Bone morphogenetic protein and cancer in spinal fusion: a propensity score-matched analysis

OBJECTIVE

Bone morphogenetic protein (BMP) has been increasingly used in spinal surgery to promote arthrodesis. Because BMP stimulates cellular proliferation, its association with tumorigenesis is a concern. Previous research has generated conflicting conclusions on the risk of cancer in patients receiving BMP. The authors aimed to compare the incidence of solid organ and hematopoietic malignancies in patients undergoing spinal arthrodesis with or without BMP.

METHODS

The PearlDiver Mariner Patient Claims Database was queried for patients undergoing thoracolumbar fusion between 2015 and 2021. Patients with preexisting malignancy were excluded. Data were analyzed for incidence of solid organ malignancy and hematopoietic malignancy diagnosed after spinal surgery. Propensity score matching using age, sex, tobacco usage, and year of surgery was performed between patients who did and those who did not receive BMP.

RESULTS

Among patients without prior solid organ malignancy, BMP was used in 22,139 patients and not used in 306,249. In the propensity score-matched group, 3.1% of the BMP group developed solid organ malignancy following surgery compared with 3.5% in the non-BMP group. The relative risk (RR) of developing solid organ malignancy after BMP exposure was 0.89 (95% CI 0.81-0.98, p = 0.02). Among patients without prior hematopoietic malignancy, BMP was used in 23,505 patients and not used in 328,796 patients. In the propensity score-matched group, 0.4% of the BMP group developed hematopoietic malignancy compared with 0.6% of the non-BMP group. The RR of developing hematopoietic malignancy after BMP exposure was 0.71 (95% CI 0.55-0.93, p = 0.015).

CONCLUSIONS

BMP use in thoracolumbar fusion was not associated with an increased risk of new malignancy, which further supports emerging data on the lack of an association between BMP use and increased malignancy.

Postoperative Lumbar Fusion Bone Morphogenic Protein-Related Epidural Cyst Formation

Bone morphogenetic protein is broadly used in spinal surgery to enhance fusion rates. Several complications have been associated with the use of bone morphogenetic protein, including postoperative radiculitis and pronounced bone resorption/osteolysis. Bone morphogenetic protein-related epidural cyst formation may represent another complication that has not been described aside from limited case reports. In this case series, we retrospectively reviewed imaging and clinical findings of 16 patients with epidural cysts on postoperative MR imaging following lumbar fusion. In 8 patients, mass effect on the thecal sac or lumbar nerve roots was noted. Of these, 6 patients developed new postoperative lumbosacral radiculopathy. During the study period, most patients were managed conservatively, and 1 patient required revision surgery with cyst resection. Concurrent imaging findings included reactive endplate edema and vertebral bone resorption/osteolysis. Epidural cysts had characteristic findings on MR imaging in this case series and may represent an important postoperative complication in patients following bone morphogenetic protein-augmented lumbar fusion.

Complications Associated With Bone Morphogenetic Protein in the Lumbar Spine

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

[Bone morphogenetic proteins (BMP): clinical application for reconstruction of bone defects]

Since the introduction of bone morphogenetic proteins, their use has become an invaluable ally for the treatment of bone defects. These proteins are potent growth factors, related to angiogenic and osteogenic activity. The osteoinductive capacity of recombinant bone morphogenetic protein (rhBMP) in the formation of bone and cartilage has been confirmed in in vitro studies and evaluated in clinical trials. To obtain a therapeutic effect, administration is systemic, by injection over the physiological dose. Among the disadvantages, ectopic bone formation or high morbidity in cases of spinal fusion is observed. In this review, the roles of bone morphogenetic proteins in bone repair and clinical applications are analyzed. These findings represent advances in the study of bone regeneration and application of growth factors for more predictable results.

Local rhBMP-12 on an Absorbable Collagen Sponge as an Adjuvant Therapy for Rotator Cuff Repair - A Phase 1, Randomized, Standard of Care Control, Multicenter Study: Safety and Feasibility

BACKGROUND

Recombinant human bone morphogenetic protein-12 (rhBMP-12) has been shown to induce tendon and ligament formation in rats and to improve tendon healing; however, the safety and feasibility of implanting rhBMP-12/absorbable collagen sponge (ACS) in humans are not known.

PURPOSE

To investigate the safety and feasibility of rhBMP-12 on an ACS as an adjuvant therapy in open rotator cuff repair.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

This study consisted of 20 patients with full-thickness rotator cuff tears. Patients were randomized either to standard of care (SOC) treatment (open rotator cuff repair) or to receive 0.015 mg/mL rhBMP-12/ACS and SOC treatment during their open rotator cuff repair (rhBMP-12/ACS group) at a rate of 1/4 SOC/rhBMP-12/ACS. The feasibility of implanting the product and the safety of the product were evaluated during the 1-year follow-up period. The evaluation involved up to 10 postoperative visits, which included physical examinations, radiographs, computed tomography (CT) scans, magnetic resonance imaging (MRI) scans with an emphasis on heterotopic ossification (HO), pharmacokinetics, immunogenicity, laboratory evaluations, and local and systemic adverse events at specified time points.

RESULTS

Small amounts of HO were seen on follow-up CT scans in 10 of 16 patients in the rhBMP-12/ACS group and in 2 of 3 patients in the SOC group. HO did not increase at 26 weeks and was not associated with any adverse events or unsatisfactory clinical outcomes. Pharmacokinetics demonstrated that circulating levels of rhBMP-12 were not detectable after administration. Five of 16 patients showed a postoperative immunogenic response but did not show any correlating adverse events. Complete healing of the rotator cuff was observed in 14 of 16 patients; 2 of 16 imaging results could not be analyzed because of artifacts in the rhBMP-12 group on MRI scans. In the SOC group, 1 of 4 patients showed a retear at 12 weeks after surgery.

CONCLUSION

The use of rhBMP-12/ACS has been shown to be feasible and safe in a concentration of 0.015 mg/mL when used in open rotator cuff repair. Higher dose concentrations of rhBMP-12 should be evaluated in the future to evaluate their safety and potential to increase rotator cuff healing after open surgical repair.

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

BACKGROUND CONTEXT

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

PURPOSE

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

STUDY DESIGN/SETTING

Administrative database study.

PATIENT SAMPLE

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

OUTCOME MEASURES

Revision rates and postoperative complications.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Allogeneic morphogenetic protein vs. recombinant human bone morphogenetic protein-2 in lumbar interbody fusion procedures: a radiographic and economic analysis

BACKGROUND

Since the introduction of rhBMP-2 (Infuse) in 2002, surgeons have had an alternative substitute to autograft and its related donor site morbidity. Recently, the prevalence of reported adverse events and complications related to the use of rhBMP-2 has raised many ethical and legal concerns for surgeons. Additionally, the cost and decreasing reimbursement landscape of rhBMP-2 use have required identification of a viable alternative. Osteo allogeneic morphogenetic protein (OsteoAMP) is a commercially available allograft-derived growth factor rich in osteoinductive, angiogenic, and mitogenic proteins. This study compares the radiographic fusion outcomes between rhBMP-2 and OsteoAMP allogeneic morphogenetic protein in lumbar interbody fusion spine procedures.

METHODS

Three hundred twenty-one (321) patients from three centers underwent a transforaminal lumbar interbody fusion (TLIF) or lateral lumbar interbody fusion (LLIF) procedure and were assessed by an independent radiologist for fusion and radiographically evident complications. The independent radiologist was blinded to the intervention, product, and surgeon information. Two hundred and twenty-six (226) patients received OsteoAMP with autologous local bone, while ninety-five (95) patients received Infuse with autologous local bone. Patients underwent radiographs (x-ray and/or CT) at standard postoperative follow-up intervals of approximately 1, 3, 6, 12, and 18 months. Fusion was defined as radiographic evidence of bridging across endplates, or bridging from endplates to interspace disc plugs. Osteobiologic surgical supply costs were also analyzed to ascertain cost differences between OsteoAMP and rhBMP-2.

RESULTS

OsteoAMP produced higher rates of fusion at 6, 12, and 18 months (p ≤ 0.01). The time required for OsteoAMP to achieve fusion was approximately 40% less than rhBMP-2 with approximately 70% fewer complications. Osteobiologic supply costs were 80.5% lower for OsteoAMP patients (73.7% lower per level) than for rhBMP-2.

CONCLUSIONS

Results of this study indicate that OsteoAMP is a viable alternative to rhBMP-2 both clinically and economically when used in TLIF and LLIF spine procedures.

Could an osteoinductor result in degeneration of a neurofibroma in NF1?

We report a case of fatal evolution of neurofibromatosis in a young boy. A laminectomy was performed when he was 9 years old. A secondary hyperkyphosis led to many surgeries resulting in recurrent malunions. When he was 23 years old, a breakage of his rods was treated by a new instrumentation and a T12-L1 interbody cage fitted with rh-BMP. Five months later, he developed a huge posterior tumour on his back. The biopsy diagnosed a neurofibrosarcoma. The growth of the tumour was extremely rapid. He died after several months from a septic shock. NF1 is characterised by neurofibromas that have a possibility of malign degeneration and conversion to a sarcoma. However, the chronology, rapidity of evolution and the exceptional volume of the tumour made us wonder whether the BMP had a part of responsibility as osteoinductor in the malignant degeneration, in this particular case, of neurofibromatosis. It seemed important to point out this case to the medical community.

Prevalence, complications, and hospital charges associated with use of bone-morphogenetic proteins in spinal fusion procedures

CONTEXT

No national data exist to examine use of bone-morphogenetic proteins (BMPs) in spinal fusion surgery.

OBJECTIVE

To determine the patterns of use and rates of complications and financial charges associated with BMP use in spinal fusion nationally.

DESIGN, SETTING, AND PATIENTS

Retrospective cohort study of 328,468 patients undergoing spinal fusion procedures from 2002-2006 identified from the Nationwide Inpatient Sample database, a 20% sample of US community hospitals.

MAIN OUTCOME MEASURES

The rates of use of BMP among patients undergoing spinal fusion procedures are examined along with complications, length of stay, and hospital charges associated with use of this fusion adjunct.

RESULTS

The nationwide usage of BMP has increased from 0.69% of all fusions in 2002 to 24.89% of all fusions in 2006. Use of BMP varied by patient sex, race, and primary payer with increased use seen in women (56.26% with BMP vs 53.35% without BMP; odds ratio [OR], 1.12; 95% confidence interval, [CI], 1.09-1.16) and Medicare patients (29.62% with BMP vs 27.16% without BMP; OR, 1.43; 95% CI, 1.31-1.56) and decreased use in nonwhite patients (8.69% with BMP vs 10.23% without BMP; OR, 0.80; 95% CI, 0.75-0.85). When comparing immediate postoperative, in-hospital rates of complications for the year 2006 among patients undergoing spinal fusion by BMP use status, no differences were seen for lumbar, thoracic, or posterior cervical procedures. On univariate analysis and after multivariable adjustment, the use of BMP in anterior cervical fusion procedures was associated with a higher rate of complication occurrence (7.09% with BMP vs 4.68% without BMP; adjusted OR, 1.43; 95% CI, 1.12-1.70) with the primary increases seen in wound-related complications (1.22% with BMP vs 0.65% without BMP; adjusted OR, 1.67; 95% CI, 1.10- 2.53) and dysphagia or hoarseness (4.35% with BMP vs 2.45% without BMP; adjusted OR, 1.63; 95% CI, 1.30-2.05). Bone-morphogenetic protein use was associated with greater inpatient hospital charges across all categories of fusion. Increases between 11% and 41% of total hospital charges were reported, with the greatest percentage increase seen for anterior cervical fusion.

CONCLUSION

Bone-morphogenetic protein was used in approximately 25% of all spinal fusions nationally in 2006, with use associated with more frequent complications for anterior cervical fusions and with greater hospital charges for all categories of fusions.

Doses of drugs in devices

Recent experiences with active molecules in spinal fusion devices points to the need to be cautious with dosing regimes and the use of products in off-label situations.

Vertebral osteolysis after posterior interbody lumbar fusion with recombinant human bone morphogenetic protein 2: a report of five cases

BACKGROUND

Recombinant human bone morphogenetic protein 2 (rh-BMP-2) is frequently used in an off-label fashion. Its application for posterior interbody fusion appears intuitive because its use obviates the need for iliac crest bone graft and shows higher fusion rates than with the use of local autologous bone graft. To date, there is no report of adverse outcomes with such use of rh-BMP-2.

PURPOSE

To draw attention to this unusual complication of posterior interbody lumbar fusion and to review the relevant literature.

STUDY DESIGN

Clinical report of five cases of vertebral osteolysis that developed postoperatively from lumbar transforaminal interbody fusion of the L5/S1 motion segment using cages and rh-BMP-2.

METHODS

Sixty-eight patients underwent transforaminal lumbar interbody fusion for spondylolisthesis or degenerative disc disease with discogenic back pain. Five of these 68 patients developed vertebral osteolysis within 4 months from their surgery. Their clinical presentation and radiographic findings are presented in this case series.

RESULTS

Each one of these five patients had uneventful surgery and postoperative recovery. Their back and leg pain improved in the immediate postoperative period. However, each patient reported worsening back pain with variable radicular pain as early as 4 weeks and as late as 3 months after the index procedure. Diagnostic workup revealed evidence of vertebral osteolysis typically involving the L5 vertebral body. In all five patients, osteolytic defects filled in spontaneously, and symptoms typically resolved within an additional 3 months of nonoperative care.

CONCLUSIONS

Vertebral osteolysis can occur with the use of rh-BMP-2 in posterior lumbar interbody fusions. Violation of the end plate during decortication may be a contributing factor. Symptoms often resolve spontaneously.

Ectopic ossification of the triceps muscle after application of bone morphogenetic protein-7 to the distal humerus for recalcitrant nonunion: a case report

We report a case of triceps muscle ectopic ossification and resultant elbow stiffness after application of recombinant human bone morphogenetic protein to a distal humerus nonunion site. We recommend caution when using this product in the upper extremity in regions where there is close approximation of soft tissue to bone and where loss of motion would be problematic.

Complications of anterior cervical discectomy and fusion using recombinant human bone morphogenetic protein-2

The use of bone morphogenetic protein-2 (rhBMP-2) in spinal fusion has increased dramatically since an FDA approval for its use in anterior lumbar fusion with the LT cage. There are several reports of its use in transforaminal lumbar interbody fusion, posterolateral fusion, and anterior cervical fusion. Reports on adverse effects of rhBMP-2 when used in spinal fusion are scarce in literature. An Institutional Review Board approved retrospective study was conducted in patients undergoing anterior spinal fusion and instrumentation following diskectomy at a single center. Forty-six consecutive patients were included. Twenty-two patients treated with rhBMP-2 and PEEK cages were compared to 24 in whom allograft spacers and demineralized bone matrix was used. Patients filled out Cervical Oswestry Scores, VAS for arm pain, neck pain, and had radiographs preoperatively as well at every follow up visit. Radiographic examination following surgery revealed end plate resorption in all patients in whom rhBMP-2 was used. This was followed by a period of new bone formation commencing at 6 weeks. In contrast, allograft patients showed a progressive blurring of end plate-allograft junction. Dysphagia was a common complication and it was significantly more frequent and more severe in patients in whom rhBMP-2 was used. Post operative swelling anterior to the vertebral body on lateral cervical spine X-ray was significantly larger in the rhBMP-2 group when measured from 1 to 6 weeks after which it was similar. These effects are possibly due to an early inflammatory response to rhBMP-2 and were observed to be dose related. With the parameters we used, there was no significant difference in the clinical outcome of patients in the two groups at 2 years. The cost of implants in patients treated with rhBMP-2 and PEEK spacers was more than three times the cost of allograft spacers and demineralized bone matrix in 1, 2, and 3-level cases. Despite providing consistently good fusion rates, we have abandoned using rhBMP-2 and PEEK cages for anterior cervical fusion, due to the side effects, high cost, and the availability of a suitable alternative.

Adverse swelling associated with use of rh-BMP-2 in anterior cervical discectomy and fusion: a case study

BACKGROUND CONTEXT

The use of recombinant bone morphogenetic protein-2 (rh-BMP-2) is effective in augmenting lumbar spinal fusions. A safe, effective dosage of rh-BMP-2 in the cervical spine has yet to be determined. Use of rh-BMP-2 is currently being evaluated and is only indicated for use in the cervical spine on Investigational Device Exempt cases.

PURPOSE

To present a potentially serious adverse event that may occur when using rh-BMP-2 in cervical spine surgery.

STUDY DESIGN

An emergent sequence of events including physical examination, radiographic studies, intubation, and surgical exploration were performed upon arrival to the emergency department.

METHODS

We report a case of a 54-year-old male patient presenting with neck swelling and difficulty swallowing 5 days after anterior cervical discectomy and fusion (ACDF) using rh-BMP-2.

RESULTS

The patient was found to have massive neck swelling including the pharyngeal tissue. The patient was admitted to the intensive care unit where parenteral steroids were administered for 24 hours during monitored intubation. The patient was extubated on the second hospital day and discharged home on the fourth hospital day after swelling subsided.

CONCLUSIONS

Caution should be exercised with rh-BMP-2 use in ACDF surgery as the correct dose and technique for application is not yet determined. Respiratory distress and dysphagia may result secondary to rh-BMP-2 induced anterior neck swelling.

Hematopoietic stem-cell contribution to ectopic skeletogenesis

BACKGROUND

Fibrodysplasia ossificans progressiva is a rare genetic disorder of ectopic skeletogenesis associated with dysregulation of bone morphogenetic protein (BMP) signaling. Hematopoietic cells have been implicated in the ectopic skeletogenesis of fibrodysplasia ossificans progressiva, and their replacement has been postulated as a possible cure. However, the definitive contribution of hematopoietic cells to the pathogenesis of ectopic skeletogenesis remains obscure.

METHODS

We employed both careful clinical observation and in vivo murine transplantation studies to more precisely determine the contribution of hematopoietic cells to ectopic skeletogenesis. We identified a patient with fibrodysplasia ossificans progressiva who had undergone bone marrow transplantation for the treatment of intercurrent aplastic anemia twenty-five years earlier and investigated whether the clinical course of the fibrodysplasia ossificans progressiva had been influenced by bone marrow replacement or immunosuppression, or both. In complementary studies, we transplanted hematopoietic stem cells from constitutively expressing LacZ transgenic mice to identify the contribution of hematopoietic cells to BMP4-induced heterotopic ossification, a histopathologic model of fibrodysplasia ossificans progressiva.

RESULTS

We found that replacement of hematopoietic cells was not sufficient to prevent ectopic skeletogenesis in the patient with fibrodysplasia ossificans progressiva but pharmacologic suppression of the apparently normal donor immune system following transplantation in the new host modulated the activity of the fibrodysplasia ossificans progressiva and diminished the expression of skeletal ectopia. In complementary murine transplantation studies, we found that cells of hematopoietic origin contributed to the early inflammatory and late marrow-repopulating stages of BMP4-induced heterotopic ossification but were not represented in the fibroproliferative, chondrogenic, or osteogenic stages of heterotopic ossification. Interestingly, both recombinant human BMP4 induction in an animal model and the dysregulated BMP signaling pathway in a patient with fibrodysplasia ossificans progressiva were sufficient to recruit at least two populations of cells, one of hematopoietic origin and at least one of non-hematopoietic origin, that contribute to the formation of an ectopic skeleton.

CONCLUSIONS

Taken together, these findings demonstrate that bone marrow transplantation did not cure fibrodysplasia ossificans progressiva in the patient in this study, most likely because the hematopoietic cell population is not the site, or at least not the dominant site, of the intrinsic dysregulation of the BMP signaling pathway in fibrodysplasia ossificans progressiva. However, following transplantation of bone marrow from a presumably normal donor, immunosuppression of the immune system appeared to ameliorate activation of ectopic skeletogenesis in a genetically susceptible host. Thus, cells of hematopoietic origin may contribute to the formation of an ectopic skeleton, although they are not sufficient to initiate the process alone.

Vertebral bone resorption after transforaminal lumbar interbody fusion with bone morphogenetic protein (rhBMP-2)

OBJECTIVE

Bone morphogenetic protein (rhBMP-2) has demonstrated an increased rate of interbody fusion when placed in the intervertebral space. Owing to this advantage, rhBMP-2 is being implanted with increasing frequency in the lumbar spine. The purpose was to quantify and describe the presence of bone resorption within the vertebral body after transforaminal lumbar interbody fusion with placement of rhBMP-2 within the disc space.

METHODS

Twenty-six patients were selected from a clinical database. Patients included in the study had undergone a transforaminal lumbar interbody fusion with BMP. Interbody implants included allograft dowels or interbody cages augmented with autograft or allograft bone. A computed tomography study of the lumbar spine a minimum of 3-month postoperatively was another inclusion criterion. Osteolytic defects were grouped into 3 categories on the basis of the size and extent of involvement in the vertebral body.

RESULTS

A total of 32 lumbar levels were reviewed. Fourteen males and 12 females with an average age of 46.0 years were included in the study. Bone resorption defects were noted in 22 of the 32 levels reviewed (69%). The defects were characterized as mild in 50% (11 of 22), moderate in 18% (4 of 22), and severe in 31% (7 of 22).

CONCLUSIONS

The benefit of rhBMP-2 to promote interbody fusion in the lumbar spine has been well documented. BMP has demonstrated an increased fusion rate and the ability to produce a robust fusion mass. rh-BMP-2's osseous remodeling potential may lead to bone resorption within the vertebral body.

Increased swelling complications associated with off-label usage of rhBMP-2 in the anterior cervical spine

STUDY DESIGN/SETTING

Independent, retrospective clinical record review with a concurrent control.

OBJECTIVE

To identify whether rhBMP-2 is associated with an increased incidence of clinically relevant postoperative prevertebral swelling problems in patients undergoing anterior cervical fusions.

SUMMARY OF BACKGROUND DATA

Bone Morphogenetic Protein-2 (rhBMP-2) is FDA approved as a bone graft substitute in anterior lumbar interbody fusions. rhBMP-2 has also been used "off-label" in anterior cervical fusions. We suspected that rhBMP-2 might increase the incidence of adverse swelling events.

METHODS

A total of 234 consecutive patients (ages 12-82 years) undergoing anterior cervical fusion with and without rhBMP-2 over a 2-year period at one institution comprised the study population. The incidence of clinically relevant prevertebral swelling was calculated. The populations were compared and statistical significance was determined.

RESULTS

A total of 234 patients met the study criteria, 69 of whom underwent anterior cervical spine fusions using rhBMP-2; 27.5% of those patients in the rhBMP-2 group had a clinically significant swelling event versus only 3.6% of patients in the non-rhBMP-2 group. This difference was statistically significant (P < 0.0001) and remained so after controlling for other significant predictors of swelling.

CONCLUSIONS

Off-label use of rhBMP-2 in the anterior cervical spine is associated with an increased rate of clinically relevant swelling events.

Heterotopic Bone Formation Around Sintered Porous-Surfaced Ti-6Al-4V Implants Coated with Native Bone Morphogenetic Proteins

PURPOSE

Coating endosseous dental implants with growth factors such as bone morphogenetic proteins (BMPs) may be one way to accelerate and/or enhance the quality of osseointegration. The purpose of this study was to investigate in the murine muscle pouch model whether sintered porous-surfaced titanium alloy implants coated with BMPs would lead to heterotopic bone formation around and within the implant surface geometry.

MATERIALS

Porous-surfaced dental implants were coated with partially purified native human BMPs, with or without a carrier of Poloxamer 407 (BASF Corp., Parsippany, NJ), placed in gelatin capsules and implanted into the hindquarter muscles of mice. Mice were euthanized after 28 days. Sections of retrieved specimens were subsequently prepared for morphometric analysis of bone formation using backscatter electron microscopic images.

RESULTS

Human BMPs, either with or without the carrier of Poloxamer 407, led to bone formation within and outside of the sintered porous implant surface. When the sintered implant surface region was subdivided into inner and outer halves, similar levels of bone ingrowth and contact were seen in the 2 halves. Evidence of bone formation to the depth of the solid implant core (i.e., the deepest level possible) also was seen.

DISCUSSION AND CONCLUSIONS

Sintered porous-surfaced dental implants can be used as substrate for partially purified BMPs in the murine muscle pouch model. With the addition of these osteoinductive factors, the porous implant surface supported bone formation within the surface porosity provided, in some instances, all the way to the solid implant core. The addition of growth factors to a sintered porous surface may be an efficient method for altering locally the healing sequence and quality of bone associated with osseointegration of bone-interfacing implants.

Resorptive Response of rhBMP2 Simulating Infection in an Anterior Lumbar Interbody Fusion With a Femoral Ring

RhBMP-2 has been available for general use since July of 2002. No literature regarding its use with femoral ring allografts exists. This case demonstrates how a resorptive effect of rhBMP-2 with a femoral ring allograft on host bone at the interbody fusion site can easily be confused with infection. Spine surgeons should be aware of this effect to avoid unnecessary antibiotic use or additional surgery.

Safety assessment of intradiscal gene transfer: a pilot study

BACKGROUND

Several recent in vitro and in vivo studies have reported the beneficial properties of gene delivery of therapeutic factors to the intervertebral disc, as a potential treatment strategy for degenerative disc disease; however, to date, no studies have assessed the safety and toxicity of the practical application of this treatment modality.

PURPOSE

To assess the safety of inappropriately dosed or misdirected gene delivery to the spinal column in an in vivo model.

STUDY DESIGN

The potential toxicity of gene therapy to the spinal column was assessed in this pilot study by monitoring clinical and histological changes in the spinal cord after intradural injections of an adenoviral vector containing the complementary deoxyribonucleic acid (cDNA) for potentially therapeutic factors in the treatment of degenerative disc disease.

METHODS

Fourteen New Zealand White rabbits were divided into experimental groups to receive an intradural injection (<10 microL) of saline alone or saline in combination with recombinant transforming growth factor beta1 (TGF-beta1) or an adenoviral vector containing the cDNA for either TGF-beta1 (at previously established therapeutic or elevated concentrations) or bone morphogenic protein-2 (BMP-2). Animals were monitored clinically and spinal cords were harvested for histological analysis.

RESULTS

No neurological deficits developed in any of the animals receiving injections of saline alone or saline in combination with the therapeutic dose of Ad-TGF-beta1, Ad-BMP-2, or with recombinant TGF-beta1. However, animals receiving a higher concentration of Ad-TGF-beta1 developed bilateral lower extremity paralysis with significant histological changes.

CONCLUSIONS

Inappropriately dosed or directed gene delivery to the spinal column may result in significant complications. However, with appropriate dosing, a therapeutic window may exist where the potential benefits of gene therapy in the treatment of degenerative disc disease outweigh its risks.

Adverse effects associated with high-dose recombinant human bone morphogenetic protein-2 use in anterior cervical spine fusion

STUDY DESIGN

A retrospective review of patients who underwent an anterior cervical fusion using recombinant human bone morphogenetic protein (rhBMP)-2 with an absorbable collagen sponge (INFUSE; Medtronic Sofamor Danek, Minneapolis, MN).

OBJECTIVE

To ascertain the complication rate after the use of high-dose INFUSE in anterior cervical fusions.

SUMMARY OF BACKGROUND DATA

The rhBMP-2 has been primarily investigated in lumbar spine fusions, where it has significantly enhanced the fusion rate and decreased the length of surgery, blood loss, and hospital stay.

METHODS

We present 151 patients who underwent either an anterior cervical discectomy and fusion (n = 138) or anterior cervical vertebrectomy and fusion (n = 13) augmented with high-dose INFUSE between July 2003 and March 2004. The rhBMP-2 (up to 2.1 mg/level) was used in the anterior cervical discectomy and fusions.

RESULTS

A total of 35 (23.2%) patients had complications after the use of high-dose INFUSE in the cervical spine. There were 15 patients diagnosed with a hematoma, including 11 on postoperative day 4 or 5, of whom 8 were surgically evacuated. Thirteen individuals had either a prolonged hospital stay (> 48 hours) or hospital readmission because of swallowing/breathing difficulties or dramatic swelling without hematoma.

CONCLUSIONS

A significant rate of complications resulted after the use of a high dose of INFUSE in anterior cervical fusions. We hypothesize that in the cervical area, the putative inflammatory effect that contributes to the effectiveness of INFUSE in inducing fusion may spread to adjacent critical structures and lead to increased postoperative morbidity. A thorough investigation is warranted to determine the optimal dose of rhBMP-2 that will promote cervical fusion and minimize complications.

Safety of transforaminal lumbar interbody fusion and intervertebral recombinant human bone morphogenetic protein-2

OBJECT

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is being increasingly used for spinal fusion. There are few data regarding its clinical safety, effectiveness, and clinical outcome when applied on an absorbable collagen sponge (ACS) in conjunction with allograft for transforaminal lumbar interbody fusion (TLIF).

METHODS

Seventy-four consecutive patients undergoing TLIF for degenerative disc disease were divided into five groups depending on whether the patient underwent a minimally invasive or open approach, as well as the number of spinal levels surgically treated. Surgery-related data, fusion results, complications, and clinical outcome were evaluated. The mean follow-up duration was 20.6 months (range 14-28 months). The radiographic fusion rate was 100% at 12 and 24 months after the surgery. No bone overgrowth or other complications related to BMP use were demonstrated.

CONCLUSIONS

Analysis of the results demonstrated that TLIF combined with a BMP-2-soaked ACS is a feasible, effective, and safe method to promote lumbar fusion. There were no significant intergroup differences in clinical outcome between patients who underwent open compared with minimally invasive procedures. Patient satisfaction rates, however, were higher in the minimally invasive procedure group. The efficacy of BMP-2 was not dependent on which approach was used or the number of spinal levels that were treated.

Application of bone morphogenetic proteins in orthopaedic practice: their efficacy and side effects

Bone morphogenetic proteins (BMPs) have been extensively studied since the discovery of agents within bone that could induce bone formation at ectopic sites by Urist in the 1960s. Extensive preclinical research has been carried out showing the efficacy of these products in promoting bone healing. Clinical trials are encouraging, with meta-analysis of results revealing better rates of healing than treatment with autologous bone grafting (risk ratio [RR]: 0.845; 95% confidence interval [CI]: 0.772 - 0.924; p < 0.001 for clinical outcome and RR: 0.884; 95% CI: 0.825 - 0.948; p < 0.001 for radiological outcome). Preclinical and clinical safety assessments have revealed little evidence of toxic effects and there have been few reports of adverse events related to their use. A small rate of immunological reaction following administration, resulting in antibody formation, has been observed in some patients, without clinical consequence, although the long-term implications of this are unknown. Ongoing research is revealing that BMPs act on an extremely wide range of body tissues in a variety of manners and this is far from fully understood. It should be noted, however, that given the role of BMP as a differentiation factor, the production of undifferentiated neoplastic tissue seems unlikely. It has also been shown in an animal model that artificially administered BMP can cross the placenta and subsequently be detected in the growing embryo. As this area has been little investigated, use in pregnancy is currently contraindicated. Until the long-term safety profile is more fully documented it would seem sensible to continue to carefully control use and monitor patients closely. However, the current evidence is very promising.

The ABCs of BMPs

Bone morphogenetic proteins (BMP) are being increasingly used in orthopaedic surgery. These small molecules are capable of inducing bone formation when delivered in the appropriate concentration and on the appropriate scaffold. Not all BMPs are equally effective, and there are currently only two Food and Drug Administration (FDA)-approved "on-label" applications. There are potential complications related to off-label use of BMPs that need to be understood. When used properly, these molecules have the potential to eliminate the need for iliac crest bone graft harvest and improve the speed and success of bone healing.

Favorable healing following space creation in rhBMP-2-induced periodontal regeneration of horizontal circumferential defects in dogs with experimental periodontitis

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is believed to be capable of inducing periodontal regeneration. However, the risk of aberrant healing events, such as root resorption and ankylosis, has been reported. We hypothesized that implantation of BMP-containing carriers directly on the root planed surface may be the cause of unfavorable healing. The purpose of this study was to evaluate the influence of a 1 mm spacer membrane, which separated the rhBMP-2 in polymer-coated gelatin sponge (PGS) and the root surface, on periodontal regeneration of experimentally induced horizontal defects in dogs.

METHODS

Horizontal circumferential periodontal defects were surgically created, and experimental periodontitis was induced in 72 maxillary and mandibular premolars of four male beagle dogs. The recipient sites of each quadrant received: 1) rhBMP-2/PGS (B group) (rhBMP-2 at 1.0 mg/ml, total implant volume/ site approximately 7.2 microl) (n = 24); 2) rhBMP-2/PGS with a spacer membrane (PB group) (n = 24); and 3) physiological saline (PS)/PGS as a control (P group) (n = 24). One quadrant was left untreated. Dogs were sacrificed at 12 weeks post-surgery, and healing was evaluated histologically.

RESULTS

Both groups treated with rhBMP-2/PGS demonstrated enhanced new bone formation and connective tissue attachment with cementum regeneration when compared to the control group. Sites treated with rhBMP-2/PGS showed a greater degree of bone formation than sites treated with rhBMP-2/PGS and spacer membrane, although the latter sites showed no ankylosis.

CONCLUSIONS

Implantation of rhBMP-2/PGS enhances bone formation and connective tissue attachment in horizontal circumferential defects. In addition, the use of a spacer membrane reduces the degree of bone formation, but minimizes ankylosis.

Local and controlled release of growth factors (combination of IGF-I and TGF-beta I, and BMP-2 alone) from a polylactide coating of titanium implants does not lead to ectopic bone formation in sheep muscle

The osteoinductive potential of growth factors leads not only to a stimulated bone formation in bony tissue but also in extra skeletal tissue. This potential depends on the dosage and potentially on the application method and may limit the clinical use. The aim of the present study was to investigate the potential of IGF-I, TGF-beta1 and BMP-2 released from a newly developed application systems of orthopaedic implants to induce ectopic bone formation in muscles. This bioactive coating showed a stimulating effect on fracture healing in several experimental studies before. Titanium discs were coated on one side with the drug carrier poly(d,l-lactide) (PDLLA), with the carrier plus IGF-I and TGF-beta1 or with the carrier plus BMP-2. The discs were implanted in the Musculus cleidomastoideus of sheep and followed up for 3 months. X-rays were taken after the operation and the day of sacrifice. The muscles plus implant were harvested and prepared for histology. Neither the radiology nor the histology revealed any signs of ectopic ossification in the implant/muscle interface or in a distance to the plate in any group. An influence of the locally applied growth factor, however, was seen in the formation of a soft tissue capsule. Histomorphometric analysis revealed a significantly larger capsule area over the growth factor coated side in comparison to the uncoated side or the pure titanium plate, indicating an effect of the applied growth factors on cells, however, not resulting in osteoinduction in muscle. The result showed that the local and controlled release of growth factors from PDLLA coated implants does not induce ectopic bone formation in sheep muscle and could be used in orthopaedic surgery to increase healing without the risk of ectopic bone formation in the surrounding soft tissue.

A pilot safety and efficacy study of OP-1 putty (rhBMP-7) as an adjunct to iliac crest autograft in posterolateral lumbar fusions

The ability of bone morphogenetic proteins (BMPs) to induce bone formation has led to an increasing interest in the potential for their use in fusion surgery. The purpose of this multi-center clinical pilot study was to evaluate the safety of one such BMP-osteogenic protein 1, in the form of OP-1 putty-combined with autograft for intertransverse process fusion of the lumbar spine in patients with symptomatic spinal stenosis and degenerative spondylolisthesis following spinal decompression. Twelve patients with spinal stenosis and degenerative lumbar spondylolisthesis underwent laminectomy and partial or complete medial facetectomy as required for decompression of the neural elements followed by intertransverse process fusion by placing iliac crest autograft and OP-1 putty between the decorticated transverse processes. No instrumentation was used. Patients were followed clinically using the Oswestry scale and radiographically using static and dynamic radiographs to assess their fusion status. Independent and blinded radiologists assessed the films for the presence of bridging bone between the transverse processes and measured translation and angulation on dynamic films using digital calipers. In addition to bridging bone, less than or equal to 5 degrees of angular motion and less than or equal to 2 mm of translation were required to classify the patients as successfully fused, as per the definition of successful fusion provided by the FDA for use in clinical trials involving investigational devices to attain spinal fusion. Radiographic outcome was compared to a historical control (autograft alone fusion without instrumentation for the treatment of degenerative spondylolisthesis). All adverse events were recorded prospectively. The results showed 9 of the 12 patients (75%) obtained at least a 20% improvement in their preoperative Oswestry score, while 6 of 11 patients (55%) with radiographic follow-up achieved a solid fusion by the criteria used in this study. Bridging bone on the anteroposterior film was observed in 10 of the 11 patients (91%). No systemic toxicity, ectopic bone formation, recurrent stenosis or other adverse events related to the OP-1 putty implant were observed. A successful fusion was observed in slightly over half the patients in this study, using stringent criteria without adjunctive spinal instrumentation. This study did not demonstrate the superiority of OP-1 combined with autograft over an autograft alone historical control, in which the fusion rate was approximately 45%. The lack of adverse events related to the OP-1 putty implant in this study is in agreement with other studies supporting the safety of bone morphogenetic proteins in spinal surgery.

The safety and utility of recombinant human bone morphogenetic protein-2 for cranial procedures in a nonhuman primate model

OBJECT

The goal of this study was to evaluate the safety and efficacy of recombinant human bone morphogenetic protein 2 (rhBMP-2) in cranial applications.

METHODS

Critical-sized calvarial defects were created bilaterally in four rhesus monkeys, and bilateral rectangular bone flaps were created in six others. Control and rhBMP-2-treated sides were randomly chosen for each animal, and an absorbable collagen sponge was used to deliver the growth factor. Over a 6-month period postoperatively, the animals were serially evaluated for bone healing and adverse BMP-related consequences by using the following methods: computerized tomography (CT) scanning, magnetic resonance (MR) imaging, electroencephalography, histological investigations, and cerebrospinal fluid (CSF) analysis. The critical-sized defects for the rhBMP-2-treated and control sides attained 71 +/- 12% and 28 +/- 11% closure, respectively (four animals; p = 0.04). The CT scans demonstrated that the bone flaps treated with rhBMP-2 had complete osteointegration in five of six animals, whereas scans of the untreated bone flaps demonstrated uniformly poor osteointegration with the intact skull. Histological analysis confirmed well-formed bridges of bone on the rhBMP-2-treated sides. No epileptogenic activity was detected in any of the animals, and MR imaging revealed no evidence of adverse effects on the brain parenchyma. Meningitic irritation was not found on postoperative CSF sample analysis.

CONCLUSIONS

Treatment of bone flaps and critical-sized cranial defects with rhBMP-2 leads to improved bone formation and osteointegration in nonhuman primates. Initial evaluation of rhBMP-2 appears to indicate a good safety profile for use in cranial procedures in primates.

Bone repair following recombinant human bone morphogenetic protein-2 stimulated periodontal regeneration

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable sponge (ACS) carrier is currently being evaluated as candidate therapy for periodontal regeneration. The objective of this study was to characterize, in some detail, tissue reactions following surgical implantation of rhBMP-2/ACS into periodontal defects.

METHODS

Four young adult, male beagle dogs with surgically induced, bilateral, critical size, supra-alveolar, mandibular premolar defects sequentially received rhBMP-2/ACS (rhBMP-2 at 0.2 mg/ml) in right and left jaw quadrants. After 4 or 8 weeks of healing, experimental teeth with surrounding tissues were harvested and processed for light and transmission electron microscopy.

RESULTS

Surgical implantation of rhBMP-2/ACS into large supra-alveolar periodontal defects resulted in a variable tissue response without marked difference between 4- and 8-week observations. New bone, exceeding the volume of the normal alveolar process, had formed within 4 weeks. The regenerated bone tissue consisted of finely trabeculated woven bone. Marrow spaces exhibited a continuous lining of osteoblasts, osteoclasts, and resting cells. The marrow spaces contained numerous large, thin-walled vessels but were almost devoid of collagen fibrils or fibroblasts. Large voids (seromas) encountered in the newly formed bone were free of structured elements except for occasional aggregates of effete erythrocytes. A variety of tissue reactions were observed along the root surface including areas of resorption, areas of hard tissue deposition, and areas without resorptive or appositional activity. Ankylosis was a frequent observation, although areas showing characteristics of a periodontal ligament with a fine layer of acellular fiber cementum and occasional inserting Sharpey's fibers were also observed. Osteoblasts facing the root surface often appeared to be in a highly active state judged by their cuboidal shape, well-developed endoplasmic reticulum and numerous mitochondria, and the presence of an adjacent layer of preosteoblasts. Conspicuous bundles of wide collagen fibrils near the dentin surface as well as within the marrow spaces were considered to represent remnants of the ACS. These fibrils were associated with areas of mineralization as verified by examination of undecalcified specimens.

CONCLUSIONS

rhBMP-2/ACS elicits a rapid osteoinductive process throughout the implant as well as along and onto the instrumented adjacent root surface. Lamellated trabecular bone was the predominant regenerated tissue. A typical cementum-periodontal ligament-alveolar bone relationship was a rare observation. The great variability in histological tissue response along the instrumented root surface indicates that the stimulus to hard tissue formation resided primarily in the rhBMP-2/ACS implant rather than in the root surface.

Clinical and radiographic outcomes of anterior lumbar interbody fusion using recombinant human bone morphogenetic protein-2

STUDY DESIGN

A prospective, nonblinded, multicenter study of outcomes in patients undergoing single-level anterior lumbar discectomy and interbody fusion with InFUSE Bone Graft.

OBJECTIVE

To determine the safety and effectiveness of InFUSE Bone Graft applied to an absorbable collagen sponge in anterior lumbar interbody fusion with threaded cortical allografts.

SUMMARY OF BACKGROUND DATA

In primates, InFUSE Bone Graft used with allograft dowels was shown to increase rates of interbody fusion by promoting osteoinduction and enhancing incorporation of the allograft. Recently, in a small series of human patients undergoing anterior lumbar interbody fusion with a tapered cylindrical metal fusion cage, InFUSE Bone Graft has been shown to promote osteoinduction and fusion.

METHODS

Forty-six patients underwent a single-level anterior lumbar discectomy and interbody fusion at five investigational sites. They were randomly assigned to one of two groups, and the results in the investigational patients who received threaded cortical allograft dowels with InFUSE Bone Graft were compared with those in the control patients who received threaded allograft dowels with autogenous iliac crest bone graft. Patients' clinical outcomes were assessed using neurologic status, work status, and Oswestry Low Back Pain Disability, Short Form-36, and back and leg pain questionnaires. Anteroposterior, lateral, flexion-extension radiographs, and computed tomography scans were used to evaluate the progression of fusion at 6, 12, and 24 months after surgery.

RESULTS

All patients who received InFUSE Bone Graft showed radiographic evidence of bony induction and early incorporation of the cortical allografts. All patients in this group had fusions at 12 months that remained fused at 24 months. At 12 and 24 months, the investigational group showed higher rates of fusion and improved neurologic status and back and leg pain when compared with the control group. There were no unanticipated adverse events related to the use of InFUSE Bone Graft.

CONCLUSION

The use of InFUSE Bone Graft is a promising method of facilitating anterior intervertebral spinal fusion, decreasing pain, and improving clinical outcomes in patients who have undergone anterior lumbar fusion surgery with structural threaded cortical allograft bone dowels.

Safety profile for the clinical use of bone morphogenetic proteins in the spine

STUDY DESIGN

A review was conducted.

OBJECTIVE

To determine the safety profiles of human recombinant bone morphogenetic protein-2 (rhBMP-2) and osteogenic protein-1 (OP-1) used clinically in spine applications.

SUMMARY OF BACKGROUND DATA

Safety issues associated with the use of bone morphogenetic proteins in spine applications include the possibility of bony overgrowth, interaction with exposed dura, cancer risk, systemic toxicity, reproductive toxicity, immunogenicity, local toxicity, osteoclastic activation, and effects on distal organs. These issues have been given detailed examination in both human and animal studies, and safety data are available for both rhBMP-2 and OP-1. The safety data available for OP-1 are less detailed.

METHODS

The study involved reviews of published reports and the safety data submitted to the Food and Drug Administration (rhBMP-2 and OP-1) and to the European Agency for the Evaluation of Medicinal Products (OP-1), as well as personal communication with the manufacturers of rhBMP-2 (Medtronic Sofamore Danek, Memphis, TN) and OP-1 (Stryker Biotech, Hopkinton, MA).

RESULTS

Application of either rhBMP-2 or OP-1 to raw decorticated bony surfaces leads to new bone formation, which is desirable in the intertransverse or interbody regions. However, new bone formation also may occur if rhBMP-2 or OP-1 comes in contact with laminectomy sites or decompressed neuroforamina, and may lead to restenosis. Inadvertent placement of either rhBMP-2 or OP-1 in the spinal canal leads to formation of bone. Leakage of rhBMP-2 or OP-1 outside the fusion area may lead to adjacent-level fusion. Accurate placement of these factors and adequate retention by their carrier are highly important factors in minimizing these problems. Subdural bone formation occurs if OP-1 is implanted directly beneath the dura. Osteoclastic overstimulation does not appear to be a significant problem with rhBMP-2. However, bone resorption has been associated with OP-1 used in the setting of thoracolumbar fractures. Findings show that RhBMP-2 has an antiproliferative effect on many cancer cells, and no evidence exists that it is carcinogenic. It is unlikely that OP-1 has carcinogenic potential, although fewer data are available. Systemic and local toxicity, significant adverse effects, and harmful effects on distant organs have not been observed in either human or animal studies on rhBMP-2 and OP-1. The benign safety profile of rhBMP-2 may result from its rapid systemic clearance, which results in very little systemic exposure. Systemic exposure to OP-1 also is low. No reproductive toxicity has been observed with either rhBMP-2 or OP-1. However, there is no human safety data. Subclinical immune responses in human subjects to collagen carriers have been reported. Antibody responses to rhBMP-2 have been detected in less than 1% of spine patients. Low titer immune responses have been observed in 38% of patients treated with OP-1. There were no associated clinical adverse effects.

CONCLUSIONS

Given the available data, both rhBMP-2 and OP-1 appear to be safe provided they are used appropriately, placed accurately, not allowed to come into contact with decompressed areas, and contained in the region of fusion. They must be used with caution in the presence of dural defects.

A histological study on experimental tooth movement into bone induced by recombinant human bone morphogenetic protein-2 in beagle dogs

OBJECTIVE

The purpose of this preliminary study was to examine experimental tooth movement into newly generated bone induced by recombinant human bone morphogenetic protein-2 (rhBMP-2).

METHOD

After extraction of the maxillary first premolars, bone defects were surgically created in eight adult beagle dogs using a 5-mm-diameter trepan bar. According to which material was grafted into the bone defects, animals were divided into the following four groups: (1) the rhBMP-2 group in which rhBMP-2 with a poly[ D,L-(lactide-co-glycolide)]/gelatin sponge complex was implanted; (2) the spongiosa group in which spongiosa from the tibia was grafted; (3) the nongrafted group in which no material was embedded; and (4) the control group in which only tooth extraction was performed. The osteoinductive activity of rhBMP-2 and tooth movement into the newly generated bone were examined by histological and morphometric comparisons of each group.

RESULTS

Considerable new bone formation was observed at the grafted site both in the rhBMP-2 and in the spongiosa groups. The area of generated bone in the rhBMP-2 group was significantly greater than that in the spongiosa group. Newly generated bone, in both the rhBMP-2 and spongisosa groups, showed a similar histological response to orthodontic force as in normal alveolar bone in the control group. However, root resorption occurred on the pressure side in the rhBMP-2 group.

CONCLUSION

These results indicated that rhBMP-2 might constitute an alternative material to autogeneous bone grafting for alveolar cleft defects. Further studies regarding tooth movement into generated bone induced by rhBMP-2 are suggested.

Tooth eruption into the newly generated bone induced by recombinant human bone morphogenetic protein-2

OBJECTIVE

The purpose of this study was to observe tooth eruption pattern into the newly generated bone induced by recombinant human bone morphogenetic protein-2 (rhBMP-2).

METHOD

Three 12-week-old beagle dogs were used. Following wound healing of the extracted maxillary third deciduous incisor at the age of 13 weeks, a resection of maxillary alveolar bone (8 mm by 8 mm by 8 mm) was carried out, accompanied by extraction of the maxillary second incisor tooth germ. The rhBMP-2 (5 microgram/100 microL or 10 microgram/100 microL) was implanted in the resected area. A group that was not implanted after resection and a nonresected group were used as controls. Serial changes of the eruption pattern of the maxillary third incisor in the implanted area were observed radiographically. Oxytetracycline and calcein were employed as bone markers. Nine weeks after the implantation, the animals were sacrificed. The samples were observed histologically and analyzed using peripheral quantitative computerized tomography to acquire the bone mineral density (BMD).

RESULTS

In the rhBMP-2 (5 microgram/100 microL)-treated group, histological findings and the BMD of the newly generated bone were almost same as in the nonresected group. The maxillary third incisor erupted through the implanted area. However, in the rhBMP-2 (10 microgram/100 microL)-treated group, more osteoinductive activity and significantly higher BMD were observed in the newly generated bone. The maxillary third incisor erupted mesially so as to avoid this implanted area.

CONCLUSION

Results showed that bone remodeling and tooth eruption through the newly generated bone appear to be dose dependent. Accordingly, proper dosage of rhBMP-2 should be determined for successful clinical application.

Rabbit bone marrow response to bovine osteoinductive proteins and anorganic bovine bone

The effects caused by the implantation of bioabsorbable hydroxyapatite (HA) bound to a pool of bone morphogenetic proteins (BMPs) and other bone noncollagenous hydrophobic proteins mixed with anorganic bovine bone inside rabbit bone marrow were assessed. Within the interior of hollow cylindric titanium prototypes, the following biomaterials were inserted: (1) test group: HA containing a pool of BMPs and noncollagenous hydrophobic proteins mixed with anorganic bovine bone; (2) control group: HA without any protein mixed with anorganic bovine bone; and (3) negative control group: blood clot. The cylinders were placed surgically into the medial portion of the tibiae of 7 rabbits in a manner that allowed the biomaterials to contact just the bone marrow. Morphometric analysis showed that: (1) the biomaterials containing the protein mixture resulted in significantly less new bone than the biomaterials without such a mixture; (2) the group without the protein pool formed larger amounts of bone within the cylinder when compared to the negative control (blood clot only); and (3) the biomaterials containing the protein pool did not show any difference in relation to the negative control. It was concluded that a pool of BMPs and other bone noncollagenous hydrophobic proteins had an inhibitory effect on osteogenesis, and that the biomaterials without a protein pool formed a favorable substrate to bone formation.

Tissue engineering in periodontics using rhBMP-2

The results of these studies show that rhBMP-2 clearly enhances regeneration in periodontal defects (Figures 2&3). The extent of regeneration appears to be significantly influenced by the nature of the carrier material used to deliver the rhBMP-2 to the periodontal wound. While the positive effects of rhBMP-2 on osteogenesis are well established, less is known about the way in which rhBMP-2 effects cementogenesis, or its role in the formation of a new periodontal ligament. From the studies reviewed, it would appear that rhBMP-2 facilitate in the formation of cellular cementum on previously denuded root surfaces. This newly formed cementum has also been shown to support an organised periodontal ligament attachment. Mechanisms related to the possible role of rhBMP-2 in ankylosis are presently unclear and will require further investigation as such sequelle may complicate the clinical utility of rhBMP-2 in periodontal regeneration. Root resorption has also been reported in the above mentioned studies and appears to be related to the concentration of rhBMP-2. Further research directed at understanding how different carriers influence the way in which the rhBMP-2 is released during wound healing should assist researchers with how to best apply these bioengineered proteins to ultimately achieve a more predictable regeneration of the periodontal attachment apparatus. Moreover, additional research into the differing biologic effects of other members of the BMP family of proteins may also hold further promise in the application of this technology to periodontal regeneration.

Osteogenic protein-1 (bone morphogenetic protein-7) in the treatment of tibial nonunions

BACKGROUND

The role of bone morphogenetic proteins (BMPs) in osseous repair has been demonstrated in numerous animal models. Recombinant human osteogenic protein-1 (rhOP-1 or BMP-7) has now been produced and was evaluated in a clinical trial conducted under a Food and Drug Administration approved Investigational Device Exemption to establish both the safety and efficacy of this BMP in the treatment of tibial nonunions. The study also compared the clinical and radiographic results with this osteogenic molecule and those achieved with fresh autogenous bone.

MATERIALS AND METHODS

One hundred and twenty-two patients (with 124 tibial nonunions) were enrolled in a controlled, prospective, randomized, partially blinded, multi-center clinical trial between February, 1992, and August, 1996, and were followed at frequent intervals over 24 months. Each patient was treated by insertion of an intramedullary rod, accompanied by rhOP-1 in a type I collagen carrier or by fresh bone autograft. Assessment criteria included the severity of pain at the fracture site, the ability to walk with full weight-bearing, the need for surgical re-treatment of the nonunion during the course of this study, plain radiographic evaluation of healing, and physician satisfaction with the clinical course. In addition, adverse events were recorded, and sera were screened for antibodies to OP-1 and type-I collagen at each outpatient visit.

RESULTS

At 9 months following the operative procedures (the primary end-point of this study), 81% of the OP-1-treated nonunions (n = 63) and 85% of those receiving autogenous bone (n = 61) were judged by clinical criteria to have been treated successfully (p = 0.524). By radiographic criteria, at this same time point, 75% of those in the OP-1-treated group and 84% of the autograft-treated patients had healed fractures (p = 0.218). These clinical results continued at similar levels of success throughout 2 years of observation, and there was no statistically significant difference in outcome between the two groups of patients at this point (p = 0.939). All patients experienced adverse events. Forty-four percent of patients in each treatment group had serious events, none of which were related to their bone grafts. More than 20% of patients treated with autografts had chronic donor site pain following the procedure.

CONCLUSIONS

rhOP-1 (BMP-7), implanted with a type I collagen carrier, was a safe and effective treatment for tibial nonunions. This molecule provided clinical and radiographic results comparable with those achieved with bone autograft, without donor site morbidity.

Evaluation of recombinant human bone morphogenetic protein-2 in oral applications including the use of endosseous implants: 3-year results of a pilot study in humans

BACKGROUND

This study evaluated patients who had been treated with recombinant human bone morphogenetic protein-2 (rhBMP-2) loaded in an absorbable collagen sponge (ACS) in human extraction sites or in sites that required alveolar ridge augmentation. An earlier report on the same patients revealed that after 4 months, implantation of rhBMP-2/ACS was safe, as determined by clinical, radiographic, systemic, and immunological analyses. In this longer-term follow-up, eligible patients were restored with endosseous dental implants in the area treated with rhBMP-2/ACS and bone biopsy samples were taken for histological analysis of the treated human bone tissue. The primary objective was to monitor the long-term safety of patients treated with rhBMP-2/ACS. Another objective was to evaluate the dental implants placed in the sites treated with rhBMP-2.

METHODS

Patient safety was evaluated by clinical examinations, periapical radiographs, and occurrence of adverse experiences. Dental implants were evaluated by radiographic and clinical examination. All 12 patients have been followed for 3 years.

RESULTS

Two years following surgical implantation of rhBMP-2/ACS, no serious or unexpected adverse experiences occurred. The adverse experiences that did occur were mostly benign and compatible with the dental implant surgeries performed in these patients. No adverse experiences were deemed as related to the rhBMP-2/ACS. Furthermore, no safety concerns in the local area of rhBMP-2/ACS placement were noted, based on oral wound examinations. In the 10 patients (6 extraction socket patients and 4 augmentation patients) who received endosseous implants, all implants were clinically stable at all assessments and all 10 patients have been functionally restored. Histological evaluation of the human bone core biopsies revealed normal bone tissue formation identical to the surrounding native bone. Three-year follow-up clinical examinations revealed that all implants had stable marginal bone levels and healthy peri-implant tissues.

CONCLUSIONS

These 3-year results demonstrate that rhBMP-2/ACS can be used safely in human patients. Human bone biopsies reveal normal bone formation in areas treated with rhBMP-2/ACS. Endosseous implants placed in these areas were all stable with no radiographic or clinical complications. The results from this study suggest that rhBMP-2/ACS (0.43 mg/ml) can be safely used in tooth extraction sites and in local ridge augmentation procedures and that endosseous dental implants placed in bony areas treated with rhBMP-2/ACS are stable and can be functionally restored without complication.