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 with recombinant human bone morphogenic protein-2 in posterolateral spine fusion: a consecutive series of 1037 cases

STUDY DESIGN

Retrospective case series.

OBJECTIVE

The purpose of this study was to report on a large consecutive series of posterolateral fusion cases using rhBMP-2/ACS.

SUMMARY OF BACKGROUND DATA

Despite evidence that rhBMP-2/ACS is effective as an iliac crest graft substitute in posterolateral fusion, concerns remain regarding potential risk for BMP use in clinical practice. These concerns have been fueled by the serious complications reported with BMP in anterior cervical spine fusion. While none of the literature on posterolateral fusion with rhBMP-2/ACS has suggested an increased complication rate versus iliac crest bone graft, this issue has not been specifically studied.

METHODS

We reviewed medical records for a consecutive series of 1037 patients who underwent posterolateral spine fusion using rhBMP-2 between 2003 and 2006. Medical complications were attributed to the surgical procedure if they occurred within the 3-month perioperative period, whereas complications potentially related to BMP were included regardless of time frame.

RESULTS

Medical and surgical complications were observed in 190 of 1037 patients (18.3%) with 81 major complications (7.8%) and 110 minor complications (10.2%). Neurologic complications were related to screw malposition in 6 patients and epidural hematoma in 3 patients. New or more severe postoperative radicular symptoms were noted in 7 patients (0.7%). Psoas hematoma was identified by CT scan in 8 patients (0.8%). Complications directly related to rhBMP-2 were observed in at least 1 patient (0.1%) and in a worst case analysis, in as many as 6 patients (0.6%).

CONCLUSION

This study in 1037 patients confirms the relative safety of rhBMP-2/ACS for posterolateral spine fusion. There were extremely few complications directly attributed to rhBMP-2/ACS, and the overall complication rates were consistent with established norms. The stark contrast between this experience and the markedly elevated complication rate reported with anterior cervical BMP usage emphasizes the need to evaluate risks and benefits of bioactive technologies in a site-specific and procedure-specific manner.

Radiographic and CT evaluation of recombinant human bone morphogenetic protein-2-assisted spinal interbody fusion

OBJECTIVE

Bone morphogenetic proteins BMPs, when used in spinal fusion, hasten healing and initiate distinct imaging features. We undertook a study to record and analyze the radiographic and CT changes after the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion surgery.

MATERIALS AND METHODS

This study included 95 patients who underwent spinal interbody fusion using rhBMP-2. The lumbar spine fusion cohort consisted of 23 patients who underwent anterior lumbar interbody fusion, 36 patients who underwent transforaminal lumbar interbody fusion, and two patients who underwent posterior lumbar interbody fusion. The remaining 34 patients underwent anterior cervical decompression and fusion.

RESULTS

A polyetheretherketone cage was used as an interbody spacer in 59 patients (82 levels) and an allograft bone was the spacer in 36 patients (55 levels). Patients were evaluated 2 and 6 weeks after the procedure and then 3, 6, 12, and 24 months after the procedure. All patients underwent radiography at every follow-up visit, and CT evaluation was performed in 32 patients.

CONCLUSION

Features observed on imaging that we attributed to the use of rhBMP-2 included an enhanced fusion rate and an increased incidence of prevertebral soft-tissue swelling in patients who underwent cervical fusion. Endplate resorption was observed in 100% of patients who underwent cervical fusion and in 82% of the lumbar levels. Subsidence of the cage resulting in narrowing of the disk space was seen in more than 50% of cases. Cage migration and heterotopic bone formation in the spinal canal and neural foramen occurred maximally in the lumbar spine of patients in whom a polyetheretherketone cage was placed using a transforaminal approach.

Effects of protein dose and delivery system on BMP-mediated bone regeneration

Delivery of recombinant proteins is a proven therapeutic strategy to promote endogenous repair mechanisms and tissue regeneration. Bone morphogenetic protein-2 (rhBMP-2) has been used to promote spinal fusion and repair of challenging bone defects; however, the current clinically-used carrier, absorbable collagen sponge, requires high doses and has been associated with adverse complications. We evaluated the hypothesis that the relationship between protein dose and regenerative efficacy depends on delivery system. First, we determined the dose-response relationship for rhBMP-2 delivered to 8-mm rat bone defects in a hybrid nanofiber mesh/alginate delivery system at six doses ranging from 0 to 5 μg. Next, we directly compared the hybrid delivery system to the collagen sponge at 0.1 and 1.0 μg. Finally, we compared the in vivo protein release properties of the two delivery methods. In the hybrid delivery system, bone volume, connectivity and mechanical properties increased in a dose-dependent manner to rhBMP-2. Consistent bridging of the defect was observed for doses of 1.0 μg and greater. Compared to collagen sponge delivery at the same 1.0 μg dose, the hybrid system yielded greater connectivity by week 4 and 2.5-fold greater bone volume by week 12. These differences may be explained by the significantly greater protein retention in the hybrid system compared to collagen sponge. This study demonstrates a clear dose-dependent effect of rhBMP-2 delivered using a hybrid nanofiber mesh/alginate delivery system. Furthermore, the effective dose was found to vary with delivery system, demonstrating the importance of biomaterial carrier properties in the delivery of recombinant proteins.

Evaluation of autologous platelet concentrate for intertransverse lumbar fusion

INTRODUCTION

The aim of the study was to analyze if the adding of autologous platelet concentrate (APC) to a mixture of local autograft plus tricalcium phosphate and hidroxiapatite (TCP/HA) would improve the fusion rate in posterolateral lumbar fusion.

MATERIALS AND METHODS

A prospective, controlled, blinded, non-randomized clinical trial was carried out in 107 patients affected by degenerative lumbar pathology. The study group consisted of 67 patients, in which autologous platelet concentration was added to a mixture of autologous local bone graft and TCP/HA. A control group of 40 patients with same pathology and surgical technique but without APC addition was used to compare the fusion mass obtained. By means of plain X-rays, a blinded evaluation of the intertransverse fusion mass quality at twelve and twenty-four months was made according to type A (bilateral uniform mass), type B (unilateral uniform mass) and type C (irregular or lack bilateral mass). Patients with type C were regarded as pseudoarthrosis.

RESULTS

In the study group 17 patients had lack or irregular fusion mass (25.4%) versus three patients in the control group (7.5%), which was statistically significant.

CONCLUSIONS

This study shows that the adding of autologous platelet concentration to a mixture of autologous bone graft plus TCP/HA has decreased our rates of posterolateral lumbar fusion.

Use of recombinant human bone morphogenetic protein-2 as an adjunct for instrumented posterior arthrodesis in the occipital cervical region: An analysis of safety, efficacy, and dosing

Background:

There have been few reports on the use of recombinant human bone morphogenetic protein (rhBMP)-2 in posterior spine. However, no study has investigated the dosing, safety, and efficacy of its use in the posterior atlantoaxial, and/or craniovertebral junction. Recent case report of the cytokine-mediated inflammatory reaction, following off label use of rhBMP-2 as an adjunct for cervical fusion, particularly in complex cases, has increased concern about complications associated with the product.

Objective:

To assess the safety, efficacy, and dosing of rhBMP-2 as an adjunct for instrumented posterior atlantoaxial and/or craniovertebral junction arthrodesis.

Materials and Methods:

We included all patients treated by the senior author that included posterior atlantoaxial and/or craniovertebral junction instrumented fusion using rhBMP-2 from 2003 to 2008 with a minimum two year follow-up. Diagnosis, levels fused, rhBMP-2 dose, complications, and fusion were assessed.

Results:

Twenty three patients with a mean age of 60.9 years (range 4 - 89 years) and an average follow-up of 45 months (range 27 to 84 months) met inclusion criteria. The indications for surgery included, atlantoaxial instability (n = 16), basilar invagination (n = 6), and kyphoscoliosis (n = 1). The specific pathologic diagnosis included type 2 dens fracture (n = 7), complex C1 and C2 ring fracture (n = 2), chordoma (n = 2), degenerative/osteoporosis (n = 3), rheumatoid disease (n = 8), and pseudogout (n = 1). The average rhBMP-2 dose was 2.38 mg/level, with a total of 76 levels treated (average 3.3 levels, SD= 1.4 levels). There were no complications. During the most recent follow-up, all patients had achieved fusion.

Conclusions:

In a series of patients with complex pathology and/or rheumatoid arthritis, 100% fusion rate was achieved with adjunct use of rhBMP-2, with a safe and effective average rhBMP-2 dose of 2.38 mg per level.

Maxillary sinus floor elevation using BMP-2 and Nell-1 gene-modified bone marrow stromal cells and TCP in rabbits

This study evaluated the synergistic osteogenic effect of bone morphogenetic protein-2 (BMP-2) and Nel-like molecule-1 (Nell-1) genes in a rabbit maxillary sinus floor elevation model. Bone marrow stromal cells (bMSCs) were cultured and transduced with AdEGFP, AdNell-1, AdBMP-2, or AdNell-1 + AdBMP-2 overexpression virus. These gene-modified autologous bMSCs were then combined with a β-tricalcium phosphate (β-TCP) granule scaffold and used to elevate the maxillary sinus floor in rabbits. bMSCs cotransduced with AdNell-1 + AdBMP-2 demonstrated a synergistic effect on osteogenic differentiation as detected by real-time PCR analysis on markers of runt-related transcription factor-2, osteocalcin, collagen type 1, alkaline phosphatase activity, and calcium deposits in vitro. As for maxillary sinus floor elevation in a rabbit model in vivo, AdNell-1 + AdBMP-2 gene-transduced autologeous bMSCs/β-TCP complex had the largest bone area and most mature bone structure among the groups, as detected by HE staining and immunohistochemistry at weeks 2 and 8 after implantation. Our data suggested that the BMP-2 and Nell-1 genes possessed a synergistic effect on osteogenic differentiation of bMSCs, while bMSCs modified with the BMP-2 and Nell-1 genes could promote new bone formation and maturation in the rabbit maxillary sinus model.

Teriparatide Therapy as an Adjuvant for Tissue Engineering and Integration of Biomaterials

Critically sized large bone defects commonly result from trauma, radical tumor resections or infections. Currently, massive allografting remain as the clinical standard to treat these critical defects. Unfortunately, allograft healing is limited by the lack of osteogenesis and bio-integration of the graft to the host bone. Based on its widely studied anabolic effects on the bone, we have proposed that teriparatide [recombinant parathyroid hormone (PTH(1-34))] could be an effective adjuvant for massive allograft healing. In support of this theory, here we review studies that have demonstrated that intermittent PTH(1-34) treatment enhances and accelerates the skeletal repair process via a number of mechanisms including: effects on mesenchymal stem cells (MSC), angiogenesis, chondrogenesis, bone formation and remodeling. We also review the current literature on the effects of PTH(1-34) therapy on bone healing, and discuss this drug's long term potential as an adjuvant for endogenous tissue engineering.

A critical review of recombinant human bone morphogenetic protein-2 trials in spinal surgery: emerging safety concerns and lessons learned

BACKGROUND CONTEXT

Increasingly, reports of frequent and occasionally catastrophic complications associated with use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion surgeries are being published. In the original peer review, industry-sponsored publications describing the use of rhBMP-2 in spinal fusion, adverse events of these types and frequency were either not reported at all or not reported to be associated with rhBMP-2 use. Some authors and investigators have suggested that these discrepancies were related to inadequate peer review and editorial oversight.

PURPOSE

To compare the conclusions regarding the safety and related efficacy published in the original rhBMP-2 industry-sponsored trials with subsequently available Food and Drug Administration (FDA) data summaries, follow-up publications, and administrative and organizational databases.

STUDY DESIGN

Systematic review.

METHODS

Results and conclusions from original industry-sponsored rhBMP-2 publications regarding safety and related efficacy were compared with available FDA data summaries, follow-up publications, and administrative and organizational database analyses.

RESULTS

There were 13 original industry-sponsored rhBMP-2 publications regarding safety and efficacy, including reports and analyses of 780 patients receiving rhBMP-2 within prospective controlled study protocols. No rhBMP-2-associated adverse events (0%) were reported in any of these studies (99% confidence interval of adverse event rate <0.5%). The study designs of the industry-sponsored rhBMP-2 trials for use in posterolateral fusions and posterior lateral interbody fusion were found to have potential methodological bias against the control group. The reported morbidity of iliac crest donor site pain was also found to have serious potential design bias. Comparative review of FDA documents and subsequent publications revealed originally unpublished adverse events and internal inconsistencies. From this review, we suggest an estimate of adverse events associated with rhBMP-2 use in spine fusion ranging from 10% to 50% depending on approach. Anterior cervical fusion with rhBMP-2 has an estimated 40% greater risk of adverse events with rhBMP-2 in the early postoperative period, including life-threatening events. After anterior interbody lumbar fusion rates of implant displacement, subsidence, infection, urogenital events, and retrograde ejaculation were higher after using rhBMP-2 than controls. Posterior lumbar interbody fusion use was associated with radiculitis, ectopic bone formation, osteolysis, and poorer global outcomes. In posterolateral fusions, the risk of adverse effects associated with rhBMP-2 use was equivalent to or greater than that of iliac crest bone graft harvesting, and 15% to 20% of subjects reported early back pain and leg pain adverse events; higher doses of rhBMP-2 were also associated with a greater apparent risk of new malignancy.

CONCLUSIONS

Level I and Level II evidence from original FDA summaries, original published data, and subsequent studies suggest possible study design bias in the original trials, as well as a clear increased risk of complications and adverse events to patients receiving rhBMP-2 in spinal fusion. This risk of adverse events associated with rhBMP-2 is 10 to 50 times the original estimates reported in the industry-sponsored peer-reviewed publications.

Bone morphogenetic protein-binding peptide reduces the inflammatory response to recombinant human bone morphogenetic protein-2 and recombinant human bone morphogenetic protein-7 in a rodent model of soft-tissue inflammation

BACKGROUND CONTEXT

Bone morphogenetic protein (BMP)-2 and BMP-7 are used to enhance bone formation in spine surgery, but the use of these materials is associated with side effects including inflammation, especially in the soft tissues of the neck. Bone morphogenetic protein-binding peptide (BBP) binds BMP-2 and BMP-7 and imparts a "slow-release" property to collagen carrier.

PURPOSE

To test the hypothesis that the addition of BBP will reduce the soft-tissue inflammation induced by the implantation of BMP-2 and BMP-7 on a collagen sponge.

STUDY DESIGN/SETTING

Prospective in vivo rodent model of inflammation.

METHODS

We implanted six different materials absorbed onto collagen sponges: absorbable collagen sponge (ACS) alone; BBP alone; recombinant human bone morphogenetic protein (rhBMP)-2 alone; rhBMP-2 plus BBP; rhBMP-7 alone; and rhBMP-7 plus BBP. Sponges were implanted bilaterally (subcutaneously [SC] and intramuscularly [IM]) into the backs of rats. Using magnetic resonance imaging, inflammation was assessed in terms of soft-tissue edema volume at 3 hours and at 2, 4, and 7 days. The animal subjects were killed on Day 7, and the dimensions of the inflammatory mass were measured manually in the case of SC tissue and those of the inflammatory zone were determined subsequently by microscopic examination in the case of muscle.

RESULTS

Both the SC and the IM soft-tissue edema volumes in the rhBMP-2 plus BBP and the rhBMP-7 plus BBP groups were significantly lower than those observed in the rhBMP-2 alone and rhBMP-7 alone groups. The edema volume associated with BBP alone was greater than that associated with ACS alone but less than that associated with the other treatment groups. The measurements of inflammatory masses and zone yielded similar results.

CONCLUSIONS

Bone morphogenetic protein-binding peptide may reduce the inflammatory response associated with the use of rhBMP-2 and rhBMP-7 in a rodent model of inflammation and in a form that has previously been shown to enhance the activity of BMPs. These preliminary studies suggest that BBP may have the potential to be used in the future to improve healing and reduce soft-tissue swelling in surgical applications of BMPs.

Recombinant human bone morphogenetic protein 2 combined with an osteoconductive bulking agent for mandibular continuity defects in nonhuman primates

PURPOSE

Recombinant human bone morphogenetic protein 2 (rhBMP-2) is an option for reconstructing mandibular continuity defects. A challenge of this technique is the need to maintain sufficient space to avoid compression of the defect. A compression-resistant matrix (CRM) provides a bulking agent that provides support during the bone formation phase.

MATERIALS AND METHODS

Thirteen Rhesus Macaque monkeys were used to evaluate different forms of an osteoconductive bulking agent compared with an absorbable collagen alone placed into a critical-sized mandibular defect. A total of 5 groups (26 defects) were evaluated: group A, rhBMP-2/absorbable collagen sponge (ACS) (1.5 mg/mL); group B, rhBMP-2/ACS with ceramic granules (15% hydroxyapatite/85% β-tricalcium phosphate) at 1.5 mg/mL; group C, rhBMP-2 (2.0 mg/mL) with a CRM; group D, rhBMP-2 (0.75 mg/mL) with a CRM; and group E, a CRM alone.

RESULTS

Histology and micro computed tomography were used to evaluate and compare new bone formation in the defects. The reconstructed bone was evaluated with regard to the new bone formation, residual voids, and density. Animals treated with the CRM and rhBMP-2 at 2.0 mg/mL (group C) showed significantly higher amounts of new bone formation, bone density, and reduced voids when compared with rhBMP-2 and ACS (1.5 mg/mL) (P < .05).

CONCLUSION

The carrier system CRM combined with rhBMP-2 and a reconstruction plate results in significantly higher bone density and better space maintenance than rhBMP-2 combined with ACS in a nonhuman primate mandibular bone repair model.

Activation of c-Jun NH(2)-terminal kinase 1 increases cellular responsiveness to BMP-2 and decreases binding of inhibitory Smad6 to the type 1 BMP receptor

Bone morphogenetic protein 2 (BMP-2) plays a critical role in the differentiation of precursor cells and has been approved for clinical application to induce new bone formation. To date, unexpectedly high doses of recombinant BMP-2 have been required to induce bone healing in humans. Thus, enhancing cellular responsiveness to BMP-2 potentially has critically important clinical implications. BMP responsiveness may be modulated in part by cross-talk with other signaling pathways, including mitogen-activated protein kinases (MAPKs). c-Jun NH(2)-terminal kinase (JNK) is a MAPK that has been reported to be required for late-stage differentiation of preosteoblasts and BMP-2-induced differentiation of preosteoblasts and pleuripotent cells. In this study we determined that MC3T3-E1-clone 24 cells (MC-24) can be induced by BMP-2 to differentiate into mineralizing osteoblast cultures. Using this inducible system, we employed both JNK loss-of-function and gain-of-function reagents to make three key observations: (1) JNK is required for phosphorylation of Smad1 by BMP-2 and subsequent activation of Smad1 signaling and osteoblast differentiation, (2) JNK1, but not JNK2, is required for BMP-2-induced formation of mineralized nodules, and (3) JNK1 activation decreases binding of inhibitory Smad6 to the type I BMP receptor (BMPR-I) and reciprocally increases binding of Smad1, both observations that would increase responsiveness to BMP-2. Understanding this and other pathways that lead to increased cellular responsiveness to BMPs could greatly aid more cost-effective and safe clinical delivery of these important molecules.

Nell-1 protein promotes bone formation in a sheep spinal fusion model

Bone morphogenetic proteins (BMPs) are widely used as bone graft substitutes in spinal fusion, but are associated with numerous adverse effects. The growth factor Nel-like molecule-1 (Nell-1) is mechanistically distinct from BMPs and can minimize complications associated with BMP therapies. This study evaluates the efficacy of Nell-1 combined with demineralized bone matrix (DBM) as a novel bone graft material for interbody spine fusion using sheep, a phylogenetically advanced animal with biomechanical similarities to human spine. Nell-1+sheep DBM or Nell-1+heat-inactivated DBM (inDBM) (to determine the osteogenic effect of residual growth factors in DBM) were implanted in surgical sites as follows: (1) DBM only (control) (n=8); (2) DBM+0.3 mg/mL Nell-1 (n=8); (3) DBM+0.6 mg/mL Nell-1 (n=8); (4) inDBM only (control) (n=4); (5) inDBM+0.3 mg/mL Nell-1 (n=4); (6) inDBM+0.6 mg/mL Nell-1 (n=4). Fusion was assessed by computed tomography, microcomputed tomography, and histology. One hundred percent fusion was achieved by 3 months in the DBM+0.6 mg/mL Nell-1 group and by 4 months in the inDBM+0.6 mg/mL Nell-1 group; bone volume and mineral density were increased by 58% and 47%, respectively. These fusion rates are comparable to published reports on BMP-2 or autograft bone efficacy in sheep. Nell-1 is an independently potent osteogenic molecule that is efficacious and easily applied when combined with DBM.

High doses of bone morphogenetic protein 2 induce structurally abnormal bone and inflammation in vivo

The major Food and Drug Association-approved osteoinductive factors in wide clinical use are bone morphogenetic proteins (BMPs). Although BMPs can promote robust bone formation, they also induce adverse clinical effects, including cyst-like bone formation and significant soft tissue swelling. In this study, we evaluated multiple BMP2 doses in a rat femoral segmental defect model and in a minimally traumatic rat femoral onlay model to determine its dose-dependent effects. Results of our femoral segmental defect model established a low BMP2 concentration range (5 and 10 μg/mL, total dose 0.375 and 0.75 μg in 75 μg total volume) unable to induce defect fusion, a mid-range BMP2 concentration range able to fuse the defect without adverse effects (30 μg/mL, total dose 2.25 μg in 75 μg total volume), and a high BMP2 concentration range (150, 300, and 600 μg/mL, total dose 11.25, 22.5, and 45 μg in 75 μg total volume) able to fuse the defect, but with formation of cyst-like bony shells filled with histologically confirmed adipose tissue. In addition, compared to control, 4 mg/mL BMP2 also induced significant tissue inflammatory infiltrates and exudates in the femoral onlay model that was accompanied by increased numbers of osteoclast-like cells at 3, 7, and 14 days. Overall, we consistently reproduced BMP2 side effects of cyst-like bone and soft tissue swelling using high BMP2 concentration approaching the typical human 1500 μg/mL.

Safety, Efficacy, and Dosing of Recombinant Human Bone Morphogenetic Protein-2 for Posterior Cervical and Cervicothoracic Instrumented Fusion With a Minimum 2-Year Follow-up

BACKGROUND:

Considerable attention has focused on concerns of increased complications with recombinant human bone morphogenetic protein-2 (rhBMP-2) use for anterior cervical fusion, but few reports have assessed its use for posterior cervical fusions.

OBJECTIVE:

To assess the safety, efficacy, and dosing of rhBMP-2 as an adjunct for instrumented posterior cervical arthrodesis.

METHODS:

All patients treated by the senior author with posterior cervical or cervicothoracic instrumented fusion using rhBMP-2 from 2003 to 2008 with a minimum of 2 years of follow-up were included. Diagnosis, levels fused, rhBMP-2 dose, complications, and fusion were assessed.

RESULTS:

Fifty-three patients with a mean age of 55.7 years (range, 2-89 years) and an average follow-up of 40 months (range, 25-80 months) met inclusion criteria. Surgical indications included basilar invagination (n = 6), fracture (n = 6), atlantoaxial instability (n = 16), kyphosis/kyphoscoliosis (n = 22), osteomyelitis (n = 1), spondylolisthesis (n = 1), and cyst (n = 1). Fifteen patients had confirmed rheumatoid disease. The average rhBMP-2 dose was 1.8 mg per level, with a total of 282 levels treated (average, 5.3 levels; SD, 2.8 levels). Among 53 patients, only 2 complications (3.8%) were identified: a superficial wound infection and an adjacent-level degeneration. No cases of dysphagia or neck swelling requiring treatment were identified. At the last follow-up, all patients had achieved fusion.

CONCLUSION:

Despite many of the patients in the present series having complex pathology and/or rheumatoid arthritis, a 100% fusion rate was achieved. Collectively, these data suggest that use of rhBMP-2 as an adjunct for posterior cervical fusion is safe and effective at an average dose of 1.8 mg per level.

NELL1 promotes high-quality bone regeneration in rat femoral distraction osteogenesis model

NELL1 (NEL-like molecule-1; NEL [a protein strongly expressed in neural tissue encoding epidermal growth factor like domain]) is a cranisynostosis-associated molecule directly regulated by Runx2, the master molecule in controlling osteoblastic differentiation. NELL1 has exhibited potent osteoinductive activity for bone regeneration in several animal models. However, its capacity for promoting repair of long-bone defects remains unknown. In this study, we investigated the osteogenic effects of NELL1 on femoral distraction osteogenesis using adenoviral gene delivery and multiple approaches of in vivo analysis. Thirty Sprague-Dawley (SD) rats were randomly assigned to 3 groups for treatment (n=10 each): adenovirus-green fluorescent protein (Ad-GFP)-NELL1 or Ad-GFP at 1×10⁹ plaque-forming units/ml diluted in saline, or saline alone. The femoral distraction was at a speed of 0.25 mm every 12h for 14 days, and a single injection of Ad-GFP-NELL1 or Ad-GFP was given at the mid-distraction period. The effective NELL1 delivery in vivo after Ad-GFP-NELL1 injection was evaluated by optical imaging. The bone regeneration was assessed quantitatively at days 21, 28, 42, and 56 by live 3-D micro-computed tomography (micro-CT), and animals were sacrificed at day 56 for biomechanical testing and histological analysis. Exogenous NELL1 was expressed in the distracted gap for at least 14 days after Ad-GFP-NELL1 transfection. The bone union rate in the distracted gap was significantly higher with Ad-GFP-NELL1 than with Ad-GFP (9/9 vs. 4/9 rats) or saline alone (5/9 rats) at day 56. The serial 3-D micro-CT images and quantitation obtained with the development and application of radiolucent external fixators showed less callus but more mature cortical bones formed with Ad-GFP-NELL1 than with Ad-GFP transfection and saline administration during distraction osteogenesis. The biomechanical properties of femur samples with Ad-GFP-NELL1 transfection were better than samples with Ad-GFP transfection or saline treatment, and were similar with unoperated femurs. Histology revealed cartilaginous tissues in the middle of distraction gaps with Ad-GFP transfection and saline treatment but only bony bridges with Ad-GFP-NELL1 transfection at the final time point (day 56). Coincidently, the expression of Runx2, BMP2, and BMP7 did not differ among groups at day 56, whereas the expression of osteocalcin and osteopontin was slightly higher with Ad-GFP-NELL1 transfection. Thus, sustained Ad-NELL1 protein delivery into a local area of a rat femoral distraction osteogenesis model remarkably improved regeneration of good-quality bones and accelerated bone union at a high rate. Acquiring serial micro-CT data during rat femoral distraction osteogenesis and regional adenovirus delivery of NELL1 may facilitate future in vivo studies.

A synthetic compound that potentiates bone morphogenetic protein-2-induced transdifferentiation of myoblasts into the osteoblastic phenotype

There is an urgent need to develop methods that lower costs of using recombinant human bone morphogenetic proteins (BMPs) to promote bone induction. In this study, we demonstrate the osteogenic effect of a low-molecular weight compound, SVAK-12, that potentiated the effects of BMP-2 in inducing transdifferentiation of C2C12 myoblasts into the osteoblastic phenotype. Here, we report a specific compound, SVAK-12, which was selected based on in silico screenings of small-molecule databases using the homology modeled interaction motif of Smurf1-WW2 domain. The enhancement of BMP-2 activity by SVAK-12 was characterized by evaluating a BMP-specific reporter activity and by monitoring the BMP-2-induced expression of mRNA for osteocalcin and alkaline phosphatase (ALP), which are widely accepted marker genes of osteoblast differentiation. Finally, we confirmed these results by also measuring the enhancement of BMP-2-induced activity of ALP. Smurf1 is an E3 ligase that targets osteogenic Smads for ubiquitin-mediated proteasomal degradation. Smurf1 is an interesting potential target to enhance bone formation based on the positive effects on bone of proteins that block Smurf1-binding to Smad targets or in Smurf1-/- knockout mice. Since Smads bind Smurf1 via its WW2 domain, we performed in silico screening to identify compounds that might interact with the Smurf1-WW2 domain. We recently reported the activity of a compound, SVAK-3. However, SVAK-3, while exhibiting BMP-potentiating activity, was not stable and thus warranted a new search for a more stable and efficacious compound among a selected group of candidates. In addition to being more stable, SVAK-12 exhibited a dose-dependent activity in inducing osteoblastic differentiation of myoblastic C2C12 cells even when multiple markers of the osteoblastic phenotype were parallelly monitored.

Trends in the use of bone morphogenetic protein as a substitute to autologous iliac crest bone grafting for spinal fusion procedures in the United States

STUDY DESIGN

Analysis of Nationwide Inpatient Sample (NIS) database for data related to spinal fusion procedures.

OBJECTIVE

To identify trends in the use of bone morphogenetic protein (BMP) versus iliac crest bone grafts in various spinal fusion procedures performed in the United States, explore stratification by patient demographics, and analyze the impact on treatment cost.

SUMMARY OF BACKGROUND DATA

BMP has been shown to achieve better clinical outcomes in anterior lumbar interbody fusions procedures, which led to its Food and Drug Administration approval for this indication in 2002. Since then, significant off-label use has occurred, without a full description of the results.

METHODS

We searched the NIS for data relating to BMP administration or iliac crest bone grafting in a variety of spinal fusion procedures performed from 1993 to 2006, based on International Classification of Diseases, Ninth Revision classification. The NIS is the largest all-payer inpatient care database, with demographic, outcome, and cost data from approximately eight million annual patient discharges throughout the United States. Demographics among patients treated with BMP versus iliac crest bone graft were compared to reduce the likelihood of bias in the analysis.

RESULTS

BMP became applied more frequently in each type of spinal fusion procedure examined over our study period, with the exception of anterior lumbar interbody fusions. Patients receiving iliac crest bone grafts versus BMP exhibited very similar demographic characteristics, including age, socioeconomic status, and type of health care setting. Although BMP typically increased the cost of the procedure itself, it improved outcomes and shorter hospital stays often provided a net benefit.

CONCLUSION

BMP is increasingly being used in spinal fusion procedures, including ones for which it is not officially approved, because of the surgical and postsurgical benefits it provides. Given the morbidity that this may entail, monitoring outcomes trends will help to inform guidelines for BMP use and ensure that its benefits continue to outweigh its costs.

Nell-1 enhances bone regeneration in a rat critical-sized femoral segmental defect model

BACKGROUND

Effective regeneration of bone is critical for fracture repair and incorporation and healing of bone grafts used during orthopedic, dental, and craniofacial reconstructions. Nel-like molecule-1 (Nell-1) is a secreted protein identified from prematurely fused cranial sutures of craniosynostosis patients that has been found to specifically stimulate osteogenic cell differentiation and bone formation. To test the in vivo osteoinductive capacity of Nell-1, a critical-sized femoral segmental defect model in athymic rats was used.

METHODS

A 6-mm defect, which predictably leads to nonunion if left untreated, was created in the left femur of each rat. Three treatment groups (n = 8 each) were created consisting of rats treated with (1) 1.5 mg/ml Nell-1, (2) 0.6 mg/ml Nell-1, and (3) phosphate-buffered saline only as a Nell-free control. Phosphate-buffered saline or Nell-1 was mixed with demineralized bone matrix as a carrier before implantation. All animals were euthanized 12 weeks after surgery, and bone regeneration was evaluated using radiographic, three-dimensional micro-computed tomographic, and histologic analysis.

RESULTS

Both Nell-1-treated groups had significantly greater bone formation compared with the Nell-free group, with bone volume increasing with increasing Nell-1 concentration.

CONCLUSIONS

Nell-1 in a demineralized bone matrix carrier can significantly improve bone regeneration in a critical-sized femoral segmental defect in a dose-dependent manner. The results of this study demonstrate that Nell-1 is a potent osteospecific growth factor that warrants further investigation. Results also support the potential application of Nell-1 as a bone graft substitute in multiple clinical scenarios involving repair of critical bone loss when autograft bone is limited or unavailable.

Biomolecular strategies of bone augmentation in spinal surgery

Autologous bone grafts and allografts are the most accepted procedures for achieving spinal fusion. Recently, breakthroughs in understanding bone biology have led to the development of novel approaches to address the clinical problem of bone regeneration in an unfavorable environment, while bypassing the drawbacks of traditional treatments, including limited availability, donor site morbidity, risk of disease transmission and reduced osteogenicity. These approaches have also been studied for their effectiveness in reaching successful spinal fusion. This review focuses on the cellular and molecular mechanisms explaining the rationale behind these methods, including bone marrow aspirate and mesenchymal stem cells, platelet-rich plasma, bone morphogenetic proteins and gene therapy, which have opened a promising perspective in the field of bone formation in spinal surgery.

Cranial bone defects: current and future strategies

Bony defects in the craniomaxillofacial skeleton remain a major and challenging health concern. Surgeons have been trying for centuries to restore functionality and aesthetic appearance using autografts, allografts, and even xenografts without entirely satisfactory results. As a result, physicians, scientists, and engineers have been trying for the past few decades to develop new techniques to improve bone growth and bone healing. In this review, the authors summarize the advantages and limitations of current animal models; describe current materials used as scaffolds, cell-based, and protein-based therapies; and lastly highlight areas for future investigation. The purpose of this review is to highlight the major scaffold-, cell-, and protein-based preclinical tools that are currently being developed to repair cranial defects.

TGF-β1 as possible link between loss of bone mineral density and chronic inflammation

BACKGROUND

The TGF family plays a key role in bone homeostasis. Systemic or topic application of proteins of this family apparently positively affects bone healing in vivo. However, patients with chronic inflammation, having increased TGF-β(1) serum-levels, often show reduced bone mineral content and disturbed bone healing. Therefore, we wanted to identify intracellular mechanisms induced by chronic presence of TGF-β(1) and their possible role in bone homeostasis in primary human osteoblasts.

METHODOLOGY/PRINCIPAL FINDINGS

Osteoblasts were isolated from femur heads of patients undergoing total hip replacement. Adenoviral reporter assays showed that in primary human osteoblasts TGF-β(1) mediates its signal via Smad2/3 and not Smad1/5/8. It induces proliferation as an intermediate response but decreases AP-activity and inorganic matrix production as a late response. In addition, expression levels of osteoblastic markers were strongly regulated (AP↓; Osteocalcin↓; Osteopontin↑; MGP↓; BMP 2↓; BSP2↓; OSF2↓; Osteoprotegerin↓; RANKL↑) towards an osteoclast recruiting phenotype. All effects were blocked by inhibition of Smad2/3 signaling with the Alk5-Inhibitor (SB431542). Interestingly, a rescue experiment showed that reduced AP-activities did not recover to base line levels, even 8 days after stopping the TGF-β(1) application.

CONCLUSIONS/SIGNIFICANCE

In spite of the initial positive effects on cell proliferation, it is questionable if continuous Smad2/3 phosphorylation is beneficial for bone healing, because decreased AP-activity and BMP2 levels indicate a loss of function of the osteoblasts. Thus, inhibition of Smad2/3 phosphorylation might positively influence functional activity of osteoblasts in patients with chronically elevated TGF-β(1) levels and thus, could lead to an improved bone healing in vivo.

Enhancement of bone morphogenetic protein-2-induced ectopic bone formation by transforming growth factor-β1

Bone morphogenetic proteins (BMPs) possess osteoinductive activities and are useful for clinical treatments, including bone regeneration. We found that transforming growth factor (TGF)-β1 strongly enhances the osteoinductive activity of BMP-2. Collagen sponges containing 5 μg of BMP-2 were implanted into mouse muscle tissues, after which lump-like masses appeared and grew until day 7. Subsequently, calcification occurred in the lump-like masses by day 14. Addition of 50 ng of TGF-β1 to the BMP-2-containing sponges markedly accelerated the growth of the lump-like masses and resulted in a fivefold increase in total bone volume as compared with BMP-2 alone. The number of osteoblasts in ectopic bone tissues at 14 days after implantation induced by BMP-2+TGF-β1 was twofold greater than that with BMP-2 alone, whereas the number of osteoclasts was decreased by half. On the other hand, TGF-β1 accelerated the differentiation of both osteoblasts and osteoclasts in the early stage (2-7 days after implantation) of ectopic bone formation. We also implanted collagen sponges into bone defects surgically created in mouse calvaria. Sponges containing 2.5 μg of BMP-2 and 25 ng of TGF-β1 caused complete filling of the defects with orthotopic bone, whereas those containing 2.5 μg of BMP-2 alone caused only partial filling. These results suggest that TGF-β1 enhances BMP-2-induced ectopic bone formation by accelerating the growth of lump-like masses, and regulates osteoblast and osteoclast generation. Our findings may contribute to the development of a new treatment method for skeletal disorders.

Do the adjacent level intervertebral discs degenerate after a lumbar spinal fusion? An experimental study using a rabbit model

STUDY DESIGN

A rabbit model of disc degeneration adjacent to a lumbar spinal fusion.

OBJECTIVE

To use a rabbit model to determine the long-term changes in the intervertebral discs at the levels above (cephalad) and below (caudad) 2 fused lumbar levels.

SUMMARY OF BACKGROUND DATA

Lumbar spinal fusion is generally carried out to eliminate motion at a specific lumbar level. However, it is commonly thought that by eliminating motion at a level, one increases the motion at the adjacent levels cephalad and caudad the fused levels. There have been studies that have reported on degeneration occurring at the cephalad and caudad levels adjacent to the fused levels.

METHODS

A total of 9 New Zealand white, female rabbits: 4 rabbits in the control group and 5 rabbits in the experimental group. The 5 rabbits in the experimental group underwent a posterolateral 2-level lumbar spinal fusion from L3 to L5. The changes in the lumbar discs were assessed using radiographs, magnetic resonance (MR) images, and histology at 6 months and 12 months.

RESULTS

The results at 6 months are less clear than those at 12 months. The results at 12 months for the experimental group are (1) the intervertebral disc height decreased at the caudad adjacent level and to a lesser extent at the cephalad adjacent level; (2) the MRI scores for the discs at the caudad and cephalad adjacent levels showed severe loss of signal intensity as compared to the discs at the same levels in the control group. This loss was more pronounced at the caudad level where the loss of signal intensity was similar to that seen at the fused levels; (3) the histologic analysis showed severe degenerative changes with a lack of live cells in the nucleus pulposus and in the endplate at the caudad adjacent level. At the cephalad level, live cells were apparent (albeit few) in the nucleus pulposus, and there was a more normal looking endplate with live cells.

CONCLUSION

The intervertebral discs at both the cephalad and the caudad levels adjacent to the 2 fused lumbar levels in this rabbit-model experiment carried out over 12 months after surgery showed degenerative changes asassessed using disc-height measurements, MR images, and histology, and the effect was more severe at the caudad adjacent level.

Extension of prior idiopathic scoliosis fusions to the sacrum: a matched cohort analysis of sixty patients with minimum two-year follow-up

STUDY DESIGN

Comparative study.

OBJECTIVE

To compare the radiographic and clinical outcomes of patients undergoing extension of a previous idiopathic scoliosis fusion to the sacrum using either autogenous bone graft or recombinant human bone morphogenetic protein-2 (rhBMP-2).

SUMMARY OF BACKGROUND DATA

Extension of an existing idiopathic scoliosis fusion to the sacrum for distal degeneration or sagittal imbalance has been associated with a high rate of pseudarthrosis. We hypothesized that rhBMP-2 could be successfully used as a substitute for distant autograft in this challenging population.

METHODS

Consecutive patients were identified from a single institution prospective database. The control group (autogenous harvesting without rhBMP-2, 1998-2002) included 24 of 25 patients with minimum 2-year follow-up while the study group (rhBMP-2 without distant autograft, 2002-2006) included 36 of 39 patients with minimum 2-year follow-up. Radiographs were measured using standard adult deformity criteria. Fusions were evaluated by independent observers using a published 4-point scale. Clinical outcomes were evaluated using Scoliosis Research Society and Oswestry Disability Index Questionnaires.

RESULTS

Groups were well matched with respect to demographic, radiographic, and surgical data with the following exceptions: the control group (autogenous graft, no BMP) was younger (43.5 vs. 49.8 years; P = 0.04), had more anterior levels fused (3.3 vs. 1.7; P = 0.01), more thoracoabdominal approaches (25% vs. 2.7%; P = 0.01), and greater estimated blood loss (1938 vs. 1221 mL; P = 0.01). There was 1 wound complication (deep infection) in each group. Rates of radiographic pseudarthrosis (11.1% vs. 20.8%) and revision for pseudarthrosis (5.6% vs. 12.5%) were lower in the rhBMP-2 group, although this did not reach statistical significance. Preoperative, postoperative, and improvements in Scoliosis Research Society and Oswestry Disability Index scores were similar between groups. We did not observe any increase in adverse events with the use of rhBMP-2.

CONCLUSION

BMP-2 is a safe and effective alternative to iliac or rib harvesting when extending an existing idiopathic scoliosis fusion to the sacrum.

Off-label use of bone morphogenetic proteins in the United States using administrative data

STUDY DESIGN

Epidemiological study using national administrative data.

OBJECTIVE

To evaluate the temporal trends in on-label and off-label bone morphogenetic protein (BMP) usage in primary and revision spine fusion by spine region and surgical approach, and nonspine applications in the United States from 2002 to 2007.

SUMMARY OF BACKGROUND DATA

The prevalence of BMP usage for spine fusion has been on the rise, but its use has not been stratified by surgical approach, particularly for lumbar fusion where it has only been Food And Drug Administration-approved for anterior lumbar interbody fusion (ALIF).

METHODS

The prevalence of BMP usage in the United States was evaluated using the Nationwide Inpatient Sample between October 1, 2002 and December 31, 2007. The Nationwide Inpatient Sample is the single largest all-payer inpatient care database in the United States. The principal procedure associated with BMP use was determined, and the prevalence of BMP use was calculated for various population subgroups.

RESULTS

A total of 340,251 inpatient procedures with BMP usage were identified. Between 2003 and 2007, the annual number of procedures involving BMP increased by 4.3-fold from 23,900 to 103,194. Spine fusion accounted for the vast majority (92.8%) of principal procedures with BMP. The predominant use of BMP was in primary posterior lumbar interbody fusion or transforaminal lumbar interbody fusion (PLIF/TLIF) (30.0%), followed by primary posterolateral spine fusion (20.4%), primary ALIF (16.6%), primary cervical fusions (13.6%), and primary thoracolumbar fusions (3.9%). Of primary ALIF with BMP, 19.3% did not involve the implantation of an interbody device.

CONCLUSION

At least 85% of principal procedures using BMP were for off-label applications. With uncertainty regarding the risks of using BMP in certain off-label applications, further research will be needed to better define the appropriate indications. Our study also demonstrates that disparities in the differential rates of BMP use exist in the spine fusion population.

Graft options in posterolateral and posterior interbody lumbar fusion

STUDY DESIGN

Review article, review of literature.

OBJECTIVE

To review the bone graft options that exist for posterolateral and posterior interbody lumbar fusion.

SUMMARY OF BACKGROUND DATA

As the number of lumbar fusion surgeries has increased over the last decade, alternative methods of grafting have been developed. Iliac crest autograft bone has traditionally been used for lumbar fusion. The downside to this graft option, however, is donor site morbidity.

METHODS

The current literature on alternatives to iliac crest autograft bone for obtaining lumbar fusion was reviewed.

RESULTS

Platelet gels, demineralized bone matrix, synthetic bone graft, and bone morphogenetic protein are potential options for bone graft supplementation or substitution. In preclinical studies, platelet gels have been beneficial to bone growth when combined with autograft, but clinical studies do not support the use of platelet gel in posterolateral lumbar fusion. Preclinical studies of demineralized bone matrix have shown significant variability in the osteoinductive properties of the available products, and clinical data showing efficacy is limited. The use of synthetic bone graft material (ceramics) in lumbar fusion surgery is increasing. Calcium phosphate compounds (i.e., beta-tricalcium phosphate and hydroxyapetite) are most commonly used and are often combined with type I collagen to form a matrix. These materials provide an osteoconductive scaffold for bony ingrowth and can be combined with bone marrow aspirate or used as a carrier for osteogenic factors. Bone morphogenetic protein (rhBMP-2) has been shown to provide similar or even increased fusion rates over autograft iliac crest bone. There are, however, potential safety concerns associated with the use of bone morphogenetic protein that are not fully understood.

CONCLUSION

Several alternatives to iliac crest autograft bone provide promising early clinical results in achieving posterolateral and posterior interbody lumbar fusion.

Luciferase labeling for multipotent stromal cell tracking in spinal fusion versus ectopic bone tissue engineering in mice and rats

Tissue engineering of bone, by combining multipotent stromal cells (MSCs) with osteoconductive scaffolds, has not yet yielded any clinically useful applications so far. The fate and contribution of the seeded cells are not sufficiently clarified, especially at clinically relevant locations. Therefore, we investigated cell proliferation around the spine and at ectopic sites using noninvasive in vivo bioluminescence imaging (BLI) in relation to new bone formation. Goat MSCs were lentivirally transduced to express luciferase. After showing both correlation between MSC viability and BLI signal as well as survival and osteogenic capacity of these cells ectopically in mice, they were seeded on ceramic scaffolds and implanted in immunodeficient rats at two levels in the spine for spinal fusion as well as subcutaneously. Nontransduced MSCs were used as a control group. All rats were monitored at day 1 and after that weekly until termination at week 7. In mice a BLI signal was observed during the whole observation period, indicating survival of the seeded MSCs, which was accompanied by osteogenic differentiation in vivo. However, these same MSCs showed a different response in the rat model, where the BLI signal was present until day 14, both in the spine and ectopically, indicating that MSCs were able to survive at least 2 weeks of implantation. Only when the signal was still present after the total implantation period ectopically, which only occurred in one rat, new bone was formed extensively and the implanted MSCs were responsible for this bone formation. Ectopically, neither a reduced proliferative group (irradiated) nor a group in which the cells were devitalized by liquid nitrogen and the produced extracellular matrix remained (matrix group) resulted in bone formation. This suggests that the release of soluble factors or the presence of an extracellular matrix is not enough to induce bone formation. For the spinal location, the question remains whether the implanted MSCs contribute to the bone regeneration or that the principal mechanism of MSC activity is through the release of soluble mediators.

rhBMP2/7 heterodimer: an osteoblastogenesis inducer of not higher potency but lower effective concentration compared with rhBMP2 and rhBMP7 homodimers

Heterodimeric bone morphogenetic proteins (BMPs) were exhibited to be more potent than and thus potential substitutes for homodimeric BMPs whose clinical application is limited for the drawbacks resulted from their higher effective doses. This study aims to delineate the biofunctional characteristics of recombinant human BMP2/7 (rhBMP2/7) heterodimer in inducing osteoblastogenesis of MC3T3-E1 through in vitro time-course and dose-response studies. rhBMP2/7 heterodimer induced cell migration with a significantly lower optimal concentration and higher peak effect than the respective homodimers. rhBMP2/7 heterodimer induced cell differentiation with significantly lower threshold concentrations but similar maximum effects. On day 28, the area of calcium depositions induced by 50 ng/mL rhBMP2/7 was 12- or 38-fold more than that of 50 ng/mL rhBMP2 or 50 ng/mL rhBMP7, respectively. The results indicated that rhBMP2/7 heterodimer was an osteoblastogenesis inducer of not higher potency but lower effective concentration compared with rhBMP2 and rhBMP7 homodimers.

Material properties and osteogenic differentiation of marrow stromal cells on fiber-reinforced laminated hydrogel nanocomposites

The fibrils in the bone matrix are glued together by extracellular matrix proteins to form laminated structures (osteons) to provide elasticity and a supportive substrate for osteogenesis. The objective of this work was to investigate material properties and osteogenic differentiation of bone marrow stromal (BMS) cells seeded on osteon-mimetic fiber-reinforced hydrogel/apatite composites. Layers of electrospun poly(l-lactide) fiber mesh coated with a poly(lactide-co-ethylene oxide fumarate) (PLEOF) hydrogel precursor solution were stacked and pressed together, and crosslinked to produce a laminated fiber-reinforced composite. Hydroxyapatite (HA) nanocrystals were added to the precursor solution to produce an osteoconductive matrix for BMS cells. Acrylamide-terminated Arg-Gly-Asp (RGD) peptide (Ac-GRGD) was conjugated to the PLEOF/HA hydrogel phase to promote focal point adhesion of BMS cells. Laminates were characterized with respect to the Young's modulus, degradation kinetics and osteogenic differentiation of BMS cells. The moduli of the laminates under dry and wet conditions were significantly higher than those of the fiber mesh and PLEOF/HA hydrogel, and within the range of values reported for wet human cancellous bone. At days 14 and 21, alkaline phosphatase (ALPase) activity of the laminates was significantly higher than those of the fiber mesh and hydrogel. Lamination significantly increased the extent of mineralization of BMS cells and laminates with HA and conjugated with RGD (Lam-RGD-HA) had 2.7-, 3.5- and 2.8-fold higher calcium content (compared to laminates without HA or RGD) after 7, 14 and 21days, respectively. The Lam-RGD-HA group had significantly higher expression of osteopontin and osteocalcin compared to the hydrogel or laminates without HA or RGD, consistent with the higher ALPase activity and calcium content of Lam-RGD-HA. Laminated osteon-mimetic structures have the potential to provide mechanical strength to the regenerating region as well as supporting the differentiation of progenitor cells to the osteogenic lineage.

Formation of Painful Seroma and Edema After the Use of Recombinant Human Bone Morphogenetic Protein-2 in Posterolateral Lumbar Spine Fusions

BACKGROUND

The use of bone morphogenetic proteins for fusion augmentation in spine surgery has increased dramatically in recent years. Information is continually emerging regarding the effectiveness and safety profile of these compounds.

OBJECTIVE

We have noted an increased incidence in sterile seroma formation and painful edema after the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) for posterolateral lumbar fusion. We present a retrospective review to determine the incidence of seroma formation and to discuss its clinical implications.

METHODS

We retrospectively reviewed the operative reports of patients who underwent posterolateral lumbar fusion with the addition of rhBMP-2. We identified all patients who required surgical exploration of a postoperative sterile seroma.

RESULTS

Of the 130 patients who underwent posterolateral lumbar fusion with rhBMP-2, 6 (4.6%) were returned to the operating room for exploration of a sterile seroma. The total amount of rhBMP-2 delivered to the posterolateral space per patient was 2.1 to 14.7 mg (mean, 8.4 mg per patient). The patients were returned to the operating room 5 to 13 days (mean, 7.7 days) after their initial surgery, and infection was ruled out in all cases by intraoperative cultures.

CONCLUSION

There seems to be an increased incidence of formation of sterile seroma and painful edema in the lumbar region after posterolateral fusion with rhBMP-2. This report, along with other series highlighting the potential complications of bone morphogenetic proteins, suggests that more caution should be used when these compounds are used. Further studies are required to better define the risks and benefits of using bone morphogenetic proteins for spine surgery.

Bone morphogenetic protein-2 and bone marrow aspirate with allograft as alternatives to autograft in instrumented revision posterolateral lumbar spinal fusion: a minimum two-year follow-up study

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

Compare the efficacy of rhBMP-2 and bone marrow aspirate with allograft (BMAA) as alternatives to autograft in instrumented revision posterolateral lumbar fusion (PLF).

SUMMARY OF BACKGROUND DATA

The use of autogenous bone graft is the current gold standard in revision PLF; however, this practice is associated with significant donor-site morbidity. Revision PLF pose the additional challenges of a less than ideal fusion environment and a limited quantity of autogenous bone graft. rhBMP-2 and BMAA have been shown to be acceptable bone graft substitutes in several primary orthopedic procedures. The role of these bone graft substitutes in instrumented revision PLF has yet to be determined.

METHODS

Sixty-two patients (125 levels) who underwent instrumented revision PLF with a minimum 2-year follow-up were included. Group 1 contained 24 patients (13 single- [group 1A] and 11 multilevel [group 1B]) who underwent instrumented revision PLF using rhBMP-2 on an absorbable collagen sponge. Group 2 included 18 patients (7 single- [group 2A] and 11 multilevel [group 2B]) with procedures using BMAA. Group 3 consisted of 20 patients (10 single- [group 3A] and 10 multilevel [group 3B]) with procedures using autograft. Demographic, surgical, and clinical data were collected from medical records. Time to solid fusion mass formation, fusion rate, complications, and clinical outcomes were evaluated. The progression of the fusion mass was evaluated by reviewing radiographs. A diagnosis of nonunion was based on exploration during an additional revision surgery or evidence of nonunion on dynamic radiographs or computerized tomography. Clinical outcomes were assessed using a visual analog scale (VAS) before surgery and at 6-week, 6-, 12-, and 24-month follow-ups.

RESULTS

Overall fusion rate was 93.5% (58/62). All single-level revision PLF achieved solid fusion. Groups 1B and 3B achieved 100% fusion, (11/11) and (10/10), respectively;whereas group 2B had a fusion rate of 63.6% (7/11). Group 1 also developed a solid fusion mass earlier than the other groups. There was a significant decrease between preoperative and 2-year postoperative VAS scores in all groups, but no significant difference among groups. Three patients in group 2 required an additional revision surgery.

CONCLUSION

rhBMP-2 may be an appropriate alternative to autogenous bone graft in both single- and multilevel revision PLF, whereas BMAA may be appropriate as a substitute in single-level revision PLF. The use of BMAA in single-level revisions may be a more cost-effective option than rhBMP-2.

Complications related to osteobiologics use in spine surgery: a systematic review

STUDY DESIGN

Systematic review.

OBJECTIVE

The objectives of this systematic review were to identify the character and rates of complications in patients after the use of BMP in spine fusion surgery and to determine whether there is a dose-response relationship of BMP with complications.

SUMMARY OF BACKGROUND DATA

BMP is used on-label for ALIF with LT-CAGE and off-label for various spine fusion applications in the cervical, thoracic, and lumbar spines because of its effectiveness in promoting arthrodesis. Multiple studies published over the past several years have highlighted complications associated with BMP in a variety of clinical fusion scenarios. There are no systematic reviews on this topic, and thus, the complication profile of off-label use or physician directed use of BMP in spinal fusion surgery is not well characterized. Some of the reported complications are unique to BMP, which underscores the need for this thorough literature review.

METHODS

A systematic review of the English language literature was performed for articles published between 1990 and June 2009. Electronic databases and reference lists of key articles were searched to identify articles examining the use of BMP in spine surgery. Two independent reviewers assessed the level of evidence using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria and disagreements were resolved by consensus.

RESULTS

Two hundred forty-' articles that assessed outcomes after BMP use in spinal surgery were identified from the literature; of these, 31 articles were selected for inclusion. We determined that multiple complications are associated after the use of rhBMP-2 in both cervical and lumbar spine fusion surgery. There is a mean incidence of 44%, 25%, and 27% of resorption, subsidence, and interbody cage migration reported for lumbar spine interbody fusion surgery although reoperation or long-term detrimental effect was rare. Cervical studies report a mean 5.8% of postoperative soft tissue problems, including dysphagia, when rhBMP-2 is used for ventral cervical fusion. It was determined that the strength of evidence of the peer-reviewed literature that report on types of complications is high for the lumbar and low for the cervical spine, respectively, and that the current strength of evidence on rates of complications with BMP is moderate and low, respectively.

CONCLUSION

The complication profile of BMP-2 for ALIF with LT-CAGE is well characterized. Because of the lack of substantive data, the same is not true for other types of lumbar fusions, or for cervical or thoracic fusion applications. BMP has been associated with a variety of unique complications in the ventral cervical and lumbar spines. The published data on BMP fail to precisely profile this product's use in fusion surgery; hence, it should be used only after a careful consideration of the relevant data. Well-designed and executed studies are necessary to completely define the incidence of various complications relative to type of BMP, type and region of fusion, surgical technique, dose, and carrier, and importantly, to define the natural history and management of associated complications.

Pseudarthrosis in multilevel anterior cervical fusion with rhBMP-2 and allograft: analysis of one hundred twenty-seven cases with minimum two-year follow-up

STUDY DESIGN

Consecutive case series.

OBJECTIVE

The purpose of this study was to analyze the pseudarthrosis rate in a large series of recombinant human bone morphogenetic protein-2 (rhBMP-2) augmented multilevel (> or =3 levels) anterior cervical fusions.

SUMMARY OF BACKGROUND DATA

The reported pseudarthrosis rate following anterior cervical fusion varies from 0% to 20% for single-level and up to 50% for multilevel fusions. It has been postulated that the use of rhBMP-2 may decrease the pseudarthrosis rate.

METHODS

A consecutive series of patients with cervical spondylosis and/or disc herniation who underwent anterior cervical fusion with rhBMP-2, structural allograft, and plate fixation with a minimum 2-year follow-up were analyzed by experienced, independent spine surgeons.

RESULTS

A total of 127 patients (54 men and 73 women with mean age of 54 +/- 10 years [range, 32-79]) were examined. Seventy-five (59.1%) patients underwent a 3-level fusion, 34 (26.7%) underwent a 4-level fusion, and 18 (14.2%) underwent a 5-level fusion. Of the 451 fusion segments, 14 segments (3.1%) in 13 of 127 patients (10.2%) had evidence of pseudarthrosis at 6 months following surgery. Of the 13 patients with a pseudarthrosis, 3 had a 3-level fusion (3/75 patients [4.0%]), 6 had a 4-level fusion (6/34 patients [17.4%]), and 4 had a 5-level fusion (4/18 patients [22.2%]). Five patients were asymptomatic and were not revised, but the remaining 8 patients required additional surgery. In 12 of 13 patients with a pseudarthrosis, the nonunion occurred at the lowest fusion level and at the cervicothoracic junction. The only statistically significant risk factor for developing a pseudarthrosis was the number of fusion levels.

CONCLUSION

In a large series of rhBMP-2 augmented multilevel fusions, the pseudarthrosis rate was 10.2% at 6 months following surgery. Since the risk of pseudarthrosis increases with the number of fusion levels, a long fusion lever arm may biomechanically overwhelm the biologic advantage of rhBMP-2. While rhBMP-2 is known to enhance fusion rates, it does not guarantee fusion in all situations.

Complications associated with the use of bone morphogenetic protein in pediatric patients

BACKGROUND

Recombinant human bone morphogenetic protein (rhBMP) has been found to be a powerful adjunct to healing nonunions and obtaining fusions. Despite the apparent clinical efficacy and good safety profile reported with rhBMP use in adults, there is little data regarding the safety of this product in pediatric patients. We evaluated the use of rhBMP-2 in pediatric patients to determine if any complications were associated with its use.

METHODS

We performed a retrospective review of 81 patients, all less then 18 years old, in whom rhBMP-2 was used. Theoretical complications associated with rhBMP-2 use were compiled based on a review of the published literature on rhBMP-2. A review of each patient's chart and radiographs was performed to record the occurrences of complications, which may have been associated with the use of rhBMP-2.

RESULTS

A total of 16 complications were found, which may have been attributed to the use of rhBMP-2. There were no incidences of systemic toxicity associated with rhBMP-2 use. Nine patients were noted to have some local operative site problem, 3 deep infections were noted, 1 patient was found to have a postoperative compartment syndrome, 2 patients were found to have neurologic complications (1 with progressive myelopathy and 1 with weakness and dural fibrosis), and 1 patient with neurofibromatosis and previously diagnosed intracranial gliomas was found to have subsequent enlargement of these gliomas. In reviewing these complications, only the case of dural fibrosis and subsequent weakness was thought to possibly be directly related to the use of rhBMP-2.

CONCLUSION

We found few complications in pediatric patients, which were felt to be directly attributable to the use of rhBMP-2. As such, rhBMP-2 use seems to be relatively safe in this young patient population. Due to the current use of this product in pediatric patients in an "off-label" fashion, we recommend a thorough discussion of the possible risks and benefits of this product with the family before its use.

LEVEL OF EVIDENCE

Therapeutic studies-Level IV.

Mid-term to long-term clinical and functional outcomes of minimally invasive correction and fusion for adults with scoliosis

Object

The goal of this study was to assess the operative outcomes of adult patients with scoliosis who were treated surgically with minimally invasive correction and fusion.

Methods

This was a retrospective study of 28 consecutive patients who underwent minimally invasive correction and fusion over 3 or more levels for adult scoliosis. Hospital and office charts were reviewed for clinical data. Functional outcome data were collected at each visit and at the last follow-up through self-administered questionnaires. All radiological measurements were obtained using standardized computer measuring tools.

Results

The mean age of the patients in the study was 67.7 years (range 22–81 years), with a mean follow-up time of 22 months (range 13–37 months). Estimated blood loss for anterior procedures (transpsoas discectomy and interbody fusions) was 241 ml (range 20–2000 ml). Estimated blood loss for posterior procedures, including L5–S1 transsacral interbody fusion (and in some cases L4–5 and L5–S1 transsacral interbody fusion) and percutaneous screw fixation, was 231 ml (range 50–400 ml). The mean operating time, which was recorded from incision time to closure, was 232 minutes (range 104–448 minutes) for the anterior procedures, and for posterior procedures it was 248 minutes (range 141–370 minutes). The mean length of hospital stay was 10 days (range 3–20 days). The preoperative Cobb angle was 22° (range 15–62°), which corrected to 7° (range 0–22°). All patients maintained correction of their deformity and were noted to have solid arthrodesis on plain radiographs. This was further confirmed on CT scans in 21 patients. The mean preoperative visual analog scale and treatment intensity scale scores were 7.05 and 53.5; postoperatively these were 3.03 and 25.88, respectively. The mean preoperative 36-Item Short Form Health Survey and Oswestry Disability Index scores were 55.73 and 39.13; postoperatively they were 61.50 and 7, respectively. In terms of major complications, 2 patients had quadriceps palsies from which they recovered within 6 months, 1 sustained a retrocapsular renal hematoma, and 1 patient had an unrelated cerebellar hemorrhage.

Conclusions

Minimally invasive surgical correction of adult scoliosis results in mid- to long-term outcomes similar to traditional surgical approaches. Whereas operating times are comparable to those achieved with open approaches, blood loss and morbidity appear to be significantly lower in patients undergoing minimally invasive deformity correction. This approach may be particularly useful in the elderly.