The Spine Journal - (2013) -

Clinical Study

Clinical and radiographic outcomes of cervical disc replacementwith a new prosthesis

Jinhao Miao, MDa, Fengbin Yu, MDb, Ye Shen, PhDc, Naya He, MPHc, Yong Kuang, MDa,Xinwei Wang, MDd, Deyu Chen, MDd,*

aDepartment of Orthopedics and Traumatology, Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine, 528 Zhangheng Rd,

Shanghai 201203, ChinabDepartment of Orthopaedic Surgery, No. 98 Hospital of PLA, 9 Chezhan Rd, Huzhou 313000, China

cDepartment of Epidemiology and Biostatistics, College of Public Health, University of Georgia, 405 College Station Rd, Athens, GA 30602, USAdDepartment of Orthopaedic Surgery, Changzheng Hospital, The Second Military Medical University, 415 Fengyang Rd, Shanghai 200003, China

Received 20 November 2012; revised 15 June 2013; accepted 13 July 2013

Abstract BACKGROUND CONTEXT: Anterior cervic

FDA device/drug

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Author disclosures

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al discectomy and interbody fusion was a classicaltreatment for cervical degenerative disc disease (CDDD). However, the rigid fusion also leads toa reduction in normal cervical spine motion and to increased biomechanical stress at adjacentlevels, which in turn accelerates degenerative changes of the discs at these levels. Cervical disc re-placement (CDR) is a new technology with the aim of addressing the limitations of fusion proces-sion and preserving motion at the treated level. Discover prosthesis (DePuy Spine, Raynham, MA,USA) is a new type artificial disc and there are few reports about it.PURPOSE: The purpose of this study was to analyze the primary clinical and radiographic out-comes of CDR with Discover prosthesis to treat mono- or bi-segment CDDD in a Chinesepopulation.STUDY DESIGN: The study design was prospective and single-center clinical trial of the Dis-cover prosthesis in the treatment of patients with mono- or bi-segment CDDD.PATIENTS SAMPLE: Seventy-nine patients with 102 Discover prosthesis arthroplasty performed(56 mono-segment and 23 bi-segment) were evaluated.OUTCOME MEASURES: Clinical outcomes based on Japanese Orthopaedic Association (JOA),visual analog scale (VAS) pain score, and Odom’s scale and radiographic outcomes including theanterior disc heights (ADH), posterior disc heights (PDH), range of motion, and performance ofheterotopic ossification (HO) of the operative segment were assessed.METHODS: Clinical and radiographic follow-up was performed. Preoperative and postoperativeADH, PDH, and range of motion were measured from lateral and flexion-extension radiographs.The paired t test was used to assess the difference of clinical and radiographic outcomes beforeand after operation. The performance of HO was observed by two independent MD.RESULTS: The mean follow-up time for all the patients was 31.6 months, ranging from 24 to 43months. Mean preoperative JOA score was 9.5, and VAS overall pain score was 7.2. At 2-, 6-, 12-,and 24-month follow-up, the mean JOA score was 14.1, 14.7, 15.3, and 14.9, whereas the meanVAS overall pain score was 1.9, 1.7, 1.8, and 1.4, respectively. Mean JOA and VAS scores showedstatistical improvements in the postoperative period. Seven patients had mild dysphagia within thefirst month after operation. According to Odom’s scale, 52 patients had excellent outcomes, 25 pa-tients had good outcomes, and 2 patients had fair outcomes at 2-year follow-up. The Mean preop-erative ADH and PDH of the operative segment were 4.9 mm and 3.1 mm. Compared with

status: Investigational (Discover Artificial Cervical

: JM: Nothing to disclose. FY: Nothing to disclose.

se. NH: Nothing to disclose. YK: Nothing to dis-

o disclose. DC: Nothing to disclose.

ceived in support of this work. No benefits in any

ill be received from a commercial party related di-

the subject of this manuscript.

JM and FY contributed equally to this work and should be considered

as co-first authors.

* Corresponding author. Department of Orthopaedic Surgery, Changz-

heng Hospital, The Second Military Medical University, 415 Fengyang Rd,

Shanghai 200003, China. Tel./fax: (86) 21-81885630.

E-mail address: kanemjh1980@126.com (D. Chen)

nt matter � 2013 Elsevier Inc. All rights reserved.

16/j.spinee.2013.07.439

2 J. Miao et al. / The Spine Journal - (2013) -

preoperative, there were significantly increased and maintenance well at 2- (7.5 mm, 5.1 mm), 6-(7.5 mm, 5.0 mm), 12- (7.4 mm, 4.9 mm) and 24-month (7.2 mm, 5.0 mm) follow-up. Range ofmotion of the operative segment in the postoperative follow-up was slightly increased than the pre-operative follow-up but not statistically significant. Heterotopic ossification was presented in sixreplaced levels at 1-year follow-up including 4 Grade I and 2 Grade II and 18 replaced levels atthe follow-up more than 2 years including 8 grade I and 10 grade II. No prosthesis subsidenceor excursion was identified.CONCLUSIONS: The use of Discover prostheses in our study resulted in satisfactory clinical andradiographic outcomes. The prostheses can restore and maintain interbody height, while preservethe motion of the treated segment. Although the results of this study demonstrate initial safetyand effectiveness in a Chinese population, we need further studies to know more about the impactof CDR with Discover prosthesis, especially on HO and adjacent segment degeneration. � 2013Elsevier Inc. All rights reserved.

Keywords: Cervical degenerative disc disease; Cervical disc replacement; Discover; Heterotopic ossification

Introduction

Since its development in the 1950s, anterior cervical dis-cectomy and interbody fusion (ACDF) has proven to bea successful and versatile treatment for cervical degenera-tive disc disease refractory to conservative therapy [1–4].The use of Cage and anterior plating have diminished pseu-darthrosis and graft site complication [5]. However, therigid fusion also leads to a reduction in normal cervicalspine motion and increased biomechanical stress at spinallevels adjacent to the fusion, which in turn acceleratesdegenerative changes of the discs at these levels [6–8]. Hi-librand et al. [9] have documented the occurrence of symp-tomatic adjacent-segment disc degeneration at a relativelyconstant incidence of 2.9% per year on a cumulative basis,with a predicted prevalence at 10 years approximating 25%.It has been estimated that 7% to 15% of the patients ulti-mately require a secondary procedure at an adjacent levelafter ACDF [10].

Cervical disc replacement (CDR) is a relatively new tech-nology in spine surgery with the aim of addressing the lim-itations of fusion procession and preserving motion at thetreated level. There are a wide variety of artificial prostheticdiscs available, among which Discover is a relatively newtype with limited reports to date. We describe the prelimi-nary clinical and radiographic outcomes from a prospectivestudy of consecutive patients undergoing mono- or bi-segment CDR with Discover artificial discs. The primary ef-ficacy was tested throughout the data analysis.

Materials and methods

Patients

A total of 79 patients (41 women and 38 men) of cervi-cal degenerative disc disease who had 3-13 months’ preop-erative history of symptoms (23 cases with radiculopathy,38 cases with myelopathy, and 18 cases with both radicul-opathy and myelopathy) and did not respond to the conser-vative treatment were enrolled and treated by CDR withDiscover prosthesis from March 2009 to November 2010.

Inclusion criteria for enrollment were disc herniation withpreserved mobility (O3� and !11�) in the affected one ortwo segments. Exclusion criteria included ossification ofthe posterior longitudinal ligament, kyphotic deformity,trauma, or instability of the cervical spine. Further exclu-sion criteria were advanced osteoporosis, ankylosing spon-dylitis, and rheumatoid arthritis. Patients above the age of60 years were also excluded from our study. The meanage of the cohort of patients was 41.3 years (range, 31–59 years). A total of 102 prosthesis were implanted with56 mono-segment and 23 bi-segment (Table 1). The meanfollow-up time was 31.6 months, ranging from 24 to 43months.

Operation procedure

Patients acquired general anesthesia and were placed insupine position. A right lateral transverse cut was imple-mented to expose the surgical segments. The compressivematerials including the posterior longitudinal ligament wereremoved. After testing the intervertebral height and width byfluoroscopy, appropriate prosthesis was implanted. Patientswere asked to get off the bed 24 hours later. A neck collarwas required to wear no more than 1 week.

Clinical evaluation

The clinical outcomes were evaluated using JapaneseOrthopaedic Association score and visual analog scale(VAS) score before and after operations. Incidence ofdysphagia-related symptoms was recorded using the systemdefined by Bazaz et al. [11] as a compensative index forclinical evaluation during the follow-up period. The Odomcriteria [12] was used to evaluate the operation effect foreach patient at 2 year’s follow-up.

Radiological evaluation

Patients were required to take cervical x-ray imaging,computed tomography, and magnetic resonance imagingbefore operation. Additional x-ray imaging was also

Table 1

Distribution of segments implanted with Discover prosthesis

Cervical segments No. of Discover prosthesis (%)

C3–C4 5 (5)

C4–C5 32 (31)

C5–C6 48 (47)

C6–C7 17 (17)

Total 102 (100)

Table 2

Operation effect at 2-year follow-up according to the Odom criteria

No. of patients (%) Score Description

52 (65.8) Excellent All preoperative symptoms relieved.

Neurologic deficits improved.

25 (31.6) Good Minimal persistence of preoperative

symptoms. Neurologic deficits

unchanged or improved.

2 (2.5) Fair Some preoperative symptoms

improved. Others unchanged or

slightly improved.

0 (0) Poor Preoperative symptoms unchanged or

exacerbated.

3J. Miao et al. / The Spine Journal - (2013) -

acquired at 2 days postoperation and 2-, 6-, 12-, 24-monthfollow-up, respectively. On the standing lateral cervical x-ray, anterior disc heights and posterior disc heights weremeasured to determine the heights at the operative segmentbefore and after operation, whereas the range of motion(ROM) of the operative segment was calculated by the dif-ference of interbody angle on flexion-extension lateralx-ray imaging using the Cobb technique (Fig. 1). The per-formance of heterotopic ossification (HO) was observed bytwo independent MD in the follow-up.

Statistical analysis

Data were analyzed using SAS version 9.2 (SAS Insti-tute Inc., Cary, NC, USA). The paired t test was used to as-sess the difference of aimed outcomes before and afteroperation. A p value of!.05 was considered as significant.

Results

In this study, the symptoms of patients have improvedwith varying degrees after operation. At 2-, 6-, 12-, and24-month follow-ups, the Japanese Orthopaedic Associa-tion scores were 14.163.1, 14.762.0, 15.362.1, and14.962.5, respectively, which was significantly higher(p!.01) than preoperative (9.562.3), whereas VAS overallpain score was 1.960.8, 1.760.9, 1.860.6, and 1.460.5,respectively, which was significantly lower (p!.01) thanpreoperative (7.261.6). No significant differences in theclinical outcomes were observed between the patientswho underwent single level versus 2-level disc replace-ment. The operation effects evaluated by Odom criteria at2-year follow-up were shown in Table 2. A total of sevenpatients had mild dysphagia after operation. The symptomsdisappeared within the first month in all cases, and no

Fig. 1. The measurement method for ADH, PDH, and IBA. ADH, ante-

rior disc heights; PDH, posterior disc heights; IBA, interbody angle.

patient had chronic dysphagia. Only one patient had thesymptom of hoarseness and was released 45 days afteroperation.

The anterior disc heights and posterior disc heights ofthe operative segment at 2-month follow-up were 7.562.2mm and 5.161.8 mm. Compared with preoperative(4.961.3 mm, 3.160.9 mm), there were significantly in-creased (p!.05) and maintenance well at 6- (7.561.9mm, 5.061.6 mm), 12- (7.462.0 mm, 4.961.4 mm) and24-month (7.262.1 mm, 5.061.9 mm) follow-ups. Rangeof motion of the operative segment in the postoperativefollow-up was slightly increased compared to the preoper-ative but not statistically significant (pO.05) (Fig. 2). Theperformance of HO was found in six replaced levels at 1-year follow-up, including 4 Grade I and 2 Grade II. The oc-currence of HO became common at the follow-up morethan 2 years that we found HO performance in 18 replacedlevels, including 8 Grade I and 10 Grade II. We observed noprosthesis displacement and had no revision surgery. Typi-cal imaging are shown in Figs 3 and 4.

Discussion

Fernstrom spherical endoprostheses have been the firstartificial discs implanted in humans in the 1960s. Fernstromreported the use of these devices in the cervical [13]. Mod-ern cervical artificial disc replacement first made its debutin 1991, with the Bristol/Cummins disc, the first of numer-ous articulating CDR devices. The original devices wereimplanted by Cummins in 20 patients, who later reported

Fig. 2. Evolution of the flexion/extension range of motion at the operative

segment preoperatively and more than 2 years of postoperative follow-up.

Results are expressed as mean6SEM at each time-point. SEM, standard

error of the mean.

Fig. 3. A 43-year-old man. The preoperative X-ray imaging (A) showed cervical degeneration. Sagittal magnetic resonance imaging T2 (B) showed spinal

cord compression secondary to disc herniation in C5/C6 and C6/C7. At the 12 months’ follow-up, the anteroposterior and flexion/extension of lateral X-ray

imaging (C–E) showed the implants were stable, and the motion of operative segment was preserved.

4 J. Miao et al. / The Spine Journal - (2013) -

that some continued to function well, up to 12 years afterimplantation [14]. The past 10 years has seen the develop-ment of CDR in an attempt to overcome some of the short-comings of ACDF. Despite the relative short-termoutcomes documented in the literature, the increasing ac-ceptance of CDR is primarily supported by the concept thatmaintaining treated segment and cervical spine mobilitycould achieve, with time, better protection of adjacentlevels than fusion. Overall results of CDR implantationsare satisfactory and promising. Level I and Level II evi-dences suggest equivalence in clinical results betweenCDR and ACDF. Furthermore, Level I evidence suggestslower revision rates and quicker return to work with CDRversus ACDF. Mummaneni et al. [15] reported on the Pres-tige ST prospective, randomized, multicenter IDE trial. Intotal, 541 patients with mono-segment disease were en-rolled, with 276 patients receiving CDR with Prestige STand 265 patients treated with ACDF. In total, 80% of theinvestigational patients and 75% of the fusion patients wereavailable for follow-up at 2 years. The study showed betterclinical results in the CDR group, although they did notreach clinical significance. There was a statistically signif-icant lower rate of surgery for adjacent segment disease,with 1.1% of disk replacement patients requiring surgeryversus 3.4% of the ACDF patients. The patients of CDRgroup were able to return to work sooner compared with

the ACDF patients. Nabhan et al. [16] evaluated 49 patientswho either underwent Prodisc-C disc replacement or ACDFin a randomized, controlled series. After 1 year’s follow-up,both groups improved clinically with no statistical signifi-cance, and both groups lost some cervical segmentalROM, with ACDF patients losing significantly more seg-mental motion. Murrey et al. [17] reported the results fromthe ProDisc-C IDE study. In total, 209 patients were en-rolled, with 103 receiving the disk replacement and 106 un-dergoing ACDF. From both groups, we obtained similarlyimproved NDI scores and VAS scores showing neurologicsuccesses. A significant difference was observed in reoper-ation rates: with 8.5% in the ACDF patients versus 1.8% inthe disc replacement group. The primary clinical results inour series of 79 patients treated with Discover prosthesisare similar to published studies on CDR. We believe thatremoving the compressive materials thoroughly is the mostimportant factor to improve the symptoms. We not only re-moved the herniated disc of the target segment but also re-sected the posterior longitudinal ligament as regular.Another explanation is that resection of posterior longitudi-nal ligament may increase ROM in CDR [18,19].

Rebuilding the intervertebral disc height after discec-tomy is an important factor to restore the cervical lordosis.In this study, the preoperative intervertebral disc height wasmore than 3 mm and was significantly higher after CDR.

Fig. 4. Lateral cervical spine films at 2 years’ follow-up. Clear signs of HO (Grade II) can be seen at the operative segment with no significant reduction in

motion of the implant on flexion and extension. HO, heterotopic ossification.

5J. Miao et al. / The Spine Journal - (2013) -

There was no prosthesis subsidence and shifting in thefollow-up. Peng et al. [20] advocated that patients withgreater disc collapse of less than 4 mm preoperative discheight benefit more in ROM after CDR, but the optimalpostoperative disc height range to maximize ROM is be-tween 5 and 7 mm.

A heightened awareness of the risk of dysphagia afteranterior approach to the cervical spine arose during the pastdecade. Segebarth et al. [21] evaluated patients for dyspha-gia who were enrolled in the ProDisc-C IDE study. Therewere 38 patients in the CDR group and 38 in the ACDFgroup. After 1 year’s follow-up, the incidence of dysphagiawas much lower in the CDR group than that of the ACDFgroup (15.8% vs. 42.1%). Although the etiology of dyspha-gia is multifactorial, the anterior plate used in ACDF wasthought to be an important risk factor. Recent studies eval-uating plate design suggest that a lower, smoother anteriorprofile may correlate with reduced incidence of dysphagiafollowing ACDF [22,23]. The Discover prosthesis has noprofile, which could avoid stimulating the esophagus di-rectly and mitigating the adhesions of the esophagus. Theincidence of dysphagia in this study was lower than thatof ACDF from the published articles, and no patient hadchronic dysphagia. Another important factor may be the re-traction pressure differences existing between ACDF andCDR. In a cadaveric study, intraesophageal pressure wassignificantly higher during insertion of anterior cervicalplate compared with the insertion of the cervical disc pros-thesis [24].

Ongoing data collection and increasing number of stud-ies describe HO resulting in decreased mobility of the pros-thesis. The McAfee classification of HO is widely used todescribe hyperosthotic changes in the cervical spine [25].In the published studies, the frequency of HO was variedwith the different prosthesis and the length of follow-up pe-riod. Bertagnoli et al. [26] reported results of 27 ProdiscCpatients with 1-year follow-up without any appearance offusion. Later, the same author [27] observed a 9.4% inci-dence of HO among 117 patients treated with the sameprosthesis and followed-up for more than 2 years. Leunget al. [28] described a 17.8% overall rate of HO occurrencewith 6.7% being Grade 2 or 3 at 1-year follow-up evalua-tion of 90 of 100 available patients with single-level proce-dures in a multicenter series of Bryan disc implantations.The incidence of HO in our study was relatively low. Ageis one of the important factors contributing to the lowHO incidence, as older age has been reported as a risk fac-tor for the development of HO [27]. In addition to this, thedesign characteristics of the Discover prostheses may alsoplay an important role. Because of the short follow-up pe-riod and relatively small number of similar studies, the ver-dict that Discover results in a lower HO rate than othercommonly used prostheses is yet to be determined.

Conclusion

The use of Discover prostheses in our study resulted insatisfactory clinical outcomes. The prostheses can be

6 J. Miao et al. / The Spine Journal - (2013) -

inserted safely in the process of CDR, restoring and main-taining interbody height, while preserving the motion of thetreated segment. The incidence of postoperative dysphagiawas low. Further studies are demanded to better understandthe impact of CDR with Discover prosthesis, especially onthe HO and adjacent segment degeneration, although the re-sults reported in this article clearly showed initial safetyand effectiveness from our patient sample.

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