Use of recombinant human bone morphogenetic protein-2 to achieve posterolateral lumbar spine fusion in humans: a prospective, randomized clinical pilot trial: 2002 Volvo Award in clinical studies

Complications Associated With Bone Morphogenetic Protein in the Lumbar Spine

Complications associated with the use of recombinant human bone morphogenetic protein in the lumbar spine include retrograde ejaculation, ectopic bone formation, vertebral osteolysis and subsidence, postoperative radiculitis, and hematoma and seroma. These complications are controversial and remain widely debated. This article discusses the reported complications and possible implications for the practicing spine surgeon. Understanding the complications associated with the use of recombinant human bone morphogenetic protein and the associated controversies allows for informed decision making by both the patient and the surgeon. [Orthopedics. 2017; 40(2):e229-e237.].

Differentiation of nerve-derived adult pluripotent stem cells into osteoblastic and endothelial cells

BACKGROUND CONTEXT

Stem cell-involved tissue engineering has gained dramatic attention as a therapeutic strategy for tissue regeneration including bone repair. However, the currently available possibilities to use embryonic stem cells and induced pluripotent stem cells (iPCs) face potential ethical issues, as well as risks of malignant transformation and immune rejection. Recently identified peripheral nerve-derived adult pluripotent stem cells (NEDAPS) that quickly proliferate after exposure to bone morphogenetic protein-2 (BMP-2) or nerve trauma and exhibit many embryonic stem cell characteristics may provide an attractive source cells for a variety of regenerative therapies.

PURPOSE

The study aimed to examine the differentiation potential of the NEDAPS cells into osteoblastic cells and endothelial cells.

STUDY DESIGN/SETTING

An in vitro investigation was undertaken to induce mouse NEDAPS cells into the phenotypes of osteoblastic and endothelial cells.

METHODS

NEDAPS cells were isolated from low-dose BMP-2-exposed mouse sciatic nerves by collagenase and trypsin extraction. The cells were cultured in a stem cell maintenance medium, and the expression of KLF4, Sox2, c-Myc, and Oct4 before differentiation was confirmed. The cells were then subcultured in a complete osteogenic cell induction medium or endothelial cell growth medium, respectively, at 37°C and 5%CO₂ atmosphere. Histologic, morphologic, and molecular assessments were performed 7 days later.

RESULTS

The cells propagated in complete osteogenic medium for 7 days showed strong staining for type I collagen and alkaline phosphatase, suggesting the structural and functional properties of the osteoblastic cells. Further, real-time polymerase chain reaction (RT-PCR) revealed a significant expression of the osteoblast markers osteocalcin, osteopontin, and type I collagen. Similarly, the cells in endothelial growth medium were successfully differentiated into cobblestone-shaped endothelial cells expressing vascular endothelial growth factor (VEGF) receptors Flk-1 and Flt-1 demonstrated by RT-PCR.

CONCLUSIONS

NEDAPS cells are readily induced to osteoblastic and endothelial cells, suggesting therapeutic potential for bone repair and other regenerative therapies.

Biomechanical comparison between cortical screw-rod construct versus pedicle screw-rod construct in transforaminal lumbar interbody fusion

OBJECTIVE

To compare construct stiffness of cortical screw (CS)-rod transforaminal lumbar interbody fusion (TLIF) construct (G2) versus pedicle screw (PS)-rod TLIF construct (G1) in the standardized porcine lumbar spine.

METHODS

Six porcine lumbar spines (L2-L5) were separated into 12 functional spine units. Bilateral total facetectomies and interlaminar decompression were performed for all specimens. Non-destructive loading to assess stiffness in lateral bending, flexion and extension as well as axial rotation was performed using a universal material testing machine.

RESULTS

PS and CS constructs were significantly stiffer than the intact spine except in axial rotation. Using the normalized ratio to the intact spine, there is no significant difference between the stiffness of PS and CS: flexion (1.41 ± 0.27, 1.55 ± 0.32), extension (1.98 ± 0.49, 2.25 ± 0.44), right lateral flexion (1.93 ± 0.57, 1.55 ± 0.30), left lateral flexion (2.00 ± 0.73, 2.16 ± 0.20), right axial rotation (0.99 ± 0.21, 0.83 ± 0.26) and left axial rotation (0.96 ± 0.22, 0.92 ± 0.25).

CONCLUSION

The CS-rod TLIF construct provided comparable construct stiffness to a traditional PS-rod TLIF construct in a 'standardized' porcine lumbar spine model.

Comparison of a calcium phosphate bone substitute with recombinant human bone morphogenetic protein-2: a prospective study of fusion rates, clinical outcomes and complications with 24-month follow-up

PURPOSE

Recombinant human bone morphogenetic protein-2 (rhBMP-2) generally provides high rates of clinical improvement and fusion. However, rhBMP-2 has been associated with adverse effects. Recently, a beta tricalcium phosphate (β-TCP) bone substitute has been developed. The aim of this study was to determine the fusion rates and clinical outcomes of patients treated with β-TCP compared to rhBMP-2.

METHODS

One hundred and thirty-five consecutive patients who underwent lateral lumbar interbody fusion with β-TCP (n = 25) or rhBMP-2 (n = 110) in the interbody cage were included in the study. The 25 β-TCP patients were a group of consecutive patients from numbers 46 to 70. Clinical outcomes included back and leg pain, Oswestry Disability Index (ODI), and SF-36 physical and mental component scores (PCS and MCS). CT scans were performed at 6, 12, 18, and 24 months until confirmation of solid interbody fusion, with no further scans performed once fusion was achieved. Targeted CT at the operative level(s) was performed to reduce radiation exposure.

RESULTS

At 24 months there was no significant difference between clinical outcomes of the β-TCP or rhBMP-2 patients, with improvements in back pain (46% and 49%; P = 0.98), leg pain (31 and 52%; P = 0.14), ODI (38 and 41%; P = 0.81), SF-36 PCS (37 and 38%; P = 0.87), and SF-36 MCS (8 and 8%; P = 0.93). The fusion rate was significantly higher for rhBMP-2 with 96% compared to 80% for β-TCP (P = 0.01). Separating patients into those with a standalone cage and those with supplemental posterior instrumentation, there was no significant difference between instrumented fusion rates of the β-TCP and rhBMP-2 patients at 6 (P = 0.44), 12 (P = 0.49), 18 (P = 0.31) or 24 (P = 0.14) months. For standalone patients there was a significant difference at 6 (P = 0.01), 12 (P = 0.008) and 18 months (P = 0.004) with higher fusion rates in the rhBMP-2 group; however, by 24 months this was not significant (P = 0.18).

CONCLUSIONS

Comparable clinical outcomes and complication rates suggest that β-TCP is a viable alternative to rhBMP-2. The difference in fusion rates for the standalone patients suggests that β-TCP may require supplemental posterior instrumentation to enhance fusion.

Spinal neuromodulation as a novel surgical option for failed back surgery syndrome following rhBMP exuberant bony growth in instrumented lumbar fusion: A case report and literature review

Background:

Bone morphogenic protein (BMP) for instrumented lumbar fusion was approved in 2002, and since then has led to an increasing incidence of BMP-related neuropathic pain. These patients are usually resistant to conventional medical therapy and frequently undergo multiple surgical revisions without any pain relief.

Case Description:

A 58-year-old male was referred to the author's outpatient clinic after four lumbar surgeries did not provide satisfactory pain relief. During his 10 years of suffering from low back pain after an injury, the patient was resistant to conventional and interventional treatment options. He was experiencing severe back pain rated 10/10, as well as right lower extremity pain, numbness, tingling, and motor deficits. Outside spine specialists had performed revision surgeries for BMP-related exuberant bone formation at L5–S1, which included the removal of the ipsilateral hardware and debridement of intradiscal and intraforamina heterotrophic exuberant bony formation. The author implanted the patient with a permanent continuous spinal cord stimulator, after which he achieved complete pain relief (0/10) and restoration of motor, sensory, autonomic, and sphincter functions.

Conclusion:

This is the first reported case of restorative function with neuromodulation therapy in a BMP-induced postoperative complication, which is considered as a primarily inflammatory process, rather than nerve root compression due to exuberant bony formation. We hypothesize that neuromodulation may enhance blood flow and interfere with inflammatory processes, in addition to functioning by the accepted gate control theory mechanism. The neuromodulation therapy should be strongly considered as a therapeutic approach, even with confirmed BMP-induced postoperative radiculitis, rather than proposing multiple surgical revisions.

Peptides for bone tissue engineering

Molecular signals in the form of growth factors are the main modulators of cell behavior. However, the use of growth factors in tissue engineering has several drawbacks, including their costs, difficult production, immunogenicity and short half-life. Furthermore, many of them are pleiotropic and, since a single growth factor can have different active domains, their effect is not always fully controllable. A very interesting alternative that has recently emerged is the use of biomimetic peptides. Sequences derived from the active domains of soluble or extracellular matrix proteins can be used to functionalize the biomaterials used as scaffolds for new tissue growth to either direct the attachment of cells or to be released as soluble ligands. Since these short peptides can be easily designed and cost-effectively synthesized in vitro, their use has opened up a world of new opportunities to obtain cheaper and more effective implants for regenerative medicine strategies. In this extensive review we will go through many of the most important peptides with potential interest for bone tissue engineering, not limiting to those that only mediate cell adhesion or induce the osteogenic differentiation of progenitor cells, but also focusing on those that direct angiogenesis because of its close relation with bone formation.

Increased osteoinductivity and mineralization by minimal concentration of bone morphogenetic protein-2 loaded onto biphasic calcium phosphate in a rabbit sinus

Purpose

The purpose of the present study was to evaluate the effectiveness of a minimal concentration of bone morphogenetic protein-2 (BMP-2) in terms of quantitative and qualitative analyses of newly formed bone in a rabbit maxillary sinus model.

Methods

In 7 rabbits, sinus windows were prepared bilaterally. Biphasic calcium phosphate (BCP) loaded with 0.05 mg/mL BMP-2 was grafted into one sinus (the BMP group) and saline-soaked BCP was placed into the other (the control group) in each animal. The animals were allowed an 8-week healing period before being sacrificed. Specimens including the augmented area and surrounding tissues were then removed and evaluated both radiographically and histologically.

Results

There was a difference in the mineralization of new bone between the groups. In the BMP group, the greater part of the new bone consisted of mature lamellar bone with an evident trabecular pattern, whereas the control group showed mostly woven bone, consisting only partially of lamellar bone. Histometrically, the area of new bone was significantly greater (4.55±1.35 mm² vs. 2.99±0.86 mm²) in the BMP group than in the control group (P<0.05); however, the total augmentation volumes were not significantly different between the groups.

Conclusions

Within the limitations of this study, it can be suggested that a minimal concentration of BMP-2 (0.05 mg/mL) had an osteoinductive effect with accelerated mineralization in a rabbit sinus model using a BCP carrier.

Local co-application of zoledronate promotes long-term maintenance of newly formed bone induced by recombinant human bone morphogenetic protein 2

Bone Morphogenetic Proteins (BMPs) strongly induce the recruitment and differentiation of mesenchymal progenitor cells into mature osteoblasts, but also directly and indirectly stimulate differentiation of osteoclast progenitor cells and acceleration of mature osteoclasts function leading excessive bone resorption. Bisphosphonates, such as zoledronate (ZOL), inhibit osteoclasts function and osteoclasts mediated bone resorption. The short or middle term effect of BMPs and bisphosphonates on bone formation were previously reported, but there was no study that argue about the long term effect of bisphosphonates on BMP-induced bone anabolism. The present study demonstrated that the local administration of ZOL with recombinant human BMP-2 (rh-BMP-2) using beta tricalcium phosphate (β-TCP) as a carrier had superior efficacy not only to augment the BMP-induced new ectopic bone formation but to maintain the trabecular bone structure inside the new bone for long period. Histological analysis showed that rh-BMP-2/β-TCP composite induced trabecular bone resorption especially inside the new bone nodules over time, whereas no trabecular bone resorption was seen in rh-BMP-2/ZOL/β-TCP composite reducing the number of TRAP-positive cells. Thus, inhibition of bone resorption by bisphosphonate, such as ZOL, would be one of the advantageous ways to augment the new bone formation induced by rh-BMP-2, and moreover local co-application of ZOL using β-TCP as a carrier can be a useful material for long term suppression of osteoclastic resorption and thereby maintain the structure of new bone formation induced by rh-BMP-2.

Low-magnitude, high-frequency vibration promotes the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells cultured on a hydroxyapatite-coated surface: The direct role of Wnt/β-catenin signaling pathway activation

The positive effect of low-magnitude, high‑frequency (LMHF) vibration on implant osseointegration has been demonstrated; however, the underlying cellular and molecular mechanisms remain unknown. The aim of this study was to explore the effect of LMHF vibration on the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) cultured on hydroxyapatite (HA)-coated surfaces in an in vitro model as well as to elucidate the molecular mechanism responsible for the effects of LMHF vibration on osteogenesis. LMHF vibration resulted in the increased expression of fibronectin, which was measured by immunostaining and RT-qPCR. Stimulation of BMSCs by LMHF vibration resulted in the rearrangement of the actin cytoskeleton with more prominent F-actin. Moreover, the expression of β1 integrin, vinculin and paxillin was notably increased following LMHF stimulation. Scanning electron microscope observations revealed that there were higher cell numbers and more extracellular matrix attached to the HA-coated surface in the LMHF group. Alkaline phosphatase activity as well as the expression of osteogenic-specific genes, namely Runx2, osterix, collagen I and osteocalcin, were significantly elevated in the LMHF group. In addition, the protein expression of Wnt10B, β-catenin, Runx2 and osterix was increased following exposure to LMHF vibration. Taken together, the findings of this study indicate that LMHF vibration promotes the adhesion and the osteogenic differentiation of BMSCs on HA-coated surfaces in vitro, and LMHF vibration may directly induce osteogenesis by activating the Wnt/β‑catenin signaling pathway. These data suggest that LMHF vibration enhances the osseointegration of bone to a HA-coated implant, and provide a scientific foundation for improving bone-implant osseointegration through the application of LMHF vibration.

Bone substitutes and expanders in Spine Surgery: A review of their fusion efficacies

STUDY DESIGN

A narrative review of literature.

OBJECTIVE

This manuscript intends to provide a review of clinically relevant bone substitutes and bone expanders for spinal surgery in terms of efficacy and associated clinical outcomes, as reported in contemporary spine literature.

SUMMARY OF BACKGROUND DATA

Ever since the introduction of allograft as a substitute for autologous bone in spinal surgery, a sea of literature has surfaced, evaluating both established and newly emerging fusion alternatives. An understanding of the available fusion options and an organized evidence-based approach to their use in spine surgery is essential for achieving optimal results.

METHODS

A Medline search of English language literature published through March 2016 discussing bone graft substitutes and fusion extenders was performed. All clinical studies reporting radiological and/or patient outcomes following the use of bone substitutes were reviewed under the broad categories of Allografts, Demineralized Bone Matrices (DBM), Ceramics, Bone Morphogenic proteins (BMPs), Autologous growth factors (AGFs), Stem cell products and Synthetic Peptides. These were further grouped depending on their application in lumbar and cervical spine surgeries, deformity correction or other miscellaneous procedures viz. trauma, infection or tumors; wherever data was forthcoming. Studies in animal populations and experimental in vitro studies were excluded. Primary endpoints were radiological fusion rates and successful clinical outcomes.

RESULTS

A total of 181 clinical studies were found suitable to be included in the review. More than a third of the published articles (62 studies, 34.25%) focused on BMP. Ceramics (40 studies) and Allografts (39 studies) were the other two highly published groups of bone substitutes. Highest radiographic fusion rates were observed with BMPs, followed by allograft and DBM. There were no significant differences in the reported clinical outcomes across all classes of bone substitutes.

CONCLUSIONS

There is a clear publication bias in the literature, mostly favoring BMP. Based on the available data, BMP is however associated with the highest radiographic fusion rate. Allograft is also very well corroborated in the literature. The use of DBM as a bone expander to augment autograft is supported, especially in the lumbar spine. Ceramics are also utilized as bone graft extenders and results are generally supportive, although limited. The use of autologous growth factors is not substantiated at this time. Cell matrix or stem cell-based products and the synthetic peptides have inadequate data. More comparative studies are needed to evaluate the efficacy of bone graft substitutes overall.

Slowly Delivered Icariin/Allogeneic Bone Marrow-Derived Mesenchymal Stem Cells to Promote the Healing of Calvarial Critical-Size Bone Defects

Bone tissue engineering technique is a promising strategy to repair large-volume bone defects. In this study, we developed a 3-dimensional construct by combining icariin (a small-molecule Chinese medicine), allogeneic bone marrow-derived mesenchymal stem cells (BMSCs), and a siliceous mesostructured cellular foams-poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (SMC-PHBHHx) composite scaffold. We hypothesized that the slowly released icariin could significantly promote the efficacy of SMC-PHBHHx/allogeneic BMSCs for repairing critical-size bone defects in rats. In in vitro cellular experiments, icariin at optimal concentration (10^-6 mol/L) could significantly upregulate the osteogenesis- and angiogenesis-related genes and proteins, such as Runx2, ALP, osteocalcin, vascular endothelial growth factors, and fibroblast growth factors, as well as the mineralization of BMSCs. Icariin that was adsorbed onto the SMC-PHBHHx scaffold showed a slow release profile within a 2-week monitoring span. Eight weeks after implantation in calvarial critical-size bone defects, the constructs with icariin were associated with significantly higher bone volume density, trabecular thickness, trabecular number, and significantly lower trabecular separation than the constructs without icariin. Histomorphometric analysis showed that icariin was also associated with a significantly higher density of newly formed blood vessels. These data suggested a promising application potential of the icariin/SMC-PHBHHx/allogeneic BMSCs constructs for repairing large-volume bone defects in clinic.

Meta-analysis of the Impact of Patient Characteristics on Estimates of Effectiveness and Harms of Recombinant Human Bone Morphogenetic Protein-2 in Lumbar Spinal Fusion

STUDY DESIGN

Meta-analysis of individual patient data from randomized controlled trials of recombinant human bone morphogenetic protein-2 (rhBMP-2) in lumbar spinal fusion.

OBJECTIVE

To determine how patient characteristics impact estimates of effectiveness and harms of rhBMP-2 versus iliac crest bone graft (ICBG) in lumbar spinal fusion.

SUMMARY OF BACKGROUND DATA

Patient characteristics are thought to impact rates of fusion in spinal fusion surgery, but no analyses examining the effect of patient characteristics on efficacy and safety of rhBMP-2 as compared with ICBG have been conducted.

METHODS

Using individual patient data obtained from the Yale Open Data Access Project, the impact of patient characteristics on the effects of rhBMP-2 on fusion, overall success, and harms were assessed using linear and generalized linear mixed effects models.

RESULTS

Ten industry-sponsored randomized controlled trials of rhBMP-2 were included in the analysis. There is preliminary support for an association between rhBMP-2 and improved outcomes for smokers (P = 0.01), individuals under the age of 60 years (P < 0.01), and patients of normal weight (P = 0.03), but not in patients who are nonsmokers, over the age of 60 years, obese or severely obese. RhBMP-2 usage was associated with decreased harms in individuals with no previous back surgeries but this was not seen in individuals with a previous back surgery (P < 0.01).

CONCLUSION

Effects of rhBMP-2 may vary according to patient characteristics. Future studies of rhBMP-2 should include planned subgroup analysis in patients over 60 years, smokers, patients that are obese and severely obese, and individuals with previous back surgeries to better identify those most likely to benefit.

LEVEL OF EVIDENCE

1.

Long-Segment Fusion for Adult Spinal Deformity Correction Using Low-Dose Recombinant Human Bone Morphogenetic Protein-2

BACKGROUND:

Although use of very high-dose recombinant human bone morphogenetic protein-2 (rhBMP-2) has been reported to markedly improve fusion rates in adult spinal deformity (ASD) surgery, most centers use much lower doses due to cost constraints. How effective these lower doses are for fusion enhancement remains unclear.

OBJECTIVE:

To assess fusion rates using relatively low-dose rhBMP-2 for ASD surgery.

METHODS:

This was a retrospective review of consecutive ASD patients that underwent thoracic to sacral fusion. Patients that achieved 2-year follow-up were analyzed. Impact of patient and surgical factors on fusion rate was assessed, and fusion rates were compared with historical cohorts.

RESULTS:

Of 219 patients, 172 (78.5%) achieved 2-year follow-up and were analyzed. Using an average rhBMP-2 dose of 3.1 mg/level (average total dose = 35.9 mg/case), the 2-year fusion rate was 73.8%. Cancellous allograft, local autograft, and very limited iliac crest bone graft (&lt;20 mL, obtained during iliac bolt placement) were also used. On multivariate analysis, female sex was associated with a higher fusion rate, whereas age, comorbidity score, deformity type, and 3-column osteotomy were not. There were no complications directly attributable to rhBMP-2.

CONCLUSION:

Fusion rates for ASD using low-dose rhBMP-2 were comparable to those reported for iliac crest bone graft but lower than for high-dose rhBMP-2. Importantly, there were substantial differences between patients in the present series and those in the historical comparison groups that could not be fully adjusted for based on available data. Prospective evaluation of rhBMP-2 dosing for ASD surgery is warranted to define the most appropriate dose that balances benefits, risks, and costs.

Trends of Posterior Long Segment Fusion with and without Recombinant Human Bone Morphogenetic Protein 2 in Patients with Scoliosis

STUDY DESIGN

Retrospective study.

OBJECTIVE

Symptomatic scoliosis can be a source of severe pain and disability. When nonoperative treatments fail, spine fusion is considered as an effective procedure in scoliosis management. The purpose of this study was to evaluate the trends of patients with scoliosis undergoing posterior long segment fusion (PLSF) with and without recombinant human bone morphogenetic protein 2 (rhBMP-2).

METHODS

Patients within the orthopedic subset of Medicare database undergoing PLSF from 2005 to 2011 were identified using the PearlDiver Patient Records Database. Both diagnosis and procedural International Classification of Diseases, ninth edition and Current Procedural Terminology codes were used. The year of procedure, age, sex, region, and rhBMP-2 use were recorded.

RESULTS

In total, 1,265,591 patients with scoliosis were identified with 29,787 PLSF surgeries between 2005 and 2011. The incidence of PLSF procedures increased gradually from 2005 to 2009, decreased in 2010 (p < 0 0.01), and grew again in 2011. Patients over age 84 years had the highest incidence of PLSF. The lowest incidence of the procedures was in the Northeast, 5.96 per 100,000 patients. Sex differences were observed with a male-to-female ratio of 0.40 (p < 0.01). The use of rhBMP-2 for PLSF increased steadily from 2005 to 2009; the numbers dropped dramatically in 2010 and returned by 2011.

CONCLUSIONS

According to our study, patients with scoliosis demonstrated a 0.6575 average incidence increase of PLSF treatments annually. There were significant differences in incidence of PLSF procedure and patient demographics. Additionally, rhBMP-2 consumption significantly changed when we stratified it by sex, age, and region respectively.

The effect of vancomycin powder on bone healing in a rat spinal rhBMP-2 model

OBJECTIVE

This study aims to quantify the impact of vancomycin powder application on new bone formation and spine fusion rates in a rat posterolateral arthrodesis model.

METHODS

Thirty-six female Sprague-Dawley rats underwent a posterolateral lumbar spinal fusion (PLF) at the L-4 and L-5 vertebrae. Fusion was elicited via implantation of an absorbable collagen sponge containing 3 µg rhBMP-2. Rats were divided into 3 groups: no vancomycin (control), standard-dose vancomycin, and high-dose vancomycin, based on what was applied to the fusion bed. Clinical studies typically describe the application of 1 g vancomycin into the surgical wound. Presuming an average individual patient weight of 70 kg, a weight-based equivalent dose of vancomycin powder was applied subfascially in the PLF model constituting a “standard-dose” treatment group (14.3 mg/kg, n = 12). To determine whether there is a critical threshold beyond which vancomycin increases the risk of pseudarthrosis, a 10-fold higher dose was administered to a “high-dose” treatment group (143 mg/kg, n = 12). No vancomycin powder was applied to the surgical site in the control group (n = 12). Fusion was evaluated with plain radiographs at 4 and 8 weeks after surgery. The spines were harvested after the 8-week radiographs were obtained and evaluated using manual palpation, microCT analysis, and histological analysis.

RESULTS

Radiographs demonstrated equivalent bridging bone formation in all groups. No significant differences in fusion scores were seen in the standard-dose (mean 2.25) or high-dose (2.13) treatment groups relative to untreated control animals (1.78). Similarly, fusion rates did not differ significantly different between vancomycin-treated animals (100% for both groups) and control animals (92%). Quantification of new bone formation via microCT imaging revealed no significant between-groups differences in the volume of newly regenerated bone (control vs standard-dose vancomycin, p = 0.57; control vs high-dose vancomycin, p = 0.53).

CONCLUSIONS

This is the first in vivo study to specifically address the development of pseudarthrosis after intrawound application of vancomycin during fusion surgery. Our results demonstrate that vancomycin powder does not inhibit fusion rates at a dose that is the weight-percentage equivalent of what is routinely used by surgeons. Moreover, bone formation and fusion rates were not reduced even after administration of a vancomycin dose that is 10-fold higher than that which is typically administered clinically. Our findings suggest that if there is a critical threshold above which vancomycin inhibits bone healing, such a dose is out of the range which might be considered reasonable for clinical use.

Choice of Approach Does Not Affect Clinical and Radiologic Outcomes: A Comparative Cohort of Patients Having Anterior Lumbar Interbody Fusion and Patients Having Lateral Lumbar Interbody Fusion at 24 Months

STUDY DESIGN

Retrospective analysis of prospectively collected registry data.

OBJECTIVE

This study aimed to compare the clinical and radiologic outcomes between comparative cohorts of patients having anterior lumbar interbody fusion (ALIF) and patients having lateral lumbar interbody fusion (LLIF).

METHODS

Ninety consecutive patients were treated by a single surgeon with either ALIF (n = 50) or LLIF (n = 40). Inclusion criteria were patients age 45 to 70 years with degenerative disk disease or grade 1 to 2 spondylolisthesis and single-level pathology from L1 to S1. Patient-reported outcome measures included pain (visual analog scale), disability (Oswestry Disability Index [ODI]), and quality of life (Short Form 36 physical component score [PCS] and mental component scores [MCS]). Assessment of fusion and measurement of lordosis and posterior disk height were performed on computed tomography scans.

RESULTS

At 24 months, patients having ALIF had significant improvements in back (64%) and leg (65%) pain and ODI (60%), PCS (44%), and MCS (26%; p < 0.05) scores. Patients having LLIF had significant improvements in back (56%) and leg (57%) pain and ODI (52%), PCS (48%), and MCS (12%; p < 0.05) scores. Fourteen complications occurred in the ALIF group, and in the LLIF group, there were 17 complications (p > 0.05). The fusion rate was 100% for ALIF and 95% for LLIF (p = 0.1948). ALIF added ∼6 degrees of lordosis and 3 mm of height, primarily measured at L5-S1, and LLIF added ∼3 degrees of lordosis and 2 mm of height between L1 to L5. Mean follow-up was 34.1 months.

CONCLUSIONS

In comparative cohorts of patients having ALIF and patients having LLIF at 24 months postoperatively, there were no significant differences in clinical outcomes, complication rates, or fusion rates.

Heparin-Based Polyelectrolyte Complex Enhances the Therapeutic Efficacy of Bone Morphogenetic Protein-2 for Posterolateral Fusion in a Large Animal Model

STUDY DESIGN

The study was based on porcine posterolateral fusion model.

OBJECTIVE

The study aims to prove that polyelectrolyte complex (PEC) carrier could enhance the efficacy and safety profile of bone morphogenetic protein-2 (BMP-2).

SUMMARY OF BACKGROUND DATA

BMP-2 was introduced to enhance posterolateral fusion; however, extremely high doses of this molecule were often used which contributed to various complications. This was attributed to the poor modulation capacity of the traditional carrier absorbable collagen sponge (ACS). To reduce the efficacious dose of BMP-2 and its associated complications, heparin-based PEC was introduced.

METHODS

L3/L4 and L5/L6 two-level posterolateral spinal fusion was performed on six pigs using two doses of BMP-2 with PEC or ACS: (1) PEC with 800 μg BMP-2 (n = 2); (2) PEC with 400 μg BMP-2 (n = 2); (3) ACS with 800 μg BMP-2 (n = 1); (4) ACS with 400 μg of BMP-2 (n = 1). The construct was loaded into a rigid bioabsorbable cage for implantation. Fusion rate and quality were assessed 2 months after operation.

RESULTS

Manual palpation revealed successful fusion in all groups. Radiological fusion score of PEC groups was, however, higher than that of ACS groups. The newly formed bone in PEC groups appeared to be well integrated into the native bone with no overgrowth into the adjacent structure. On comparison, in ACS groups, large gaps were observed between the newly formed bone and the fusion bed with heterotopic ossification into the psoas muscle. The microarchitecture on the newly formed bone in PEC groups was superior to that in ACS groups, which was demonstrated by higher three-dimensional parameters.

CONCLUSION

The present study demonstrated that BMP-2 delivered by PEC induced successful posterolateral fusion in porcine model. The efficacy of BMP-2 was improved and bony overgrowth was reduced. The microarchitecture of BMP-2-induced bone tissue was also enhanced by PEC.

LEVEL OF EVIDENCE

N/A.

Bone morphogenetic protein 2 stimulates chondrogenesis of equine synovial membrane-derived progenitor cells

OBJECTIVES

Bone morphogenetic protein 2 (BMP-2) is critical for skeletal and cartilage development, homeostasis and repair. This study was conducted to clone and characterize equine BMP-2, develop expression constructs for equine BMP-2, and to determine whether BMP-2 can stimulate chondrogenesis of equine synovial membrane-derived progenitor cells (SMPC).

METHODS

Equine BMP-2 cDNA was amplified from chondrocyte RNA, and then transferred into an expression plasmid and adenoviral vector. Effective expression of equine BMP-2 was confirmed using a BMP reporter cell line. SMPC were isolated from synovium, expanded through two passages and transferred to chondrogenic cultures, with recombinant human (rh) transforming growth factor beta 1 (TGF-β1) or rhBMP-2. Chondrogenesis was assessed by up-regulation of collagen types II and X, and aggrecan mRNA, secretion of collagen type II protein and sulfated glycosaminoglycans (sGAG), and by alkaline phosphatase induction. Chondrogenic stimulation of SMPC by the equine BMP-2 adenovirus was assessed by sGAG secretion and histology.

RESULTS

The mature equine BMP-2 peptide is identical to human and murine peptides. Recombinant human BMP-2 and TGF-β1 stimulated equivalent amounts of collagen type II protein in SMPC pellets, but sGAG secretion was doubled by BMP-2. Neither factor stimulated hypertrophic marker expression. The equine BMP-2 adenoviral vector induced chondrogenesis comparably to rhBMP-2 protein, with no indication of hypertrophy.

CLINICAL SIGNIFICANCE

Bone morphogenetic protein 2 is a potent inducer of SMPC non-hypertrophic chondrogenesis, supporting the use of this combination for articular cartilage repair applications.

Distinct Gene Expression Patterns Defining Human Osteoblasts' Response to BMP2 Treatment: Is the Therapeutic Success All a Matter of Timing?

BACKGROUND

Bone morphogenetic proteins (BMPs) play a key role in bone formation. Local application of BMP2 (Dibotermin alfa) supports bone formation when applied to complex fractures. However, up to 33% of patients do not respond to this therapy.

PURPOSE

Aiming to investigate whether inter-individual responses to BMP2 treatment can be predicted by gene expression patterns, we investigated the effect of BMP2 on primary human osteoblasts and THP-1 cell-derived osteoclasts from 110 donors.

METHODS

Osteoblasts were obtained by collagenase digestion of spongy bone tissues. Osteoclasts were differentiated from THP-1 cells using the conditioned media of the osteoblasts. Viability was determined by resazurin conversion. As functional characteristics AP and Trap5B activity were measured. Gene expression levels were determined by RT-PCR in 21 of the 110 evaluated donors and visualized by electrophoresis.

RESULTS

Based on our data, we could classify three response groups: (i) In 51.8% of all donors, BMP2 treatment induced osteoblast function. These donors strongly expressed the BMP2 inhibitor Noggin (NOG), the alternative BMP2 receptors repulsive guidance molecule B (RGMb) and activin receptor-like kinase 6 (Alk6), as well as the Wnt inhibitor sclerostin (SOST). (ii) In 17.3% of all donors, BMP2 treatment induced viability. In these donors, the initial high SOST expression significantly dropped with BMP2 treatment. (iii) 30.9% of all donors were not directly affected by BMP2 treatment. These donors expressed high levels of the pseudoreceptor BMP and activin membrane-bound inhibitor (BAMBI) and lacked SOST expression. In all donors, SOST expression correlated directly with receptor activator of NF-κB ligand (RANKL) expression, defining the cells' potential to stimulate osteoclastogenesis.

CONCLUSIONS

Our data identified three donor groups profiting from BMP2 treatment either directly via stimulation of osteoblast function or viability and/or indirectly via inhibition of osteoclastogenesis, depending on their expression of BAMBI, SOST, NOG, and RANKL. On the basis of patients' respective expression profiles, the clinical application of BMP2 as well as its timing might be modified in order to better fit the patients' needs to promote bone formation or to inhibit bone resorption.

Modeling and remodeling effects of intermittent administration of teriparatide (parathyroid hormone 1-34) on bone morphogenetic protein-induced bone in a rat spinal fusion model

Background

Bone morphogenetic protein (BMP)-based tissue engineering has focused on inducing new bone efficiently. However, modeling and remodeling of BMP-induced bone have rarely been discussed. Teriparatide (parathyroid hormone [PTH] 1-34) administration initially increases markers of bone formation, followed by an increase in bone resorption markers. This unique activity would be expected to accelerate the modeling and remodeling of new BMP-induced bone.

Methods

Male Sprague-Dawley rats underwent posterolateral spinal fusion surgery and implantation of collagen sponge containing either 50 μg recombinant human (rh)BMP-2 or saline. PTH 1-34 (60 μg/kg, 3 times/week) or saline injections were continued from preoperative week 2 week to postoperative week 12. The volume and quality of newly formed bone were monitored by in vivo micro-computed tomography and analyses of bone histomorphometry and serum bone metabolism markers were conducted at postoperative week 12.

Results

Microstructural indices of the newly formed bone were significantly improved by PTH 1-34 administration, which significantly decreased the tissue volumes of the fusion mass at postoperative week 12 compared to that at postoperative week 2. Bone histomorphometry and serum analyses showed that PTH administration significantly increased both bone formation and resorption markers. Analysis of the histomorphometry of cortical bone identified predominant periosteal bone resorption and endosteal bone formation.

Conclusions

Long-term intermittent administration of PTH 1-34 significantly accelerated the modeling and remodeling of new BMP-induced bone.

Clinical relevance

Our results suggest that the combined administration of rhBMP-2 and PTH 1-34 facilitates qualitative and quantitative improvements in bone regeneration, by accelerating bone modeling and remodeling.

•

The present study found that intermittent administration of PTH 1-34 significantly decreased the TV of new rhBMP-2-induced bone, following the initial formation of a fusion mass equivalent to that of the control group.

•

Bone histomorphometry demonstrated predominant bone resorption at the periosteum and bone formation at the endosteum in rats receiving PTH 1-34.

•

These results indicated that PTH 1-34 supported modeling of rhBMP-2-induced bone in addition to the remodeling effect which confirmed by bone histomorphometry and serum markers.

Binding to COMP Reduces the BMP2 Dose for Spinal Fusion in a Rat Model

STUDY DESIGN

The aim of this study is to test the effect of cartilage oligomeric matrix protein (COMP) on enhancing rhBMP-2 induced spinal fusion in a prospective 8-week interventional trial of spinal fusion in rats.

OBJECTIVE

To determine whether the amount of bone morphogenetic protein-2 (BMP-2) required to achieve spinal fusion in a pre-clinical model can be reduced by the addition of COMP.

SUMMARY OF BACKGROUND DATA

BMPs are applied clinically at supraphysiological doses to promote spinal fusion by inducing osseous growth, but dose-related limitations include ectopic bone formation and local inflammatory reactions. COMP is a matricellular BMP-binding protein expressed during endochondral ossification and fracture healing. In vitro studies demonstrate enhanced activity of BMP bound to COMP. We hypothesized that BMP bound to COMP could achieve equivalent spinal fusion rates at lower doses and with fewer complications.

METHODS

Posterolateral intertransverse process spinal fusion at L4 to L5 was performed in 36 Lewis rats. COMP (10 μg) was tested with or without "low-dose" rhBMP-2 (2 μg), and the results were compared with the "low-dose" (2 μg rhBMP-2) and "high-dose" (10 μg rhBMP-2) groups. All groups utilized insoluble collagen bone matrix carrier (ICBM). Fusion was evaluated by radiology, histology, and manual palpation. BMP release kinetics were evaluated in vitro.

RESULTS

Fusion grading of microCT images demonstrated that the fusion rate with the COMP+LoBMP was statistically equivalent to HiBMP, and significantly better than LoBMP without COMP. These results were confirmed with radiographs and manual palpation. BMP release kinetics suggest that COMP increased local concentrations of BMP due to decreased growth factor retention on the scaffold.

CONCLUSION

COMP enhances BMP-induced bone formation, enabling lower doses of BMP to achieve the same level of spinal fusion. COMP may function by affecting the availability and biological presentation of BMP-2. A decrease of BMP-2 required for fusion may reduce dose-related adverse effects, surgical costs, and improve clinical outcomes.

LEVEL OF EVIDENCE

N/A.

rhBMP-2 protects against reoperation for pseudoarthrosis and/or instrumentation failure: A matched case-control study of 448 patients

The objective of this independent study is to determine the impact of recombinant human bone morphogenetic protein 2 (rhBMP-2) on reoperation for pseudarthrosis and/or instrumentation failure. A nested case-control study of first-time posterolateral, instrumented fusion of the lumbar spine for degenerative spinal disease was undertaken. Cases of reoperation for pseudoarthrosis and/or instrumentation failure were assigned to controls, who did not experience the primary outcome measure at the time of reoperation. Cases and controls were matched on number of interspaces fused and inclusion of interbody. Predictors of reoperation for pseudoarthrosis and/or instrumentation failure were assessed with a conditional logistical regression controlling for rhBMP-2, age, obesity, and smoking. Of the 448 patients, 155 cases of reoperation for pseudoarthrosis and/or instrumentation were matched with 293 controls. Twenty-six percent of first-time surgeries included rhBMP-2, which was statistically more commonly used in the control cohort (33.11%) versus the case cohort (12.90%) (Unadjusted odds ratio [ORunadj]=0.28) (95% confidence interval [CI]: 0.16-0.49). Following a multivariate analysis controlling for age, obesity, and smoking, the rhBMP-2 recipients incurred a 73% lower odds of reoperation for pseudoarthrosis and/or instrumentation failure (95% CI, 0.15-0.48). Neither sarcomatous nor osseous neoplasm was detected in the study population. Mean follow up did not differ between the cases (81.57±standard deviation [SD] 4.98months) versus controls (74.75±2.49month) (ORunadj=1.01) (95% CI: 1.00-1.01). rhBMP-2 in lumbar fusion constructs protects against reoperation for pseudoarthrosis and/or instrumentation failure. However, the decision to include fusion supplements should be weighted between surgical determinants and clinical outcomes.

Posterior Cervical Fusion With Recombinant Human Bone Morphogenetic Protein-2: Complications and Fusion Rate at Minimum 2-Year Follow-Up

STUDY DESIGN

Retrospective case series.

OBJECTIVE

The purpose of this study was to determine the fusion rate and evaluate the complications associated with the application of recombinant human bone morphogenetic protein-2 (rhBMP-2) in posterior cervical fusion.

SUMMARY OF BACKGROUND DATA

The rates of fusion and complications associated with the use of rhBMP-2 in posterior cervical fusion is unclear, though recent work has shown up to a 100% fusion rate.

METHODS

We independently reviewed consecutive series of patients who underwent posterior cervical, occipitocervical, or cervicothoracic instrumented fusion augmented with rhBMP-2. Two surgeons at a tertiary-referral, academic medical center performed all operations, and each patient had a minimum of 2-year follow-up. Fusion status was determined by bony bridging on computed tomography scans, absence of radiolucency around instrumentation, and absence of motion on lateral flexion/extension radiographs.

RESULTS

Fifty-seven patients with a mean age of 56.7±13.2 years and mean follow-up of 37.7±20.6 months were analyzed. Forty-eight patients (84.2%) had undergone previous cervical surgery, and 42.1% had a preexisting nonunion. Constructs spanned 5.6±2.6 levels; 19.3% involved the occiput, whereas 61.4% crossed the cervicothoracic junction. The mean rhBMP-2 dose was 21.1±8.7 mg per operation. Iliac crest autograft was used for 29.8% of patients. Six patients (10.5%) experienced nonunion; only 2 required revision. In each case of nonunion, instrumentation crossed the occipitocervical or cervicothoracic junction. However, none of the analyzed variables was statistically associated with nonunion. Fourteen patients (24.6%) suffered complications, with 7 requiring additional surgery.

CONCLUSIONS

The observed fusion rate of rhBMP-2-augmented posterior cervical, occipitocervical, and cervicothoracic fusions was 89.5%. This reflects the complicated nature of the patients included in the current study and demonstrates that rhBMP-2 cannot always overcome the biomechanical challenges entailed in spanning the occipitocervical or cervicothoracic junction.

Reoperation Rates After Long Posterior Spinal Fusion: Use of Recombinant Bone Morphogenetic Protein in Idiopathic and Non-idiopathic Scoliosis

INTRODUCTION

Bone morphogenetic protein (BMP) can increase the likelihood of solid arthrodesis in spinal surgery. This would imply fewer reoperations for pseudarthrosis, but small cohort sizes are inadequate to monitor these events. We sought to examine adolescent idiopathic (AIS) and non-idiopathic scoliosis (NIS) for reoperation events with and without the use of BMP using a large statewide database.

METHODS

The 2008-2011 New York State Inpatient Database was queried using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. Patients age 10 and older with a diagnosis of scoliosis and an index fusion of greater than 2 spinal motion segments were included. Patient identifiers and linkage variables were used to identify revisits. The relative risk of reoperation was calculated. The use of BMP at the initial inpatient stay was used to define the two cohorts for relative risk assessment.

RESULTS

A total of 2,658 and 2,431 cases were identified of AIS and NIS, respectively. The use of BMP at the initial visit was performed at a rate of 4.5% for AIS and 21.0% for NIS fusion surgery. For posterior fusion cases longer than eight levels, the reoperation rate for pseudarthrosis was 1.0% in AIS and 18.4% in NIS (p < .001). For NIS fusions greater than eight levels, the rate of reoperation for pseudarthrosis after using BMP at the index surgery was 5% and 22% when BMP was not used, a relative risk of 4.0 (p < .001). For AIS, there was no substantial increase in risk when not using BMP for fusion greater than eight levels (p < .001).

CONCLUSION

We found a significant decrease in the risk of reoperation for pseudarthrosis after long fusions when using BMP in the case of NIS. In contrast, use of BMP does not benefit the AIS population.

Recombinant Human Bone Morphogenetic Protein-2 in Posterolateral Spinal Fusion: What's the Right Dose?

STUDY DESIGN

Single center retrospective cohort analysis.

PURPOSE

The goal was to evaluate the influence of varying amount of recombinant human bone morphogenetic protein 2 (rhBMP-2) per level on fusion rates and complications in posterolateral spinal fusions.

OVERVIEW OF LITERATURE

rhBMP-2 has been utilized for lumbar posterolateral fusions for many years. Initial rhBMP-2 recommendations were 20 mg/level of fusion. Dose and concentration per level in current studies vary from 4.2 to 40 mg and 1.5 to 2.0 mg/mL, respectively. Variable fusion and complication rates have been reported.

METHODS

Patients (n=1,610) undergoing instrumented lumbar spinal fusion (2003-2009) with utilization of rhBMP-2 were retrospectively evaluated. Patient demographics, body mass index (BMI), comorbidities, number of levels, associated interbody fusion, and types of bone void filler were analyzed. Fusions rates and nonunions were subdivided into number of levels and amount of rhBMP-2 used per level.

RESULTS

Patients (n=559) were evaluated with 58.5% females having an average age of 63 years, BMI of 31 kg/m(2). Number of levels fused ranged from 1 to 8. rhBMP-2 averaged 7.3 mg/level (range, 1.5-24 mg/level) based upon length of collagen sponge in relation to length of fusion levels. Patients with non-union formation had lower rhBMP-2 dose per level (p=0.016). A significant difference in non-union rate was found between patients undergoing fusion with <6 mg/level compared to those with >6 mg/level (9.1% vs. 2.4%, χ(2)=0.012). No significant differences were noted between 6-11.9 mg/level and ≥12 mg/level. No threshold was found for seroma formation or bone overgrowth.

CONCLUSIONS

Previous recommendation of 20 mg/level of rhBMP-2 is more than what is required for predictable fusion rates of 98%. No dose related increase of infection, seroma formation, and bone overgrowth has been found. In order to provide variable dosing and cost reduction, industry generated rhBMP-2 kit size should be optimized.

Anatomic feasibility of a new endopelvic approach for iliac crest bone harvesting

PURPOSE

For the past few years, anterior exposure for surgery of the lumbar spine has gained popularity for the treatment of disk disease or spondylosis. Cancellous bone remains the gold standard for fusion. Iliac crest bone harvesting is safe but there are donor site complications. Bone substitutes exist, like recombinant human bone morphogenic protein-2 rhBMP-2. This alternative offers a high rate of fusion but with local and general complications. The aim of our study is to show the feasibility of an endopelvic approach for iliac bone crest harvesting to avoid donor site complication.

METHOD

Twenty anterior retroperitoneal lumbar spine approaches have been realized in the anatomy department of the University of Bordeaux. The volumes of cancellous bone have been measured and procedure complications have been reported.

RESULTS

The mean volume of cancellous bone was 5.9 cc, the maximum volume was 8.2 cc and the minimum volume was 4.5 cc. No complications have been reported during the approach or the bone harvesting.

CONCLUSIONS

Anterior retroperitoneal approach for iliac bone crest harvesting is a safe way to obtain sufficient volume of cancellous bone for a single lumbar spinal fusion. This exposure avoids the risks of an iliac crest donor site complications or rhBMP-2 complications.

Off-label innovation: characterization through a case study of rhBMP-2 for spinal fusion

OBJECTIVE Off-label therapies are widely used in clinical practice by spinal surgeons. Some patients and practitioners have advocated for increased regulation of their use, and payers have increasingly questioned reimbursment for off-label therapies. In this study, the authors applied a model that quantifies publication data to analyze the developmental process from initial on-label use to off-label innovation, using as an example recombinant human bone morphogenetic protein 2 (rhBMP-2) because of its wide off-label use. METHODS As a case study of off-label innovation, the developmental patterns of rhBMP-2 from FDA-approved use for anterior lumbar interbody fusion to several of its off-label uses, including posterolateral lumbar fusion, anterior cervical discectomy and fusion, and posterior lumbar interbody fusion/transforaminal lumbar interbody fusion, were evaluated using the "progressive scholarly acceptance" (PSA) model. In this model, PSA is used as an end point indicating acceptance of a therapy or procedure by the relevant scientific community and is reached when the total number of peer-reviewed studies devoted to refinement or improvement of a therapy surpasses the total number assessing initial efficacy. Report characteristics, including the number of patients studied and study design, were assessed in addition to the time to and pattern of community acceptance, and results compared with previous developmental study findings. Disclosures and reported conflicts of interest for all articles were reviewed, and these data were also used in the analysis. RESULTS Publication data indicated that the acceptance of rhBMP-2 off-label therapies occurred more rapidly and with less evidence than previously studied on-label therapies. Additionally, the community appeared to respond more robustly (by rapidly changing publication patterns) to reports of adverse events than to new questions of efficacy. CONCLUSIONS The development of off-label therapies, including the influence of investigative methods, regulation, and changing perspectives, can be characterized on the basis of publication patterns. The approach and findings in this report could inform future off-label development of therapies and procedures as well as attempts to regulate off-label use.

A Review of the Clinical Side Effects of Bone Morphogenetic Protein-2

Bone morphogenetic protein-2 (BMP-2) is currently the only Food and Drug Administration (FDA)-approved osteoinductive growth factor used as a bone graft substitute. However, with increasing clinical use of BMP-2, a growing and well-documented side effect profile has emerged. This includes postoperative inflammation and associated adverse effects, ectopic bone formation, osteoclast-mediated bone resorption, and inappropriate adipogenesis. Several large-scale studies have confirmed the relative frequency of adverse events associated with the clinical use of BMP-2, including life-threatening cervical spine swelling. In fact, the FDA has issued a warning of the potential life-threatening complications of BMP-2. This review summarizes the known adverse effects of BMP-2, including controversial areas such as tumorigenesis. Next, select animal models that replicate BMP-2's adverse clinical effects are discussed. Finally, potential molecules to mitigate the adverse effects of BMP-2 are reviewed. In summary, BMP-2 is a potent osteoinductive cytokine that has indeed revolutionized the bone graft substitute market; however, it simultaneously has accrued a worrisome side effect profile. Better understanding of these adverse effects among both translational scientists and clinicians will help determine the most appropriate and safe use of BMP-2 in the clinical setting.

The use of recombinant morphogenic protein-2(rhBMP-2) in children undergoing revision surgery for persistent non-union

The purpose of the study was to evaluate the safety and efficacy with the use of BMP-2 for treating persistent non-unions in children with underlying complex conditions. Between October 2006 and November 2010 in our unit, 15 patients were treated with rhBMP-2 to enhance bone union. There were nine females and six males with a mean age of 9.5 years (range 4–15) at time of surgery. Seventy-five per cent of the patients required revision of internal fixation with insertion of rhBMP-2 to the non-union site, and the reminder had freshening of the non-union site with rhBMP-2 application. Patients had undergone a mean of 2 (1–5) operations prior to implantation of rhBMP-2. All the patients in the study group were available for review with mean follow-up of 44 months (range 21–70). The mean time to union was 16 weeks (range 10–28 weeks). No adverse events related to BMP-2 application were noted in our study group. Healing occurred clinically and radiographically in 16 of the 17 sites. Our study demonstrates that BMP-2 enhances healing of the persistent non-unions without any adverse events

LIPUS promotes spinal fusion coupling proliferation of type H microvessels in bone

Low-intensity pulsed ultrasound (LIPUS) has been found to accelerate spinal fusion. Type H microvessels are found in close relation with bone development. We analyzed the role of type H vessels in rat spinal fusion model intervened by LIPUS. It was found LIPUS could significantly accelerate bone fusion rate and enlarge bone callus. Osteoblasts were specifically located on the bone meshwork of the allograft, and were surrounded by type H microvessels. LIPUS could significantly increase the quantity of osteoblasts during spine fusion, which process was coupled with elevated angiogenesis of type H microvessels. Our results suggest that LIPUS may be a noninvasive adjuvant treatment modality in spinal fusion for clinical use. The treatment is recommended for usage for at least one month.

Novel Wnt Regulator NEL-Like Molecule-1 Antagonizes Adipogenesis and Augments Osteogenesis Induced by Bone Morphogenetic Protein 2

The differentiation factor NEL-like molecule-1 (NELL-1) has been reported as osteoinductive in multiple in vivo preclinical models. Bone morphogenetic protein (BMP)-2 is used clinically for skeletal repair, but in vivo administration can induce abnormal, adipose-filled, poor-quality bone. We demonstrate that NELL-1 combined with BMP2 significantly optimizes osteogenesis in a rodent femoral segmental defect model by minimizing the formation of BMP2-induced adipose-filled cystlike bone. In vitro studies using the mouse bone marrow stromal cell line M2-10B4 and human primary bone marrow stromal cells have confirmed that NELL-1 enhances BMP2-induced osteogenesis and inhibits BMP2-induced adipogenesis. Importantly, the ability of NELL-1 to direct BMP2-treated cells toward osteogenesis and away from adipogenesis requires intact canonical Wnt signaling. Overall, these studies establish the feasibility of combining NELL-1 with BMP2 to improve clinical bone regeneration and provide mechanistic insight into canonical Wnt pathway activity during NELL-1 and BMP2 osteogenesis. The novel abilities of NELL-1 to stimulate Wnt signaling and to repress adipogenesis may highlight new treatment approaches for bone loss in osteoporosis.

Clinical translation of controlled protein delivery systems for tissue engineering

Strategies that utilize controlled release of drugs and proteins for tissue engineering have enormous potential to regenerate damaged organs and tissues. The multiple advantages of controlled release strategies merit overcoming the significant challenges to translation, including high costs and long, difficult regulatory pathways. This review highlights the potential of controlled release of proteins for tissue engineering and regenerative medicine. We specifically discuss treatment modalities that have reached preclinical and clinical trials, with emphasis on controlled release systems for bone tissue engineering, the most advanced application with several products already in clinic. Possible strategies to address translational and regulatory concerns are also discussed.

Use of Recombinant Bone Morphogenetic Protein Is Associated With Reduced Risk of Reoperation After Spine Fusion for Adult Spinal Deformity

STUDY DESIGN

Retrospective review.

OBJECTIVE

This study follows the inpatient-stay administrative data that were collected for a cohort of thousands of patients who had spine fusion surgery in the state of New York. We sought to examine adult spinal deformity (ASD) for reoperation events with and without the use of bone morphogenetic protein-2 (BMP).

SUMMARY OF BACKGROUND DATA

Randomized controlled trials have suggested that BMP may increase the likelihood of solid arthrodesis in spinal surgery. This would imply fewer reoperations for pseudarthrosis, but small cohort sizes are inadequate to monitor these events.

METHODS

The 2008-2011 New York State Inpatient Database was queried using International Classification of Diseases, Ninth Revision, Clinical Modification codes. Patients age 21 years and older with a diagnosis of scoliosis and an index fusion of greater than 2 spinal motion segments were included. Patient identifiers and linkage variables were used to identify revisits. The relative risk of reoperation was calculated. The use of BMP at the initial inpatient stay was used to define the 2 cohorts for relative risk assessment.

RESULTS

A total of 3751 patients of ASD were identified in 2008. The use of BMP at the initial visit was performed at a rate of 37.6% for ASD. For posterior fusion cases longer than 8 levels, the rate of reoperation for a pseudarthrosis was 23.4%. For ASD fusions greater than 8 levels, the rate of reoperation for pseudarthrosis after using BMP at the index surgery was 5% and 33.9% when BMP was not used, a relative risk of 7.5 (P < 0.001).

CONCLUSION

Using relevant inhospital patient records from the New York State Inpatient Sample, we found a 7.5-fold decrease in the risk of reoperation for pseudarthrosis after long fusions when using BMP. Decreased reoperation rates are caused by the improved fusion with the use of BMP. If subsequent unnecessary hospitals stays can be avoided, the economics of BMP use should be reexamined.

Comparison of Silicate-Substituted Calcium Phosphate (Actifuse) with Recombinant Human Bone Morphogenetic Protein-2 (Infuse) in Posterolateral Instrumented Lumbar Fusion

Study Design Randomized controlled trial. Objective The aim of this study was to assess the efficacy of the bone grafting substitute silicate-substituted calcium phosphate (SiCaP) compared with recombinant human bone morphogenetic protein 2 (rhBMP-2) and to evaluate the clinical outcomes over a period of 2 years. Methods Patients undergoing PLF surgery for DDD at a single center were recruited and randomized to one of two groups: SiCaP (n = 9) or rhBMP-2 (n = 10). One patient withdrew prior to randomization and another from the rhBMP-2 group after randomization. The radiologic and clinical outcomes were examined and compared. Fusion was assessed at 12 months with computed tomography and plain radiographs. Clinical outcomes were evaluated by recording measures of pain, quality of life, disability, and neurologic status from 6 weeks to 2 years postoperatively. Results In the SiCaP and rhBMP-2 groups, fusion was observed in 9/9 and 8/9 patients, respectively. Pain and disability scores were reduced and quality of life increased in both groups. Leg pain, disability, and satisfaction scores were similar between the groups at each postoperative point; however, back pain was less at 6 weeks and quality of life was higher at 6 months in the SiCaP group than the rhBMP-2 group. Conclusions SiCaP and rhBMP-2 were comparable in terms of achieving successful bone growth and fusion. Both groups achieved similar alleviation of pain and improved quality of life and neurologic, satisfaction, and return to work outcomes following PLF surgery.

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.

Ordinary and Activated Bone Grafts: Applied Classification and the Main Features

Bone grafts are medical devices that are in high demand in clinical practice for substitution of bone defects and recovery of atrophic bone regions. Based on the analysis of the modern groups of bone grafts, the particularities of their composition, the mechanisms of their biological effects, and their therapeutic indications, applicable classification was proposed that separates the bone substitutes into “ordinary” and “activated.” The main differential criterion is the presence of biologically active components in the material that are standardized by qualitative and quantitative parameters: growth factors, cells, or gene constructions encoding growth factors. The pronounced osteoinductive and (or) osteogenic properties of activated osteoplastic materials allow drawing upon their efficacy in the substitution of large bone defects.

Assessment and classification of subsidence after lateral interbody fusion using serial computed tomography

OBJECT

Intervertebral cage settling during bone remodeling after lumbar lateral interbody fusion (LIF) is a common occurrence during the normal healing process. Progression of this settling with endplate collapse is defined as subsidence. The purposes of this study were to 1) assess the rate of subsidence after minimally invasive (MIS) LIF by CT, 2) distinguish between early cage subsidence (ECS) and delayed cage subsidence (DCS), 3) propose a descriptive method for classifying the types of subsidence, and 4) discuss techniques for mitigating the risk of subsidence after MIS LIF.

METHODS

A total of 128 consecutive patients (with 178 treated levels in total) underwent MIS LIF performed by a single surgeon. The subsidence was deemed to be ECS if it was evident on postoperative Day 2 CT images and was therefore the result of an intraoperative vertebral endplate injury and deemed DCS if it was detected on subsequent CT scans (≥ 6 months postoperatively). Endplate breaches were categorized as caudal (superior endplate) and/or cranial (inferior endplate), and as ipsilateral, contralateral, or bilateral with respect to the side of cage insertion. Subsidence seen in CT images (radiographic subsidence) was measured from the vertebral endplate to the caudal or cranial margin of the cage (in millimeters). Patient-reported outcome measures included visual analog scale, Oswestry Disability Index, and 36-Item Short Form Health Survey physical and mental component summary scores.

RESULTS

Four patients had ECS in a total of 4 levels. The radiographic subsidence (DCS) rates were 10% (13 of 128 patients) and 8% (14 of 178 levels), with 3% of patients (4 of 128) exhibiting clinical subsidence. In the DCS levels, 3 types of subsidence were evident on coronal and sagittal CT scans: Type 1, caudal contralateral, in 14% (2 of 14), Type 2, caudal bilateral with anterior cage tilt, in 64% (9 of 14), and Type 3, both endplates bilaterally, in 21% (3 of 14). The mean subsidence in the DCS levels was 3.2 mm. There was no significant difference between the numbers of patients in the subsidence (DCS) and no-subsidence groups who received clinical benefit from the surgical procedure, based on the minimum clinically important difference (p > 0.05). There was a significant difference between the fusion rates at 6 months (p = 0.0195); however, by 12 months, the difference was not significant (p = 0.2049).

CONCLUSIONS

The authors distinguished between ECS and DCS. Radiographic subsidence (DCS) was categorized using descriptors for the location and severity of the subsidence. Neither interbody fusion rates nor clinical outcomes were affected by radiographic subsidence. To protect patients from subsidence after MIS LIF, the surgeon needs to take care with the caudal endplate during cage insertion. If a caudal bilateral (Type 2) endplate breach is detected, supplemental posterior fixation to arrest progression and facilitate fusion is recommended.

Bone Morphogenetic Proteins in Spinal Surgery: What Is the Fusion Rate and Do They Cause Cancer?

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

The aim of this study was to determine the fusion rate using recombinant human bone morphogenetic protein (rhBMP) in spinal surgery and to estimate the risk of cancer subsequent to their use.

SUMMARY OF BACKGROUND DATA

rhBMP may obviate the need for iliac crest bone graft harvest and provides similar or higher fusion rates than autologous bone graft. Recently, there are concerns that rhBMPs may either cause cancer or accelerate progression.

METHODS

Patients were treated by 2 spine surgeons between 2002 and 2012. Inclusion criteria were patients who resided in the state of Victoria, Australia, undergoing lumbar fusion (anterior, lateral, posterior, and posterolateral) with rhBMP [either rhBMP-2 (Infuse) or rhBMP-7 (OP-1)]. Exclusion criteria were patients who reported having an invasive cancer diagnosis before the spinal fusion procedure. The occurrence of incident cancers was obtained from record linkage to the Victorian Cancer Registry.

RESULTS

A total of 527 patients were included in the cohort, with a mean follow-up of 4.4 years (1.8-11.5). Patients received Infuse in 77% of cases and OP-1 in 23%. The mean Infuse does was 10.2  mg (2.5-48.0) and 3.3  mg (1.7-6.6) for OP-1. There was no significant difference in fusion rates between Infuse (90.1%) and OP-1 (91.9%) (P = 0.42). The overall success of interbody fusion with rhBMP was 93.5% at 12 months. Twenty-seven patients were diagnosed with an invasive cancer since treatment (20 Infuse and 7 OP-1 patients). Comparing the observed numbers in our study cohort with those expected on the basis of the Victorian population's age and sex-specific rates, we observed that the study cohort was not at a significantly increased risk of cancer. The standardized incidence ratio for cancer overall (of any type) was 0.84 [95% confidence interval (95% CI) 0.56-1.21].

CONCLUSION

Off-label use of rhBMP provided high fusion rates with no evidence of a significantly increased risk of cancer.

LEVEL OF EVIDENCE

4.

Comparison of rhBMP-2 versus Autogenous Iliac Crest Bone Graft for 2-Level Anterior Cervical Discectomy and Fusion for Cervical Spondylotic Myelopathy

Background

Few studies have examined the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2) in 2-level anterior cervical discectomy and fusion (ACDF). The purpose of this study was to compare the outcomes in a series of patients with CSM treated with 2-level ACDF with or without rhBMP-2.

Material/Methods

The retrospective study included a total of 146 patients with CSM. The rhBMP-2 group consisted of 73 patients who underwent 2-level ACDF with rhBMP-2. A total of 73 patients who also received 2-level ACDF with autogenous ICBG alone were included in the matched-pair ICBG group with a ratio of 1:1, based on age, sex, and BMI. All data, including fusion rate and time, VAS, JOA score, operative date, and complications, were assessed.

Results

With respect to the length of hospital stay, operative times, and blood loss, there were no significant difference between the 2 groups. However, the rhBMP-2 group presented a shorter fusion time (P<0.013) and higher fusion rate (P<0.036) than the ICBG group. In the rhBMP-2 group, 22% required additional treatment for complications compared to 18% of patients in the ICBG group, which showed no significant difference (P=0.543).

Conclusions

The application of rhBMP-2 in 2-level ACDF showed higher fusion rates, shorter fusion time, and similar function outcomes compared to those who received ACDF with ICBG alone.

Use of salicylic acid polymers and bone morphogenetic protein-2 to promote bone regeneration in rabbit parietal bone defects

The ability of bone defects to heal spontaneously is inversely related to the size of the defect, such that defects larger than a critical size will not heal without additional therapeutic intervention. Typically, large bone defects are filled with autologous bone harvested from another skeletal site, an osteoconductive bone graft material, treated with an osteoinductive factor such as bone morphogenetic protein-2, or by a combination of these approaches. Despite these interventions, unsatisfactory success and complication rates show that alternative treatment methods are needed. Here, we test whether salicylic acid polymers can be used as guided bone regeneration barriers in conjunction with bone morphogenetic protein-2 to treat 1-cm-diameter defects in rabbit parietal bones. Porous, 1-cm round polycaprolactone scaffolds were infused with calcium sulfate–containing bone morphogenetic protein-2 and then capped on one side with salicylic acid polymers. The polymers slowed resorption of calcium sulfate that was used as a carrier for bone morphogenetic protein-2, indicating that bone morphogenetic protein-2 release into the parietal bone defect was extended by the use of the salicylic acid polymer. Microcomputerized tomography and histomorphometric analysis of the parietal bones 8 weeks after implantation showed that the salicylic acid polymer did not impair bone formation in the defect. These observations indicate that salicylic polymers paired with bone morphogenetic protein-2 can be optimized for use in guided bone regeneration to help repair large bone defects.

Osteonecrosis of the femoral head: treatment with ancillary growth factors

Osteonecrosis (ON) of the femoral head, also known as avascular necrosis (AVN) of the femoral head, is a progressive disease that predominantly affects younger patients. During early stage of ON, decompression of the femoral head has been commonly used to improve pain. The decompression has been augmented with nonvascularized or vascularized bone grafts, mesenchymal stems cells, and growth factors. The use of adjuvant growth factors to supplement the core decompression has mainly been limited to animal models in an attempt to regenerate the necrotic lesion of ON. Factors utilized include bone morphogenetic proteins, vascular endothelial growth factors, hepatocyte growth factors, fibroblast growth factors, granulocyte colony-stimulating factors, and stem cells factors. In animal models, the use of these factors has been shown to increase bone formation and angiogenesis. Although promising, the use of these growth factors and cell-based therapies clinically remains limited.

Platelet concentrates in spine fusion: meta-analysis of union rates and complications in controlled trials

PURPOSE

Platelet concentrates in spine fusion gained increasing popularity among spine surgeons. They avoid morbidity of bone harvest and promise good union rates without additional device-related adverse events. Therefore, they seem to be a safe and effective alternative to common bone substitutes. This meta-analysis assesses the available evidence for union rate and overall complications with the use of platelet concentrates in spine fusion.

METHODS

We conducted an online search for relevant controlled trials and extracted data on union rates, complications, and revision rates. These data were synthesized in a meta-analysis using fixed-effects odds ratios (OR). To assess covariates, meta-regression was performed as well.

RESULTS

Our search produced 166 results, ten of which were eligible for inclusion. These studies report on a total of 763 patients (328 experimental, 435 controls) with a mean age of 50.3 ± 7.5 years. Mean follow-up was 1.9 ± 0.0.4 years. With the use of platelet concentrates, union rate decreased significantly, OR 0.53 (95 % CI 0.35-0.79, p = 0.002), compared with the control group. There was no statistically significant difference in complication rates OR 1.34 (95 % CI 0.62-2.90, p = 0.46) or in revision rates OR 3.0 (95 % CI 0.90-10.00, p = 0.74). Meta-regression showed no statistically significant influence of randomization, Jadad score, or assessment of fusion.

CONCLUSION

The use of platelet concentrates in spine fusion shows significantly decreased union rates compared with the control group. However, complication and revision rates were not significantly increased. The current data do not recommend the use of platelet concentrate in spine fusion.

Bone graft substitutes for spine fusion: A brief review

Bone graft substitutes are widely used in the field of orthopedics and are extensively used to promote vertebral fusion. Fusion is the most common technique in spine surgery and is used to treat morbidities and relieve discomfort. Allograft and autograft bone substitutes are currently the most commonly used bone grafts to promote fusion. These approaches pose limitations and present complications to the patient. Numerous alternative bone graft substitutes are on the market or have been developed and proposed for application. These options have attempted to promote spine fusion by enhancing osteogenic properties. In this review, we reviewed biology of spine fusion and the current advances in biomedical materials and biological strategies for application in surgical spine fusion. Our findings illustrate that, while many bone graft substitutes perform well as bone graft extenders, only osteoinductive proteins (recombinant bone morphogenetic proteins-2 and osteogenic protein-1) provide evidence for use as both bone enhancers and bone substitutes for specific types of spinal fusion. Tissue engineered hydrogels, synthetic polymer composites and viral based gene therapy also holds the potential to be used for spine fusion in future, though warrants further investigation to be used in clinical practice.