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ORIGINAL ARTICLE
Surg Neurol Int 2011,  2:109

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


1 Medical Scientist Training Program, Johns Hopkins School of Medicine; Department of Neurosurgery, Johns Hopkins Hospital; Spinal Biomechanics and Surgical Outcomes Laboratory, Johns Hopkins School of Medicine, USA
2 Department of Neurosurgery, Johns Hopkins Hospital; Spinal Biomechanics and Surgical Outcomes Laboratory, Johns Hopkins School of Medicine, USA

Date of Submission27-Apr-2011
Date of Acceptance07-Jul-2011
Date of Web Publication13-Aug-2011

Correspondence Address:
Ali Bydon
Department of Neurosurgery, Johns Hopkins Hospital; Spinal Biomechanics and Surgical Outcomes Laboratory, Johns Hopkins School of Medicine
USA
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© 2011 Xu et al; This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


DOI: 10.4103/2152-7806.83726

PMID: 21886882

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   Abstract 

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.

Keywords: Arthrodesis, cervical, fusion, neck pain, non-fusion, pseudoarthrodesis


How to cite this article:
Xu R, Bydon M, Sciubba DM, Witham TF, Wolinsky JP, Gokaslan ZL, Bydon A. Safety and efficacy of rhBMP2 in posterior cervical spinal fusion for subaxial degenerative spine disease: Analysis of outcomes in 204 patients. Surg Neurol Int 2011;2:109

How to cite this URL:
Xu R, Bydon M, Sciubba DM, Witham TF, Wolinsky JP, Gokaslan ZL, Bydon A. Safety and efficacy of rhBMP2 in posterior cervical spinal fusion for subaxial degenerative spine disease: Analysis of outcomes in 204 patients. Surg Neurol Int [serial online] 2011 [cited 2014 Oct 31];2:109. Available from: http://www.surgicalneurologyint.com/text.asp?2011/2/1/109/83726


   Introduction Top


At present, there exists little data on the safety and efficacy of bone morphogenic protein (BMP) usage in posterior cervical fusion procedures. In 2009, Cahill et al. examined the prevalence of BMP usage in spinal fusion procedures and the complications, and cost of treatment associated with its use from 2002-2006 in the nationwide inpatient sample database and found that unlike anterior cervical fusion procedures, posterior cervical fusion procedures did not demonstrate a statistically increased risk for postoperative dysphagia/hoarseness or wound complications. [4] Nevertheless, their analysis was not able to measure definitive endpoints of BMP usage, such as success of arthrodesis, resolution of presenting symptoms, or neurologic outcome.

In this retrospective analysis, we present the outcomes of patients undergoing posterior cervical fusion for subaxial degenerative spinal pathologies at a single institution in order to better understand the benefits and potential drawbacks of BMP use in the posterior cervical spine. We compare the preoperative characteristics, intra-/perioperative factors, as well as postoperative outcomes of control patients vs patients treated with BMP.


   Materials and Methods Top


We reviewed patient data obtained for 204 patients undergoing posterior cervical arthrodesis for symptomatic primary degenerative cervical pathologies over the past 5 years at our institution. Patients receiving posterior cervical fusion due to trauma, tumor, or infectious etiologies were excluded, as were patients who only received C1-C2 fusion. Patients with systemic metabolic disorders that secondarily affect bone quality-such as renal osteodystrophy-were not included in our study. Patient demographics and presenting symptoms were documented, and preoperative neurologic function was assessed from clinic notes on the Nurick and ASIA scales. The age, sex, and comorbidities of patients were comparable in the treatment and control groups [Table 1]. None of the presenting preoperative symptoms or lengths of duration differed statistically between treatment vs control groups. Moreover, patients did not differ significantly in neurologic function preoperatively as assessed on both the Nurick and ASIA scales (P=0.11 and P=.10, respectively).
Table 1: Characteristics of all patients undergoing surgical management of degenerative cervical spinal disease via a posterior approach

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Operative notes were reviewed for the use of BMP, demineralized bone matrix (DBM), local autograft, allograft, and/or hydroxyapatite crystals. Intra- and perioperative data were obtained from operative, discharge, and clinic notes. Postoperative follow-up durations as well as functional outcomes were ascertained from follow-up clinical notes and telephone calls. The presence of bony fusion was determined radiographically using both plain radiographs and CT images.

Pre-, intra-, and postoperative variables were compared between the treatment cohort (patients who received BMP intraoperatively) vs the control group (patients who did not receive BMP) using the Student's t-test for continuous, normally distributed data, and the Mann-Whitney U test for continuous non-Gaussian data (reported as medians, with interquartile range) or non-continuous data. Categorical data were compared with the chi-squared test. Data analysis was performed using Prism 5® (GraphPad Software Inc.). Statistical significance was defined as P<0.05.

Kaplan-Meir curves of postoperative neck pain and presence of radiologic fusion were generated and compared between the treatment vs control groups using the log-rank (Mantel-Cox) analysis. Patients with less than 6 months follow-up were excluded. Data analysis was performed on Prism 5® (GraphPad Software Inc.). Cox proportional hazard regression models were generated for treatment vs control groups for both postoperative neck pain and fusion status. Data analysis was performed on StatView 5.0® (SAS Institute Inc.). Statistical significance for all tests and regression models was defined as P<0.05.


   Results Top


Intra-/perioperative outcomes

In general, for patients who do not receive BMP, it is the practice at our institution to give DBM and allograft (P<0.0001 for both variables) [Table 2]. The majority of patients in both cohorts received local autograft bone. Those patients who received BMP also received concomitant hydroxyapatite crystal application (P<0.0001). There was no statistically significant difference in the amount of intraoperative blood loss or incidental durotomies between patients in the two cohorts [Table 2].
Table 2: Intraoperative variables for surgical management of cervical degenerative disease via a posterior approach

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The non-BMP treatment group experienced the only cases of CSF leakage [2 patients (1.3%)], deep vein thrombosis (DVT) [3 patients (1.9%)], and pulmonary embolism (PE) [2 patients (1.3%)], although this was not statistically significant [Table 3]. There was no significant difference between the groups in rates of infection (P=0.93), dysphagia (P=0.48), pneumonia (P=0.85), hematoma (P=0.94), C5 palsy (P=0.62), wound dehiscence (P=0.37), reoperations (P=0.36), or discharges to rehabilitation (P=0.29). Of note, 11 (7.1%) patients in the non-BMP group experienced instrumentation failure (screw pullout, instrumentation breakage, or halo sign) vs none in the BMP group. This approached but did not reach statistical significance (P=0.06).
Table 3: Perioperative variables for surgical management of cervical degenerative disease via a posterior approach

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Postoperative outcomes

Patients were followed-up for an average of 24.2±10.1 months (range: 1-39.6 months. During this period, 169 patients (82.8%) had radiographic follow-up times of greater than 6 months. Of these, 154 (91.1%) had spinal fusion as demonstrated by CT imaging and x-rays. While 48 (100%) patients in the BMP treatment group experienced arthrodesis, 106 (87.6%) had documented fusion in the control group [Table 3]; this was statistically significant (P=.01). Kaplan-Meier analysis showed that patients who did not receive BMP were more likely to experience non-fusion over time (P=.026) compared to patients who did receive BMP [Figure 1].
Figure 1: Kaplan-Meier plots of postoperative nonfusion. Patients who did not receive bone morphogenic protein had a significantly higher chance of non-fusion over time (P=0.026) when compared with patients who received bone morphogenic protein

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Fifty (28.9%) patients experienced recurrent neck pain during the follow-up period. Interestingly, 31 (23.3%) patients were in the non-BMP treatment group and 19 (47.5%) were in the BMP group. Thus, at last follow-up, patients who received BMP were more likely to experience neck pain (P=.003). Kaplan Meier analysis showed that when time was taken into account [Figure 2], this trend still held true (P=0.01). At last follow-up, patients improved neurologically on both the Nurick and ASIA scales, although final neurologic outcomes were not statistically significantly different between the treatment vs control groups. Notably, no patient in either cohort had clinically significant neurologic deficit attributable to hyperostosis on CT.
Figure 2: Kaplan-Meier plots of postoperative recurrent neck pain over time. Patients who received bone morphogenic protein had a significantly higher chance of recurrent neck pain (P=0.010) compared to patients who did not receive bone morphogenic protein

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   Discussion Top


Although posterior cervical fusions are performed on fewer cases as compared to anterior cervical fusions, the rate of these procedures has increased markedly over the last 20 years. From 1990-2000, the number of posterior fusions increased 330%, and from 1992-2005, by 464%. [21],[34] Commensurate with this rise in cervical fusions has been a large increase in the frequency of BMP usage. Cahill et al. reported that the national rate of BMP application increased from less than 1% of all fusions in 2002 to close to 25% of all fusions in 2006. [4] As BMP use has been associated with increases of 11%-41% in total hospital charges, as well as longer lengths of hospitalization for patients, [3],[6],[7],[8],[15],[16],[21],[24],[26],[31] it is imperative to fully understand the risks and benefits of BMP.

To the best of our knowledge, our manuscript is the first to summarize the outcomes of patients treated with BMP in posterior cervical fusions, and to compare these results with a control group. Like Cahill et al. we found no statistically significant difference in total complications between BMP vs non-BMP (autograft, allograft, and/or DBM)-treated patients undergoing posterior cervical fusion. In our series we specifically looked at blood loss, incidental durotomy, CSF leakage, DVT, PE, wound infection, pneumonia, dysphagia, hematoma, C5 palsy, wound dehiscence, instrumentation failure (11 in the non-BMP group vs 0 in the BMP group; this approached, but did not reach significance), and reoperation rates; we found no statistically significant difference between the two groups. [4] Our control group had complications comparable with that reported in other cervical fusion case series. [1],[2],[3],[4],[5],[8],[9],[10],[11],[12],[13],[14],[17],[18],[19],[20],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35] Unlike Cahill et al. who found a 12.1% increase in length of hospitalization for posterior cervical fusions, we found that patients who received BMP had approximately the same - if not slightly shorter - length of hospitalization (BMP vs non-BMP, 6.1±4.7 days vs 7.4±6.9 days; P=0.23).

Importantly, patients who received BMP with instrumented fusion had a statistically higher rate of arthrodesis compared with those receiving DBM, autograft, and/or allograft alone, both over time and at last follow-up [Figure 1]. In addition, with our maximum dose of 8 cc/12 mg (standard large kit of INFUSE® , Medtronic), neither the BMP treatment group nor the control group experienced symptomatic spinal cord compression due to hyperostosis within the spinal canal. However, it is important to keep in mind that those who received BMP also had the highest recurrence rate for neck pain [Figure 2]. As this neck pain is not due to pseudarthrosis or instability, it is likely that this pain is multifactorial in etiology. Although no inflammatory radiculitis was noted in patients receiving BMP, it is possible that the increased inflammation associated with BMP may play a contributory role in the postoperative neck pain. [26] BMP dosage has been proposed as a factor contributing to unwanted side effects, and future studies need to explore the possibility that BMP dose is correlated to persistent/recurrent postoperative neck pain.

One must acknowledge that as with all retrospective studies, the patient cohorts in this study are nonrandomized and thus subject to selection bias. Nonetheless, we attempted to minimize bias by only including patients with degenerative cervical disease and only those with subaxial pathologies. Moreover, by demonstrating that the two cohorts were not significantly different with regard to comorbidities or presenting symptoms, we hoped to control for such biases during data analysis.


   Conclusions Top


We conducted a retrospective analysis of 204 who underwent instrumented posterior fusion, with or without BMP, for degenerative cervical pathologies. Patients were followed up for 24.2±10.1 months and, during this time, patients who underwent fusion with BMP were statistically more likely to undergo arthrodesis compared to the non-BMP treatment group. However, patients who underwent fusion with BMP were also statistically more likely to experience postoperative persistent/recurrent neck pain. Equally important is the finding that BMP use in posterior cervical fusions does not increase complication rates compared with non-BMP control patients. This is one of the first retrospective studies to quantitatively examine the risks and benefits of BMP use in the posterior cervical spine. Additional prospective studies should be performed to corroborate our findings.

 
   References Top

1.Benglis D, Wang MY, Levi AD. A comprehensive review of the safety profile of bone morphogenetic protein in spine surgery. Neurosurgery 2008;62:ONS423-31; discussion ONS431.   Back to cited text no. 1
[PUBMED]  [FULLTEXT]  
2.Boakye M, Mummaneni PV, Garrett M, Rodts G, Haid R. Anterior cervical discectomy and fusion involving a polyetheretherketone spacer and bone morphogenetic protein. J Neurosurg Spine 2005;2:521-5.   Back to cited text no. 2
[PUBMED]  [FULLTEXT]  
3.Buttermann GR. Prospective nonrandomized comparison of an allograft with bone morphogenic protein versus an iliac-crest autograft in anterior cervical discectomy and fusion. Spine J 2008;8:426-35.   Back to cited text no. 3
[PUBMED]  [FULLTEXT]  
4.Cahill KS, Chi JH, Day A, Claus EB. Prevalence, complications, and hospital charges associated with use of bone-morphogenetic proteins in spinal fusion procedures. JAMA 2009;302:58-66.   Back to cited text no. 4
[PUBMED]  [FULLTEXT]  
5.Connolly ES, Seymour RJ, Adams JE. Clinical evaluation of anterior cervical fusion for degenerative cervical disc disease. J Neurosurg 1965;23:431-7.   Back to cited text no. 5
[PUBMED]  [FULLTEXT]  
6.Deyo RA, Cherkin D, Conrad D, Volinn E. Cost, controversy, crisis: low back pain and the health of the public. Annu Rev Public Health 1991;12:141-56.   Back to cited text no. 6
[PUBMED]  [FULLTEXT]  
7.Deyo RA, Mirza SK. Trends and variations in the use of spine surgery. Clin Orthop Relat Res 2006;443:139-46.   Back to cited text no. 7
[PUBMED]    
8.Deyo RA, Nachemson A, Mirza SK. Spinal-fusion surgery - the case for restraint. N Engl J Med 2004;350:722-6.   Back to cited text no. 8
[PUBMED]  [FULLTEXT]  
9.Haid RW Jr, Branch CL Jr, Alexander JT, Burkus JK. Posterior lumbar interbody fusion using recombinant human bone morphogenetic protein type 2 with cylindrical interbody cages. Spine J 2004;4:527-38; discussion 538.   Back to cited text no. 9
[PUBMED]  [FULLTEXT]  
10.Joseph V, Rampersaud YR. Heterotopic bone formation with the use of rhBMP2 in posterior minimal access interbody fusion: A CT analysis. Spine (Phila Pa 1976) 2007;32:2885-90.   Back to cited text no. 10
    
11.Kaiser MG, Haid RW Jr, Subach BR, Barnes B, Rodts GE Jr. Anterior cervical plating enhances arthrodesis after discectomy and fusion with cortical allograft. Neurosurgery 2002;50:229-36; discussion 236.   Back to cited text no. 11
[PUBMED]  [FULLTEXT]  
12.Kepler CK, Rawlins BA. Mesh cage reconstruction with autologous cancellous graft in anterior cervical discectomy and fusion. J Spinal Disord Tech 2010;23:328-32.  Back to cited text no. 12
[PUBMED]  [FULLTEXT]  
13.Lanman TH, Hopkins TJ. Early findings in a pilot study of anterior cervical interbody fusion in which recombinant human bone morphogenetic protein-2 was used with poly(L-lactide-co-D,L-lactide) bioabsorbable implants. Neurosurg Focus 2004;16:E6.   Back to cited text no. 13
    
14.Marawar S, Girardi FP, Sama AA, Ma Y, Gaber-Baylis LK, Besculides MC, et al. National trends in anterior cervical fusion procedures. Spine (Phila Pa 1976) 2010;35:1454-9.  Back to cited text no. 14
    
15.Martin BI, Deyo RA, Mirza SK, Turner JA, Comstock BA, Hollingworth W, et al. Expenditures and health status among adults with back and neck problems. JAMA 2008;299:656-64.   Back to cited text no. 15
[PUBMED]  [FULLTEXT]  
16.Martin BI, Turner JA, Mirza SK, Lee MJ, Comstock BA, Deyo RA. Trends in health care expenditures, utilization, and health status among US adults with spine problems, 1997-2006. Spine (Phila Pa 1976) 2009;34:2077-84.   Back to cited text no. 16
    
17.Martin GJ Jr, Haid RW Jr, MacMillan M, Rodts GE Jr, Berkman R. Anterior cervical discectomy with freeze-dried fibula allograft. Overview of 317 cases and literature review. Spine (Phila Pa 1976) 1999;24:852-8; discussion 858-9.   Back to cited text no. 17
    
18.Miyamoto S, Takaoka K, Yonenobu K, Ono K. Ossification of the ligamentum flavum induced by bone morphogenetic protein: An experimental study in mice. J Bone Joint Surg Br 1992;74:279-83.   Back to cited text no. 18
    
19.Newman M. The outcome of pseudarthrosis after cervical anterior fusion. Spine (Phila Pa 1976) 1993;18:2380-2.   Back to cited text no. 19
    
20.Park Y, Riew KD, Cho W. The long-term results of anterior surgical reconstruction in patients with postlaminectomy cervical kyphosis. Spine J 2010;10:380-7.   Back to cited text no. 20
[PUBMED]  [FULLTEXT]  
21.Patil PG, Turner DA, Pietrobon R. National trends in surgical procedures for degenerative cervical spine disease: 1990-2000. Neurosurgery 2005;57:753-8; discussion 753-8.   Back to cited text no. 21
[PUBMED]  [FULLTEXT]  
22.Perri B, Cooper M, Lauryssen C, Anand N. Adverse swelling associated with use of rh-BMP-2 in anterior cervical discectomy and fusion: A case study. Spine J 2007;7:235-9.   Back to cited text no. 22
[PUBMED]  [FULLTEXT]  
23.Samartzis D, Shen FH, Goldberg EJ, An HS. Is autograft the gold standard in achieving radiographic fusion in one-level anterior cervical discectomy and fusion with rigid anterior plate fixation? Spine (Phila Pa 1976) 2005;30:1756-61.   Back to cited text no. 23
    
24.Shamji MF, Cook C, Pietrobon R, Tackett S, Brown C, Isaacs RE. Impact of surgical approach on complications and resource utilization of cervical spine fusion: A nationwide perspective to the surgical treatment of diffuse cervical spondylosis. Spine J 2009;9:31-8.   Back to cited text no. 24
[PUBMED]  [FULLTEXT]  
25.Shields LB, Raque GH, Glassman SD, Campbell M, Vitaz T, Harpring J, et al. Adverse effects associated with high-dose recombinant human bone morphogenetic protein-2 use in anterior cervical spine fusion. Spine (Phila Pa 1976) 2006;31:542-7.   Back to cited text no. 25
    
26.Shimer AL, Oner FC, Vaccaro AR. Spinal reconstruction and bone morphogenetic proteins: Open questions. Injury 2009;40 Suppl 3:S32-8.   Back to cited text no. 26
[PUBMED]  [FULLTEXT]  
27.Silber JS, Anderson DG, Daffner SD, Brislin BT, Leland JM, Hilibrand AS, et al. Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. Spine (Phila Pa 1976) 2003;28:134-9.   Back to cited text no. 27
    
28.Smucker JD, Rhee JM, Singh K, Yoon ST, Heller JG. Increased swelling complications associated with off-label usage of rhBMP-2 in the anterior cervical spine. Spine (Phila Pa 1976) 2006;31:2813-9.   Back to cited text no. 28
    
29.Song KJ, Taghavi CE, Lee KB, Song JH, Eun JP. The efficacy of plate construct augmentation versus cage alone in anterior cervical fusion. Spine (Phila Pa 1976) 2009;34:2886-92.   Back to cited text no. 29
    
30.Tumialan LM, Pan J, Rodts GE, Mummaneni PV. The safety and efficacy of anterior cervical discectomy and fusion with polyetheretherketone spacer and recombinant human bone morphogenetic protein-2: A review of 200 patients. J Neurosurg Spine 2008;8:529-35.   Back to cited text no. 30
    
31.Vaidya R, Carp J, Sethi A, Bartol S, Craig J, Les CM. Complications of anterior cervical discectomy and fusion using recombinant human bone morphogenetic protein-2. Eur Spine J 2007;16:1257-65.   Back to cited text no. 31
[PUBMED]  [FULLTEXT]  
32.Villavicencio AT, Burneikiene S, Nelson EL, Bulsara KR, Favors M, Thramann J. Safety of transforaminal lumbar interbody fusion and intervertebral recombinant human bone morphogenetic protein-2. J Neurosurg Spine 2005;3:436-43.   Back to cited text no. 32
[PUBMED]  [FULLTEXT]  
33.Wang MC, Chan L, Maiman DJ, Kreuter W, Deyo RA. Complications and mortality associated with cervical spine surgery for degenerative disease in the United States. Spine (Phila Pa 1976) 2007;32:342-7.   Back to cited text no. 33
    
34.Wang MC, Kreuter W, Wolfla CE, Maiman DJ, Deyo RA. Trends and variations in cervical spine surgery in the United States: Medicare beneficiaries, 1992 to 2005. Spine (Phila Pa 1976) 2009;34:955-61; discussion 962.   Back to cited text no. 34
    
35.Wong DA, Kumar A, Jatana S, Ghiselli G, Wong K. Neurologic impairment from ectopic bone in the lumbar canal: A potential complication of off-label PLIF/TLIF use of bone morphogenetic protein-2 (BMP-2). Spine J 2008;8:1011-8.  Back to cited text no. 35
[PUBMED]  [FULLTEXT]  


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]


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