences in the extent of differentiation, revealing that without BMP-2, MC3T3-E1 cells showed a higher expression of Dmp1 (low ratio), but an equivalent expression with tethered BMP-2 and more abundant bone sialoprotein. In addition, this work identified that dexamethasone contributed to Ibsp expression but not Bglap or Dmp1 and confirmed that tethered BMP-2 induced the BMP canonical signaling pathway. This work presents an effective method for the modification and incorporation of BMP-2 into hydrogels to enhance osteogenesis.

Complications, Costs, and Quality Outcomes of Patients Undergoing Cervical Deformity Surgery With Intraoperative BMP Use

STUDY DESIGN

An epidemiological study using national administrative data from the MarketScan database.

OBJECTIVE

The aim of this study was to identify the impact of bone morphogenetic protein (BMP) on postoperative outcomes in patients undergoing adult cervical deformity (ACD) surgery.

SUMMARY OF BACKGROUND DATA

BMP has been shown to stimulate bone growth and improve fusion rates in spine surgery. However, the impact of BMP on reoperation rates and postoperative complication rate is controversial.

METHODS

We queried the MarketScan database to identify patients who underwent ACD surgery from 2007 to 2015. Patients were stratified by BMP use in the index operation. Patients <18 years and those with any history of tumor or trauma were excluded. Baseline demographics and comorbidities, postoperative complication rates, and reoperation rates were analyzed.

RESULTS

A total of 13,549 patients underwent primary ACD surgery, of which 1155 (8.5%) had intraoperative BMP use. The overall 90-day complication rate was 27.6% in the non-BMP cohort and 31.1% in the BMP cohort (P < 0.05). Patients in the BMP cohort had longer average length of stay (4.0 days vs. 3.7 days, P < 0.05) but lower revision surgery rates at 90 days (14.5% vs. 28.3%, P < 0.05), 6 months (14.9% vs. 28.6%, P < 0.05), 1 year (15.7% vs. 29.2%, P < 0.05), and 2 years (16.5% vs. 29.9%, P < 0.05) postoperatively. BMP use was associated with higher payments throughout the 2-year follow-up period ($107,975 vs. $97,620, P < 0.05). When controlling for baseline group differences, BMP use independently increased the odds of postoperative complication (odds ratio [OR] 1.22, 95% confidence interval [CI] 1.1-1.4) and reduced the odds of reoperation throughout 2 years of follow-up (OR 0.49, 95% CI 0.4-0.6).

CONCLUSION

Intraoperative BMP use has benefits for fusion integrity in ACD surgery but is associated with increased postoperative complication rate. Spine surgeons should weigh these benefits and drawbacks to identify optimal candidates for BMP use in ACD surgery.

LEVEL OF EVIDENCE

3.

Guided bone regeneration with a gelatin layer and adenoviral delivery of c-myb enhances bone healing in rat tibia

Aim: Bone healing becomes problematic during certain states, such as trauma. This study verifies whether the application of c-myb with gelatin promotes bone healing during bone injuries. Materials & methods: A biodegradable membrane was modified with adenoviral vector c-myb (Ad/c-myb) and gelatin and applied in the bone injury site of rat tibia. Results: c-myb enhanced osteogenic differentiation and mineralization in bone marrow stromal cells after induction with osteogenic media. In vivo examination of rat tibia after application of the biodegradable membrane with Ad/c-myb and a gelatin layer demonstrated increased bone volume, bone mineral density, new bone formation and osteogenic molecules, compared with Ad/LacZ. Conclusion: c-myb has the potential to assist bone healing and may be applicable to the treatment of bone during injury.

A Composite Tissue Engineered Bone Material Consisting of Bone Mesenchymal Stem Cells, Bone Morphogenetic Protein 9 (BMP9) Gene Lentiviral Vector, and P3HB4HB Thermogel (BMSCs-LV-BMP9-P3HB4HB) Repairs Calvarial Skull Defects in Rats by Expression of Osteogenic Factors

Background

Bone tissue engineering has been proven to be an appropriate approach for treating bone defects. This study aimed to investigate the effects and mechanism of a composite tissue engineered bone material consisting of bone mesenchymal stem cells (BMSCs), bone morphogenetic protein (BMP9) gene lentiviral vector, and P3HB4HB thermogel (BMSCs-LV-BMP9-P3HB4HB) on calvarial skull defects in rats.

Material/Methods

LV-BMP9 viral vector was structured and infected to BMSCs-P3HB4HB composite scaffold, which was named as BMSCs-P3HB4HB composite bone repair material. Adipogenic differentiation was determined by oil-red O (ORO) and alkaline phosphatase (ALP) staining. Osteogenic differentiation was measured using Alizarin red staining. Cell viability was examined using Cell-Counting Kit-8 (CCK-8) assay. Protein expression of osteogenic factors, including BMP9, runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), osteopontin (OPN), and osterix (OSX), was detected with Western blot assay and immunohistochemistry. mRNA of these osteogenic factors was examined by RT-PCR. Histological changes were examined with hematoxylin and eosin (H&E) and Masson’s trichrome staining. Bone repair was measured using micro-computed tomography (micro-CT).

Results

BMSCs and LV-BMP9-infected BMSCs demonstrated adipogenic and osteogenic differentiation potential. BMSCs-P3HB4HB scaffold demonstrated good cell-tissue compatibility. BMSCs-LV-BMP9-P3HB4HB exhibited significantly higher osteogenic ability and cell viability of BMSCs compared to BMSCs-LV-P3HB4HB (p<0.05). BMSCs-LV-BMP9-P3HB4HB significantly promoted osteogenic factors (RUNX2, OCN, OPN, and OSX) expression compared to the BMSCs-LV-P3HB4HB group (p<0.05) in both BMSCs and in calvarial defect rats. BMSCs-LV-BMP9-P3HB4HB demonstrated stronger repair ability. BMSCs-LV-BMP9-P3HB4HB significantly alleviated pathological injury and increased collagen fiber production compared to the BMSCs-LV-P3HB4HB group (p<0.05).

Conclusions

BMSCs-LV-BMP9-P3HB4HB composite bone repair material can effectively repair injured skull tissues of calvarial defect rats through triggering osteogenic factors expression. The present generated bone repair material may have applications in tissue engineering in regeneration of bone defects.

Fibrin Glue/Fibronectin/Heparin-Based Delivery System of BMP2 Induces Osteogenesis in MC3T3-E1 Cells and Bone Formation in Rat Calvarial Critical-Sized Defects

Bone morphogenetic proteins (BMPs) have been used to promote bone formation in many clinical scenarios. However, the BMPs are inherently unstable in vivo and therefore need to be combined with carriers for controlled delivery. In this study, an innovative and efficient fibrin glue/fibronectin/heparin (FG/Fn/Hep)-based delivery system was developed for controlled release of BMP2. The incorporation of heparin can significantly slow the release of BMP2 without substantially affecting the structure and stiffness of the FG/Fn. The BMP2 release from the FG/Fn/Hep-BMP2 hydrogel is largely dominated by hydrogel degradation rather than simple diffusion. In vitro release experiments and MC3T3-E1 cell induction experiments showed that BMP2 can be released steadily and can induce MC3T3-E1 cells to differentiate into osteoblasts efficiently. This process is characterized by the significantly increased expression of calcium deposits, alkaline phosphatase, runt-related transcription factor-2, osteopontin, osteocalcin, and collagen I in comparison with the negative control. In vivo assessments revealed that the FG/Fn/Hep-BMP2 hydrogel significantly promotes bone regeneration in a rat calvarial critical-sized defect model. Our investigation indicates that FG/Fn/Hep-BMP2 hydrogel holds promise to be used as an alternative biomaterial for the repair of bone defects.

Biomimetic UHMWPE/HA scaffolds with rhBMP-2 and erythropoietin for reconstructive surgery

A promising direction for the replacement of expanded bone defects is the development of bioimplants based on synthetic biocompatible materials impregnated with growth factors that stimulate bone remodeling. Novel biomimetic highly porous ultra-high molecular weight polyethylene (UHMWPE)/40% hydroxyapatite (HA) scaffold for reconstructive surgery with the porosity of 85 ± 1% vol. and a diameter of pores in the range of 50-800 μm was developed. The manufacturing process allowed the formation of trabecular-like architecture without additional solvents and thermo-oxidative degradation. Biomimetic UHMWPE/HA scaffold was biocompatible and provided effective tissue ingrowth on a model of critical-sized cranial defects in mice. The combined use of UHMWPE/HA with Bone Morphogenetic Protein-2 (BMP-2) demonstrated intensive mineralized bone formation as early as 3 weeks after surgery. The addition of erythropoietin (EPO) significantly enhanced angiogenesis in newly formed tissues. The effect of EPO of bacterial origin on bone tissue defect healing was demonstrated for the first time. The developed biomimetic highly porous UHMWPE/HA scaffold can be used separately or in combination with rhBMP-2 and EPO for reconstructive surgery to solve the problems associated with difference between implant architecture and trabecular bone, low osteointegration and bioinertness.

Efficacy and safety of bone substitutes in lumbar spinal fusion: a systematic review and network meta-analysis of randomized controlled trials

PURPOSE

A variety of alternative grafts to autologous iliac crest bone (ICBG) have been developed for lumbar spondylodesis, due to frequent complications following ICBG harvest. The optimal alternative graft to ICBG, however, remains elusive till now. The purpose of this study was to compare the efficacy and safety of fusion materials in lumbar degeneration diseases and to provide a ranking spectrum of the grafts.

METHODS

Randomized controlled trials (RCTs) comparing different bone grafts in lumbar arthrodesis were eligible for inclusion. A network meta-analysis was performed for endpoints including fusion rate and incidence of adverse events.

RESULTS

Twenty-seven RCTs involving 2488 patients and 13 available interventions were included. rhBMP-2 provided the highest fusion rate, being significantly superior to that of ICBG (OR = 0.21, p < 0.001), autograft local bone (ALB) (OR = 0.18, p = 0.022), rhBMP-7 (OR = 0.15, p < 0.001), allograft (OR = 0.13, p = 0.009), and DBM + ALB (OR = 0.07, p = 0.048). The treatment efficacy of allograft could be significantly enhanced by bone marrow concentrate (BMC) supplying (OR = 0.16, p = 0.010). ICBG ranks second on the frequency of complications, which is significantly higher than that of allograft (OR = 0.14, p = 0.041) and ALB (OR = 0.14, p = 0.030). All of the other comparisons showed similar efficacy and safety profiles between groups.

CONCLUSION

Ranking spectrums of the efficacy and safety for various bone grafts were provided graphically. Though rhBMP-2 was of the highest success rate, the application should be taken with proper caution because of the widely proposed life-threatening adverse events. ALB, ALB plus synthetic ceramic materials and allograft mixed with BMC were also proved to be potentially effective alternative graft to ICBG. These slides can be retrieved under Electronic Supplementary Material.

Sustained release of GDF5 from a designed coacervate attenuates disc degeneration in a rat model

Low back pain is often caused by intervertebral disc degeneration, which is characterized by nucleus pulposus (NP) and extracellular matrix (ECM) degeneration. Human adipose-derived stem cells (hADSCs) induced by growth and differentiation factor-5 (GDF5) can differentiate into an NP-like phenotype. Although stem cell-based therapy with prolonged exposure to growth factors is regarded as a promising treatment, the efficacy of this approach in attenuating the disc degeneration process is limited by the short lifespan of growth factors. In our study, a unique growth factor delivery vehicle composed of heparin and the synthetic polycation poly(ethylene argininylaspartate diglyceride) (PEAD) was used to sustain GDF5 release. The results showed that sustained release of GDF5 by the PEAD:heparin delivery system promoted hADSC differentiation to an NP-like phenotype in vitro. After injection of the PEAD:heparin:GDF5 delivery platform and hADSCs into intervertebral spaces of coccygeal (Co) vertebrae Co7/Co8 and Co8/Co9 of the rat, the disc height, water content, and structure of the NPs decreased more slowly than other treatment groups. This new strategy may be used as an alternative treatment for attenuating intervertebral disc degeneration with hADSCs without the need for gene therapy. STATEMENT OF SIGNIFICANCE: Low back pain is often caused by intervertebral disc degeneration, which is characterized by nucleus pulposus (NP) and extracellular matrix (ECM) degeneration. Human adipose-derived stem cells (hADSCs) induced by growth and differentiation factor-5 (GDF-5) can differentiate into an NP-like phenotype. Although stem cell-based therapy with prolonged exposure to growth factor is regarded as a promising treatment, the efficacy of this approach in the disc regeneration process is limited by the short life of growth factors. In our study, a unique growth factor delivery vehicle comprised of heparin and the synthetic polycation poly(ethylene argininylaspartate diglyceride) (PEAD) was used to sustain the release of GDF-5. Numerous groups have explored IDD regeneration methods in vitro and in vivo. Our study differs in that GDF5 was incorporated into a vehicle through charge attraction and exhibited a sustained release profile. Moreover, GDF-5 seeded coacervate combined with hADSC injection could be a minimally invasive approach for tissue engineering that is suitable for clinical application. We investigated the stimulatory effects of our GDF-5 seeded coacervate on the differentiation of ADSCs in vitro and the reparative effect of the delivery system on degenerated NP in vivo.

Bone marrow-derived stem/stromal cells (BMSC) 3D microtissues cultured in BMP-2 supplemented osteogenic induction medium are prone to adipogenesis

Bone marrow-derived mesenchymal stem/stromal cells (BMSC) may facilitate bone repair through secretion of factors that stimulate endogenous repair processes or through direct contribution to new bone through differentiation into osteoblast-like cells. BMSC microtissue culture and differentiation has been widely explored recently, with high-throughput platforms making large-scale manufacture of microtissues increasingly feasible. Bone-like BMSC microtissues could offer an elegant method to enhance bone repair, especially in small-volume non-union defects, where small diameter microtissues could be delivered orthoscopically. Using a high-throughput microwell platform, our data demonstrate that (1) BMSC in 3D microtissue culture result in tissue compaction, rather than growth, (2) not all mineralised bone-like matrix is incorporated in the bulk microtissue mass and (3) a significant amount of lipid vacuole formation is observed in BMSC microtissues exposed to BMP-2. These factors should be considered when optimising BMSC osteogenesis in microtissues or developing BMSC microtissue-based therapeutic delivery processes.

Efficacy of Escherichia coli-derived recombinant human bone morphogenetic protein-2 in posterolateral lumbar fusion: an open, active-controlled, randomized, multicenter trial

BACKGROUND CONTEXT

The efficacy and safety of recombinant human bone morphogenetic protein-2 (rhBMP-2) as a bone graft substitute in spinal fusion has been widely researched. However, no study of the efficacy and safety of Escherichia coli-derived rhBMP-2 (E.BMP-2) with a hydroxyapatite (HA) carrier has been proposed.

PURPOSE

This study aimed to compare the efficacy and safety of fusion materials between E.BMP-2 and autogenous iliac bone graft in posterolateral fusion (PLF).

STUDY DESIGN/SETTING

An open, active-controlled, randomized, multicenter trial was carried out.

PATIENT SAMPLE

This study included 93 patients who underwent single-level lumbar or lumbosacral PLF.

OUTCOME MEASURES

The primary outcome measure was computed tomography (CT)-based fusion rate at 12 and 24 weeks. Secondary outcome measures were fusion grade by radiographs and CT at 12 and 24 weeks and changes in Oswestry Disability Index (ODI), Short Form-36 (SF-36) Health Survey, and visual analogue scale (VAS).

METHODS

Patients who underwent 1-level PLF (between L1 and S1) for severe spinal stenosis or grade 1 spondylolisthesis were randomized to receive E.BMP-2 with an HA carrier (E.BMP-2 group) or autogenous iliac bone graft (AIBG group). Thin-section CT (<2 mm), VAS, ODI, and SF-36 were obtained pre- and postoperatively at 12 and 24 weeks. Outcome measures were compared between the groups.

RESULTS

A total of 100 patients were enrolled in this trial. Among them, 93 patients underwent planned surgery. Preoperative demographic and clinical data showed no difference between groups. CT-based fusion rates were 100.0% (41/41) for the E.BMP-2 group and 90.2% (46/51) for the AIBG group (p=.062) at 12 weeks and 100.0% (41/41) and 94.1% (48/51) (p=.251) at 24 weeks, respectively. Fusion grade based on radiographs and CT showed non-inferiority of the E.BMP-2 group compared with the AIBG group. All clinical parameters improved postoperatively. However, there was no difference in changes in VAS, ODI, or SF-36 between the groups. No serious adverse event related to E.BMP-2 was found.

CONCLUSIONS

The fusion rate of E.BMP-2 was comparable with that of AIBG following PLF. Good clinical efficacy and safety of E.BMP-2 in spinal fusion were also revealed. It was also suggested that HA shows suitability as a carrier for E.BMP-2. Thus, E.BMP-2 with an HA carrier can be an alternative bone graft material in spinal fusion.

Clinical application of bone morphogenetic proteins for bone healing: a systematic review

PURPOSE

This paper documents the existing evidence on bone morphogenetic proteins (BMPs) use for the treatment of bone fractures, non-union, and osteonecrosis, through a review of the clinical literature, underlying potential and limitations in terms of cost effectiveness and risk of complications.

METHODS

A systematic review was performed on the PubMed database using the following string: (bone morphogenetic proteins OR BMPs) and (bone repair OR bone regeneration) including papers from 2000 to 2016. The search focused on clinical trials dealing with BMPs application to favor bone regeneration in bone fractures, non-union, and osteonecrosis, in English language, with level of evidence I, II, III, and IV. Relevant data (type of study, number of patients, BMPs delivery material, dose, site, follow-up, outcome, and adverse events) were extracted and analyzed.

RESULTS

Forty-four articles met the inclusion criteria: 10 randomized controlled trials (RCTs), 7 comparative studies, 18 case series, and 9 case reports. rhBMP-2 was documented mainly for the treatment of fractures, and rhBMP-7 mainly for non-unions and osteonecrosis. Mixed results were found among RCTs and comparative papers: 11 reported positive results for BMPs augmentation, 3 obtained no significant effects, and 2 showed negative results. The only study comparing the two BMPs showed a better outcome with rhBMP-2 for non-union treatment.

CONCLUSION

Clinical evidence on BMPs use for the treatment of fractures, non-union, and osteonecrosis is still controversial, with the few available reports being mainly of low quality. While positive findings have been described in many studies, mixed results are still present in the literature in terms of efficacy and adverse events. The difficulties in drawing clear conclusions are also due to the studies heterogeneity, mainly in terms of different BMPs applied, with different concomitant treatments for each bone pathology. Therefore, further research with well-designed studies is needed in order to understand the real potential of this biological approach to favour bone healing.

Transient Local Bone Remodeling Effects of rhBMP-2 in an Ovine Interbody Spine Fusion Model

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a powerful osteoinductive morphogen capable of stimulating the migration of mesenchymal stem cells (MSCs) to the site of implantation and inducing the proliferation and differentiation of these MSCs into osteoblasts. Vertebral end-plate and vertebral body resorption has been reported after interbody fusion with high doses of rhBMP-2. In this study, we investigated the effects of 2 rhBMP-2 doses on peri-implant bone resorption and bone remodeling at 7 time points in an end-plate-sparing ovine interbody fusion model.

METHODS

Twenty-one female sheep underwent an end-plate-sparing discectomy followed by interbody fusion at L2-L3 and L4-L5 using a custom polyetheretherketone (PEEK) interbody fusion device. The PEEK interbody device was filled with 1 of 2 different doses of rhBMP-2 on an absorbable collagen sponge (ACS): 0.13 mg (1×) or 0.90 mg (7×). Bone remodeling and interbody fusion were assessed via high-resolution radiography and histological analyses at 1, 2, 3, 4, 8, 12, and 20 weeks postoperatively.

RESULTS

Peri-implant bone resorption peaked between 3 and 8 weeks in both the 1× and the 7× rhBMP-2/ACS-dose group. Osteoclastic activity and corresponding peri-implant bone resorption was dose-dependent, with moderate-to-marked resorption at the 7×-dose level and less resorption at the 1×-dose level. Both dose (p < 0.0007) and time (p < 0.0025) affected bone resorption significantly. Transient bone-resorption areas were fully healed by 12 weeks. Osseous bridging was seen at all but 1 spinal level at 12 and at 20 weeks.

CONCLUSIONS

In the ovine end-plate-sparing interbody fusion model, rhBMP-2 dose-dependent osteoclastic resorption is a transient phenomenon that peaks at 4 weeks postoperatively.

CLINICAL RELEVANCE

Using the U.S. Food and Drug Administration (FDA)-approved rhBMP-2 concentration and matching the volume of rhBMP-2/ACS with the volume of desired bone formation within the interbody construct may limit the occurrence of transient bone resorption.

Bone Morphogenic Protein Is a Viable Adjunct for Fusion in Minimally Invasive Transforaminal Lumbar Interbody Fusion

Study Design

Comparison of prospectively collected data of patients undergoing minimally invasive surgery transforaminal lumbar interbody fusion (MIS-TLIF) with and without recombinant human bone morphogenic protein 2 (BMP).

Purpose

To compare the clinical, radiological outcome and complications of patients undergoing MIS-TLIF with and without BMP.

Overview of Literature

BMP is an effective fusion enhancer with potential complications. Direct comparison of MIS-TLIF with and without BMP is limited to retrospective studies with short follow-up.

Methods

From June 2005 to February 2011, consecutive cases of MIS-TLIF performed by a single surgeon were included. North American Spine Society (NASS) score, Oswestry disability index (ODI), Short Form-36 (SF-36), and visual analogue score (VAS) were assessed preoperatively and at 6 and 24 months postoperatively. Fusion rates and complications were noted.

Results

The 252 cases comprised 104 non-BMP and 148 BMP cases. The BMP group was significantly older (mean age, 60.2 vs. 53.9; p<0.01). Preoperative scores were similar. Immediate postoperative morphine usage was significantly lower in the BMP group (12.4 mg vs. 20.1 mg, p<0.01). At 6 months, the BMP group had lower VAS back and leg pain scores (p<0.01). At 2 years, the BMP group had better leg pain scores (p<0.01), ODI (15.4 vs. 20.3, p=0.04) and NASS scores (8.8 vs. 15.8, p<0.01). Both groups showed significant clinical improvement compared to their preoperative levels. The BMP group attained a significantly higher rate of fusion at 6 months follow-up (88.4% vs. 76.8%, p=0.016) with no difference at 2 years. The non-BMP and BMP group had 12 (11.5%) and 9 (6.1%) complications and 5 (4.8%) and 2 (1.4%) reoperations, respectively.

Conclusions

The use of BMP to augment fusion in MIS-TLIF is an acceptable alternative that has potential benefits of less pain in early and intermediate postoperative follow-up.

Allograft versus autograft for pediatric posterior cervical and occipito-cervical fusion: a systematic review of factors affecting fusion rates

OBJECT Fusion rates are high for children undergoing posterior cervical fusion (PCF) and occipito-cervical fusion (OCF). Autologous bone has been widely used as the graft material of choice, despite the risk of donor-site morbidity associated with harvesting the bone, possibly because very low fusion rates were reported with posterior allograft cervical fusions in children several decades ago. Higher overall fusion rates using allograft in adults, associated with improvements in internal fixation techniques and the availability of osteoinductive substances such as bone morphogenetic protein (BMP), have led to heightened enthusiasm for the use of bank bone during pediatric PCF. A systematic review was performed to study factors associated with successful bone fusion, including the type of bone graft used. METHODS The authors performed a comprehensive PubMed search of English-language articles pertaining to PCF and OCF in patients less than 18 years old. Of the 561 abstracts selected, 148 articles were reviewed, resulting in 60 articles that had sufficient detail to be included in the analysis. A meta-regression analysis was performed to determine if and how age, fusion technique, levels fused, fusion substrate, BMP use, postoperative bracing, and radiographic fusion criteria were related to the pooled prevalence estimates. A systematic review of the literature was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. RESULTS A total of 604 patients met the specific inclusion and exclusion criteria. The overall fusion rate was 93%, with a mean age of 9.3 years and mean follow-up of 38.7 months. A total of 539 patients had fusion with autograft (94% fusion rate) and 65 patients with allograft (80% fusion rate). Multivariate meta-regression analysis showed that higher fusion rates were associated with OCF compared with fusions that excluded the occiput (p < 0.001), with the use of autograft instead of allograft (p < 0.001), and with the use of CT to define fusion instead of plain radiography alone. The type of internal fixation, the use of BMP, patient age, and the duration of follow-up were not found to be associated with fusion rates in the multivariate analysis. CONCLUSIONS Fusion rates for PCF are high, with higher rates of fusion seen when autograft is used as the bone substrate and when the occiput is included in the fusion construct. Further study of the use of allograft as a viable alternative to autograft bone fusion is warranted because limited data are available regarding the use of allograft in combination with more rigid internal fixation techniques and osteoinductive substances, both of which may enhance fusion rates with allograft.

Exploratory meta-analysis on dose-related efficacy and morbidity of bone morphogenetic protein in spinal arthrodesis surgery

OBJECT

Bone morphogenetic protein (BMP) is frequently used for spinal arthrodesis procedures in an "off-label" fashion. Whereas complications related to BMP usage are well recognized, the role of dosage is less clear. The objective of this meta-analysis was to assess dose-dependent effectiveness (i.e., bone fusion) and morbidity of BMP used in common spinal arthrodesis procedures. A quantitative exploratory meta-analysis was conducted on studies reporting fusion and complication rates following anterior cervical discectomy and fusion (ACDF), posterior cervical fusion (PCF), anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), posterior lumbar interbody fusion (PLIF), and posterolateral lumbar fusion (PLF) supplemented with BMP.

METHODS

A literature search was performed to identify studies on BMP in spinal fusion procedures reporting fusion and/or complication rates. From the included studies, a database for each spinal fusion procedure, including patient demographic information, dose of BMP per level, and data regarding fusion rate and complication rates, was created. The incidence of fusion and complication rates was calculated and analyzed as a function of BMP dose. The methodological quality of all included studies was assessed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Data were analyzed using a random-effects model. Event rates are shown as percentages, with a 95% CI.

RESULTS

Forty-eight articles met the inclusion criteria: ACDF (n = 7), PCF (n = 6), ALIF (n = 9), TLIF/PLIF (n = 17), and PLF (n = 9), resulting in a total of 5890 patients. In ACDF, the lowest BMP concentration analyzed (0.2-0.6 mg/level) resulted in a fusion rate similar to the highest dose (1.1-2.1 mg/level), while permitting complication rates comparable to ACDF performed without BMP. The addition of BMP to multilevel constructs significantly (p < 0.001) increased the fusion rate (98.4% [CI 95.4%-99.4%]) versus the control group fusion rate (85.8% [CI 77.4%-91.4%]). Studies on PCF were of poor quality and suggest that BMP doses of ≤ 2.1 mg/level resulted in similar fusion rates as higher doses. Use of BMP in ALIF increased fusion rates from 79.1% (CI 57.6%-91.3%) in the control cohort to 96.9% (CI 92.3%-98.8%) in the BMP-treated group (p < 0.01). The rate of complications showed a positive correlation with the BMP dose used. Use of BMP in TLIF had only a minimal impact on fusion rates (95.0% [CI 92.8%-96.5%] vs 93.0% [CI 78.1%-98.0%] in control patients). In PLF, use of ≥ 8.5 mg BMP per level led to a significant increase of fusion rate (95.2%; CI 90.1%-97.8%) compared with the control group (75.3%; CI 64.1%-84.0%, p < 0.001). BMP did not alter the rate of complications when used in PLF.

CONCLUSIONS

The BMP doses used for various spinal arthrodesis procedures differed greatly between studies. This study provides BMP dosing recommendations for the most common spine procedures.

The efficacy of routine use of recombinant human bone morphogenetic protein-2 in occipitocervical and atlantoaxial fusions of the pediatric spine: a minimum of 12 months' follow-up with computed tomography

OBJECT The purpose of this study focusing on fusion rate was to determine the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2) use in posterior instrumented fusions of the craniocervical junction in the pediatric population. The authors previously reported the short-term (mean follow-up 11 months) safety and efficacy of rhBMP-2 use in the pediatric age group. The present study reports on their long-term results (minimum of 12 months' follow-up) and focuses on efficacy. METHODS The authors performed a retrospective review of 83 consecutive pediatric patients who had undergone posterior occipitocervical or atlantoaxial spine fusion at Texas Children's Hospital or Riley Children's Hospital during the period from October 2007 to October 2012. Forty-nine patients were excluded from further analysis because of death, loss to follow-up, or lack of CT evaluation of fusion at 12 or more months after surgery. Fusion was determined by postoperative CT scan at a minimum of 12 months after surgery. The fusion was graded and classified by a board-certified fellowship-trained pediatric neuroradiologist. Other factors, such as patient age, diagnosis, number of vertebral levels fused, use of allograft or autograft, dosage of bone morphogenetic protein (BMP), and use of postoperative orthosis, were recorded. RESULTS Thirty-four patients had a CT scan at least 12 months after surgery. The average age of the patients at surgery was 8 years, 1 month (range 10 months-17 years). The mean follow-up was 27.7 months (range 12-81 months). There were 37 fusion procedures in 34 patients. Solid fusion (CT Grade 4 or 4-) was achieved in 89.2% of attempts (33 of 37), while incomplete fusion or failure of fusion was seen in 10.8%. Based on logistic regression analysis, there was no significant association between solid fusion and age, sex, BMP dose, type of graft material, use of postoperative orthosis, or number of levels fused. Three of 34 patients (8.8%) required revision surgery. CONCLUSIONS Despite the large number of adult studies reporting positive effects of BMP on bone fusion, our long-term outcomes using rhBMP-2 in the pediatric population suggest that rates of fusion failure are higher than observed in contemporary adult and pediatric reports of occipitocervical and atlantoaxial spine fusions.

Routine use of recombinant human bone morphogenetic protein-2 in posterior fusions of the pediatric spine and incidence of cancer

OBJECT The aim of this study was to determine the safety of recombinant human bone morphogenetic protein-2 (rhBMP-2) use in posterior instrumented fusions in the pediatric population, focusing on cancer risk. In a previous study, the authors reported the short-term (mean follow-up of 11 months) safety and efficacy of rhBMP-2 in the pediatric age group. The present study reports their results with a minimum of 24 months' follow-up. METHODS The authors retrospectively reviewed 57 consecutive cases involving pediatric patients who underwent posterior occiptocervical, cervical, thoracic, lumbar, or lumbosacral spine fusion from October 1, 2007, to June 30, 2011, at Texas Children's Hospital. Seven cases were excluded from further analysis because of loss to follow-up. Three patients died during the follow-up period and were placed in a separate cohort. RESULTS The patients' average age at the time of surgery was 11 years, 4 months (range 9 months to 20 years). The mean duration of follow-up was 48.4 months (range 24-70 months). Cancer status was determined at the most recent encounter with the patient and/or caretaker(s) in person, or in telephone follow-up. Twenty-four or more months after administration of rhBMP-2, there were no cases of new malignancy, degeneration, or metastasis of existing tumors. The cause of death of the patients who died during the study period was not related to BMP or to the development, degeneration, or metastasis of cancer. CONCLUSIONS Despite the large number of adult studies reporting increased cancer risk associated with BMP use, the authors' outcomes with rhBMP-2 in the pediatric population suggest that it is a safe adjunct to posterior spine fusions of the occipitocervical, cervical, thoracic, lumbar, and lumbosacral spine. There were no new cases of cancer, or degeneration or metastasis of existing malignancies in this series.

In silico Mechano-Chemical Model of Bone Healing for the Regeneration of Critical Defects: The Effect of BMP-2

The healing of bone defects is a challenge for both tissue engineering and modern orthopaedics. This problem has been addressed through the study of scaffold constructs combined with mechanoregulatory theories, disregarding the influence of chemical factors and their respective delivery devices. Of the chemical factors involved in the bone healing process, bone morphogenetic protein-2 (BMP-2) has been identified as one of the most powerful osteoinductive proteins. The aim of this work is to develop and validate a mechano-chemical regulatory model to study the effect of BMP-2 on the healing of large bone defects in silico. We first collected a range of quantitative experimental data from the literature concerning the effects of BMP-2 on cellular activity, specifically proliferation, migration, differentiation, maturation and extracellular matrix production. These data were then used to define a model governed by mechano-chemical stimuli to simulate the healing of large bone defects under the following conditions: natural healing, an empty hydrogel implanted in the defect and a hydrogel soaked with BMP-2 implanted in the defect. For the latter condition, successful defect healing was predicted, in agreement with previous in vivo experiments. Further in vivo comparisons showed the potential of the model, which accurately predicted bone tissue formation during healing, bone tissue distribution across the defect and the quantity of bone inside the defect. The proposed mechano-chemical model also estimated the effect of BMP-2 on cells and the evolution of healing in large bone defects. This novel in silico tool provides valuable insight for bone tissue regeneration strategies.

Mosaic tetrasomy 20p associated with osteoporosis and recurrent fractures

Tetrasomy 20p is a very rare chromosome abnormality, with only two single cases previously reported in the literature, both fetuses with multiple congenital anomalies, osteopenia, and fractures. We report on the first case of mosaic tetrasomy 20p in a 13-year-old male. Amniocentesis karyotype showed mosaicism (73% of cells) for a supernumerary marker chromosome, an isodicentric chromosome 20p. At birth, cord blood karyotype was normal in all cells but uroepithelial cells showed the marker chromosome in 30% of cells analyzed. Chromosomal single nucleotide polymorphism (SNP) microarray using buccal cells confirmed the previous result with mosaicism estimated at 59% of cells. His course has been complicated by profound osteoporosis with recurrent nontraumatic fractures and vertebral compression leading to significant disability. This report describes the phenotype and evaluation of mosaic pure tetrasomy 20p syndrome and compares to nonmosaic tetrasomy 20p and trisomy 20p syndromes, both of which have been previously reported in association with osteopenia and fractures. The pathophysiology of osteoporosis in tetrasomy 20p is unknown. We hypothesize that overexpression of bone morphogenetic protein 2 may be the underlying mechanism of osteoporosis and recurrent fractures.

A review paper on biomimetic calcium phosphate coatings

Biomimetic calcium phosphate coatings have been developed for bone regeneration and repair because of their biocompatibility, osteoconductivity, and easy preparation. They can be rendered osteoinductive by incorporating an osteogenic agent, such as bone morphogenetic protein 2 (BMP-2), into the crystalline lattice work in physiological situations. The biomimetic calcium phosphate coating enables a controlled, slow and local release of BMP-2 when it undergoes cell mediated coating degradation induced by multinuclear cells, such as osteoclasts and foreign body giant cells, which mimics a physiologically similar release mode, to achieve sustained ectopic or orthotopic bone formation. Therefore, biomimetic calcium phosphate coatings are considered to be a promising delivery vehicle for osteogenic agents. In this review, we present an overview of biomimetic calcium phosphate coatings including their preparation techniques, physico-chemical properties, potential as drug carrier, and their pre-clinical application both in ectopic and orthotopic animal models. We briefly review some features of hydroxyapatite coatings and their clinical applications to gain insight into the clinical applications of biomimetic calcium phosphate coatings in the near future.

Vancomycin-bearing synthetic bone graft delivers rhBMP-2 and promotes healing of critical rat femoral segmental defects

BACKGROUND

Bone grafts simultaneously delivering therapeutic proteins and antibiotics may be valuable in orthopaedic trauma care. Previously, we developed a poly(2-hydroxyethyl methacrylate)-nanocrystalline hydroxyapatite (pHEMA-nHA) synthetic bone graft that, when preabsorbed with 400-ng rhBMP-2/7, facilitated the functional repair of critical-size rat femoral defects. Recently, we showed that pHEMA-nHA effectively retains/releases vancomycin and rhBMP-2 in vitro. The success of such a strategy requires that the incorporation of vancomycin does not compromise the structural integrity of the graft nor its ability to promote bone healing.

QUESTIONS/PURPOSES

(1) To evaluate the ability of pHEMA-nHA-vancomycin composites in combination with 3-µg rhBMP-2 to repair 5 mm rat femoral segmental defects, and (2) To determine if the encapsulated vancomycin impairs the graft/rhBMP-2-assisted bone repair.

METHODS

pHEMA-nHA-vancomycin, pHEMA-nHA, or collagen sponge control with/without 3-µg rhBMP-2 were press-fit in 5 mm femoral defects in SASCO-SD male rats (289-300 g). Histology, microcomputed tomography, and torsion testing were performed on 8- and 12-week explants to evaluate the extent and quality of repair. The effect of vancomycin on the temporal absorption of endogenous BMP-2 and stromal cell-derived factor-1 was evaluated by immunohistochemistry. These factors are important for bone healing initiation and stem cell recruitment, respectively.

RESULTS

Partial bridging of the defect with bony callus by 12 weeks was observed with pHEMA-nHA-vancomycin without rhBMP-2 while full bridging with substantially mineralized callus and partial restoration of torsional strength was achieved with 3-µg rhBMP-2. The presence of vancomycin changed the absorption patterns of endogenous proteins on the grafts, but did not appear to substantially compromise graft healing.

CONCLUSIONS

The composite pHEMA-nHA-vancomycin preabsorbed with 3-µg rhBMP-2 promoted repair of 5 mm rat femoral segmental defects. With the sample sizes applied, vancomycin encapsulation did not appear to have a negative effect on bone healing.

CLINICAL RELEVANCE

pHEMA-nHA-vancomycin preabsorbed with rhBMP-2 may be useful in the repair of critical-size long bone defects prone to infections.

The use of bone morphogenetic protein in thoracolumbar spine procedures: analysis of the MarketScan longitudinal database

BACKGROUND CONTEXT

The use of recombinant human bone morphogenetic protein (BMP) in the thoracolumbar spine remains controversial, with many questioning the risks and benefits of this new biologic.

PURPOSE

To describe national trends, incidence of complications, and revision rates associated with BMP use in thoracolumbar spine procedures.

STUDY DESIGN/SETTING

Administrative database study.

PATIENT SAMPLE

A matched cohort of 52,259 patients undergoing thoracolumbar fusion surgery from 2006 to 2010 were identified in the MarketScan database. Patients without BMP treatment were matched 2:1 to patients receiving intraoperative BMP.

OUTCOME MEASURES

Revision rates and postoperative complications.

METHODS

The MarketScan database was used to select patients undergoing thoracolumbar fusion procedures, with and without intraoperative BMP. We ascertained outcome measures using either International Classification of Disease, ninth revision, or Current Procedural Terminology coding, and matched groups were evaluated using a bivariate and multivariate analyses. Kaplan-Meier estimates of fusions failure rates were also calculated.

RESULTS

Patients receiving intraoperative BMP underwent fewer refusions, decompressions, posterior and anterior revisions, or any revision procedure (single level 4.53% vs. 5.85%, p<.0001; multilevel 5.02% vs. 6.83%, p<.0001; overall cohort 4.73% vs. 6.09%, p<.0001). After adjusting for comorbidities, demographics, and levels of procedure, BMP was not associated with the postoperative development of cancer (odds ratio 0.92). Bone morphogenetic protein use was associated with an increase in any complication at 30 days (15.8% vs. 14.9%, p=.0065), which is only statistically significant among multilevel procedures (19.74% vs. 18.02%, p=.0013). Thirty-day complications in multilevel procedures associated with BMP use included new dysrhythmia (4.68% vs. 4.01%, p=.0161) and delirium (1.08% vs. 0.69%, p=.0024). A new diagnosis of chronic pain was associated with BMP use in both single-level (2.74% vs. 2.15%, p=.0019) and multilevel (3.7% vs. 2.52%, p<.0001) procedures. Bone morphogenetic protein was negatively associated with infection in single-level procedures (2.12% vs. 2.64%, p=.0067) and wound dehiscence in multilevel procedures (0.84% vs. 1.18%, p=.0167).

CONCLUSIONS

In national data analysis of thoracolumbar procedures, we found that BMP was associated with decreased incidence of revision spinal surgery and with a slight increased risk of overall complications at 30 days. Although no BMP-associated increased risk of malignancy was found, lack of long-term follow-up precludes detection of between-group differences in malignancies and other rare events that may not appear until later.

Nationwide practice patterns in the use of recombinant human bone morphogenetic protein-2 in pediatric spine surgery as a function of patient-, hospital-, and procedure-related factors

OBJECT

Current national patterns as a function of patient-, hospital-, and procedure-related factors, and complication rates in the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) as an adjunct to the practice of pediatric spine surgery have scarcely been investigated.

METHODS

The authors conducted a cross-sectional study using data from the Healthcare Cost and Utilization Project Kids' Inpatient Database. Univariate and multivariate logistic regression were used to calculate unadjusted and adjusted odds ratios and 95% confidence intervals, and p values < 0.05 were considered to be statistically significant.

RESULTS

The authors identified 9538 hospitalizations in pediatric patients 20 years old or younger who had undergone spinal fusion in the US in 2009; 1541 of these admissions were associated with rhBMP-2 use. By multivariate logistic regression, the following factors were associated with rhBMP-2 use: patient age 15-20 years; length of hospital stay (adjusted odds ratio [aOR] 1.01, p = 0.017); insurance status (private [aOR 1.49, p < 0.001] compared with Medicaid); hospital type (nonchildren's hospital); region (Midwest [aOR 2.49, p = 0.008] compared with Northeast); spinal refusion (aOR 2.20, p < 0.001); spinal fusion approach/segment (anterior lumbar [aOR 1.73, p < 0.001] and occipitocervical [aOR 1.86, p = 0.013] compared with posterior lumbar); short segment length (aOR 1.42, p = 0.016) and midlength (aOR 1.44, p = 0.005) compared with long; and preoperative diagnosis (Scheuermann kyphosis [aOR 1.56, p < 0.017] and spondylolisthesis [aOR 1.93, p < 0.001]).

CONCLUSIONS

Use of BMP in pediatric spine procedures now comprises more than 10% of pediatric spinal fusion. Patient-related (age, insurance type, diagnosis); hospital-related (children's hospital vs general hospital, region in the US); and procedure-related (redo fusion, anterior vs posterior approach, spinal levels, number of levels fused) factors are associated with the variation in BMP use in the US.

Usage of recombinant human bone morphogenetic protein in cervical spine procedures: analysis of the MarketScan longitudinal database

BACKGROUND

Usage of recombinant human bone morphogenetic protein (rhBMP) in anterior cervical discectomy and fusion (ACDF) procedures is controversial. Studies suggest increased rates of dysphagia, hematoma or seroma, and severe airway compromise in anterior cervical spine procedures using rhBMP. The purpose of the present study was to determine and describe national utilization trends and complication rates associated with rhBMP usage in anterior cervical spine procedures.

METHODS

The MarketScan database from 2006 to 2010 was retrospectively queried to identify 91,543 patients who underwent ACDF with or without cervical corpectomy. Patient selection and outcomes were ascertained with use of ICD-9-CM (International Classification of Diseases, Ninth Revision, Clinical Modification) and CPT (Current Procedural Terminology) coding. A total of 3197 patients were treated with rhBMP intraoperatively. Mean follow-up was 588 days (interquartile range [IQR], 205 to 886 days) in the non-treated cohort and 591 days (IQR, 203 to 925 days) in the rhBMP-treated cohort. Multivariate logistic regression as well as propensity score analysis were used to evaluate the association of rhBMP usage with postoperative complications.

RESULTS

In propensity score-adjusted models, rhBMP usage was associated with an increased risk of any complication (odds ratio [OR] = 1.34, 95% confidence interval [CI] = 1.2 to 1.5) and specific complications such as hematoma or seroma (OR = 1.8, 95% CI = 1.4 to 2.3), dysphagia (OR = 1.3, 95% CI = 1.1 to 1.5), and any pulmonary complication (OR = 1.5, 95% CI = 1.2 to 1.8) within thirty days postoperatively. There were no significant differences in the rates of readmission, in-hospital mortality, referral to pain management, new malignancy, or reoperation between the two cohorts. Usage of rhBMP was associated with a mean increase of $5545 (19%) in total payments to the hospital and primary physician (p < 0.001).

CONCLUSIONS

We found an increased overall rate of postoperative complications in patients receiving rhBMP for cervical spinal fusion procedures compared with patients not receiving rhBMP. Hematoma or seroma, pulmonary complications, and dysphagia were also more common in the rhBMP cohort. Usage of rhBMP in a case was associated with $311 greater payments to the surgeon and $4213 greater payments to the hospital.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

A review of pediatric lumbar spine trauma

Pediatric spine fractures constitute 1%–3% of all pediatric fractures. Anywhere from 20% to 60% of these fractures occur in the thoracic or lumbar spine, with the lumbar region being more affected in older children. Younger children tend to have a higher proportion of cervical injuries. The pediatric spine differs in many ways from the adult spine, which can lead to increased ligamentous injuries without bone fractures. The authors discuss and review pediatric lumbar trauma, specifically focusing on epidemiology, radiographic findings, types and mechanisms of lumbar spine injury, treatment, and outcomes.

No advantage to rhBMP-2 in addition to autogenous graft for fracture nonunion

Bone morphogenetic proteins are a necessary component of the fracture healing cascade. Few studies have delineated the efficacy of iliac crest bone graft and recombinant human bone morphogenetic protein 2 (rhBMP-2), especially, in comparison with the gold standard treatment of nonunion, which is autogenous bone graft alone. This study compared the outcome of patients with fracture nonunion treated with autogenous bone graft plus rhBMP-2 adjuvant vs patients treated with autogenous bone graft alone. A total of 118 consecutive patients who were to undergo long bone nonunion surgery with autogenous bone graft (50) or autogenous bone graft plus rhBMP-2 (68) were identified. Surgical intervention included either harvested iliac autogenous bone graft or autogenous bone graft plus 1.5 mg/mL of rhBMP-2 placed in and around the site of nonunion. No differences were found in the distribution of nonunion sites included within each group. Twelve-month follow-up was obtained on 100 of 118 patients (84.7%). Analyses of demographic characteristics (including tobacco), medical comorbidities, previous surgeries, and nonunion type (atrophic vs hypertrophic) did not differ. Postoperative complication rates did not differ. The percentage of patients who progressed to union did not differ. Mean time to union in the autogenous bone graft plus rhBMP-2 group was 6.6 months (±3.9) vs 5.4 (±2.7) months in the autogenous bone graft-only group (P=.06). Rates of revision (16.2% for rhBMP-2 plus autogenous bone graft vs 8% for autogenous bone graft) did not differ statistically (P=.19), nor did 12-month scores of pain and functional assessment. Although rhBMP-2 is a safe adjuvant, there was no benefit seen when rhBMP-2 was added to autogenous bone graft in the treatment of long bone nonunion. Given its high cost, rhBMP-2 should be reconsidered as an aid to autogenous bone graft in the treatment of nonunion.

Low-dose recombinant human bone morphogenetic protein-2 to enhance the osteogenic potential of the Schneiderian membrane in the early healing phase: in vitro and in vivo studies

PURPOSE

The objectives of this study were to confirm the osteogenic potential of the Schneiderian membrane and to elucidate the early healing pattern of low-dose recombinant human bone morphogenetic protein-2 (rhBMP-2)-coated biphasic calcium phosphate (BCP).

MATERIALS AND METHODS

The osteogenic potential of the Schneiderian membrane and enhancement by rhBMP-2 were evaluated by in vitro analysis. RhBMP-2-coated BCP (experimental group) and BCP soaked with saline (control group) were applied to the maxillary sinus in rabbits. After 2 weeks, micro-computed tomographic and histometric analyses were performed.

RESULTS

Enhanced osteogenic potential was found when cells from the Schneiderian membrane were treated with rhBMP-2. Micro-computed tomographic analysis showed that the total augmented volume was significantly larger in the experimental group. Different healing patterns were observed in 3 regions, although the area of new bone did not differ significantly. Although more newly formed bone appeared, particularly along the Schneiderian membrane in the experimental group, the difference was not statistically significant.

CONCLUSIONS

RhBMP-2 enhanced the osteogenic potential of the Schneiderian membrane in vitro. However, low-dose rhBMP-2-coated BCP failed to exert a statistically significant effect in vivo, although it appeared to be effective in sinus augmentation specifically for the volumetric increase in the early phase.

In-vitro analysis of rhBMP-2 effects in human osteogenic cells

This study evaluated the in vitro expression of bone-related proteins by osteoblasts in the presence of different concentrations of human recombinant bone morphogenetic protein-2 (rhBMP-2). Immortalized human fetal osteoblastic cell line 1.19 (hFOB) were exposed to different concentrations of rhBMP-2 (10, 50, or 100 ng/mL) for 72 h. Cell proliferation and viability (MTT assay), as well as the expression of fibronectin, osteonectin, and osteopontin were assessed by indirect immunofluorescence and Western blot. Neither of the 3 concentrations of rhBMP-2 caused statistically significant alterations in cell proliferation and viability, although the concentration of 100 ng/mL showed lower values for both assays after both 48 and 72 h of exposure. There was no alteration in the expression of noncollagenous proteins, as analyzed by immunofluorescence, when compared with the control group. Furthermore, in the Western blot assay we observed a statistically significant decrease in fibronectin and osteonectin at 100 ng rhBMP-2/mL (p < 0.05) by comparison with the medium alone. The expression of osteopontin decreased slightly in all 3 concentrations of rhBMP-2 tested; however, the change was not statistically significant (p > 0.05). In this in-vitro study, the tested concentrations of rhBMP-2 appeared to decrease the expression of important bone-related molecules in pre-osteoblast cells.

Bone Regeneration Based on Tissue Engineering Conceptions - A 21st Century Perspective

The role of Bone Tissue Engineering in the field of Regenerative Medicine has been the topic of substantial research over the past two decades. Technological advances have improved orthopaedic implants and surgical techniques for bone reconstruction. However, improvements in surgical techniques to reconstruct bone have been limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have provided attractive alternatives to bone grafting expanding the surgical options for restoring the form and function of injured bone. Specifically, novel bioactive (second generation) biomaterials have been developed that are characterised by controlled action and reaction to the host tissue environment, whilst exhibiting controlled chemical breakdown and resorption with an ultimate replacement by regenerating tissue. Future generations of biomaterials (third generation) are designed to be not only osteoconductive but also osteoinductive, i.e. to stimulate regeneration of host tissues by combining tissue engineering and in situ tissue regeneration methods with a focus on novel applications. These techniques will lead to novel possibilities for tissue regeneration and repair. At present, tissue engineered constructs that may find future use as bone grafts for complex skeletal defects, whether from post-traumatic, degenerative, neoplastic or congenital/developmental "origin" require osseous reconstruction to ensure structural and functional integrity. Engineering functional bone using combinations of cells, scaffolds and bioactive factors is a promising strategy and a particular feature for future development in the area of hybrid materials which are able to exhibit suitable biomimetic and mechanical properties. This review will discuss the state of the art in this field and what we can expect from future generations of bone regeneration concepts.

Enhanced osteogenesis of adipose derived stem cells with Noggin suppression and delivery of BMP-2

Bone morphogenetic proteins (BMPs) are believed to be the most potent osteoinductive factors. However, BMPs are highly pleiotropic molecules and their supra-physiological high dose requirement leads to adverse side effects and inefficient bone formation. Thus, there is a need to develop alternative osteoinductive growth factor strategies that can effectively complement BMP activity. In this study, we intrinsically stimulated BMP signaling in adipose derived stem cells (ASCs) by downregulating noggin, a potent BMP antagonist, using an RNAi strategy. ASCs transduced with noggin shRNA significantly enhanced osteogenic differentiation of cells. The potency of endogenous BMPs was subsequently enhanced by stimulating ASCs with exogenous BMPs at a significantly reduced dose. The level of mineralization in noggin shRNA treated ASCs when treated with BMP-2 was comparable to that of control shRNA treated cell treated with 10-fold more BMP-2. The complementary strategy of noggin suppression + BMP-2 to enhance osteogenesis was further confirmed in 3D in vitro environments using scaffolds consisting of chitosan (CH), chondroitin sulfate (CS), and apatite layer on their surfaces designed to slowly release BMP-2. This finding supports the novel therapeutic potential of this complementary strategy in bone regeneration.

Sustained release of bone morphogenetic protein 2 via coacervate improves the osteogenic potential of muscle-derived stem cells

Muscle-derived stem cells (MDSCs) isolated from mouse skeletal muscle by a modified preplate technique exhibit long-term proliferation, high self-renewal, and multipotent differentiation capabilities in vitro. MDSCs retrovirally transduced to express bone morphogenetic proteins (BMPs) can differentiate into osteocytes and chondrocytes and enhance bone and articular cartilage repair in vivo, a feature that is not observed with nontransduced MDSCs. These results emphasize that MDSCs require prolonged exposure to BMPs to undergo osteogenic and chondrogenic differentiation. A sustained BMP protein delivery approach provides a viable and potentially more clinically translatable alternative to genetic manipulation of the cells. A unique growth factor delivery platform comprised of native heparin and a synthetic polycation, poly(ethylene argininylaspartate diglyceride) (PEAD), was used to bind, protect, and sustain the release of bone morphogenetic protein-2 (BMP2) in a temporally and spatially controlled manner. Prolonged exposure to BMP2 released by the PEAD:heparin delivery system promoted the differentiation of MDSCs to an osteogenic lineage in vitro and induced the formation of viable bone at an ectopic site in vivo. This new strategy represents an alternative approach for bone repair mediated by MDSCs while bypassing the need for gene therapy.

BMP2-induced inflammation can be suppressed by the osteoinductive growth factor NELL-1

Bone-morphogenetic protein 2 (BMP2) is currently the only Food and Drug Administration-approved osteoinductive growth factor used in clinical settings for bone regeneration and repair. However, the use of BMP2 is encumbered by numerous clinical complications, including postoperative inflammation and life-threatening cervical swelling. Thus, methods to prevent BMP2-induced inflammation would have far-reaching clinical implications toward improving current BMP2-based methods for bone regeneration. For the first time, we investigate the potential role of the growth factor Nel-like molecule-1 (NELL-1) in inhibiting BMP2-induced inflammation. Adult rats underwent a femoral bone onlay procedure, treated with either BMP2 protein (4 mg/mL), NELL-1 protein (4 mg/mL), or both proteins combined. Animals were evaluated at 3, 7, and 14 days postoperatively by histology, histomorphometry, immunohistochemistry, and real-time PCR for markers of inflammation (TNFα, IL6). The relative levels of TNFα and IL6 in serum were also detected by ELISA. The mechanism for NELL-1's anti-inflammatory effect was further assessed through examining inflammatory markers and generation of reactive oxygen species (ROS) in the mouse embryonic fibroblast NIH3T3 cells. BMP2 significantly induced local inflammation, including an early and pronounced polymorphonuclear cell infiltration accompanied by increased expression of TNFα and IL6. Treatment with NELL-1 alone elicited no significant inflammatory response. However, NELL-1 significantly attenuated BMP2-induced inflammation by all markers and at all timepoints. These local findings were also confirmed using systemic serum inflammatory biomarkers (TNFα, IL6). In each case, NELL-1 fully reversed BMP2-induced systemic inflammation. Lastly, our findings were recapitulated in vitro, where NELL-1 suppressed BMP2 induced expression of inflammatory markers, as well as NF-κB transcriptional activity and generation of ROS. BMP2-induced inflammation is a serious public health concern with potentially life-threatening complications. In the present study, we observed that the growth factor, NELL-1, significantly attenuates or completely reverses BMP2-induced inflammation. The mechanisms of NELL-1's anti-inflammatory effect are only partially elucidated, and may include reduction of NF-κB transcriptional activity or ROS generation.

Multilevel anterior cervical discectomy and fusion with and without rhBMP-2: a comparison of dysphagia rates and outcomes in 150 patients

OBJECT

Reported complications of recombinant human bone morphogenetic protein-2 (rhBMP-2) use in anterior cervical discectomy and fusion (ACDF) cases include dysphagia and cervical swelling. However, dysphagia often occurs after multilevel ACDF procedures performed with allograft (without BMP) as well. To date, there has been no large study comparing the dysphagia rates of patients who have undergone multilevel ACDF using allograft spacers with those who underwent ACDF using polyetheretherketone (PEEK) cages filled with rhBMP2. The authors report one of the first such comparisons between these 2 patient cohorts.

METHODS

The authors retrospectively reviewed 150 patient records. Group 1 (BMP group) consisted of 100 patients who underwent multilevel ACDF with PEEK cages filled with rhBMP-2 and instrumented with a cervical plate. Group 2 (allograft group) included a matched control cohort of 50 patients who underwent multilevel ACDF with allograft spacers and anterior plate fixation (without rhBMP-2). Patient demographics were not significantly different between the groups. Fusion was assessed by means of dynamic radiographs and/or CT at routine intervals. Complications, dysphagia incidence, standardized dysphagia score, Nurick grades, and fusion rates were assessed.

RESULTS

The mean follow-up for the BMP group (Group 1) was 35 months while the mean follow-up for the allograft group (Group 2) was 25 months. There was a complication rate of 13% in the BMP group compared with 8% in the allograft group (p < 0.005). There was no significant difference in overall dysphagia incidence between the BMP group and the allograft group (40% vs 44%, respectively; p > 0.05). However, there was a significant difference in the severity of dysphagia (using the SWAL-QOL dysphagia scoring system) between the 2 groups: 0.757 for the BMP group versus 0.596 for the allograft group (p < 0.005). In subgroup analysis, the use of rhBMP-2 significantly increased the severity of dysphagia in patients undergoing 2-level ACDF (p < 0.005). However, the severity of dysphagia did not differ significantly between groups when 3- or 4-level ACDF cases were compared. There was no pseudarthrosis in Group 1 (the BMP group) compared with a 16% pseudarthrosis rate in Group 2 (the allograft group) (p < 0.05). There was a weak correlation between the total rhBMP-2 dose and the dysphagia score (Kendall tau rank correlation coefficient 0.166, p = 0.046).

CONCLUSIONS

The use of rhBMP-2 in patients undergoing 2-level ACDF significantly increases the severity of dysphagia (dysphagia score) without affecting the overall incidence of dysphagia. However, there is no statistically significant difference in the incidence or severity of dysphagia between patients undergoing 3-level or 4-level ACDF treated with PEEK/rhBMP-2 and those treated with only allograft. The use of rhBMP-2 appears to reduce the risk of pseudarthrosis. This benefit is most pronounced in patients who undergo 4-level ACDF and are smokers.

Transient soft-tissue edema associated with implantation of increasing doses of rhBMP-2 on an absorbable collagen sponge in an ectopic rat model

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is an osteoinductive protein. However, soft-tissue edema adjacent to the site of rhBMP-2 implantation has been reported. This animal study was designed to examine soft-tissue edema associated with increasing rhBMP-2 doses with implantation on an absorbable collagen sponge (ACS) and with injection directly into muscle.

METHODS

Thirty-six Lewis rats received intramuscular implantation of rhBMP-2 on an ACS (Part I) or intramuscular injection of rhBMP-2 solution (Part II). Part-I sites received rhBMP-2/ACS at doses of 0 μg, 30 μg (normal), 129 μg (mid), or 450 μg (high). Part-II sites received rhBMP-2/ACS or rhBMP-2 intramuscular injection at doses of 10 μg (normal) or 150 μg (mid). A previous rat model showed 10 μg to be 100% effective at inducing osseous spinal fusion. In our study, T2-weighted magnetic resonance imaging (MRI) was performed at two and seven days to assess edema volume, and statistical comparisons were carried out with analysis of variance (ANOVA). Cellular response, vascularity, and ossification were examined histologically.

RESULTS

Quantitative MRI demonstrated similar peri-implant edema volumes in the control (buffer on an ACS) and normal-dose rhBMP-2 groups. Higher doses resulted in increased edema volume. Edema decreased significantly from two to seven days. Similar capillary densities were observed in all rhBMP-2 groups at two days, and there was dose-dependent increased ossification at seven days. Compared with the rhBMP-2 injection, implantation of the rhBMP-2/ACS resulted in increased edema. This edematous response was transient in all groups. Minimal or no ossification occurred after the rhBMP-2 injections.

CONCLUSIONS

Transient peri-implant soft-tissue edema occurred in a dose-dependent manner following implantation of rhBMP-2/ACS in this rat model. The normal dose of rhBMP-2/ACS produced edema similar to that in the controls. Finally, rhBMP-2 solutions injected directly into muscle resulted in minimal soft-tissue edema.

BMP-2 and TGF-β3 do not prevent spontaneous degeneration in rabbit disc explants but induce ossification of the annulus fibrosus

INTRODUCTION

Different approaches for disc regeneration are currently under investigation. Beside gene therapy and tissue engineering techniques, the application of growth and differentiation factors own promising potential. Studies using reduced intervertebral disc models, such as cell or tissue fragment cultures, have limited validity and show controversial results depending on the employed experimental model. Therefore, the goal of the current study was to investigate the effect of BMP-2 and TGF-β3 on intervertebral disc degeneration using an in vitro full-organ disc/endplate culture system.

MATERIALS AND METHODS

Intervertebral rabbit disc explants were cultured in the presence of 1 μg/ml BMP-2 or TGF-β3 for 21 days in DMEM/F12 media. Nucleus and annulus were analyzed for gene expression of collagen type I and II (Col I/II), aggrecan, collagenases (MMP-1/MMP-13) with RT-qPCR, histological changes with bone and proteoglycan-specific staining (von Kossa, toluidine blue) and differences in cellularity (DNA) and proteoglycan content (alcian blue binding assay).

RESULTS

The results demonstrate that disc proteoglycan concentration decreased with time in the TGF-β3 and BMP-2 groups. In the annulus fibrosus (AF), TGF-β3 and BMP-2 resulted in an up-regulation of Col I and type II, and of aggrecan gene expression. In contrast, MMP genes were inhibited. In the nucleus, the growth factors decreased gene expression of aggrecan and spontaneous Col I up-regulation was inhibited by TGF-β3, whereas expression of Col II was decreased with BMP-2. There was no effect on expression of MMP-1 and MMP-13 for most sampling points. However, TGF-β3 and BMP-2 induced ossification of the AF was demonstrated by histology.

CONCLUSION

It can be concluded that both growth factors, at the tested concentrations, may not be suitable to regenerate the whole intervertebral disc organ but they are interesting candidates for being injected alone or in combination into a painful intervertebral disc to induce osseous fusion (spondylodesis).

A comparison of mesenchymal precursor cells and amnion epithelial cells for enhancing cervical interbody fusion in an ovine model

BACKGROUND

Rapid, reliable fusion is the goal in anterior cervical diskectomy and fusion. Iliac crest autograft has a high rate of donor-site morbidity. Alternatives such as bone graft substitutes lack osteoinductivity, and recombinant bone morphogenetic proteins risk life-threatening complications. Both allogeneic mesenchymal precursor cells (MPCs) and amnion derived epithelial cells (AECs) have osteogenic potential.

OBJECTIVE

To compare for the first time the capacity of MPCs and AECs to promote osteogenesis in an ovine model.

METHODS

Five groups of 2-year-old ewes were subjected to C3-4 anterior cervical diskectomy and fusion with a Fidji interbody cage packed with iliac crest autograft alone (group A; n = 6), hydroxyapatite-tricalcium phosphate Mastergraft granules (HA/TCP) alone (group B; n = 6), HA/TCP containing 5 million MPCs (group C; n = 6), or HA/TCP containing 5 million AECs (group D; n = 5); group E was made up of age-matched nonoperative controls (n = 6). At 3 months, animals were euthanized and quantitative multislice computed tomography, functional radiography, biomechanics, histology, and histomorphometry were performed.

RESULTS

No procedure- or cell-related adverse events were observed. There was significantly more fusion in the MPC group (C) than in group A, B, or D. Computed tomography scan at 3 months revealed that 5 of 6 MPC-treated animals (83%) had continuous bony bridging compared with 0 of 5 AEC-treated and only 1 of 6 autograft- and 2 of 6 HA/TCP-treated animals (P = .01).

CONCLUSION

Implantation of allogeneic MPCs in combination with HA/TCP within an interbody spacer facilitates interbody fusion after diskectomy. The earlier, more robust fusion observed with MPCs relative to autograft and HA/TCP bone substitute indicates that this approach may offer a therapeutic benefit.

BMPs are mediators in tissue crosstalk of the regenerating musculoskeletal system

The musculoskeletal system is a tight network of many tissues. Coordinated interplay at a biochemical level between tissues is essential for development and repair. Traumatic injury usually affects several tissues and represents a large challenge in clinical settings. The current demand for potent growth factors in such applications thus accompanies the keen interest in molecular mechanisms and orchestration of tissue formation. Of special interest are multitasking growth factors that act as signals in a variety of cell types, both in a paracrine and in an autocrine manner, thereby inducing cell differentiation and coordinating not only tissue assembly at specific sites but also maturation and homeostasis. We concentrate here on bone morphogenetic proteins (BMPs), which are important crosstalk mediators known for their irreplaceable roles in vertebrate development. The molecular crosstalk during embryonic musculoskeletal tissue formation is recapitulated in adult repair. BMPs act at different levels from the initiation to maturation of newly formed tissue. Interestingly, this is influenced by the spatiotemporal expression of different BMPs, their receptors and co-factors at the site of repair. Thus, the regenerative potential of BMPs needs to be evaluated in the context of highly connected tissues such as muscle and bone and might indeed be different in more poorly connected tissues such as cartilage. This highlights the need for an understanding of BMP signaling across tissues in order to eventually improve BMP regenerative potential in clinical applications. In this review, the distinct members of the BMP family and their individual contribution to musculoskeletal tissue repair are summarized by focusing on their paracrine and autocrine functions.

Basic fibroblast growth factor enhances the osteogenic differentiation induced by bone morphogenetic protein-6 in vitro and in vivo

Some members of the bone morphogenetic protein subfamily (BMP-2 and -7) are currently used in orthopedic surgery for several applications. Although their use is considered safe at short term, the high doses of growth factors needed make these treatments expensive and their safety uncertain at long term. BMP-6 has been much less studied than BMP-2 and -7, but some authors suggest that this BMP might have a stronger osteogenic activity than the previously mentioned. Having in mind that angiogenesis plays a well-known role during bone formation, the aim of this work was to study the effect of combining BMP-6 with bFGF on both the growth and differentiation of MC3T3-E1 mouse preosteoblasts and rat bone marrow-derived mesenchymal stem cells (MSCs), as well as on in vivo osteogenesis. We demonstrate that a low dose of bFGF enhances the osteogenic differentiation of MSCs induced by BMP-6 in vitro. Furthermore, we also demonstrate that bone formation in vivo induced by BMP-6 can be accelerated and enhanced by adding a low dose of bFGF, what might suggest a synergic effect between these growth factors on in vivo osteogenesis.