A comprehensive review of the safety profile of bone morphogenetic protein in spine surgery

BMP-2 gene-fibronectin-apatite composite layer enhances bone formation

Background

Safe and efficient gene transfer systems are needed for tissue engineering. We have developed an apatite composite layer including the bone morphogenetic protein-2 (BMP-2) gene and fibronectin (FB), and we evaluated its ability to induce bone formation.

Methods

An apatite composite layer was evaluated to determine the efficiency of gene transfer to cells cultured on it. Cells were cultured on a composite layer including the BMP-2 gene and FB, and BMP-2 gene expression, BMP-2 protein concentrations, alkaline phosphatase (ALP) activity, and osteocalcin (OC) concentrations were measured. A bone defect on the cranium of rats was treated with hydroxyapatite (HAP)-coated ceramic buttons with the apatite composite layer including the BMP-2 gene and FB (HAP-BMP-FB). The tissue concentration of BMP-2, bone formation, and the expression levels of the BMP-2, ALP, and OC genes were all quantified.

Results

The apatite composite layer provided more efficient gene transfer for the cultured cells than an apatite composite layer without FB. The BMP-2 concentration was approximately 100~600 pg/mL in the cell-culture medium. Culturing the cells on the apatite composite layer for 27 days increased ALP activity and OC concentrations. In animal experiments, the tissue concentrations of BMP-2 were over 100 pg/mg in the HAP-BMP-FB group and approximately 50 pg/mg in the control groups. Eight weeks later, bone formation was more enhanced in the HAP-BMP-FB group than in the control groups. In the tissues surrounding the HAP button, the gene expression levels of ALP and OC increased.

Conclusion

The BMP-2 gene-FB-apatite composite layer might be useful for bone engineering.

Safety and efficacy of rhBMP2 in posterior cervical spinal fusion for subaxial degenerative spine disease: Analysis of outcomes in 204 patients

Background:

Many studies offer excellent demonstration of the ability of bone morphogenic protein (BMP) to enhance fusion rates in anterior as well as posterior lumbar surgery. Recently, BMP has also been shown to increase arthrodesis rates in anterior cervical surgery, albeit with concomitant increases in complication rates. To date, however, few studies have investigated the safety and efficacy of BMP in cervical surgeries approached posteriorly.

Methods:

We retrospectively reviewed 204 consecutive patients with degenerative cervical spinal conditions necessitating posterior cervical fusion at a single institution over the past 4 years. The incidence of postoperative mechanical neck pain, fusion rates, as well as neurologic outcomes were compared between patients who received BMP vs those who did not receive BMP intraoperatively.

Results:

There were no significant differences in preoperative variables between the non-BMP vs the BMP cohorts. Over an average follow-up of 24.2 months, there were no significant differences between the two cohorts in duration of hospitalization, cerebrospinal fluid leakage, deep vein thrombosis, pulmonary embolism, hyperostosis, infection, pneumonia, hematoma, C5 palsy, wound dehiscence, reoperation rates, or Nurick/ASIA scores. Eleven (7.1%) patients in the non-BMP group experienced instrumentation failure vs none in the BMP group (P=0.06). Patients receiving BMP had a significantly increased rate of fusion by the chi-square test (P=0.01) and the log-rank test (P=0.02). However, patients receiving BMP also had the highest rates of recurrent/persistent neck pain by the chi-square test (P=0.003) and the log-rank test (P=0.01).

Conclusions:

To date, few studies have evaluated the safety and efficacy of BMP in the posterior cervical spine. Here, we show that BMP usage does not increase complication rates, but it significantly increases arthrodesis rates and also may increase the rate of recurrent/persistent neck pain.

Promoting fusion in minimally invasive lumbar interbody stabilization with low-dose bone morphogenic protein-2--but what is the cost?

BACKGROUND

Using bone morphogenic protein (BMP) to augment fusion in spine surgery is widespread and lends itself in particular to minimally invasive lumbar fusion, where the surface area for fusion is significantly less than the equivalent open procedure.

PURPOSE

Here we described the use of very low-dose BMP in promoting fusion in minimally invasive lumbar interbody fixation but also highlight some of the potential complications of BMP-2 use and techniques available to reduce or avoid them.

STUDY DESIGN

Prospective observational study of consecutive patients undergoing minimally invasive lumbar interbody fusion with percutaneous pedicle screws.

PATIENT SAMPLE

Thirty patients aged between 22 and 78 years (mean 53 years).

OUTCOME MEASURES

Thin-slice lumbar computed tomography scanning with multiplanar reconstruction at 6 and 12 months postoperative.

METHODS

Thirty-six spinal levels were instrumented in total, of which four underwent posterior lumbar interbody fusion and 32 underwent transforaminal lumbar interbody fusion. Bone graft harvested locally was placed in the disc space with low-dose BMP-2 (1.4 mg per level).

RESULTS

Thirty-three of 36 spinal levels showed complete fusion at a mean postoperative scan time of 7.1 months. Two levels demonstrated partial fusion at 6 months, which was complete at 12 months. There was one case of nonunion at 12 months, which also demonstrated vertebral body osteolysis. Despite very low-dose BMP-2, two cases of asymptomatic heterotopic ossification were observed, and there were two cases of perineural cyst formation, one of whom required revision of the interbody cage.

CONCLUSIONS

The use of BMP with autograft in the disc space during minimally invasive lumbar interbody fusion is associated with a high rate of early fusion. Even with very low-dose BMP used in this study, complications related to BMP usage were not avoided completely.

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.

Complications associated with recombinant human bone morphogenetic protein use in pediatric craniocervical arthrodesis

OBJECT

Management of pediatric occipitocervical instability remains especially challenging. The off-label use of recombinant human bone morphogenetic protein (rhBMP)-2 for spinal fusion has increased with a well-documented increase in fusion rate in many case series. Unfortunately, recent reports have documented complications associated with rhBMP use in adult spinal fusions. Complications associated with the use of rhBMP in pediatric spinal surgery is less well understood. In this study the authors report on the fusion rate and complications associated with rhBMP in pediatric occipitocervical arthrodesis.

METHODS

The authors reviewed the medical records of those patients 18 years old and younger who underwent dorsal occipitocervical fusion from January 2004 to December 2007 at the University of Iowa Hospitals and Clinics. Forty-eight patients were identified who received rhBMP-augmented fusion. The clinical outcome and complications of these fusions were analyzed.

RESULTS

All 48 patients had fusion confirmed on lateral radiographs within 4-14 months with an average fusion time of 6.7 months. There were 6 complications, 5 of which included seroma formation. Two of 5 patients who developed postoperative seroma presented with symptoms suggesting brainstem compression and obstructive hydrocephalus requiring emergency reoperation. One patient developed heterotopic bone formation causing cervicomedullary compression requiring reoperation.

CONCLUSIONS

The use of rhBMP to augment autograft in occipitocervical fusion allows for a high rate of successful arthrodesis, but is associated with potentially life-threatening complications in pediatric patients.

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.

Potent inhibition of heterotopic ossification by nuclear retinoic acid receptor-γ agonists

Heterotopic ossification consists of ectopic bone formation within soft tissues after surgery or trauma. It can have debilitating consequences, but there is no definitive cure. Here we show that heterotopic ossification was essentially prevented in mice receiving a nuclear retinoic acid receptor-γ (RAR-γ) agonist. Side effects were minimal, and there was no significant rebound effect. To uncover the mechanisms of these responses, we treated mouse mesenchymal stem cells with an RAR-γ agonist and transplanted them into nude mice. Whereas control cells formed ectopic bone masses, cells that had been pretreated with the RAR-γ agonist did not, suggesting that they had lost their skeletogenic potential. The cells became unresponsive to rBMP-2 treatment in vitro and showed decreases in phosphorylation of Smad1, Smad5 and Smad8 and in overall levels of Smad proteins. In addition, an RAR-γ agonist blocked heterotopic ossification in transgenic mice expressing activin receptor-like kinase-2 (ALK2) Q207D, a constitutively active form of the receptor that is related to ALK2 R206H found in individuals with fibrodysplasia ossificans progressiva. The data indicate that RAR-γ agonists are potent inhibitors of heterotopic ossification in mouse models and, thus, may also be effective against injury-induced and congenital heterotopic ossification in humans.

Delivery of lyophilized Nell-1 in a rat spinal fusion model

Nell-1 (Nel-like molecule-1; Nel: protein strongly expressed in neural tissue containing epidermal growth factor-like domain) is a promising osteoblast-specific growth factor for osteoinductive therapies that may circumvent adverse effects, such as nonspecific function and ectopic bone formation, associated with more established osteogenic growth factors such as bone morphogenetic proteins. Beta-tricalcium phosphate (beta-TCP), an osteoconductive, biodegradable ceramic biomaterial, has been used successfully to deliver osteoinducers for bone regeneration. The aim of this study was to develop a carrier system for efficiently delivering biologically active Nell-1 protein. After a 40% initial burst release, beta-TCP particles retained the majority of adsorbed Nell-1 protein in vitro. To test this system in vivo, L4/L5 spinal fusion was performed in three groups of rats (n = 8 each): (1) 5 microg Nell-1 in beta-TCP/demineralized bone matrix putty (DBX); (2) 2.5 microg Nell-1 in beta-TCP/DBX; (3) beta-TCP/DBX only. Fusion was assessed by radiography, palpation, microcomputed tomography, and histological analysis. After 4 weeks, 75% of Nell-1-treated animals exhibited fusion, with a significant increase in new bone volume, whereas only 25% of Nell-free control animals exhibited fusion. Our findings suggest that beta-TCP/DBX can increase both the biochemical stability and biological efficiency of Nell-1 protein.

Enhancement of bone formation in an experimental bony defect using ferumoxide-labelled mesenchymal stromal cells and a magnetic targeting system

We used interconnected porous calcium hydroxyapatite ceramic to bridge a rabbit ulnar defect. Two weeks after inducing the defect we percutaneously injected rabbit bone marrow-derived mesenchymal stromal cells labelled with ferumoxide. The contribution of an external magnetic targeting system to attract these cells into the ceramic and their effect on subsequent bone formation were evaluated. This technique significantly facilitated the infiltration of ferumoxide-labelled cells into ceramic and significantly contributed to the enhancement of bone formation even in the chronic phase. As such, it is potentially of clinical use to treat fractures, bone defects, delayed union and nonunion.

An alginate-based hybrid system for growth factor delivery in the functional repair of large bone defects

The treatment of challenging fractures and large osseous defects presents a formidable problem for orthopaedic surgeons. Tissue engineering/regenerative medicine approaches seek to solve this problem by delivering osteogenic signals within scaffolding biomaterials. In this study, we introduce a hybrid growth factor delivery system that consists of an electrospun nanofiber mesh tube for guiding bone regeneration combined with peptide-modified alginate hydrogel injected inside the tube for sustained growth factor release. We tested the ability of this system to deliver recombinant bone morphogenetic protein-2 (rhBMP-2) for the repair of critically-sized segmental bone defects in a rat model. Longitudinal μ-CT analysis and torsional testing provided quantitative assessment of bone regeneration. Our results indicate that the hybrid delivery system resulted in consistent bony bridging of the challenging bone defects. However, in the absence of rhBMP-2, the use of nanofiber mesh tube and alginate did not result in substantial bone formation. Perforations in the nanofiber mesh accelerated the rhBMP-2 mediated bone repair, and resulted in functional restoration of the regenerated bone. μ-CT based angiography indicated that perforations did not significantly affect the revascularization of defects, suggesting that some other interaction with the tissue surrounding the defect such as improved infiltration of osteoprogenitor cells contributed to the observed differences in repair. Overall, our results indicate that the hybrid alginate/nanofiber mesh system is a promising growth factor delivery strategy for the repair of challenging bone injuries.

Bone grafting options for lumbar spine surgery: a review examining clinical efficacy and complications

Background

Iliac crest harvest has been considered the “gold standard” at producing successful arthrodesis of the lumbar spine but is also associated with many donor-site morbidities. Many alternatives have been used to avoid iliac crest harvest, including autologous bone from other donor sites, allogeneic bone, ceramics, and recombinant human bone morphogenetic proteins (rhBMPs). This review will highlight the properties and preparations of these graft types and their potential complications and reported clinical efficacy.

Methods

A Medline search was conducted via PubMed by use of the following terms in various combinations: lumbar fusion, freeze-dried allograft, fresh-frozen allograft, autograft, iliac crest, demineralized bone matrix, rhBMP-2, rhBMP-7, scoliosis, bone marrow aspirate, HEALOS, coralline hydroxyapatite, beta tricalcium phosphate, synthetic, ceramics, spinal fusion, PLF, PLIF, ALIF, and TLIF. Only articles written in English were assessed for appropriate material. Related articles were also assessed depending on the content of articles found in the original literature search.

Conclusions

Although iliac crest remains the gold standard, reported success with alternative approaches, especially in combination, has shown promise. Stronger evidence with limited sources of potential bias is necessary to provide a clear picture of their clinical efficacy.

The role of NELL-1, a growth factor associated with craniosynostosis, in promoting bone regeneration

Efforts to enhance bone regeneration in orthopedic and dental cases have grown steadily for the past decade, in line with increasingly sophisticated regenerative medicine. To meet the unprecedented demand for novel osteospecific growth factors with fewer adverse effects compared with those of existing adjuncts such as BMPs, our group has identified a craniosynostosis-associated secreted molecule, NELL-1, which is a potent growth factor that is highly specific to the osteochondral lineage, and has demonstrated robust induction of bone in multiple in vivo models from rodents to pre-clinical large animals. NELL-1 is preferentially expressed in osteoblasts under direct transcriptional control of Runx2, and is well-regulated during skeletal development. NELL-1/Nell-1 can promote orthotopic bone regeneration via either intramembranous or endochondral ossification, both within and outside of the craniofacial complex. Unlike BMP-2, Nell-1 cannot initiate ectopic bone formation in muscle, but can induce bone marrow stromal cells (BMSCs) to form bone in a mouse muscle pouch model, exhibiting specificity that BMPs lack. In addition, synergistic osteogenic effects of Nell-1 and BMP combotherapy have been observed, and are likely due to distinct differences in their signaling pathways. NELL-1's unique role as a novel osteoinductive growth factor makes it an attractive alternative with promise for future clinical applications. [Note: NELL-1 and NELL-1 indicate the human gene and protein, respectively; Nell-1 and Nell-1 indicate the mouse gene and protein, respectively.]

Absence of bone morphogenetic protein-2 in human breast milk after spinal surgery

BACKGROUND CONTEXT

Bone morphogenetic protein-2 (BMP-2) has been used extensively in recent years to enhance the process of spinal fusion. However, numerous side effects have been reported. This raises concerns regarding the safety of using this material in human beings. There are no published reports, that we are aware of, that demonstrate detectable levels of BMP-2 in human milk.

PURPOSE

The purpose of this study was to determine the presence/absence of recombinant human bone morphogenetic protein-2 (rhBMP-2) in milk samples taken from a patient who underwent spinal surgery using rhBMP-2 shortly after delivering a child.

STUDY DESIGN/SETTING

The study design comprises a case report dealing with analyzing milk from a patient who underwent spinal surgery using rhBMP-2 shortly after delivering a child.

METHODS

We report the analysis of milk samples from a patient who underwent spinal surgery using rhBMP-2 shortly after delivering a child to determine the presence/absence of rhBMP-2. The milk samples were taken before and after the spinal surgery. Enzyme-linked immunosorbent assays were performed repeatedly to the samples.

RESULTS

The standard curve for the assay had an r(2) value of 0.9853 indicating an acceptable degree of statistical reliability. The dose range for the standard curve was 62.5 to 2,000 pg/mL. None of the samples had an optical density greater than that of the lowest standard.

CONCLUSIONS

No rhBMP-2 was detected in human milk in this single case report. Although this result seemed promising, it did not eliminate the concern regarding the potential risk of rhBMP-2 on child development. We still need further studies including more cases to verify this conclusion.

The role of simvastatin in the osteogenesis of injectable tissue-engineered bone based on human adipose-derived stromal cells and platelet-rich plasma

An injectable tissue-engineered bone (ITB) composed of human adipose-derived stromal cells (hADSCs) and platelet-rich plasma (hPRP) was preliminarily constructed, but its osteogenic capability needs improving. This study aimed to evaluate if simvastatin can be applied as a bone anabolic agent for this ITB. We found 0.01 microm, 0.1 microm, and 1 microm simvastatin could induce hADSCs' osteoblastic differentiation in vitro that accompanied with non-inhibition on cell proliferation, high alkaline phosphatase activity, more mineralization deposition and more expression of osteoblast-related genes such as osteocalcin, core binding factor alpha1, bone morphogenetic protein-2, vascular endothelial growth factor, and basic fibroblast growth factor. Simvastatin at 1 mum seemed the most optimal concentration due to its high osteocalcin secretion in media (P < 0.01). Quantitative mineralization assay also showed 1 microm SIM had the most obvious synergistic effect on hPRP's induction for matrix mineralization of hADSCs (P < 0.01). When 1 microm Simvastatin was applied to this ITB to restore the critical-sized calvarial defects in mice, more bone formation was observed in defected regions, and the peripheries just outside the defect margins by X-ray analysis, and H&E staining. These findings indicate that simvastatin at optimal concentrations can be used to promote this ITB's osteogenesis. However, simvastatin's effects on this ITB await long-term investigation.

Bone morphogenetic proteins in critical-size bone defects: what are the options?

The recent development of new orthopaedic devices and advanced techniques for soft-tissue reconstruction have clearly improved the outcome in trauma and orthopaedic surgery. Nevertheless, large bone defects are still difficult to treat and require a careful analysis of the situation. Individual planning of the reconstructive strategy is desirable. Bone morphogenetic proteins (BMPs) have successfully been applied in the clinical setting for the treatment of spinal fusion, fracture healing and delayed and non-unions. Following the 'diamond concept', surgeons have begun using BMPs for treatment of critical-size defects also--in most cases, 'off label'; different treatment strategies are currently being evaluated. BMPs are often used in combination with autogenic, allogenic, xenogenic or synthetic grafting materials and even with mesenchymal stem cells. In addition, gene therapy approaches present an attractive option. Experimental studies and first clinical results are promising in the use of BMPs for treatment of critical-size defects; however, there is obvious need for further controlled studies to define strategies.

Complications of recombinant human BMP-2 for treating complex tibial plateau fractures: a preliminary report

Bone morphogenic proteins (BMPs) are potent osteoinductive agents. Their use in fracture surgery is still being studied and the clinical indications are evolving. Heterotopic bone after BMP use in spine surgery is a known complication. While some literature describes the ability of BMP to enhance fracture healing, few articles describe complications of BMP. In tibial plateau fractures, after elevating the cartilage en mass, a subchondral void may be created in these fractures. Structural support provided by bone void-filling agents can be augmented with osteoinduction achieved by BMP. We asked whether heterotopic bone formation would occur more frequently with BMP-2 when used in tibial plateau fractures and whether BMP-2 enhanced the ability to maintain surgically restored subchondral bone integrity. Heterotopic bone developed more frequently in patients receiving BMP (10 of 17) than in patients not receiving BMP (one of 23). Four patients receiving BMP and no patients not receiving BMP underwent removal of heterotopic bone. Maintenance of subchondral bone integrity was similar without and with the use of BMP. BMP is a potent osteoinductive agent; however, when used for an off-label indication in periarticular situations, complications such as heterotopic bone are common and increase reoperation rates.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Screw fixation of the upper cervical spine in the pediatric population. Clinical article

OBJECT

Rigid fixation of the upper cervical spine has become an established method of durable stabilization for a variety of craniocervical pathological entities in children. In children, specifically, the use of C1-2 transarticular screws has been proposed in recent literature to be the gold standard configuration for pathology involving these levels. The authors reviewed the use of rigid fixation techniques alternative to C1-2 transarticular screws in children. Factors evaluated included ease of placement, complications, and postoperative stability.

METHODS

Seventeen patients, ranging in age from 3 to 17 years (mean 9.6 years), underwent screw fixation involving the atlas or axis for a multitude of pathologies, including os odontoideum, Down syndrome, congenital instability, iatrogenic instability, or posttraumatic instability. All patients had preoperative instability of the occipitocervical or atlantoaxial spine demonstrated on dynamic lateral cervical spine radiographs. All patients also underwent preoperative CT scanning and MR imaging to evaluate the anatomical feasibility of the selected hardware placement. Thirteen patients underwent C1-2 fusion, and 4 underwent occipitocervical fusion, all incorporating C-1 lateral mass screws, C-2 pars screws, and/or C-2 laminar screws within their constructs. Patients who underwent occipitocervical fusion had no instrumentation placed at C-1. One patient's construct included sublaminar wiring at C-2. All patients received autograft onlay either from from rib (in 15 patients), split-thickness skull (1 patient), or local bone harvested within the operative field (1 patient). Nine patients' constructs were supplemented with recombinant human bone morphogenetic protein at the discretion of the attending physician. Eight patients had surgical sacrifice of 1 or both C-2 nerve roots to better facilitate visualization of the C-1 lateral mass. One patient was placed in halo-vest orthosis postoperatively, while the rest were maintained in rigid collars.

RESULTS

All 17 patients underwent immediate postoperative CT scanning to evaluate hardware placement. Follow-up was achieved in 16 cases, ranging from 2 to 39 months (mean 14 months), and repeated dynamic lateral cervical spine radiography was performed in these patients at the end of their follow-up period. Some, but not all patients, also underwent delayed postoperative CT scans, which were done at the discretion of the treating attending physician. No neurovascular injuries were encountered, no hardware revisions were required, and no infections were seen. No postoperative pain was seen in patients who underwent C-2 nerve root sacrifice. Stability was achieved in all patients postoperatively. In all patients who underwent delayed postoperative CT scanning, the presence of bridging bone was shown spanning the fused levels.

CONCLUSIONS

Screw fixation of the atlas using lateral mass screws, in conjunction with C-2 root sacrifice in selected cases, and of the axis using pars or laminar screws is a safe method for achieving rigid fixation of the upper cervical spine in the pediatric population.