The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 93, Issue 13

Scientific Articles | July 06, 2011

Adjacent-Level Cervical Ossification After Bryan Cervical Disc Arthroplasty Compared with Anterior Cervical Discectomy and Fusion

Ben J. Garrido, MD¹; Jon Wilhite, MD³; Masato Nakano, MD²; Charles Crawford, MD²; Christine Baldus, RN, MHS²; K. Daniel Riew, MD²; Rick C. Sasso, MD³

¹ Lake Norman Orthopedic Spine Center, 170 Medical Park Road, Suite 102, Mooresville, NC 28117. E-mail address for B.J. Garrido: bgarrido@yahoo.com
³ Indiana Spine Group, 8402 Harcourt Road, Suite 400, Indianapolis, IN 46260
² Suite 11300 West Pavilion, One Barnes-Jewish Hospital Plaza, St. Louis, MO 63110

View Disclosures and Other Information

Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of the original FDA IDE Bryan disc study, from which a single site's data were extracted for this study. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by the authors of this work are available with the online version of this article at jbjs.org.

Disclosure statement for author(s): PDF

Investigation performed at Indiana Spine Group, Indianapolis, Indiana

A commentary by Robert A. Hart, MD, MA, is linked to the online version of this article at jbjs.org.

J Bone Joint Surg Am, 2011 Jul 06;93(13):1185-1189. doi: 10.2106/JBJS.J.00029

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Abstract

Background:

Ossification of the anterior longitudinal ligament and the anulus adjacent to an anterior cervical arthrodesis has been termed adjacent-level ossification development. Initial studies suggested an association with the placement of plates <5 mm from an adjacent disc space. A follow-up study demonstrated that this ossification rarely occurs in association with arthrodeses without plate fixation. In the present study, our goal was to determine the incidence of adjacent-level ossification in patients who underwent cervical arthrodesis with plate fixation as compared with that in patients who underwent cervical arthroplasty.

Methods:

We performed a post hoc analysis of prospectively collected data. Radiographic data for all patients from a single site were used. All postoperative, two-year, and four-year follow-up lateral cervical spine radiographs were collected and formatted to occlude the surgical level, blinding the readers as to the procedure performed. Three independent blinded surgeons graded the cephalad adjacent level for the degree of ossification at each time point. The data were statistically analyzed for significant ossification grade differences between arthrodesis and arthroplasty.

Results:

A total of forty-six patients (twenty-one with a Bryan total disc arthroplasty and twenty-five with an arthrodesis) were included. Both cohorts were derived from previous participation in a Level-I multicenter prospective randomized controlled trial stratified by site. Ossification scores based on independent assessment by three readers at multiple follow-up times were used. The arthrodesis group had significantly higher ossification scores than the arthroplasty group at both the two-year (p = 0.003) and the four-year follow-up interval (p = 0.004). Both cohorts showed significant increases in ossification from the two-year follow-up to the latest follow-up (p = 0.001 for the anterior cervical arthrodesis group and p = 0.008 for the arthroplasty group).

Conclusions:

Our data conclusively demonstrate that cervical intervertebral arthroplasty is associated with a significantly lower incidence of adjacent-level ossification than arthrodesis with plate fixation at both the two-year and the four-year follow-up. Arthroplasty has the advantage of not being associated with adjacent-level ossification, which may decrease cervical spine motion above and below the surgical level.

Level of Evidence:

Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

Since Smith and Robinson¹ introduced anterior cervical discectomy and arthrodesis in 1958, this surgical procedure has become a popular, standard treatment of cervical spine disc disease². This anterior cervical procedure has produced highly successful outcomes for most patients with persistent radicular and/or myelopathic signs and/or symptoms that have failed to respond to nonsurgical methods. However, unique adverse events have now been associated with this procedure, including adjacent-level disc disease^3,4. It has been proposed that the development of adjacent-level degenerative disc disease with associated adjacent-level ossification can occur as a result of this procedure^5-7. Multiple previous publications have described long-term radiographic changes associated with anterior cervical arthrodesis^8-10, described as adjacent-level ossification development. The proposed etiologies of adjacent-level ossification development include plate-to-disc distances, stripping of the anterior longitudinal ligament, the use of Caspar pins (Aesculap AG, Center Valley, Pennsylvania), and other technical as well as biomechanical considerations associated with arthrodesis with plate fixation^5,6,11,12. However, those studies on adjacent-level ossification development have been criticized for the lack of a control group of patients who underwent a similar procedure, performed by the same surgeons, without the use of plates. Furthermore, there is controversy as to whether these adjacent-level degenerative ossification changes produce clinical symptoms and/or affect long-term outcomes¹³. Cervical spondylosis adjacent to fused segments is likely multifactorial, being both genetically predetermined as part of a degenerative cascade and iatrogenically altered through arthrodesis of normal motion segments.

Several artificial cervical discs have undergone rigorous Level-I multicenter investigational device exemption (IDE) studies comparing them with arthrodesis^14-16. In those studies, arthroplasty was compared with arthrodesis with an anterior cervical plate, with all other cohort outcomes being equivalent. In the present study, we used a single site's data, obtained from an IDE study, to determine whether adjacent-level ossification development occurs more frequently in association with arthrodesis with plate fixation than it does in association with arthroplasty in which the device is restricted to the disc space and has a so-called "zero profile" with no anterior protrusion and is flush with the anterior vertebral body.

Materials and Methods

Methods

Our patients who were enrolled in a multicenter IDE trial comparing the Bryan disc (Medtronic, Memphis, Tennessee) with anterior cervical discectomy and fusion, the twenty-four-month results of which have been published¹⁴, were used for the present study. All patients had single-level cervical spine disease (C3 through C7) that had presented as radiculopathy or myelopathy and had failed to respond to at least six weeks of nonoperative treatment. The exclusion criteria included notable anatomic abnormalities, defined as an angular deformity of >11°, translation of >3.5 mm, and/or evidence of advanced spondylosis or previous adjacent-level ossification development on cervical radiographs. Forty-six patients at our site were enrolled and randomized into this Level-I prospective study. Randomization was stratified by site. At our site (Indiana Spine Group, Indianapolis, Indiana), twenty-one patients were managed with the Bryan disc and twenty-five were managed with arthrodesis. There were no significant demographic differences between the cohorts (see Appendix). Postoperative, two-year, and four-year follow-up cervical spine radiographs were independently prepared as PowerPoint images, with the single surgical level blacked out through photo editing (Figs. 1-A and 1-B). These edited images prevented the readers from knowing whether the patient had been managed with an arthroplasty or arthrodesis at the adjacent level.

Fig. 1-A Fig. 1-B

Figs. 1-A and 1-B Postoperative (Fig. 1-A) and two-year follow-up (Fig. 1-B) formatted lateral cervical spine radiographs for the same patient.

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Radiographic Analysis

Two spine fellows and an experienced spine surgeon independently reviewed the final edited lateral cervical spine radiographic images. The cephalad adjacent-level ossification at each follow-up time point was graded for all patients. Each observer utilized a previously published classification system⁵ for adjacent-level ossification development to rate each level (Fig. 2). Grade 1 is characterized by ossification occupying <50% of the adjacent disc space height, Grade 2 is characterized by ossification extending beyond 50% of the adjacent disc space height, and Grade 3 is characterized by bridging of 100% of the adjacent disc space with bone. A higher grade or score indicated worse adjacent-level ossification development. The ratings were then statistically analyzed for ossification differences within and between surgical cohorts (anterior cervical discectomy and fusion versus Bryan artificial disc) at the different follow-up time points. The plate-to-disc distance was also measured for the patients in the arthrodesis cohort. Statistical analysis was completed with use of Mann Whitney U and Wilcoxon signed-rank tests (Table I). The level of significance was set at p < 0.05.

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TABLE I Mann-Whitney Test*

	Median Rank	Sum of Ranks	P Value
Baseline ossification score			0.289
Arthroplasty (n = 19)	19.61	372.50
ACDF (n = 22)	22.20	488.50
2-year ossification score			0.003
Arthroplasty (n = 21)	18.36	404.00
ACDF (n = 25)	28.96	724.00
4-year ossification score			0.004
Arthroplasty (n = 20)	16.00	320.00
ACDF (n = 22)	26.50	583.00

*This test is for chances of obtaining greater observations in one population versus the other (nonparametric equivalent of t test). The null hypothesis in the Mann-Whitney test is that the two samples are drawn from a single population and therefore that their probability distributions are equal. In this example, we reject our null hypothesis at the two-year and four-year follow-up intervals in favor of the alternative hypothesis, specifically, that the probability of observing ossification in the ACDF (anterior cervical discectomy and fusion) population exceeds the probability of observing ossification in the arthroplasty group.

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TABLE I Mann-Whitney Test*

	Median Rank	Sum of Ranks	P Value
Baseline ossification score			0.289
Arthroplasty (n = 19)	19.61	372.50
ACDF (n = 22)	22.20	488.50
2-year ossification score			0.003
Arthroplasty (n = 21)	18.36	404.00
ACDF (n = 25)	28.96	724.00
4-year ossification score			0.004
Arthroplasty (n = 20)	16.00	320.00
ACDF (n = 22)	26.50	583.00

Fig. 2

Radiographs illustrating the adjacent-level ossification classification scheme described by Park et al.⁵. (These radiographs are examples and do not represent study patients.)

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Source of Funding

There was no external funding source for the present study.

Results

A total of forty-six patients (twenty-one in the Bryan artificial disc cohort and twenty-five in the arthrodesis cohort) were included in this study. Median ossification scores were used for the different time-point measurements for both cohorts. Differences within and between the cohorts in terms of adjacent-level ossification were compared. Preoperatively, the prevalence of adjacent-level ossification development was not different between groups and the patients were not subjected to any intervention to avoid adjacent-level ossification development.

The two-year and four-year follow-up median scores were determined for both cohorts. The arthrodesis group had significantly higher ossification scores than the arthroplasty group at both two years (p = 0.003) and four years (p = 0.004). Both cohorts showed significant increases in ossification from the two-year follow-up to the four-year follow-up (p = 0.001 for the anterior cervical arthrodesis group and p = 0.008 for the arthroplasty group) (Table I). In the anterior cervical discectomy and fusion group, nine patients (36%) had no ossification at two years and four patients (16%) had no ossification at four years. In the arthroplasty group, sixteen patients (75%) had no ossification at two years and ten patients (48%) had no ossification at four years (see Appendix). In the arthrodesis cohort, six patients had a plate-to-disc distance of <5 mm. Of those, only three developed adjacent-level ossification.

Discussion

Adjacent-level ossification has been described as an unintended consequence of anterior cervical arthrodesis with use of plate fixation. Park et al. reported that if the plate was <5 mm from the adjacent disc space, the prevalence of adjacent-level ossification development was significantly increased⁵. In the present study, plate-to-disc distance was also measured to evaluate it as a potential source for adjacent-level ossification development. In six of twenty-five patients in the arthrodesis group, the plate-to-disc distance was found to be <5 mm; however, only three had development of adjacent-level ossification. We sought to determine if arthroplasty leads to adjacent-level ossification, similar to that described by Park et al.⁵ following arthrodesis with a plate. To our knowledge, this is the first study to compare Bryan arthroplasty with arthrodesis in terms of the development of adjacent-level ossification in the cervical spine.

There was a significant difference in the grade of adjacent-level ossification development between the cohorts at two years (p = 0.003) as well as at four years (p = 0.004), supporting the concept that motion preservation may defer or limit adjacent-level ossification development. In this short-term four-year follow-up, adjacent-level ossification development occurred less frequently in patients who had arthroplasty. Whether this finding will continue over the long term is unknown, although a previous study on the timing of adjacent-level ossification development demonstrated that if adjacent-level ossification did not occur by twelve to twenty-four months after surgery it was unlikely to occur in the longer term⁷. Eck et al.¹¹ also demonstrated significantly increased cervical spine intradiscal pressures at adjacent levels with flexion (p = 0.002 at C4-C5 and p = 0.006 at C6-C7), and Fuller et al.¹² reported altered biomechanics in the cervical spine after simulated fusion. Whether these altered biomechanical states contribute to or accelerate the degenerative process and/or adjacent-level ossification compared with the normal aging process remains controversial. Yang et al.⁶ demonstrated that adjacent-level ossification was uncommon after anterior cervical arthrodesis without plate fixation, developing in 5.5% of 165 patients, in contrast with the rate of 45.4% following arthrodesis with plate fixation as reported by Park et al.⁵. This finding suggests that the fusion itself is not a major contributor to adjacent-level ossification development⁶. However, one criticism of that study was that the fusions without plate fixation were performed without Caspar pins⁶, whereas the fusions with plate fixation were performed with Caspar pins⁵, leading to the possibility that Caspar pin use incited the adjacent-level ossification development^5-7. It is uncertain what caused the lower rate of adjacent-level ossification development in the disc arthroplasty cohort. Whether the surgical dissection, the placement of Caspar pins, and/or the inaccurate replication of normal kinematics with the Bryan prosthesis are etiologic factors is difficult to determine. What are apparent are the similarities of the procedures in both of the cohorts in the present study, including the use of Caspar pins and the extent of anterior vertebral body surgical exposure.

The present study had multiple limitations. One limitation was the smaller number of patients available from this single randomized IDE study site as compared with a multicenter study, although the numbers were sufficient to reach significance. Another limitation is that we cannot isolate the use of Caspar pins alone as a contributor to adjacent-level ossification development. We can only state that Caspar pins were used for both procedures and were not the subject of this study. Another limitation relates to the subjective rating of adjacent-level ossification development among the three physician readers. Although the restrictions placed on score validity are uncertain, inter-rater reliability tests demonstrated lower agreement between Physicians 1 and 3 (κ = 0.152, p = 0.198) and between Physicians 2 and 3 (κ = 0.273, p = 0.025) when grading the four-year ossification scores for the anterior cervical discectomy and fusion group. There was moderate agreement between all three readers at two years (κ = 0.466 to 0.660) for the assessments of the arthroplasty and anterior cervical discectomy and fusion groups. Likewise, there was moderate agreement between all three observers at four years for the assessment of the arthroplasty group. In conjunction with these limitations, our data reflect the use of only the Bryan disc arthroplasty and may not be applicable to other arthroplasty devices. Long-term studies as well as multicenter studies of other disc designs will be required to determine whether these observed differences in adjacent-level ossification between cohorts will modify future anterior cervical surgical procedures to treat degenerative disc disease.

Appendix

Tables showing the demographic data and ossification frequency by follow-up time points are available with the online version of this article at jbjs.org.

References

Smith GW; Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958;40:607-24. [PubMed]

Bohlman HH; Emery SE; Goodfellow DB; Jones PK. Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am. 1993;75:1298-307. [PubMed]

Daniels AH; Riew KD; Yoo JU; Ching A; Birchard KR; Kranenburg AJ; Hart RA. Adverse events associated with anterior cervical spine surgery. J Am Acad Orthop Surg. 2008;16:729-38. [PubMed]

Hilibrand AS; Carlson GD; Palumbo MA; Jones PK; Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999;81:519-28. [PubMed]

Park JB; Cho YS; Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am. 2005;87:558-63. [PubMed][CrossRef]

Yang JY; Song HS; Lee M; Bohlman HH; Riew KD. Adjacent level ossification development after anterior cervical fusion without plate fixation. Spine (Phila Pa 1976). 2008;34:30-3. [CrossRef]

Park JB; Watthanaaphisit T; Riew KD. Timing of development of adjacent-level ossification after anterior cervical arthrodesis with plates. Spine J. 2007;7:633-6. [PubMed][CrossRef]

Braunstein EM; Hunter LY; Bailey RW. Long term radiographic changes following anterior cervical fusion. Clin Radiol. 1980;31:201-3. [PubMed][CrossRef]

Gore DR; Gardner GM; Sepic SB; Murray MP. Roentgenographic findings following anterior cervical fusion. Skeletal Radiol. 1986;15:556-9. [PubMed][CrossRef]

Baba H; Furusawa N; Imura S; Kawahara N; Tsuchiya H; Tomita K. Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine (Phila Pa 1976). 1993;18:2167-73. [PubMed][CrossRef]

Eck JC; Humphreys SC; Lim TH; Jeong ST; Kim JG; Hodges SD; An HS. Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine (Phila Pa 1976). 2002;27:2431-4. [PubMed][CrossRef]

Fuller DA; Kirkpatrick JS; Emery SE; Wilber RG; Davy DT. A kinematic study of the cervical spine before and after segmental arthrodesis. Spine (Phila Pa 1976). 1998;23:1649-56. [PubMed][CrossRef]

Goffin J; van Loon J; Van Calenbergh F; Plets C. Long-term results after anterior cervical fusion and osteosynthetic stabilization for fractures and/or dislocations of the cervical spine. J Spinal Disord. 1995;8:499-508. [CrossRef]

Sasso RC; Smucker JD; Hacker RJ; Heller JG. Clinical outcomes of BRYAN cervical disc arthroplasty: a prospective, randomized, controlled, multicenter trial with 24-month follow-up. J Spinal Disord Tech. 2007;20:481-91. [PubMed][CrossRef]

Murrey D; Janssen M; Delamarter R; Goldstein J; Zigler J; Tay B; Darden B. Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J. 2009;9:275-86. [PubMed][CrossRef]

Mummaneni PV; Burkus JK; Haid RW; Traynelis VC; Zdeblick TA. Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine. 2007;6:198-209. [PubMed] [CrossRef]

Topics

bone plates ; osteogenesis ; arthroplasty ; cervical spine ; arthrodesis ; intervertebral disc of cervical vertebra ; cervical arthrodesis ; cervical diskectomy

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Bruce Baird, MD

Posted on July 14, 2011

Plate Placement

North Country Orthopaedic Group

This is an interesting article that will prompt me to look harder for adjacent level ossification in my own patients. Given the relatively small cohort of ACDF patients considered, it might have been reasonable to exclude patients with plate placement <5mm from the adjacent level. In the radiographs used to demonstrate the classification system, it might have been helpful to utilize images that did not also illustrate suboptimal plate placement.

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Ben J. Garrido, Jon Wilhite, Masato Nakano, Charles Crawford, Christine Baldus, K. Daniel Riew, Rick C. Sasso; Adjacent-Level Cervical Ossification After Bryan Cervical Disc Arthroplasty Compared with Anterior Cervical Discectomy and Fusion. The Journal of Bone & Joint Surgery. 2011 Jul;93(13):1185-1189.

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