- Email: [email protected]
Comparison of Heterotopic Ossification After Fixed- and Mobile-Core Cervical Disc Arthroplasty
Original Article
Comparison of Heterotopic Ossification After Fixed- and Mobile-Core Cervical Disc Arthroplasty Junfeng Zeng, Hao Liu, Hua Chen, Chen Ding, Xin Rong, Yang Meng, Yi Yang
OBJECTIVE: To compare the heterotopic ossification (HO) between cervical disc arthroplasty (CDA) with fixed- and mobile-core prosthesis and to compare the clinical and radiographic outcomes.
-
METHODS: This was a retrospective analysis of patients who underwent CDA in our institute. Patients were divided into a fixed-core group (Prodisc-C and Discover disc) and mobile-core group (Bryan and Prestige-LP disc). HO was assessed based on the McAfee classification. The visual analogue scale, Neck Disability Index, and Japanese Orthopaedic Association scores were used to evaluate clinical outcomes. In addition, radiographic assessments included cervical sagittal alignment (C2eC7 angle), segmental angle, and range of motion of the index level.
However, both CDA with fixed- and mobile-core prostheses obtained good clinical outcomes and maintained cervical sagittal alignment.
-
RESULTS: A total of 218 patients were included with a minimal follow-up of 24 months. There were 137 patients in mobile-core group (Prestige-LP, 102; Bryan, 35) and 81 patients in the fixed-core group (Discover, 43; and Prodisc-C, 38). The mean follow-up time was 46.8 months. At the final follow-up, the overall incidence of HO was 39.9%. The incidence of HO in the fixed-core group was significantly greater than that in the mobile-core group (50.6% vs. 33.6%, P [ 0.013). However, there were no significant differences in visual analogue scale, Neck Disability Index, or Japanese Orthopaedic Association scores, C2eC7 angle, segmental angle, or range of motion of the index level between the 2 groups.
-
CONCLUSIONS: The fixed-core prosthesis had a greater incidence of HO than mobile-core prosthesis after CDA.
-
Key words Cervical disc arthroplasty - Fixed-core - Heterotopic ossification - Mobile-core -
Abbreviations and Acronyms CDA: Cervical disc arthroplasty HO: Heterotopic ossification JOA: Japanese Orthopaedic Association NDI: Neck Disability Index ROM: Range of motion
INTRODUCTION
C
ervical disc arthroplasty (CDA) has been proposed as an alternative to conventional cervical arthrodesis for the treatment of cervical degenerative disc diseases. Recently, an increasing number of long-term studies have demonstrated that CDA has obtained satisfactory clinical outcomes in comparison with cervical arthrodesis.1-3 Previous studies reported that CDA maintained range of motion (ROM) of the surgical segment, delayed adjacent segment degeneration, and reduced the reoperation rate.4,5 However, the development of heterotopic ossification (HO), which may decrease the ROM, is a common complication after CDA.6 HO is defined as mature bone formation outside the skeletal system.7 Parkinson and Sekhon8 first reported in 2005 a 55-yearold woman who underwent CDA with Bryan artificial cervical disc and developed HO. After that, various studies reported HO formation after CDA with different incidences, ranging from 7.7% to 94.1%.9-11 However, the definitive mechanism of HO formation still remains unclear. Yi et al.12 reported that different prosthesis types can influence the formation of HO after CDA. Kim et al.13 reported that postoperative biomechanical changes may induce HO after CDA. The cervical artificial disc currently used can be classified as fixed- or mobile-core according to its biomechanical properties. In the present study, we hypothesized that CDAs
SA: Segmental angle VAS: Visual analogue scale Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, Sichuan Province, China To whom correspondence should be addressed: Hao Liu, M.D. Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.09.075 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY -: e1-e6, - 2018
www.WORLDNEUROSURGERY.org
e1
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
HO AFTER FIXED- AND MOBILE-CORE CDA
Figure 1. (A) The C2eC7 angle was defined as the angle formed between the lower endplate of the C2 and C7 vertebral body. The segmental angle (SA) was measured by the angle formed between the upper and lower
with fixed cores and mobile cores have different rates of HO. The purpose of our study is to compare the incidence of HO between CDA with fixed- and mobile-core prosthesis and also compare the clinical and radiographic outcomes. MATERIAL AND METHODS Study Design We retrospectively included patients who underwent single-level CDA from February 2005 to September 2015 in our institute. Patients who underwent CDA with Prodisc-C (Synthes; West Chester, Pennsylvania, USA) and Discover (DePuy, Raynham, Massachusetts, USA) disc formed the fixed-core group and patients who underwent CDA with Bryan (Medtronic, Memphis, Tennessee, USA) and Prestige-LP (Medtronic) disc formed the mobile-core group. Approval of the local ethics committee was obtained, but no informed consent was collected because of the retrospective nature of the study. The inclusion criteria included single-level cervical degenerative disc disease causing myelopathy or radiculopathy between C3 and C7, age 18e65 years, unresponsive to conservative treatment for at least 6 weeks, and follow-up time longer than 24 months. The exclusion criteria included severe spondylosis or facet joint degeneration, ossification of the posterior longitudinal ligament, radiographic signs of instability, previous cervical spine surgery, osteoporosis (T-score 2.5), ankylosing spondylitis, rheumatoid arthritis, and infection. Based on the aforementioned criteria, a total of 218 patients were enrolled in this study. All surgeries were performed by the same single senior surgeon using a standard surgical technique. Clinical and radiographic data of all patients were routinely
e2
www.SCIENCEDIRECT.com
endplate of the index intervertebral space. (BeC) The range of motion of the index level was calculated by the changes of SA on the full flexion and extension radiographs.
collected preoperatively, immediately postoperatively, 3, 6, 12, 24 months postoperatively, and then biennially. Outcome Assessments Neck and arm pain of all the patients were evaluated by the visual analogue scale (VAS) score. The Neck Disability Index (NDI) score was used to assess the function of the neck. For patients with myelopathy, the Japanese Orthopaedic Association (JOA) scores were applied to evaluate the neurologic status. The C2eC7 angle and segmental angle (SA), which were measured on the lateral radiographs, were used to assess the cervical sagittal alignment (Figure 1A). The ROM of the index level was measured on the full flexion and extension radiographs (Figure 1BeC). In addition, HO was evaluated according to the McAfee classification by 2 spine surgeons who were independent from the surgeries (Figure 2AeD).14 They were asked to determine the appropriate grade of HO by radiographs and computed tomography. Any discrepancies between them were resolved through a consensus. Statistical Analysis All statistical analyses were conducted using SPSS, version 24.0 software (IBM Corp., Armonk, New York, USA). Quantitative variables were described as the mean standard deviation. The interobserver reliability was measured by calculating the weighted kappa (k) coefficient values to assess consistency between raters. The paired t test was applied to compare the pre- and postoperative data. Comparison of the other quantitative variables between the fixed- and mobile-core groups was analyzed with the independent t test. Categorical variables were analyzed with the c2
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.09.075
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
Figure 2. McAfee classification for heterotopic ossification. (A) Grade I: bone formation outside the disc space; (B) Grade II: bone formation within the intervertebral disc space but does not influence the
test. A value of P less than 0.05 was defined as statistically significant. RESULTS The mean follow-up time of all 218 patients was 46.8 23.9 months (range, 24e134 months). The average age was 43.1 7.9 years (range, 24e64 years). There were 81 patients (43 Discover, 38 Prodisc-C) in the fixed-core group, and 137 patients (102 PrestigeLP, 35 Bryan) in the mobile-core group. There were no statistically significant differences in age, sex, follow-up time, or levels of surgery distribution between the 2 groups (Table 1). At the final follow-up, the overall incidence of HO was 39.9% (87/218). The interobserver reliability for 2 independent raters determining HO classification was found to be k ¼ 0.863 (P < 0.001), 95% confidence interval 0.822e0.904. The incidence of HO in fixed-core group was 50.6% (41/81) and in the mobilecore group was 33.6% (46/137). The incidence of HO in fixed-core group was significantly greater than those in the mobile-core group (P ¼ 0.013). The incidence of HO in each type of prosthesis is demonstrated in Figure 3. The distribution of
WORLD NEUROSURGERY -: e1-e6, - 2018
HO AFTER FIXED- AND MOBILE-CORE CDA
segmental motion; (C) Grade III: bone formation within the intervertebral disc space and restricts the segmental motion; and (D) Grade IV: bone formation causing arthrodesis.
different grade of HO in each type of prosthesis is shown in Figure 4. Regarding the clinical outcome, preoperative NDI, VAS neck and arm, and JOA scores and were all comparable between the Table 1. Baseline Demographics Variables No. of patients Age, years Sex, male:female Follow-up time, months
Fixed-Core Group Mobile-Core Group P Value 81
137
42.8 8.6
43.3 7.5
0.652
41:40
73:64
0.703
45.6 22.2
47.4 24.8
Index level
0.587 0.583
C3eC4
7
12
C4eC5
17
20
C5eC6
42
72
C6eC7
15
33
www.WORLDNEUROSURGERY.org
e3
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
HO AFTER FIXED- AND MOBILE-CORE CDA
final follow-up (P > 0.05). However, the ROM of the index level in both groups was statically significantly decreased at the final follow-up (P < 0.05). In addition, the study showed that patients with HO had significant less ROM than patients without HO in the fixed-core group (5.2 3.7 vs. 8.8 3.0, P < 0.001). Similar results were found in the mobile-core group (5.1 3.1 vs. 9.6 3.4, P < 0.001). DISCUSSION
Figure 3. The incidences of heterotopic ossification (HO) of the 4 types of prostheses (Prestige-LP , Bryan, Discover, and Prodisc-C).
fixed- and mobile-core groups (P > 0.05, Table 2). Both groups demonstrated statically significant improvement in NDI, VAS neck and arm, and JOA scores at the final follow-up (P < 0.05). However, we found no significant differences in NDI, VAS neck and arm, or JOA scores between the fixed- and mobile-core groups at the final follow-up (P > 0.05). In addition, no significant differences were observed in NDI, VAS neck and arm, or JOA scores between patients with HO and without HO (P > 0.05). The preoperative radiographic data including C2eC7 angle, SA, and ROM of the index level were all comparable between the fixed- and mobile-core groups (P > 0.05, Table 3). In addition, there were no statically significant differences in C2eC7 angle, SA, or ROM of the index level between the 2 groups at the final follow-up (P > 0.05). The cervical sagittal alignment including SA and C2eC7 angle in the 2 groups were both maintained at the
The present study analyzed 218 patients who underwent CDA a mean follow-up of 46.8 months. Patients were divided into fixedcore (Prodisc-C and Discover) or mobile-core (Prestige-LP and Bryan) group according to the spinal kinematics of prosthesis. We found that the fixed-core groups showed a significantly greater incidence of HO formation than the mobile-core group. However, there were no significant differences in clinical outcomes including NDI, VAS neck and arm, or JOA scores between the 2 groups. Similarly, no significant differences were observed in cervical sagittal alignment (C2eC7 angle and SA) or ROM of the index level between the 2 groups. Although HO is a common complication after CDA, the mechanism of HO formation remains unknown. Prosthesis type had been reported to be one of the factors that may influence the occurrence of HO after CDA.12,15,16 Yi et al.12 retrospectively investigated 170 patients who underwent CDA with 3 types of prosthesis (Bryan, Mobi-C, and Prodisc-C) and identified differences in occurrence rate of HO according to prosthesis type. They found that the incidence of HO was 21% in the Bryan group, 52.5% in the Mobi-C groups, and 71.4% in the Prodisc-C group. Similarly, Jin et al.15 reported that the occurrence rate of HO in the Bryan disc was 49%, in the Prestige-LP disc 60%, and in the PCM disc 80%. Noriega et al.16 reported that the incidence of high-grade (Grade 3 and 4) HO was observed in 18.5% of the Baguera group, 65.0% of the PCM group, and 73.7% of the
Figure 4. The distribution of grades of heterotopic ossification in the 4 types of prostheses (Prestige-LP , Bryan, Discover, and Prodisc-C).
e4
www.SCIENCEDIRECT.com
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.09.075
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
HO AFTER FIXED- AND MOBILE-CORE CDA
Table 2. Clinical Outcome Between the 2 Groups Fixed-Core Group (n [ 81)
Variables
Mobile-Core Group (n [ 137)
P Value
Pre-JOA score
10.8 2.1
10.9 1.9
0.729
Last FU JOA score
14.6 1.5*
14.3 1.4*
0.380
Pre-NDI score
34.7 7.7
34.4 8.7
0.800
Last FU NDI score
14.4 3.9*
14.9 5.2*
0.430
Pre-VAS—neck
6.1 1.5
6.2 2.1
0.835
Last FU VAS—neck
2.0 1.1*
2.2 1.2*
0.565
Pre-VAS—arm
6.1 1.7
6.1 2.1
0.911
Last FU VAS—arm
2.1 1.1*
2.0 1.2*
0.902
Pre, preoperative; JOA, Japanese Orthopaedic Association; FU, follow-up; NDI, Neck Disability Index; VAS, visual analogue scale. *P < 0.05 compared with preoperatively.
Prodisc-C group. In our study, we found that the incidences of HO in the Bryan, Prestige-LP, Discover, and Prodisc-C were 31.4%, 34. 3% 46.5%, and 55.3%, respectively. Interestingly, the aforementioned studies, together with the present study, generally adhere to the result that the fixed-core prosthesis had a greater incidence of HO than mobile-core prosthesis. The artificial cervical disc can be classified into 2 types of design with regard to spinal kinematics: fixed-core and mobile-core. Similarly, as the natural segmental movement of cervical spine, the mobile-core prosthesis allows segmental motion in 6 degrees of freedom, with rotations and translations about 3 independent axes (e.g., Prestige-LP and Bryan).17 However, the fixed-core prosthesis has a fixed axis of rotation, which the translation is coupled with rotation (e.g., Prodisc-C and Discover). To date, previous studies mainly focused on in vitro biomechanical comparison between the fixed- and mobile-core
Table 3. Radiographic Outcomes Between the 2 Groups
prostheses.17-20 Moumene and Geisler20 reported that fixed-core prosthesis would suffer greater stresses at the endplate-implant interface and prosthesis core than mobile-core prosthesis. The present study in vivo compared the HO formation between the fixed- and mobile-core prostheses. We found that the fixed-core prosthesis had a greater incidence of HO formation than the mobile-core prosthesis. We speculated that the reason may be as follows: greater stresses at the endplate-implant interface in the fixed-core prosthesis; greater stresses at the prosthesis core induce wear debris in the fixed-core prosthesis; and the mobile-core prosthesis can better mimic the natural cervical kinematics. It can be assumed that after implantation of one cervical disc prosthesis, the more precisely the prosthesis mimics the natural cervical kinematics, the lower incidence of HO. With regard to clinical outcome, the present study demonstrated that there were no significant differences in NDI, VAS neck and arm, or JOA scores between the fixed- and mobile-core groups. Furthermore, we found that the HO did not influence the clinical outcome. Similar results were reported in previous studies. Lee et al.21 reported that the formation of HO was not significantly correlated with the clinical outcome. Zhou et al.22 reported that clinical outcomes were not adversely influenced by the presence of HO after CDA. These results indicate that the remission of clinical symptoms mostly depends on thorough neurologic decompression rather than prosthesis type and segmental motion. Concerning the radiographic outcome, the present study showed the formation of HO adversely affected the segmental ROM in both fixed- and mobile-core groups. Similarly, Zhao et al.23 retrospectively investigated patients who underwent CDA with Bryan discs and found that the segmental ROM in HO group was significantly less than those in non-HO group (2.6 vs. 9.3 ). However, our study showed that the prosthesis type did not influence the segmental ROM and cervical sagittal alignment. The results correspond to the fact that the coupling of rotation and translation in the fixed-core prosthesis is the essential difference from the mobile-core prosthesis, rather than the degrees of segmental ROM.20 The present study, for the first time, investigated the formation of HO between the fixed- and mobile-core prostheses. However, our study has some limitations. First, the retrospective nature of our study may be associated with bias. Second, because of the different approval times of the prosthesis in clinical use, some prostheses were not allowed to be used at the initial stage of cervical arthroplasty. However, there were no significant differences in follow-up time between the 2 groups. Furthermore, the types of prosthesis included in our study were limited. More types of prostheses should be investigated in the future.
Fixed-Core Group (n [ 81)
Mobile-Core Group (n [ 137)
P Value
10.7 5.5
10.7 7.1
0.996
10.1 4.4
11.0 6.6
0.219
3.5 1.8
3.4 2.0
0.680
3.4 1.4
3.3 2.8
0.758
CONCLUSIONS
Pre-ROM of the index level,
9.3 3.1
9.1 3.2
0.607
Last FU ROM of the index level,
7.4 4.0*
7.6 3.7*
0.631
The present retrospective study demonstrated that the fixed-core prosthesis had a significantly greater incidence of HO than the mobile-core prosthesis after CDA. Both CDA with fixed- and mobile-core prostheses gained satisfactory clinical outcomes and maintained cervical sagittal alignment. The formation of HO influenced the segmental ROM but did not adversely affect the clinical outcome.
Variables Pre C2eC7,
Last FU C2eC7, Pre SA,
Last FU SA,
Pre, preoperative, FU, follow-up; SA, segmental angle; ROM, range of motion. *P < 0.05 compared with preoperatively.
WORLD NEUROSURGERY -: e1-e6, - 2018
www.WORLDNEUROSURGERY.org
e5
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
REFERENCES 1. Loumeau TP, Darden BV, Kesman TJ, Odum SM, Van Doren BA, Laxer EB, et al. A RCT comparing 7-year clinical outcomes of one level symptomatic cervical disc disease (SCDD) following ProDisc-C total disc arthroplasty (TDA) versus anterior cervical discectomy and fusion (ACDF). Eur Spine J. 2016;25:2263-2270. 2. Gornet MF, Lanman TH, Burkus JK, Hodges SD, McConnell JR, Dryer RF, et al. Cervical disc arthroplasty with the Prestige LP disc versus anterior cervical discectomy and fusion, at 2 levels: results of a prospective, multicenter randomized controlled clinical trial at 24 months. J Neurosurg Spine. 2017;26:653-667. 3. Zeng J, Liu H, Wang B, Deng Y, Ding C, Chen H, et al. Clinical and radiographic comparison of cervical disc arthroplasty with Prestige-LP Disc and anterior cervical fusion: a minimum 6-year follow-up study. Clin Neurol Neurosurg. 2018;164: 97-102. 4. Delamarter RB, Zigler J. Five-year reoperation rates, cervical total disc replacement versus fusion, results of a prospective randomized clinical trial. Spine (Phila Pa 1976). 2013;38:711-717. 5. Lei T, Liu Y, Wang H, Xu J, Ma Q, Wang L, et al. Clinical and radiological analysis of Bryan cervical disc arthroplasty: eight-year follow-up results compared with anterior cervical discectomy and fusion. Int Orthop. 2016;40:1197-1203. 6. Mehren C, Suchomel P, Grochulla F, Barsa P, Sourkova P, Hradil J, et al. Heterotopic ossification in total cervical artificial disc replacement. Spine (Phila Pa 1976). 2006;31:2802-2806. 7. Vanden Bossche L, Vanderstraeten G. Heterotopic ossification: a review. J Rehabil Med. 2005;37: 129-136. 8. Parkinson JF, Sekhon LH. Cervical arthroplasty complicated by delayed spontaneous fusion. Case report. J Neurosurg Spine. 2005;2:377-380.
e6
www.SCIENCEDIRECT.com
HO AFTER FIXED- AND MOBILE-CORE CDA
9. Suchomel P, Jurak L, Benes V 3rd, Brabec R, Bradac O, Elgawhary S. Clinical results and development of heterotopic ossification in total cervical disc replacement during a 4-year followup. Eur Spine J. 2010;19:307-315.
18. Lee SH, Im YJ, Kim KT, Kim YH, Park WM, Kim K. Comparison of cervical spine biomechanics after fixed- and mobile-core artificial disc replacement: a finite element analysis. Spine (Phila Pa 1976). 2011;36:700-708.
10. Pimenta L, Oliveira L, Coutinho E, Marchi L. Bone formation in cervical total disk replacement (CTDR) up to the 6-year follow-up: experience from 272 levels. Neurosurg Q. 2013;23:1-6.
19. Lou J, Li Y, Wang B, Meng Y, Wu T, Liu H. In vitro biomechanical comparison after fixed- and mobile-core artificial cervical disc replacement versus fusion. Medicine (Baltimore). 2017;96:e8291.
11. Park JH, Rhim SC, Roh SW. Mid-term follow-up of clinical and radiologic outcomes in cervical total disk replacement (Mobi-C): incidence of heterotopic ossification and risk factors. J Spinal Disord Tech. 2013;26:141-145.
20. Moumene M, Geisler FH. Comparison of biomechanical function at ideal and varied surgical placement for two lumbar artificial disc implant designs: mobile-core versus fixed-core. Spine (Phila Pa 1976). 2007;32:1840-1851.
12. Yi S, Kim KN, Yang MS, Yang JW, Kim H, Ha Y, et al. Difference in occurrence of heterotopic ossification according to prosthesis type in the cervical artificial disc replacement. Spine (Phila Pa 1976). 2010;35:1556-1561.
21. Lee JH, Jung TG, Kim HS, Jang JS, Lee SH. Analysis of the incidence and clinical effect of the heterotopic ossification in a single-level cervical artificial disc replacement. Spine J. 2010;10: 676-682.
13. Kim KS, Heo DH. Do postoperative biomechanical changes induce heterotopic ossification after cervical arthroplasty? A 5-year follow-up study. Clin Spine Surg. 2016;29:E309-E313.
22. Zhou F, Ju KL, Zhao Y, Zhang F, Pan S, Heller JG, et al. Progressive bone formation after cervical disc replacement: minimum of 5-year follow-up. Spine (Phila Pa 1976). 2018;43:E163-E170.
14. McAfee PC, Cunningham BW, Devine J, Williams E, Yu-Yahiro J. Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech. 2003;16:384-389.
23. Zhao Y, Zhang Y, Sun Y, Pan S, Zhou F, Liu Z. Application of cervical arthroplasty with bryan cervical disc. Spine (Phila Pa 1976). 2016;41:111-115.
15. Jin YJ, Park SB, Kim MJ, Kim KJ, Kim HJ. An analysis of heterotopic ossification in cervical disc arthroplasty: a novel morphologic classification of an ossified mass. Spine J. 2013;13:408-420. 16. Noriega DC, Ramajo RH, Sanchez-Lite I, Toribio B, Delen E, Sahin S. Heterotopic ossification in cervical disk surgery is still a problem. what are the key factors for a solution? World Neurosurg. 2016;96:585-590. 17. Cunningham BW, Gordon JD, Dmitriev AE, Hu N, McAfee PC. Biomechanical evaluation of total disc replacement arthroplasty: an in vitro human cadaveric model. Spine (Phila Pa 1976). 2003;28: S110-S117.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 27 June 2018; accepted 11 September 2018 Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.09.075 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.09.075
Comparison of Heterotopic Ossification After Fixed- and Mobile-Core Cervical Disc Arthroplasty Junfeng Zeng, Hao Liu, Hua Chen, Chen Ding, Xin Rong, Yang Meng, Yi Yang
OBJECTIVE: To compare the heterotopic ossification (HO) between cervical disc arthroplasty (CDA) with fixed- and mobile-core prosthesis and to compare the clinical and radiographic outcomes.
-
METHODS: This was a retrospective analysis of patients who underwent CDA in our institute. Patients were divided into a fixed-core group (Prodisc-C and Discover disc) and mobile-core group (Bryan and Prestige-LP disc). HO was assessed based on the McAfee classification. The visual analogue scale, Neck Disability Index, and Japanese Orthopaedic Association scores were used to evaluate clinical outcomes. In addition, radiographic assessments included cervical sagittal alignment (C2eC7 angle), segmental angle, and range of motion of the index level.
However, both CDA with fixed- and mobile-core prostheses obtained good clinical outcomes and maintained cervical sagittal alignment.
-
RESULTS: A total of 218 patients were included with a minimal follow-up of 24 months. There were 137 patients in mobile-core group (Prestige-LP, 102; Bryan, 35) and 81 patients in the fixed-core group (Discover, 43; and Prodisc-C, 38). The mean follow-up time was 46.8 months. At the final follow-up, the overall incidence of HO was 39.9%. The incidence of HO in the fixed-core group was significantly greater than that in the mobile-core group (50.6% vs. 33.6%, P [ 0.013). However, there were no significant differences in visual analogue scale, Neck Disability Index, or Japanese Orthopaedic Association scores, C2eC7 angle, segmental angle, or range of motion of the index level between the 2 groups.
-
CONCLUSIONS: The fixed-core prosthesis had a greater incidence of HO than mobile-core prosthesis after CDA.
-
Key words Cervical disc arthroplasty - Fixed-core - Heterotopic ossification - Mobile-core -
Abbreviations and Acronyms CDA: Cervical disc arthroplasty HO: Heterotopic ossification JOA: Japanese Orthopaedic Association NDI: Neck Disability Index ROM: Range of motion
INTRODUCTION
C
ervical disc arthroplasty (CDA) has been proposed as an alternative to conventional cervical arthrodesis for the treatment of cervical degenerative disc diseases. Recently, an increasing number of long-term studies have demonstrated that CDA has obtained satisfactory clinical outcomes in comparison with cervical arthrodesis.1-3 Previous studies reported that CDA maintained range of motion (ROM) of the surgical segment, delayed adjacent segment degeneration, and reduced the reoperation rate.4,5 However, the development of heterotopic ossification (HO), which may decrease the ROM, is a common complication after CDA.6 HO is defined as mature bone formation outside the skeletal system.7 Parkinson and Sekhon8 first reported in 2005 a 55-yearold woman who underwent CDA with Bryan artificial cervical disc and developed HO. After that, various studies reported HO formation after CDA with different incidences, ranging from 7.7% to 94.1%.9-11 However, the definitive mechanism of HO formation still remains unclear. Yi et al.12 reported that different prosthesis types can influence the formation of HO after CDA. Kim et al.13 reported that postoperative biomechanical changes may induce HO after CDA. The cervical artificial disc currently used can be classified as fixed- or mobile-core according to its biomechanical properties. In the present study, we hypothesized that CDAs
SA: Segmental angle VAS: Visual analogue scale Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, Sichuan Province, China To whom correspondence should be addressed: Hao Liu, M.D. Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.09.075 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY -: e1-e6, - 2018
www.WORLDNEUROSURGERY.org
e1
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
HO AFTER FIXED- AND MOBILE-CORE CDA
Figure 1. (A) The C2eC7 angle was defined as the angle formed between the lower endplate of the C2 and C7 vertebral body. The segmental angle (SA) was measured by the angle formed between the upper and lower
with fixed cores and mobile cores have different rates of HO. The purpose of our study is to compare the incidence of HO between CDA with fixed- and mobile-core prosthesis and also compare the clinical and radiographic outcomes. MATERIAL AND METHODS Study Design We retrospectively included patients who underwent single-level CDA from February 2005 to September 2015 in our institute. Patients who underwent CDA with Prodisc-C (Synthes; West Chester, Pennsylvania, USA) and Discover (DePuy, Raynham, Massachusetts, USA) disc formed the fixed-core group and patients who underwent CDA with Bryan (Medtronic, Memphis, Tennessee, USA) and Prestige-LP (Medtronic) disc formed the mobile-core group. Approval of the local ethics committee was obtained, but no informed consent was collected because of the retrospective nature of the study. The inclusion criteria included single-level cervical degenerative disc disease causing myelopathy or radiculopathy between C3 and C7, age 18e65 years, unresponsive to conservative treatment for at least 6 weeks, and follow-up time longer than 24 months. The exclusion criteria included severe spondylosis or facet joint degeneration, ossification of the posterior longitudinal ligament, radiographic signs of instability, previous cervical spine surgery, osteoporosis (T-score 2.5), ankylosing spondylitis, rheumatoid arthritis, and infection. Based on the aforementioned criteria, a total of 218 patients were enrolled in this study. All surgeries were performed by the same single senior surgeon using a standard surgical technique. Clinical and radiographic data of all patients were routinely
e2
www.SCIENCEDIRECT.com
endplate of the index intervertebral space. (BeC) The range of motion of the index level was calculated by the changes of SA on the full flexion and extension radiographs.
collected preoperatively, immediately postoperatively, 3, 6, 12, 24 months postoperatively, and then biennially. Outcome Assessments Neck and arm pain of all the patients were evaluated by the visual analogue scale (VAS) score. The Neck Disability Index (NDI) score was used to assess the function of the neck. For patients with myelopathy, the Japanese Orthopaedic Association (JOA) scores were applied to evaluate the neurologic status. The C2eC7 angle and segmental angle (SA), which were measured on the lateral radiographs, were used to assess the cervical sagittal alignment (Figure 1A). The ROM of the index level was measured on the full flexion and extension radiographs (Figure 1BeC). In addition, HO was evaluated according to the McAfee classification by 2 spine surgeons who were independent from the surgeries (Figure 2AeD).14 They were asked to determine the appropriate grade of HO by radiographs and computed tomography. Any discrepancies between them were resolved through a consensus. Statistical Analysis All statistical analyses were conducted using SPSS, version 24.0 software (IBM Corp., Armonk, New York, USA). Quantitative variables were described as the mean standard deviation. The interobserver reliability was measured by calculating the weighted kappa (k) coefficient values to assess consistency between raters. The paired t test was applied to compare the pre- and postoperative data. Comparison of the other quantitative variables between the fixed- and mobile-core groups was analyzed with the independent t test. Categorical variables were analyzed with the c2
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.09.075
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
Figure 2. McAfee classification for heterotopic ossification. (A) Grade I: bone formation outside the disc space; (B) Grade II: bone formation within the intervertebral disc space but does not influence the
test. A value of P less than 0.05 was defined as statistically significant. RESULTS The mean follow-up time of all 218 patients was 46.8 23.9 months (range, 24e134 months). The average age was 43.1 7.9 years (range, 24e64 years). There were 81 patients (43 Discover, 38 Prodisc-C) in the fixed-core group, and 137 patients (102 PrestigeLP, 35 Bryan) in the mobile-core group. There were no statistically significant differences in age, sex, follow-up time, or levels of surgery distribution between the 2 groups (Table 1). At the final follow-up, the overall incidence of HO was 39.9% (87/218). The interobserver reliability for 2 independent raters determining HO classification was found to be k ¼ 0.863 (P < 0.001), 95% confidence interval 0.822e0.904. The incidence of HO in fixed-core group was 50.6% (41/81) and in the mobilecore group was 33.6% (46/137). The incidence of HO in fixed-core group was significantly greater than those in the mobile-core group (P ¼ 0.013). The incidence of HO in each type of prosthesis is demonstrated in Figure 3. The distribution of
WORLD NEUROSURGERY -: e1-e6, - 2018
HO AFTER FIXED- AND MOBILE-CORE CDA
segmental motion; (C) Grade III: bone formation within the intervertebral disc space and restricts the segmental motion; and (D) Grade IV: bone formation causing arthrodesis.
different grade of HO in each type of prosthesis is shown in Figure 4. Regarding the clinical outcome, preoperative NDI, VAS neck and arm, and JOA scores and were all comparable between the Table 1. Baseline Demographics Variables No. of patients Age, years Sex, male:female Follow-up time, months
Fixed-Core Group Mobile-Core Group P Value 81
137
42.8 8.6
43.3 7.5
0.652
41:40
73:64
0.703
45.6 22.2
47.4 24.8
Index level
0.587 0.583
C3eC4
7
12
C4eC5
17
20
C5eC6
42
72
C6eC7
15
33
www.WORLDNEUROSURGERY.org
e3
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
HO AFTER FIXED- AND MOBILE-CORE CDA
final follow-up (P > 0.05). However, the ROM of the index level in both groups was statically significantly decreased at the final follow-up (P < 0.05). In addition, the study showed that patients with HO had significant less ROM than patients without HO in the fixed-core group (5.2 3.7 vs. 8.8 3.0, P < 0.001). Similar results were found in the mobile-core group (5.1 3.1 vs. 9.6 3.4, P < 0.001). DISCUSSION
Figure 3. The incidences of heterotopic ossification (HO) of the 4 types of prostheses (Prestige-LP , Bryan, Discover, and Prodisc-C).
fixed- and mobile-core groups (P > 0.05, Table 2). Both groups demonstrated statically significant improvement in NDI, VAS neck and arm, and JOA scores at the final follow-up (P < 0.05). However, we found no significant differences in NDI, VAS neck and arm, or JOA scores between the fixed- and mobile-core groups at the final follow-up (P > 0.05). In addition, no significant differences were observed in NDI, VAS neck and arm, or JOA scores between patients with HO and without HO (P > 0.05). The preoperative radiographic data including C2eC7 angle, SA, and ROM of the index level were all comparable between the fixed- and mobile-core groups (P > 0.05, Table 3). In addition, there were no statically significant differences in C2eC7 angle, SA, or ROM of the index level between the 2 groups at the final follow-up (P > 0.05). The cervical sagittal alignment including SA and C2eC7 angle in the 2 groups were both maintained at the
The present study analyzed 218 patients who underwent CDA a mean follow-up of 46.8 months. Patients were divided into fixedcore (Prodisc-C and Discover) or mobile-core (Prestige-LP and Bryan) group according to the spinal kinematics of prosthesis. We found that the fixed-core groups showed a significantly greater incidence of HO formation than the mobile-core group. However, there were no significant differences in clinical outcomes including NDI, VAS neck and arm, or JOA scores between the 2 groups. Similarly, no significant differences were observed in cervical sagittal alignment (C2eC7 angle and SA) or ROM of the index level between the 2 groups. Although HO is a common complication after CDA, the mechanism of HO formation remains unknown. Prosthesis type had been reported to be one of the factors that may influence the occurrence of HO after CDA.12,15,16 Yi et al.12 retrospectively investigated 170 patients who underwent CDA with 3 types of prosthesis (Bryan, Mobi-C, and Prodisc-C) and identified differences in occurrence rate of HO according to prosthesis type. They found that the incidence of HO was 21% in the Bryan group, 52.5% in the Mobi-C groups, and 71.4% in the Prodisc-C group. Similarly, Jin et al.15 reported that the occurrence rate of HO in the Bryan disc was 49%, in the Prestige-LP disc 60%, and in the PCM disc 80%. Noriega et al.16 reported that the incidence of high-grade (Grade 3 and 4) HO was observed in 18.5% of the Baguera group, 65.0% of the PCM group, and 73.7% of the
Figure 4. The distribution of grades of heterotopic ossification in the 4 types of prostheses (Prestige-LP , Bryan, Discover, and Prodisc-C).
e4
www.SCIENCEDIRECT.com
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.09.075
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
HO AFTER FIXED- AND MOBILE-CORE CDA
Table 2. Clinical Outcome Between the 2 Groups Fixed-Core Group (n [ 81)
Variables
Mobile-Core Group (n [ 137)
P Value
Pre-JOA score
10.8 2.1
10.9 1.9
0.729
Last FU JOA score
14.6 1.5*
14.3 1.4*
0.380
Pre-NDI score
34.7 7.7
34.4 8.7
0.800
Last FU NDI score
14.4 3.9*
14.9 5.2*
0.430
Pre-VAS—neck
6.1 1.5
6.2 2.1
0.835
Last FU VAS—neck
2.0 1.1*
2.2 1.2*
0.565
Pre-VAS—arm
6.1 1.7
6.1 2.1
0.911
Last FU VAS—arm
2.1 1.1*
2.0 1.2*
0.902
Pre, preoperative; JOA, Japanese Orthopaedic Association; FU, follow-up; NDI, Neck Disability Index; VAS, visual analogue scale. *P < 0.05 compared with preoperatively.
Prodisc-C group. In our study, we found that the incidences of HO in the Bryan, Prestige-LP, Discover, and Prodisc-C were 31.4%, 34. 3% 46.5%, and 55.3%, respectively. Interestingly, the aforementioned studies, together with the present study, generally adhere to the result that the fixed-core prosthesis had a greater incidence of HO than mobile-core prosthesis. The artificial cervical disc can be classified into 2 types of design with regard to spinal kinematics: fixed-core and mobile-core. Similarly, as the natural segmental movement of cervical spine, the mobile-core prosthesis allows segmental motion in 6 degrees of freedom, with rotations and translations about 3 independent axes (e.g., Prestige-LP and Bryan).17 However, the fixed-core prosthesis has a fixed axis of rotation, which the translation is coupled with rotation (e.g., Prodisc-C and Discover). To date, previous studies mainly focused on in vitro biomechanical comparison between the fixed- and mobile-core
Table 3. Radiographic Outcomes Between the 2 Groups
prostheses.17-20 Moumene and Geisler20 reported that fixed-core prosthesis would suffer greater stresses at the endplate-implant interface and prosthesis core than mobile-core prosthesis. The present study in vivo compared the HO formation between the fixed- and mobile-core prostheses. We found that the fixed-core prosthesis had a greater incidence of HO formation than the mobile-core prosthesis. We speculated that the reason may be as follows: greater stresses at the endplate-implant interface in the fixed-core prosthesis; greater stresses at the prosthesis core induce wear debris in the fixed-core prosthesis; and the mobile-core prosthesis can better mimic the natural cervical kinematics. It can be assumed that after implantation of one cervical disc prosthesis, the more precisely the prosthesis mimics the natural cervical kinematics, the lower incidence of HO. With regard to clinical outcome, the present study demonstrated that there were no significant differences in NDI, VAS neck and arm, or JOA scores between the fixed- and mobile-core groups. Furthermore, we found that the HO did not influence the clinical outcome. Similar results were reported in previous studies. Lee et al.21 reported that the formation of HO was not significantly correlated with the clinical outcome. Zhou et al.22 reported that clinical outcomes were not adversely influenced by the presence of HO after CDA. These results indicate that the remission of clinical symptoms mostly depends on thorough neurologic decompression rather than prosthesis type and segmental motion. Concerning the radiographic outcome, the present study showed the formation of HO adversely affected the segmental ROM in both fixed- and mobile-core groups. Similarly, Zhao et al.23 retrospectively investigated patients who underwent CDA with Bryan discs and found that the segmental ROM in HO group was significantly less than those in non-HO group (2.6 vs. 9.3 ). However, our study showed that the prosthesis type did not influence the segmental ROM and cervical sagittal alignment. The results correspond to the fact that the coupling of rotation and translation in the fixed-core prosthesis is the essential difference from the mobile-core prosthesis, rather than the degrees of segmental ROM.20 The present study, for the first time, investigated the formation of HO between the fixed- and mobile-core prostheses. However, our study has some limitations. First, the retrospective nature of our study may be associated with bias. Second, because of the different approval times of the prosthesis in clinical use, some prostheses were not allowed to be used at the initial stage of cervical arthroplasty. However, there were no significant differences in follow-up time between the 2 groups. Furthermore, the types of prosthesis included in our study were limited. More types of prostheses should be investigated in the future.
Fixed-Core Group (n [ 81)
Mobile-Core Group (n [ 137)
P Value
10.7 5.5
10.7 7.1
0.996
10.1 4.4
11.0 6.6
0.219
3.5 1.8
3.4 2.0
0.680
3.4 1.4
3.3 2.8
0.758
CONCLUSIONS
Pre-ROM of the index level,
9.3 3.1
9.1 3.2
0.607
Last FU ROM of the index level,
7.4 4.0*
7.6 3.7*
0.631
The present retrospective study demonstrated that the fixed-core prosthesis had a significantly greater incidence of HO than the mobile-core prosthesis after CDA. Both CDA with fixed- and mobile-core prostheses gained satisfactory clinical outcomes and maintained cervical sagittal alignment. The formation of HO influenced the segmental ROM but did not adversely affect the clinical outcome.
Variables Pre C2eC7,
Last FU C2eC7, Pre SA,
Last FU SA,
Pre, preoperative, FU, follow-up; SA, segmental angle; ROM, range of motion. *P < 0.05 compared with preoperatively.
WORLD NEUROSURGERY -: e1-e6, - 2018
www.WORLDNEUROSURGERY.org
e5
ORIGINAL ARTICLE JUNFENG ZENG ET AL.
REFERENCES 1. Loumeau TP, Darden BV, Kesman TJ, Odum SM, Van Doren BA, Laxer EB, et al. A RCT comparing 7-year clinical outcomes of one level symptomatic cervical disc disease (SCDD) following ProDisc-C total disc arthroplasty (TDA) versus anterior cervical discectomy and fusion (ACDF). Eur Spine J. 2016;25:2263-2270. 2. Gornet MF, Lanman TH, Burkus JK, Hodges SD, McConnell JR, Dryer RF, et al. Cervical disc arthroplasty with the Prestige LP disc versus anterior cervical discectomy and fusion, at 2 levels: results of a prospective, multicenter randomized controlled clinical trial at 24 months. J Neurosurg Spine. 2017;26:653-667. 3. Zeng J, Liu H, Wang B, Deng Y, Ding C, Chen H, et al. Clinical and radiographic comparison of cervical disc arthroplasty with Prestige-LP Disc and anterior cervical fusion: a minimum 6-year follow-up study. Clin Neurol Neurosurg. 2018;164: 97-102. 4. Delamarter RB, Zigler J. Five-year reoperation rates, cervical total disc replacement versus fusion, results of a prospective randomized clinical trial. Spine (Phila Pa 1976). 2013;38:711-717. 5. Lei T, Liu Y, Wang H, Xu J, Ma Q, Wang L, et al. Clinical and radiological analysis of Bryan cervical disc arthroplasty: eight-year follow-up results compared with anterior cervical discectomy and fusion. Int Orthop. 2016;40:1197-1203. 6. Mehren C, Suchomel P, Grochulla F, Barsa P, Sourkova P, Hradil J, et al. Heterotopic ossification in total cervical artificial disc replacement. Spine (Phila Pa 1976). 2006;31:2802-2806. 7. Vanden Bossche L, Vanderstraeten G. Heterotopic ossification: a review. J Rehabil Med. 2005;37: 129-136. 8. Parkinson JF, Sekhon LH. Cervical arthroplasty complicated by delayed spontaneous fusion. Case report. J Neurosurg Spine. 2005;2:377-380.
e6
www.SCIENCEDIRECT.com
HO AFTER FIXED- AND MOBILE-CORE CDA
9. Suchomel P, Jurak L, Benes V 3rd, Brabec R, Bradac O, Elgawhary S. Clinical results and development of heterotopic ossification in total cervical disc replacement during a 4-year followup. Eur Spine J. 2010;19:307-315.
18. Lee SH, Im YJ, Kim KT, Kim YH, Park WM, Kim K. Comparison of cervical spine biomechanics after fixed- and mobile-core artificial disc replacement: a finite element analysis. Spine (Phila Pa 1976). 2011;36:700-708.
10. Pimenta L, Oliveira L, Coutinho E, Marchi L. Bone formation in cervical total disk replacement (CTDR) up to the 6-year follow-up: experience from 272 levels. Neurosurg Q. 2013;23:1-6.
19. Lou J, Li Y, Wang B, Meng Y, Wu T, Liu H. In vitro biomechanical comparison after fixed- and mobile-core artificial cervical disc replacement versus fusion. Medicine (Baltimore). 2017;96:e8291.
11. Park JH, Rhim SC, Roh SW. Mid-term follow-up of clinical and radiologic outcomes in cervical total disk replacement (Mobi-C): incidence of heterotopic ossification and risk factors. J Spinal Disord Tech. 2013;26:141-145.
20. Moumene M, Geisler FH. Comparison of biomechanical function at ideal and varied surgical placement for two lumbar artificial disc implant designs: mobile-core versus fixed-core. Spine (Phila Pa 1976). 2007;32:1840-1851.
12. Yi S, Kim KN, Yang MS, Yang JW, Kim H, Ha Y, et al. Difference in occurrence of heterotopic ossification according to prosthesis type in the cervical artificial disc replacement. Spine (Phila Pa 1976). 2010;35:1556-1561.
21. Lee JH, Jung TG, Kim HS, Jang JS, Lee SH. Analysis of the incidence and clinical effect of the heterotopic ossification in a single-level cervical artificial disc replacement. Spine J. 2010;10: 676-682.
13. Kim KS, Heo DH. Do postoperative biomechanical changes induce heterotopic ossification after cervical arthroplasty? A 5-year follow-up study. Clin Spine Surg. 2016;29:E309-E313.
22. Zhou F, Ju KL, Zhao Y, Zhang F, Pan S, Heller JG, et al. Progressive bone formation after cervical disc replacement: minimum of 5-year follow-up. Spine (Phila Pa 1976). 2018;43:E163-E170.
14. McAfee PC, Cunningham BW, Devine J, Williams E, Yu-Yahiro J. Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech. 2003;16:384-389.
23. Zhao Y, Zhang Y, Sun Y, Pan S, Zhou F, Liu Z. Application of cervical arthroplasty with bryan cervical disc. Spine (Phila Pa 1976). 2016;41:111-115.
15. Jin YJ, Park SB, Kim MJ, Kim KJ, Kim HJ. An analysis of heterotopic ossification in cervical disc arthroplasty: a novel morphologic classification of an ossified mass. Spine J. 2013;13:408-420. 16. Noriega DC, Ramajo RH, Sanchez-Lite I, Toribio B, Delen E, Sahin S. Heterotopic ossification in cervical disk surgery is still a problem. what are the key factors for a solution? World Neurosurg. 2016;96:585-590. 17. Cunningham BW, Gordon JD, Dmitriev AE, Hu N, McAfee PC. Biomechanical evaluation of total disc replacement arthroplasty: an in vitro human cadaveric model. Spine (Phila Pa 1976). 2003;28: S110-S117.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 27 June 2018; accepted 11 September 2018 Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.09.075 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.09.075