- Email: [email protected]
Long-term kinematic analysis of cervical spine after single-level implantation of Bryan cervical disc prosthesis
The Spine Journal 13 (2013) 628–634
Clinical Study
Long-term kinematic analysis of cervical spine after single-level implantation of Bryan cervical disc prosthesis Won Hyung A. Ryu, MSca, Izabela Kowalczyk, BHScb,c, Neil Duggal, MD, MSc, FRCS(C)a,b,c,d,* a
Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada b Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada c Centre for Functional and Metabolic Mapping, Robarts Research Institute, University of Western Ontario, London, Ontario, Canada d Division of Neurosurgery, Department of Clinical Neurological Science, London Health Sciences Centre, University Hospital, 339 Windermere Rd, London, Ontario, Canada N6A 5A5 Received 4 October 2011; revised 10 July 2012; accepted 18 February 2013
Abstract
BACKGROUND CONTEXT: Cervical arthroplasty theoretically reduces the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion. An essential argument in confirming the utility of cervical arthroplasty is long-term confirmation that cervical disc replacements can maintain physiological kinematics at the index and adjacent levels. PURPOSE: The purpose of this in vivo prospective study was to characterize the long-term segmental kinematic outcomes after cervical arthroplasty. STUDY DESIGN/SETTING: Prospective cohort study. PATIENT SAMPLE: Twenty patients with a 5-year clinical follow-up who underwent anterior cervical discectomy with insertion of the Bryan cervical disc. OUTCOME MEASURES: Physiological measures (kinematic analysis of lateral neutral, flexion, and extension radiographic imaging). METHODS: Twenty consecutive patients with degenerative disc disease were followed with regular radiographic imaging after implantation of the Bryan cervical disc prosthesis. Lateral neutral, flexion, and extension radiographs (n5240) were analyzed using Quantitative Motion Analysis software (Medical Metrics, Inc., Houston, TX, USA) to measure the biomechanical profile at the index level and adjacent levels up to 5 years after surgery. Parameters collected included range of motion (ROM), functional spinal unit (FSU) angle, anterior and posterior disc heights, sagittal translation, and center of rotation (COR). RESULTS: Biomechanics of the implanted artificial cervical disc was maintained up to 5 years with no significant changes in ROM, FSU angle, disc height, sagittal translation, and COR values when compared with early postoperative performance. Artificial discs were able to adequately restore and maintain preoperative kinematics. Early differences seen in disc height and FSU angle did not change during the duration of follow-up. No significant kyphotic changes or decrease in ROM were seen at the adjacent spinal levels. CONCLUSIONS: The Bryan cervical disc prosthesis provides for a durable solution for functional spinal motion at the operated level and maintained the preoperative kinematics at adjacent levels at the 5-year follow-up. Crown Copyright Ó 2013 Published by Elsevier Inc. All rights reserved.
Keywords:
Cervical arthroplasty; Kinematics; Total disc replacement; Bryan disc; Cervical disc replacement
FDA device/drug status: Approved for this indication (Bryan Cervical Disc Prosthesis). Author disclosures: WHAR: Nothing to disclose. IK: Nothing to disclose. ND: Stock Ownership: Synergy Disc Replacement, Inc. The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. Neil Duggal was a consultant for Medtronic Sofamor Danek and Synthes Spine at the time of patient recruitment but not manuscript
composition. The other authors report no conflict of interest concerning the material or methods used in this study or the findings specified in this article. * Corresponding author. Division of Neurosurgery, Department of Clinical Neurological Science, London Health Sciences Centre, University Hospital, 339 Windermere Rd, London, Ontario, Canada N6A 5A5. Tel.: (519) 663-2926; fax: (519) 663-2947. E-mail address: [email protected] (N. Duggal)
1529-9430/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.02.046
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
629
Introduction Since the first preliminary European trials of cervical arthroplasty by Goffin et al. [1,2], the Bryan cervical disc prosthesis has been implemented worldwide as an alternative to anterior cervical discetomy and fusion (ACDF) for degenerative disc disease (DDD). Cervical arthroplasty theoretically reduces the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion [3–5]. An essential argument in confirming the utility of cervical arthroplasty is long-term confirmation that cervical disc replacements can maintain physiological kinematics at the index and adjacent levels. Given that the first Bryan disc was inserted in Europe more than 10 years ago, studying this patient population provides the opportunity of addressing long-term kinematic outcomes of cervical arthroplasty. Numerous studies have reported the early to intermediate clinical and radiologic outcomes after Bryan cervical disc prosthesis implantation, with most showing positive results [1,2,6–9]. Prospective randomized trials reported for various cervical disc replacements have had follow-up limited to approximately 2 years [10–12]. Three published clinical studies have described the long-term clinical outcomes beyond 4-year follow-up [13–15]. Goffin et al. [13] focused on patient-derived questionnaires to assess clinical outcome and reported on range of motion (ROM). Quan et al. [15] and Walraevens et al. [16] used additional radiographic measurements, such as adjacent level intervertebral disc degeneration and heterotopic ossification. The purpose of this prospective cohort study was to describe the long-term in vivo kinematic behavior of the Bryan cervical disc prosthesis. Specifically, we characterized the preoperative changes that occur with DDD and quantitatively assessed the longitudinal performance of the artificial cervical disc based on ROM, functional spinal unit (FSU) angle, anterior disc height (ADH), and posterior disc height (PDH), sagittal translation, and center of rotation (COR). In additional, we examined the long-term kinematic impact of cervical arthroplasty on adjacent level kinematics.
Methods Twenty prospectively enrolled patients with radiculopathy and/or myelopathy secondary to DDD were included in this study. All patients underwent anterior cervical discectomy, followed by implantation of Bryan cervical disc prosthesis. The operative technique has been previously described [17]. Static and dynamic standing radiographic images of upright neutral, flexion, and extension cervical spine were obtained for all 20 patients preoperatively and at multiple postoperative time points: 1 year, 2 to 3 years (3 and 17 patients, respectively), and 4 to 5 years (3 and 17 patients, respectively). A total of 240 radiographs were
Context One potential benefit of disc replacement is that motion preservation might decrease the risk of degeneration at adjacent levels. In this study the authors assess motion preservation 5 years after cervical arthroplasty. Contribution In a small cohort of consecutive patients, the authors found that some motion, although not exactly physiologic, was maintained at the implanted prosthesis level. They also noted that adjacent levels initially become hyper-mobile (at year 1) and then stabilize (years 2 to 5). Implication The findings suggest that maintenance of some motion persisted at the operated level, although the small numbers of subjects lowers the confidence that this is a universal effect. Longer-term, controlled follow-up is needed to determine whether the observed findings impact device longevity and adjacent segment degeneration. —The Editors analyzed for the study. All patients underwent clinical and radiographic assessment at 5 years. Because of poor imaging quality at the 5-year follow-up, in three cases the 4-year (instead of 5 year) radiographs were used for analysis. Radiographic technique has been described previously [18]. This study was approved by the Health Sciences Research Ethics Board at the University of Western Ontario. Quantitative Motion Analysis software (Medical Metrics, Inc., Houston, TX, USA) was used to analyze the kinematic profile of the cervical spine at the index level along with the superior and inferior adjacent levels. This validated radiographic analysis software uses an advanced pattern-recognition algorithm to generate accurate measurements of ROM, FSU angle, ADH/PDH, sagittal plane translation, and COR in X and Y directions (Fig. 1) [15,18–21]. The COR was obtained for the spinal levels and reported as (X, Y) offset from the midline of the superior end plate of the caudal vertebral body [6,18]. The FSU angle was defined as the angle formed by lines drawn at the superior margin of the superior vertebral body defining the disc space and the inferior margin of the inferior body [6,18]. Mean values and standard deviations were determined for ROM, FSU angle, ADH/PDH, sagittal translation, and COR X and Y. The radiologic measurements were grouped into preoperative, early postoperative outcome (1 year), intermediate postoperative outcome (2–3 years), and late postoperative outcome (4–5 years). The Student t test was used to compare the kinematic and biomechanical profiles at the aforementioned time points (significance p!.05).
630
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
Fig. 1. Lateral radiograph of single-level Bryan disc prosthesis and the corresponding kinematic parameters assessed for each spine level using Quantitative Motion Analysis software. These parameters include range of motion (ROM), functional spinal unit (FSU) angle, anterior disc height (ADH), posterior disc height (PDH), sagittal translation, as well as center of rotation (COR) X and Y.
Results In our series, 20 patients (13 males, 7 females) underwent single-level cervical arthroplasty, including 1 patient at C3–C4, 1 patient at C4–C5, 10 patients at C5–C6, and 8 patients at C6–C7 levels. There was immediate relief of radiculopathy and/or myelopathy in all cases, with no operative or device-related complications over the follow-up period. Range of motion There was no significant change in mean ROM from the preoperative values (9.465.0 ) to the postoperative values (preoperative vs. early postoperative, p5.51; early postoperative vs. intermediate postoperative, p5.68; and intermediate postoperative vs. late postoperative, p5.62). Fig. 2 presents the longitudinal observed mean sagittal rotation values. Of the 20 patients, three patients showed marked decreases in disc motion at the surgical level (ranging from 67% to 89% decrease) and one patient with almost complete loss of motion (99% decrease). Although all four of these patients showed loss of lordosis at the surgical level, only one of four patients had postoperative kyphotic FSU, which was present preoperatively. At the superior adjacent
Fig. 2. Line graph showing the mean sagittal ROM values at the (Top) superior adjacent level, (Middle) surgical level, and (Bottom) inferior adjacent level preoperatively and at early, intermediate, and late follow-ups postoperatively. At 1 year postoperatively, significant increase in ROM was at the superior level (p5.01, represented by *). No significant change was seen even at 6 years after disc implantation for the surgical level or inferior level. ROM, range of motion.
level, there was a significant increase in mean ROM from 12.164.7 to 14.364.0 at 1-year follow-up compared with the preoperative value (preoperative vs. early postoperative, p5.01; early postoperative vs. intermediate postoperative, p5.17; and intermediate postoperative vs. late postoperative, p5.75; Fig. 2). The ROM of the inferior level did not change significantly (preoperative vs. early postoperative, 9.763.2 vs. 12.663.8 , p5.14; early postoperative vs. intermediate postoperative, 12.663.8 vs. 12.564.1 ,
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
p5.61; and intermediate postoperative vs. late postoperative, 12.564.1 vs. 10.864.4 , p5.47). FSU angle
631
postoperative, p5.73; and late postoperative, p5.30). At the superior adjacent level, there was a significant change in COR Y at 1-year follow-up (COR X 3.261.0 mm to 2.760.8 mm; p5.05 and COR Y 9.262.3 mm to 7.861.8 mm; p5.001). Significant changes were also seen in COR Y at intermediate follow-up from to the early postoperative value of 7.861.8 to 7.262.5 mm (p5.04). The COR X and Y remained stable in the inferior spinal level (pO.05).
The mean FSU angle changed significantly during the first year after the cervical arthroplasty, becoming more kyphotic ( 1.065.6 to 4.265.2 ; p!.001). At the examination of the individual patients’ measurements, 18 of 20 patients demonstrated FSU angle change that was either a decrease in lordosis, lordosis to kyphosis, or an increase in kyphosis from preoperative values. Ten of 20 patients had lordotic FSU at preoperative imaging, and 3 of these 10 patients showed changes toward kyphosis at follow-up. The remaining 10 patients had preoperative straightening of focal kyphosis of the spine. Patients with a straight spine demonstrated kyphosis after surgery at the index level. Arthroplasty increased the kyphosis at the index level in patients with preoperative kyphosis. In the subsequent follow-up, the FSU angle remained stable up to 5 years after surgery (Fig. 3). No significant changes in FSU were seen in either adjacent levels (pO.05). There was no clear relationship between the development of kyphotic changes and the loss in ROM (Pearson r50.1). Furthermore, there was no relationship between the extent of kyphotic changes at the surgical level compared with the adjacent levels (Pearson r50.1 index level vs. superior; Pearson r50.2 index level vs. inferior).
Preoperatively, the mean ADH was 4.461.0 mm, whereas the mean PDH was 3.460.9 mm. At the 1-year follow-up, the ADH decreased by 19% (3.261.1 mm, p!.001) and the PDH by 12% (3.061.0 mm, p!.001). Subsequent radiologic measurements, both at intermediate and late follow-ups, showed stable ADH (p5.30 and .34, respectively) and PDH (p5.55 and .86, respectively; Fig. 4). The ADH and PDH at the superior level remained comparable at all follow-up time points to the preoperative value (pO.05). At the inferior level, there was a significant increase in ADH at the 1-year follow-up from 5.561.2 to 5.861.4 mm, which stabilized at intermediate and late follow-ups (p5.05), whereas no changes were seen in PDH (pO.05). Comparing the preoperative measurements to the late follow-up values for the inferior level, there was a mean decrease in ADH by 4%.
Center of rotation
Sagittal plane translation
The preoperative COR in the X direction was measured as 2.861.2 mm from the midline. The COR X did not change after arthroplasty (early postoperative, p5.16; intermediate postoperative, p5.28; and late postoperative, p5.90). The COR Y values also did not change significantly after surgery and remained stable over the course of follow-up (early postoperative, p5.13; intermediate
Before the insertion of the Bryan disc, the mean segmental translation at the surgical level was 1.060.7 mm. At the early follow-up, the translation at the surgical and inferior levels did not change compared with the preoperative values (p5.95 and .62, respectively). The translation remained stable at the subsequent follow-ups (pO.05). At the superior level, there was a significant change in sagittal translation at the 1-year follow-up from 1.760.7 to 2.060.8
Fig. 3. Line graph showing the mean FSU angle values preoperatively and at early, intermediate, and late follow-ups postoperatively. The FSU angle shows significant kyphotic change at 1 year after surgery (p!.001; represented by *). FSU, functional spinal unit.
Disc height
Fig. 4. Bar graph showing the mean ADH and PDH values preoperatively and at early, intermediate, and late follow-ups postoperatively. No significant change was seen even at 6 years after disc implantation. At 1-year follow-up, the ADH decreased by 27% and the PDH by 18% (p!.001; represented by *). ADH, anterior disc height; PDH, posterior disc height.
632
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
mm, but this stabilized at the intermediate and late followup (early postoperative, p5.02; intermediate postoperative, p5.35; and late postoperative, p5.34).
Discussion The primary purpose of our study was to broadly examine the kinematics at the index and adjacent levels to determine if cervical arthroplasty provided a durable lasting impact on cervical kinematics. Our results provide support that there is minimal change in the device kinematic behavior at early follow-up and that kinematics of the Bryan disc are predictable and durable even at 5 years after surgery. The literature describes excellent clinical outcomes after the insertion of the Bryan disc [22,23]. There is, however, limited information on the long-term kinematic performance of the device. Our results suggest that the kinematic impact of the implanted artificial cervical disc did not degrade over time, compared with the early postoperative performance. Results of this study found that the in vivo kinematics of artificial cervical disc is maintained up to 5 years with no significant changes in ROM, FSU angle, disc height, translation, or COR values when compared with early postoperative performance. The three previous long-term outcome studies show comparable results in terms of angular motion [13,15,16]. Goffin et al. [13] followed 30 patients with single-level arthroplasty up to 6 years and found that the mean ROM at the last follow-up (7.765.6 ) was within 2 of the preoperative value of 9.365.5 . Similarly, Walraevens et al. [16] reported stable ROM in 26 patients at 8 years after disc insertion; 8.965.7 at preoperative and 8.065.1 at 8 years after surgery. Minimal anteroposterior migration was noted for the same patients at 8-year followup [16]. Quan et al. [15] also reported that 78% of the operated segments remained mobile at 8-year follow-up with average ROM of 8.465.8 . In our series, preoperative ROM at the index level was maintained 5 years after surgery. However, it is important to highlight that there was a small but significant increase in ROM at the superior adjacent levels after surgery. There may be multiple reasons attributable to this initial increase in ROM. First, it may be related to surgical technique, with disruption of the anterior vertebral column stabilizing ligaments and soft-tissue disruption associated with the surgical approach. Given that the device inserted for this study used first-generation instrumentation for insertion of the Bryan disc, it is possible that an extended exposure of the vertebral column was required for the instrumentation, which in some may weaken the adjacent level. Powell et al. [24] also reported increased sagittal rotation at the superior adjacent level of Bryan arthroplasty and fusion groups, which he attributed to symptom relief compared with the limited ROM before surgery. It is reassuring that this observed increase in ROM only occurred at the superior level and also stabilized after the early follow-
up and remained stable up to 5 years after surgery. The transient hypermobility at the superior adjacent level may alternatively imply that cervical disc replacements cannot protect the spine from adjacent level degeneration. Although this is a possible explanation for the observed findings, if this were the case, we would have expected to see consistent or worsening hypermobility or progression of degenerative changes over the duration of the follow-up period. Instead, we found that the adjacent level changes stabilized and remained consistent with preoperative levels at intermediate and late follow-ups. As Powell et al. [24] proposed, the increased ROM may be related to the patients’ relief of preoperative neck pain after surgery and improved patient effort for flexion-extension cervical radiographs. Alternatively, implantation of the disc replacement at the symptomatic level may allow healthy adjacent levels to more closely approximate ROM seen in asymptomatic controls [22,23,25–27]. In fact, the postoperative ROM values of superior adjacent levels in 18 of 20 patients in our study are within the range of the reported historical controls in the literature [25–27]. It is, however, important to note that there is a wide variability in the reported ROM for each cervical level, which can influence the comparison between the values charted in this study and the normal controls [18]. The ability of an artificial disc to replicate preoperative kinematics is significantly influenced by the COR provided by the device. The Bryan artificial disc incorporates translation into the design, allowing a mobile COR. Previously, Pickett et al. [18] determined that the Bryan disc effectively mimics the anterior/posterior (COR X) and cephalad/caudal (COR Y) values. The advantage of preserving preoperative COR includes theoretically preventing abnormal stresses on the facets and surrounding soft-tissue structures. Maintaining normal CORs may also contribute to the maintained ROM as no cases of late heterotopic fusion or degradation of ROM was seen. Results of our study provide additional evidence that the early postoperative COR at the index level is sustained and is durable up to 5 years after implantation with the Bryan disc. This may be the key differentiating feature when compared with devices with a fixed COR, for example, ProDisc-C. It is, however, important to note that the superior adjacent level did show significant changes in COR X and Y at the postoperative follow-up in our study. The implication of this change in COR is unclear, but it may reflect the change in disc height and/or FSU angle at the surgical level. The effect of artificial disc in preserving cervical alignment is another important component in assessing device behavior after implantation. Cervical kyphosis has been associated with an increased incidence of segmental instability, adjacent-segment degenerative changes, and poor functional outcome [28–30]. Katsuura et al. [31] suggested that the loss of physiological lordosis in ACDF may load posterior forces on the adjacent spinal levels leading to faster adjacent disc degeneration. One of the potential concerns
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
of Bryan disc prosthesis may be related to its passive design; it is not intended to correct preoperative diseased FSU from kyphosis to lordosis. Mixed reports exist regarding the development of cervical kyphosis after Bryan disc insertion [32,33]. Pickett et al. [6,33] reported kyphotic FSU angle during early postoperative period with Bryan disc arthroplasty, particularly for patients with preexisting kyphosis. Conversely, more recent studies have noted that the artificial disc effectively maintained lordotic sagittal alignment 2 years after surgery [23,34,35]. These reports suggest that postoperative kyphosis may actually be because of overmilling at the dorsal end plate, angle of disc insertion, removal of the posterior longitudinal ligament, and pre-existing kyphosis [16,23,34–36]. Although the results of this study show a kyphotic change in the mean FSU angle at 1-year follow-up, 7 of 10 patients with preoperative lordosis had comparable sagittal alignment up to 5-year follow-up. Although the factors influencing development of kyphosis after disc insertion remain unproven, it is clear that cervical alignment at the index level does not become more kyphotic with the passage of time. Furthermore, no significant kyphotic changes were seen in either the superior adjacent levels or the inferior adjacent levels throughout the course of this study; paralleling previously reports that Bryan disc seems to protect against acceleration of adjacent level degeneration when compared with data from patients with ACDF [16]. This is relevant as surgeons can expect to see very little change in the FSU angle at the site of surgery over the long term. In this study, disc height at the surgical level was found to decrease significantly at the early follow-up. This is consistent with a previously published report in which patients undergoing arthroplasty with the Bryan cervical prosthesis experienced a reduced posterior vertebral height at the surgical level, postoperatively [32]. In our 4- to 5-year followup data, we found that the disc height remains stable at the early postoperative value and does not show any progressive decrease. In addition, the disc heights of adjacent spinal levels were maintained at the preoperative value up to 5 years after surgery. The major limitation of this study is the inherent potential of error in radiographic imaging. Specifically, quality of flexion-extension imaging, imaging technique, out-of-plane motion, patient discomfort, and body habitus are all sources of random variability [18,37]. Given the small sample size of this study, these factors can introduce significant inaccuracies into the calculation of all kinematic parameters. In particular, 8 of 20 patients who received arthroplasty at the C6–C7 level, the inferior adjacent level (C7–T1) analyses were often not possible because of the overlap of shoulders. Although the implications of these missing data are unclear, it is of interest to note that Walraevens et al. [16] reported, at 8-year follow-up, the superior adjacent level showed significant postoperative degeneration, whereas the inferior level did not when compared with preoperative images.
633
Conclusion The Bryan cervical disc prosthesis allowed functional spinal motion at the operated level and maintained the preoperative kinematics of the cervical spine. Specifically, preoperative ROM, sagittal translation, and COR were maintained up to 5 years after surgery. Although the disc height and FSU angle changed at 1-year follow-up, the subsequent measurements remained stable. There was a significant increase in ROM at the superior adjacent level at the early follow-up. No significant loss of disc height or kyphotic changes were seen at the adjacent levels.
References [1] Goffin J, Casey A, Kehr P, et al. Preliminary clinical experience with the Bryan cervical disc prosthesis. Neurosurgery 2002;51:840–7. [2] Goffin J, Van Calenbergh F, van Loon J, et al. Intermediate follow-up after treatment of degenerative disc disease with the Bryan cervical disc prosthesis: single-level and bi-level. Spine 2003;28:2673–8. [3] Heller JG, Sasso RC, Papadopoulos SM, et al. Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine 2009;34:101–7. [4] Matsunaga S, Kabayama S, Yamamoto T, et al. Strain on intervertebral discs after anterior cervical decompression and fusion. Spine 1999;24:670–5. [5] Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999;81:519–28. [6] Pickett GE, Mitsis DK, Sekhon LH, et al. Effects of a cervical disc prosthesis on segmental and cervical spine alignment. Neurosurg Focus 2004;17:E5. [7] Sasso RC, Best NM. Cervical kinematics after fusion and Bryan disc arthroplasty. J Spinal Disord Tech 2008;21:19–22. [8] Sasso RC, Best NM, Metcalf NH, Anderson PA. Motion analysis of Bryan cervical disc arthroplasty versus anterior discectomy and fusion: results from a prospective, randomized, multicenter, clinical trial. J Spinal Disord Tech 2008;21:393–9. [9] 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. [10] Mummaneni PV, Robinson JC, Haid RW Jr. Cervical arthroplasty with the PRESTIGE LP cervical disc. Neurosurgery 2007;60:310–5. [11] Murrey D, Janssen M, Delamarter R, et al. 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. [12] Burkus JK, Haid RW, Traynelis VC, Mummaneni PV. Long-term clinical and radiographic outcomes of cervical disc replacement with the prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg Spine 2010;13:308–18. [13] Goffin J, van Loon J, Van Calenbergh F, Lipscomb B. A clinical analysis of 4- and 6-year follow-up results after cervical disc replacement surgery using the Bryan cervical disc prosthesis. J Neurosurg Spine 2010;12:261–9. [14] Walraevens J, Demaerel P, Suetens P, et al. Longitudinal prospective long-term radiographic follow-up after treatment of single-level cervical disk disease with the Bryan cervical disc. Neurosurgery 2010;67:679–87.
634
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
[15] Quan GM, Vital JM, Hansen S, Pointillart V. Eight-year clinical and radiological follow-up of the Bryan cervical disc arthroplasty. Spine 2011;36:639–46. [16] Walraevens JR, Liu B, Sloten JV, et al. Postoperative segmental malalignment after surgery with the Bryan cervical disc prosthesis: is it related to the mechanics and design of the prosthesis? J Spinal Disord Tech 2010;23:372–6. [17] Pickett GE, Duggal N. Artificial disc insertion following anterior cervical discectomy. Can J Neurol Sci 2003;30:278–83. [18] Pickett GE, Rouleau JP, Duggal N. Kinematic analysis of the cervical spine following implantation of an artificial cervical disc. Spine 2005;30:1949–54. [19] Reitman CA, Hipp JA, Nguyen L, Esses SI. Changes in segmental intervertebral motion adjacent to cervical arthrodesis: a prospective study. Spine 2004;29:E221–6. [20] Reitman CA, Mauro KM, Nguyen L, et al. Intervertebral motion between flexion and extension in asymptomatic individuals. Spine 2004;29:2832–43. [21] Sears WR, Duggal N, Sekhon LH, Williamson OD. Segmental malalignment with the Bryan cervical disc prosthesis—contributing factors. J Spinal Disord Tech 2007;20:111–7. [22] Wenger M, Hoonacker P, Zachee B, et al. Bryan cervical disc prostheses: preservation of function over time. J Clin Neurosci 2009; 16:220–5. [23] Yang S, Wu X, Hu Y, et al. Early and intermediate follow-up results after treatment of degenerative disc disease with the Bryan cervical disc prosthesis: single- and multiple-level. Spine 2008;33: E371–7. [24] Powell JW, Sasso RC, Metcalf NH, et al. Quality of spinal motion with cervical disc arthroplasty. J Spinal Disord Tech 2010;23:89–95. [25] Dvorak J, Panjabi MM, Grob D, et al. Clinical validation of functional flexion/extension radiographs of the cervical spine. Spine 1993;18:120–7.
[26] Lind B, Sihlbom H, Nordwall A, Malchau H. Normal range of motion of the cervical spine. Arch Phys Med Rehabil 1989;70:692–5. [27] Ordway NR, Seymour RJ, Donelson RG, et al. Cervical flexion, extension, protrusion, and retraction. A radiographic segmental analysis. Spine 1999;24:240–7. [28] Ferch RD, Shad A, Cadoux-Hudson TA, Teddy PJ. Anterior correction of cervical kyphotic deformity: effects on myelopathy, neck pain, and sagittal alignment. J Neurosurg 2004;100:13–9. [29] Katsuura A, Hukuda S, Imanaka T, et al. Anterior cervical plate used in degenerative disease can maintain cervical lordosis. J Spinal Disord 1996;9:470–6. [30] Kawakami M, Tamaki T, Iwasaki H, et al. A comparative study of surgical approaches for cervical compressive myelopathy. Clin Orthop Relat Res 2000;381:129–36. [31] Katsuura A, Hukuda S, Saruhashi Y, Mori K. Kyphotic malalignment after anterior cervical fusion is one of the factors promoting the degenerative process in adjacent intervertebral levels. Eur Spine J 2001;10:320–4. [32] Fong SY, DuPlessis SJ, Casha S, Hurlbert RJ. Design limitations of Bryan disc arthroplasty. Spine J 2006;6:233–41. [33] Pickett GE, Sekhon LH, Sears WR, Duggal N. Complications with cervical arthroplasty. J Neurosurg Spine 2006;4:98–105. [34] Yang YC, Nie L, Cheng L, Hou Y. Clinical and radiographic reports following cervical arthroplasty: a 24-month follow-up. Int Orthop 2009;33:1037–42. [35] Yoon DH, Yi S, Shin HC, et al. Clinical and radiological results following cervical arthroplasty. Acta Neurochir (Wien) 2006;148:943–50. [36] Kim SW, Paik SH, Castro PA, et al. Analysis of factors that may influence range of motion after cervical disc arthroplasty. Spine J 2010;10:683–8. [37] Rabin D, Pickett GE, Bisnaire L, Duggal N. The kinematics of anterior cervical discectomy and fusion versus artificial cervical disc: a pilot study. Neurosurgery 2007;61:100–5.
Clinical Study
Long-term kinematic analysis of cervical spine after single-level implantation of Bryan cervical disc prosthesis Won Hyung A. Ryu, MSca, Izabela Kowalczyk, BHScb,c, Neil Duggal, MD, MSc, FRCS(C)a,b,c,d,* a
Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada b Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada c Centre for Functional and Metabolic Mapping, Robarts Research Institute, University of Western Ontario, London, Ontario, Canada d Division of Neurosurgery, Department of Clinical Neurological Science, London Health Sciences Centre, University Hospital, 339 Windermere Rd, London, Ontario, Canada N6A 5A5 Received 4 October 2011; revised 10 July 2012; accepted 18 February 2013
Abstract
BACKGROUND CONTEXT: Cervical arthroplasty theoretically reduces the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion. An essential argument in confirming the utility of cervical arthroplasty is long-term confirmation that cervical disc replacements can maintain physiological kinematics at the index and adjacent levels. PURPOSE: The purpose of this in vivo prospective study was to characterize the long-term segmental kinematic outcomes after cervical arthroplasty. STUDY DESIGN/SETTING: Prospective cohort study. PATIENT SAMPLE: Twenty patients with a 5-year clinical follow-up who underwent anterior cervical discectomy with insertion of the Bryan cervical disc. OUTCOME MEASURES: Physiological measures (kinematic analysis of lateral neutral, flexion, and extension radiographic imaging). METHODS: Twenty consecutive patients with degenerative disc disease were followed with regular radiographic imaging after implantation of the Bryan cervical disc prosthesis. Lateral neutral, flexion, and extension radiographs (n5240) were analyzed using Quantitative Motion Analysis software (Medical Metrics, Inc., Houston, TX, USA) to measure the biomechanical profile at the index level and adjacent levels up to 5 years after surgery. Parameters collected included range of motion (ROM), functional spinal unit (FSU) angle, anterior and posterior disc heights, sagittal translation, and center of rotation (COR). RESULTS: Biomechanics of the implanted artificial cervical disc was maintained up to 5 years with no significant changes in ROM, FSU angle, disc height, sagittal translation, and COR values when compared with early postoperative performance. Artificial discs were able to adequately restore and maintain preoperative kinematics. Early differences seen in disc height and FSU angle did not change during the duration of follow-up. No significant kyphotic changes or decrease in ROM were seen at the adjacent spinal levels. CONCLUSIONS: The Bryan cervical disc prosthesis provides for a durable solution for functional spinal motion at the operated level and maintained the preoperative kinematics at adjacent levels at the 5-year follow-up. Crown Copyright Ó 2013 Published by Elsevier Inc. All rights reserved.
Keywords:
Cervical arthroplasty; Kinematics; Total disc replacement; Bryan disc; Cervical disc replacement
FDA device/drug status: Approved for this indication (Bryan Cervical Disc Prosthesis). Author disclosures: WHAR: Nothing to disclose. IK: Nothing to disclose. ND: Stock Ownership: Synergy Disc Replacement, Inc. The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. Neil Duggal was a consultant for Medtronic Sofamor Danek and Synthes Spine at the time of patient recruitment but not manuscript
composition. The other authors report no conflict of interest concerning the material or methods used in this study or the findings specified in this article. * Corresponding author. Division of Neurosurgery, Department of Clinical Neurological Science, London Health Sciences Centre, University Hospital, 339 Windermere Rd, London, Ontario, Canada N6A 5A5. Tel.: (519) 663-2926; fax: (519) 663-2947. E-mail address: [email protected] (N. Duggal)
1529-9430/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.02.046
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
629
Introduction Since the first preliminary European trials of cervical arthroplasty by Goffin et al. [1,2], the Bryan cervical disc prosthesis has been implemented worldwide as an alternative to anterior cervical discetomy and fusion (ACDF) for degenerative disc disease (DDD). Cervical arthroplasty theoretically reduces the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion [3–5]. An essential argument in confirming the utility of cervical arthroplasty is long-term confirmation that cervical disc replacements can maintain physiological kinematics at the index and adjacent levels. Given that the first Bryan disc was inserted in Europe more than 10 years ago, studying this patient population provides the opportunity of addressing long-term kinematic outcomes of cervical arthroplasty. Numerous studies have reported the early to intermediate clinical and radiologic outcomes after Bryan cervical disc prosthesis implantation, with most showing positive results [1,2,6–9]. Prospective randomized trials reported for various cervical disc replacements have had follow-up limited to approximately 2 years [10–12]. Three published clinical studies have described the long-term clinical outcomes beyond 4-year follow-up [13–15]. Goffin et al. [13] focused on patient-derived questionnaires to assess clinical outcome and reported on range of motion (ROM). Quan et al. [15] and Walraevens et al. [16] used additional radiographic measurements, such as adjacent level intervertebral disc degeneration and heterotopic ossification. The purpose of this prospective cohort study was to describe the long-term in vivo kinematic behavior of the Bryan cervical disc prosthesis. Specifically, we characterized the preoperative changes that occur with DDD and quantitatively assessed the longitudinal performance of the artificial cervical disc based on ROM, functional spinal unit (FSU) angle, anterior disc height (ADH), and posterior disc height (PDH), sagittal translation, and center of rotation (COR). In additional, we examined the long-term kinematic impact of cervical arthroplasty on adjacent level kinematics.
Methods Twenty prospectively enrolled patients with radiculopathy and/or myelopathy secondary to DDD were included in this study. All patients underwent anterior cervical discectomy, followed by implantation of Bryan cervical disc prosthesis. The operative technique has been previously described [17]. Static and dynamic standing radiographic images of upright neutral, flexion, and extension cervical spine were obtained for all 20 patients preoperatively and at multiple postoperative time points: 1 year, 2 to 3 years (3 and 17 patients, respectively), and 4 to 5 years (3 and 17 patients, respectively). A total of 240 radiographs were
Context One potential benefit of disc replacement is that motion preservation might decrease the risk of degeneration at adjacent levels. In this study the authors assess motion preservation 5 years after cervical arthroplasty. Contribution In a small cohort of consecutive patients, the authors found that some motion, although not exactly physiologic, was maintained at the implanted prosthesis level. They also noted that adjacent levels initially become hyper-mobile (at year 1) and then stabilize (years 2 to 5). Implication The findings suggest that maintenance of some motion persisted at the operated level, although the small numbers of subjects lowers the confidence that this is a universal effect. Longer-term, controlled follow-up is needed to determine whether the observed findings impact device longevity and adjacent segment degeneration. —The Editors analyzed for the study. All patients underwent clinical and radiographic assessment at 5 years. Because of poor imaging quality at the 5-year follow-up, in three cases the 4-year (instead of 5 year) radiographs were used for analysis. Radiographic technique has been described previously [18]. This study was approved by the Health Sciences Research Ethics Board at the University of Western Ontario. Quantitative Motion Analysis software (Medical Metrics, Inc., Houston, TX, USA) was used to analyze the kinematic profile of the cervical spine at the index level along with the superior and inferior adjacent levels. This validated radiographic analysis software uses an advanced pattern-recognition algorithm to generate accurate measurements of ROM, FSU angle, ADH/PDH, sagittal plane translation, and COR in X and Y directions (Fig. 1) [15,18–21]. The COR was obtained for the spinal levels and reported as (X, Y) offset from the midline of the superior end plate of the caudal vertebral body [6,18]. The FSU angle was defined as the angle formed by lines drawn at the superior margin of the superior vertebral body defining the disc space and the inferior margin of the inferior body [6,18]. Mean values and standard deviations were determined for ROM, FSU angle, ADH/PDH, sagittal translation, and COR X and Y. The radiologic measurements were grouped into preoperative, early postoperative outcome (1 year), intermediate postoperative outcome (2–3 years), and late postoperative outcome (4–5 years). The Student t test was used to compare the kinematic and biomechanical profiles at the aforementioned time points (significance p!.05).
630
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
Fig. 1. Lateral radiograph of single-level Bryan disc prosthesis and the corresponding kinematic parameters assessed for each spine level using Quantitative Motion Analysis software. These parameters include range of motion (ROM), functional spinal unit (FSU) angle, anterior disc height (ADH), posterior disc height (PDH), sagittal translation, as well as center of rotation (COR) X and Y.
Results In our series, 20 patients (13 males, 7 females) underwent single-level cervical arthroplasty, including 1 patient at C3–C4, 1 patient at C4–C5, 10 patients at C5–C6, and 8 patients at C6–C7 levels. There was immediate relief of radiculopathy and/or myelopathy in all cases, with no operative or device-related complications over the follow-up period. Range of motion There was no significant change in mean ROM from the preoperative values (9.465.0 ) to the postoperative values (preoperative vs. early postoperative, p5.51; early postoperative vs. intermediate postoperative, p5.68; and intermediate postoperative vs. late postoperative, p5.62). Fig. 2 presents the longitudinal observed mean sagittal rotation values. Of the 20 patients, three patients showed marked decreases in disc motion at the surgical level (ranging from 67% to 89% decrease) and one patient with almost complete loss of motion (99% decrease). Although all four of these patients showed loss of lordosis at the surgical level, only one of four patients had postoperative kyphotic FSU, which was present preoperatively. At the superior adjacent
Fig. 2. Line graph showing the mean sagittal ROM values at the (Top) superior adjacent level, (Middle) surgical level, and (Bottom) inferior adjacent level preoperatively and at early, intermediate, and late follow-ups postoperatively. At 1 year postoperatively, significant increase in ROM was at the superior level (p5.01, represented by *). No significant change was seen even at 6 years after disc implantation for the surgical level or inferior level. ROM, range of motion.
level, there was a significant increase in mean ROM from 12.164.7 to 14.364.0 at 1-year follow-up compared with the preoperative value (preoperative vs. early postoperative, p5.01; early postoperative vs. intermediate postoperative, p5.17; and intermediate postoperative vs. late postoperative, p5.75; Fig. 2). The ROM of the inferior level did not change significantly (preoperative vs. early postoperative, 9.763.2 vs. 12.663.8 , p5.14; early postoperative vs. intermediate postoperative, 12.663.8 vs. 12.564.1 ,
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
p5.61; and intermediate postoperative vs. late postoperative, 12.564.1 vs. 10.864.4 , p5.47). FSU angle
631
postoperative, p5.73; and late postoperative, p5.30). At the superior adjacent level, there was a significant change in COR Y at 1-year follow-up (COR X 3.261.0 mm to 2.760.8 mm; p5.05 and COR Y 9.262.3 mm to 7.861.8 mm; p5.001). Significant changes were also seen in COR Y at intermediate follow-up from to the early postoperative value of 7.861.8 to 7.262.5 mm (p5.04). The COR X and Y remained stable in the inferior spinal level (pO.05).
The mean FSU angle changed significantly during the first year after the cervical arthroplasty, becoming more kyphotic ( 1.065.6 to 4.265.2 ; p!.001). At the examination of the individual patients’ measurements, 18 of 20 patients demonstrated FSU angle change that was either a decrease in lordosis, lordosis to kyphosis, or an increase in kyphosis from preoperative values. Ten of 20 patients had lordotic FSU at preoperative imaging, and 3 of these 10 patients showed changes toward kyphosis at follow-up. The remaining 10 patients had preoperative straightening of focal kyphosis of the spine. Patients with a straight spine demonstrated kyphosis after surgery at the index level. Arthroplasty increased the kyphosis at the index level in patients with preoperative kyphosis. In the subsequent follow-up, the FSU angle remained stable up to 5 years after surgery (Fig. 3). No significant changes in FSU were seen in either adjacent levels (pO.05). There was no clear relationship between the development of kyphotic changes and the loss in ROM (Pearson r50.1). Furthermore, there was no relationship between the extent of kyphotic changes at the surgical level compared with the adjacent levels (Pearson r50.1 index level vs. superior; Pearson r50.2 index level vs. inferior).
Preoperatively, the mean ADH was 4.461.0 mm, whereas the mean PDH was 3.460.9 mm. At the 1-year follow-up, the ADH decreased by 19% (3.261.1 mm, p!.001) and the PDH by 12% (3.061.0 mm, p!.001). Subsequent radiologic measurements, both at intermediate and late follow-ups, showed stable ADH (p5.30 and .34, respectively) and PDH (p5.55 and .86, respectively; Fig. 4). The ADH and PDH at the superior level remained comparable at all follow-up time points to the preoperative value (pO.05). At the inferior level, there was a significant increase in ADH at the 1-year follow-up from 5.561.2 to 5.861.4 mm, which stabilized at intermediate and late follow-ups (p5.05), whereas no changes were seen in PDH (pO.05). Comparing the preoperative measurements to the late follow-up values for the inferior level, there was a mean decrease in ADH by 4%.
Center of rotation
Sagittal plane translation
The preoperative COR in the X direction was measured as 2.861.2 mm from the midline. The COR X did not change after arthroplasty (early postoperative, p5.16; intermediate postoperative, p5.28; and late postoperative, p5.90). The COR Y values also did not change significantly after surgery and remained stable over the course of follow-up (early postoperative, p5.13; intermediate
Before the insertion of the Bryan disc, the mean segmental translation at the surgical level was 1.060.7 mm. At the early follow-up, the translation at the surgical and inferior levels did not change compared with the preoperative values (p5.95 and .62, respectively). The translation remained stable at the subsequent follow-ups (pO.05). At the superior level, there was a significant change in sagittal translation at the 1-year follow-up from 1.760.7 to 2.060.8
Fig. 3. Line graph showing the mean FSU angle values preoperatively and at early, intermediate, and late follow-ups postoperatively. The FSU angle shows significant kyphotic change at 1 year after surgery (p!.001; represented by *). FSU, functional spinal unit.
Disc height
Fig. 4. Bar graph showing the mean ADH and PDH values preoperatively and at early, intermediate, and late follow-ups postoperatively. No significant change was seen even at 6 years after disc implantation. At 1-year follow-up, the ADH decreased by 27% and the PDH by 18% (p!.001; represented by *). ADH, anterior disc height; PDH, posterior disc height.
632
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
mm, but this stabilized at the intermediate and late followup (early postoperative, p5.02; intermediate postoperative, p5.35; and late postoperative, p5.34).
Discussion The primary purpose of our study was to broadly examine the kinematics at the index and adjacent levels to determine if cervical arthroplasty provided a durable lasting impact on cervical kinematics. Our results provide support that there is minimal change in the device kinematic behavior at early follow-up and that kinematics of the Bryan disc are predictable and durable even at 5 years after surgery. The literature describes excellent clinical outcomes after the insertion of the Bryan disc [22,23]. There is, however, limited information on the long-term kinematic performance of the device. Our results suggest that the kinematic impact of the implanted artificial cervical disc did not degrade over time, compared with the early postoperative performance. Results of this study found that the in vivo kinematics of artificial cervical disc is maintained up to 5 years with no significant changes in ROM, FSU angle, disc height, translation, or COR values when compared with early postoperative performance. The three previous long-term outcome studies show comparable results in terms of angular motion [13,15,16]. Goffin et al. [13] followed 30 patients with single-level arthroplasty up to 6 years and found that the mean ROM at the last follow-up (7.765.6 ) was within 2 of the preoperative value of 9.365.5 . Similarly, Walraevens et al. [16] reported stable ROM in 26 patients at 8 years after disc insertion; 8.965.7 at preoperative and 8.065.1 at 8 years after surgery. Minimal anteroposterior migration was noted for the same patients at 8-year followup [16]. Quan et al. [15] also reported that 78% of the operated segments remained mobile at 8-year follow-up with average ROM of 8.465.8 . In our series, preoperative ROM at the index level was maintained 5 years after surgery. However, it is important to highlight that there was a small but significant increase in ROM at the superior adjacent levels after surgery. There may be multiple reasons attributable to this initial increase in ROM. First, it may be related to surgical technique, with disruption of the anterior vertebral column stabilizing ligaments and soft-tissue disruption associated with the surgical approach. Given that the device inserted for this study used first-generation instrumentation for insertion of the Bryan disc, it is possible that an extended exposure of the vertebral column was required for the instrumentation, which in some may weaken the adjacent level. Powell et al. [24] also reported increased sagittal rotation at the superior adjacent level of Bryan arthroplasty and fusion groups, which he attributed to symptom relief compared with the limited ROM before surgery. It is reassuring that this observed increase in ROM only occurred at the superior level and also stabilized after the early follow-
up and remained stable up to 5 years after surgery. The transient hypermobility at the superior adjacent level may alternatively imply that cervical disc replacements cannot protect the spine from adjacent level degeneration. Although this is a possible explanation for the observed findings, if this were the case, we would have expected to see consistent or worsening hypermobility or progression of degenerative changes over the duration of the follow-up period. Instead, we found that the adjacent level changes stabilized and remained consistent with preoperative levels at intermediate and late follow-ups. As Powell et al. [24] proposed, the increased ROM may be related to the patients’ relief of preoperative neck pain after surgery and improved patient effort for flexion-extension cervical radiographs. Alternatively, implantation of the disc replacement at the symptomatic level may allow healthy adjacent levels to more closely approximate ROM seen in asymptomatic controls [22,23,25–27]. In fact, the postoperative ROM values of superior adjacent levels in 18 of 20 patients in our study are within the range of the reported historical controls in the literature [25–27]. It is, however, important to note that there is a wide variability in the reported ROM for each cervical level, which can influence the comparison between the values charted in this study and the normal controls [18]. The ability of an artificial disc to replicate preoperative kinematics is significantly influenced by the COR provided by the device. The Bryan artificial disc incorporates translation into the design, allowing a mobile COR. Previously, Pickett et al. [18] determined that the Bryan disc effectively mimics the anterior/posterior (COR X) and cephalad/caudal (COR Y) values. The advantage of preserving preoperative COR includes theoretically preventing abnormal stresses on the facets and surrounding soft-tissue structures. Maintaining normal CORs may also contribute to the maintained ROM as no cases of late heterotopic fusion or degradation of ROM was seen. Results of our study provide additional evidence that the early postoperative COR at the index level is sustained and is durable up to 5 years after implantation with the Bryan disc. This may be the key differentiating feature when compared with devices with a fixed COR, for example, ProDisc-C. It is, however, important to note that the superior adjacent level did show significant changes in COR X and Y at the postoperative follow-up in our study. The implication of this change in COR is unclear, but it may reflect the change in disc height and/or FSU angle at the surgical level. The effect of artificial disc in preserving cervical alignment is another important component in assessing device behavior after implantation. Cervical kyphosis has been associated with an increased incidence of segmental instability, adjacent-segment degenerative changes, and poor functional outcome [28–30]. Katsuura et al. [31] suggested that the loss of physiological lordosis in ACDF may load posterior forces on the adjacent spinal levels leading to faster adjacent disc degeneration. One of the potential concerns
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
of Bryan disc prosthesis may be related to its passive design; it is not intended to correct preoperative diseased FSU from kyphosis to lordosis. Mixed reports exist regarding the development of cervical kyphosis after Bryan disc insertion [32,33]. Pickett et al. [6,33] reported kyphotic FSU angle during early postoperative period with Bryan disc arthroplasty, particularly for patients with preexisting kyphosis. Conversely, more recent studies have noted that the artificial disc effectively maintained lordotic sagittal alignment 2 years after surgery [23,34,35]. These reports suggest that postoperative kyphosis may actually be because of overmilling at the dorsal end plate, angle of disc insertion, removal of the posterior longitudinal ligament, and pre-existing kyphosis [16,23,34–36]. Although the results of this study show a kyphotic change in the mean FSU angle at 1-year follow-up, 7 of 10 patients with preoperative lordosis had comparable sagittal alignment up to 5-year follow-up. Although the factors influencing development of kyphosis after disc insertion remain unproven, it is clear that cervical alignment at the index level does not become more kyphotic with the passage of time. Furthermore, no significant kyphotic changes were seen in either the superior adjacent levels or the inferior adjacent levels throughout the course of this study; paralleling previously reports that Bryan disc seems to protect against acceleration of adjacent level degeneration when compared with data from patients with ACDF [16]. This is relevant as surgeons can expect to see very little change in the FSU angle at the site of surgery over the long term. In this study, disc height at the surgical level was found to decrease significantly at the early follow-up. This is consistent with a previously published report in which patients undergoing arthroplasty with the Bryan cervical prosthesis experienced a reduced posterior vertebral height at the surgical level, postoperatively [32]. In our 4- to 5-year followup data, we found that the disc height remains stable at the early postoperative value and does not show any progressive decrease. In addition, the disc heights of adjacent spinal levels were maintained at the preoperative value up to 5 years after surgery. The major limitation of this study is the inherent potential of error in radiographic imaging. Specifically, quality of flexion-extension imaging, imaging technique, out-of-plane motion, patient discomfort, and body habitus are all sources of random variability [18,37]. Given the small sample size of this study, these factors can introduce significant inaccuracies into the calculation of all kinematic parameters. In particular, 8 of 20 patients who received arthroplasty at the C6–C7 level, the inferior adjacent level (C7–T1) analyses were often not possible because of the overlap of shoulders. Although the implications of these missing data are unclear, it is of interest to note that Walraevens et al. [16] reported, at 8-year follow-up, the superior adjacent level showed significant postoperative degeneration, whereas the inferior level did not when compared with preoperative images.
633
Conclusion The Bryan cervical disc prosthesis allowed functional spinal motion at the operated level and maintained the preoperative kinematics of the cervical spine. Specifically, preoperative ROM, sagittal translation, and COR were maintained up to 5 years after surgery. Although the disc height and FSU angle changed at 1-year follow-up, the subsequent measurements remained stable. There was a significant increase in ROM at the superior adjacent level at the early follow-up. No significant loss of disc height or kyphotic changes were seen at the adjacent levels.
References [1] Goffin J, Casey A, Kehr P, et al. Preliminary clinical experience with the Bryan cervical disc prosthesis. Neurosurgery 2002;51:840–7. [2] Goffin J, Van Calenbergh F, van Loon J, et al. Intermediate follow-up after treatment of degenerative disc disease with the Bryan cervical disc prosthesis: single-level and bi-level. Spine 2003;28:2673–8. [3] Heller JG, Sasso RC, Papadopoulos SM, et al. Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine 2009;34:101–7. [4] Matsunaga S, Kabayama S, Yamamoto T, et al. Strain on intervertebral discs after anterior cervical decompression and fusion. Spine 1999;24:670–5. [5] Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999;81:519–28. [6] Pickett GE, Mitsis DK, Sekhon LH, et al. Effects of a cervical disc prosthesis on segmental and cervical spine alignment. Neurosurg Focus 2004;17:E5. [7] Sasso RC, Best NM. Cervical kinematics after fusion and Bryan disc arthroplasty. J Spinal Disord Tech 2008;21:19–22. [8] Sasso RC, Best NM, Metcalf NH, Anderson PA. Motion analysis of Bryan cervical disc arthroplasty versus anterior discectomy and fusion: results from a prospective, randomized, multicenter, clinical trial. J Spinal Disord Tech 2008;21:393–9. [9] 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. [10] Mummaneni PV, Robinson JC, Haid RW Jr. Cervical arthroplasty with the PRESTIGE LP cervical disc. Neurosurgery 2007;60:310–5. [11] Murrey D, Janssen M, Delamarter R, et al. 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. [12] Burkus JK, Haid RW, Traynelis VC, Mummaneni PV. Long-term clinical and radiographic outcomes of cervical disc replacement with the prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg Spine 2010;13:308–18. [13] Goffin J, van Loon J, Van Calenbergh F, Lipscomb B. A clinical analysis of 4- and 6-year follow-up results after cervical disc replacement surgery using the Bryan cervical disc prosthesis. J Neurosurg Spine 2010;12:261–9. [14] Walraevens J, Demaerel P, Suetens P, et al. Longitudinal prospective long-term radiographic follow-up after treatment of single-level cervical disk disease with the Bryan cervical disc. Neurosurgery 2010;67:679–87.
634
W.H.A. Ryu et al. / The Spine Journal 13 (2013) 628–634
[15] Quan GM, Vital JM, Hansen S, Pointillart V. Eight-year clinical and radiological follow-up of the Bryan cervical disc arthroplasty. Spine 2011;36:639–46. [16] Walraevens JR, Liu B, Sloten JV, et al. Postoperative segmental malalignment after surgery with the Bryan cervical disc prosthesis: is it related to the mechanics and design of the prosthesis? J Spinal Disord Tech 2010;23:372–6. [17] Pickett GE, Duggal N. Artificial disc insertion following anterior cervical discectomy. Can J Neurol Sci 2003;30:278–83. [18] Pickett GE, Rouleau JP, Duggal N. Kinematic analysis of the cervical spine following implantation of an artificial cervical disc. Spine 2005;30:1949–54. [19] Reitman CA, Hipp JA, Nguyen L, Esses SI. Changes in segmental intervertebral motion adjacent to cervical arthrodesis: a prospective study. Spine 2004;29:E221–6. [20] Reitman CA, Mauro KM, Nguyen L, et al. Intervertebral motion between flexion and extension in asymptomatic individuals. Spine 2004;29:2832–43. [21] Sears WR, Duggal N, Sekhon LH, Williamson OD. Segmental malalignment with the Bryan cervical disc prosthesis—contributing factors. J Spinal Disord Tech 2007;20:111–7. [22] Wenger M, Hoonacker P, Zachee B, et al. Bryan cervical disc prostheses: preservation of function over time. J Clin Neurosci 2009; 16:220–5. [23] Yang S, Wu X, Hu Y, et al. Early and intermediate follow-up results after treatment of degenerative disc disease with the Bryan cervical disc prosthesis: single- and multiple-level. Spine 2008;33: E371–7. [24] Powell JW, Sasso RC, Metcalf NH, et al. Quality of spinal motion with cervical disc arthroplasty. J Spinal Disord Tech 2010;23:89–95. [25] Dvorak J, Panjabi MM, Grob D, et al. Clinical validation of functional flexion/extension radiographs of the cervical spine. Spine 1993;18:120–7.
[26] Lind B, Sihlbom H, Nordwall A, Malchau H. Normal range of motion of the cervical spine. Arch Phys Med Rehabil 1989;70:692–5. [27] Ordway NR, Seymour RJ, Donelson RG, et al. Cervical flexion, extension, protrusion, and retraction. A radiographic segmental analysis. Spine 1999;24:240–7. [28] Ferch RD, Shad A, Cadoux-Hudson TA, Teddy PJ. Anterior correction of cervical kyphotic deformity: effects on myelopathy, neck pain, and sagittal alignment. J Neurosurg 2004;100:13–9. [29] Katsuura A, Hukuda S, Imanaka T, et al. Anterior cervical plate used in degenerative disease can maintain cervical lordosis. J Spinal Disord 1996;9:470–6. [30] Kawakami M, Tamaki T, Iwasaki H, et al. A comparative study of surgical approaches for cervical compressive myelopathy. Clin Orthop Relat Res 2000;381:129–36. [31] Katsuura A, Hukuda S, Saruhashi Y, Mori K. Kyphotic malalignment after anterior cervical fusion is one of the factors promoting the degenerative process in adjacent intervertebral levels. Eur Spine J 2001;10:320–4. [32] Fong SY, DuPlessis SJ, Casha S, Hurlbert RJ. Design limitations of Bryan disc arthroplasty. Spine J 2006;6:233–41. [33] Pickett GE, Sekhon LH, Sears WR, Duggal N. Complications with cervical arthroplasty. J Neurosurg Spine 2006;4:98–105. [34] Yang YC, Nie L, Cheng L, Hou Y. Clinical and radiographic reports following cervical arthroplasty: a 24-month follow-up. Int Orthop 2009;33:1037–42. [35] Yoon DH, Yi S, Shin HC, et al. Clinical and radiological results following cervical arthroplasty. Acta Neurochir (Wien) 2006;148:943–50. [36] Kim SW, Paik SH, Castro PA, et al. Analysis of factors that may influence range of motion after cervical disc arthroplasty. Spine J 2010;10:683–8. [37] Rabin D, Pickett GE, Bisnaire L, Duggal N. The kinematics of anterior cervical discectomy and fusion versus artificial cervical disc: a pilot study. Neurosurgery 2007;61:100–5.