Subsequent surgery rates after cervical total disc replacement using a Mobi-C Cervical Disc Prosthesis versus anterior cervical discectomy and fusion: a prospective randomized clinical trial with 5-year follow-up

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OBJECTIVE

Cervical total disc replacement (TDR) has been shown in a number of prospective clinical studies to be a viable treatment alternative to anterior cervical discectomy and fusion (ACDF) for the treatment of symptomatic degenerative disc disease. In addition to preserving motion, evidence suggests that cervical TDR may result in a lower incidence of subsequent surgical intervention than treatment with fusion. The goal of this study was to evaluate subsequent surgery rates up to 5 years in patients treated with TDR or ACDF at 1 or 2 contiguous levels between C-3 and C-7.

METHODS

This was a prospective, multicenter, randomized, unblinded clinical trial. Patients with symptomatic degenerative disc disease were enrolled to receive 1- or 2-level treatment with either TDR as the investigational device or ACDF as the control treatment. There were 260 patients in the 1-level study (179 TDR and 81 ACDF patients) and 339 patients in the 2-level study (234 TDR and 105 ACDF patients).

RESULTS

At 5 years, the occurrence of subsequent surgical intervention was significantly higher among ACDF patients for 1-level (TDR, 4.5% [8/179]; ACDF, 17.3% [14/81]; p = 0.0012) and 2-level (TDR, 7.3% [17/234]; ACDF, 21.0% [22/105], p = 0.0007) treatment. The TDR group demonstrated significantly fewer index- and adjacent-level subsequent surgeries in both the 1- and 2-level cohorts.

CONCLUSIONS

Five-year results showed treatment with cervical TDR to result in a significantly lower rate of subsequent surgical intervention than treatment with ACDF for both 1 and 2 levels of treatment.

Clinical trial registration no.: NCT00389597 (clinicaltrials.gov)

ABBREVIATIONSACDF = anterior cervical discectomy and fusion; IDE = Investigational Device Exemption; NDI = neck disability index; TDR = total disc replacement.

OBJECTIVE

Cervical total disc replacement (TDR) has been shown in a number of prospective clinical studies to be a viable treatment alternative to anterior cervical discectomy and fusion (ACDF) for the treatment of symptomatic degenerative disc disease. In addition to preserving motion, evidence suggests that cervical TDR may result in a lower incidence of subsequent surgical intervention than treatment with fusion. The goal of this study was to evaluate subsequent surgery rates up to 5 years in patients treated with TDR or ACDF at 1 or 2 contiguous levels between C-3 and C-7.

METHODS

This was a prospective, multicenter, randomized, unblinded clinical trial. Patients with symptomatic degenerative disc disease were enrolled to receive 1- or 2-level treatment with either TDR as the investigational device or ACDF as the control treatment. There were 260 patients in the 1-level study (179 TDR and 81 ACDF patients) and 339 patients in the 2-level study (234 TDR and 105 ACDF patients).

RESULTS

At 5 years, the occurrence of subsequent surgical intervention was significantly higher among ACDF patients for 1-level (TDR, 4.5% [8/179]; ACDF, 17.3% [14/81]; p = 0.0012) and 2-level (TDR, 7.3% [17/234]; ACDF, 21.0% [22/105], p = 0.0007) treatment. The TDR group demonstrated significantly fewer index- and adjacent-level subsequent surgeries in both the 1- and 2-level cohorts.

CONCLUSIONS

Five-year results showed treatment with cervical TDR to result in a significantly lower rate of subsequent surgical intervention than treatment with ACDF for both 1 and 2 levels of treatment.

Clinical trial registration no.: NCT00389597 (clinicaltrials.gov)

Anterior cervical discectomy and fusion (ACDF) has been a standard surgical procedure for cervical disc decompression. It functions to decompress affected neural components, provide mechanical stability and lordosis, and preserve intradiscal height.26 However, investigators have also reported an increase in motion, shear strain, and intradiscal pressure in adjacent vertebrae after treatment.10,21 The displacement of motion and mechanical stress to adjacent segments is a major concern because force and motion translocation are believed to lead to increased rates of adjacent-segment degeneration in patients treated with ACDF.6,10,16,17,21 It is also hypothesized that adjacent-segment degeneration is further heightened in multilevel ACDF treatment.11

Cervical total disc replacement (TDR) is a treatment option for symptomatic radiculopathy and myelopathy. A number of clinical trials have shown that TDR is a safe and effective alternative to ACDF for 1- and 2-level cervical decompression.3,5,7,11,15,19,22,27–29 As with ACDF, cervical TDR acts to decompress the affected segment, provide stabilization, and preserve intradiscal height while maintaining mobility.3,22,28 Investigators have suggested that the preservation of mobility may result in a decreased frequency of adjacent-segment degeneration compared with that observed in patients treated with ACDF.1,5,31

The results of multiple independent studies suggest that cervical TDR at 1 level may also result in decreased rates of subsequent operations at the treatment and adjacent levels.5,9,12,15,22,23,28–30 Long-term studies have shown that treatment with ACDF results in significantly higher subsequent surgery rates than cervical TDR, although few studies have analyzed 2-level subsequent surgery outcomes.2,9,24 In long-term studies, the ACDF subsequent surgery rate was observed to be as high as 5 times the rate of TDR subsequent surgical intervention.9 The purpose of this study was to evaluate 5-year subsequent surgery rates at index and adjacent levels in patients treated at 1 or 2 contiguous levels with TDR or with the ACDF control procedure, as part of an FDA Investigational Device Exemption (IDE) clinical trial.

Methods

Study Design

This study elaborates on the results from prospective, multicenter, 2-arm, randomized (2:1), unblinded, concurrently enrolled, noninferiority clinical trials comparing the safety and effectiveness of the Mobi-C Cervical Disc Prosthesis (LDR Medical) at 1 or 2 contiguous levels with an ACDF control.

The study design has been previously described in detail.7,18 The patient population included a total of 260 1-level and 339 2-level subjects randomized (2:1) to receive either TDR or ACDF treatment at 1 of 24 investigational sites. These 1- and 2-level results include 5 years of patient follow-up data. Institutional review board approval was obtained for all investigational sites. This study was registered with the ClinicalTrials.gov database (http://clinicaltrials.gov), and its registration no. is NCT00389597.

Patient Population

Eligible patients had degenerative disc disease with radiculopathy or myeloradiculopathy symptomatic at 1 or 2 contiguous levels from C-3 to C-7 and had a neck disability index (NDI) score ≥ 15/50. Patients must have been unresponsive or shown progressive symptoms after nonoperative, conservative treatment for at least 6 weeks from symptom onset. See Tables 1 and 2 for complete inclusion and exclusion criteria.

TABLE 1.

Inclusion criteria for 599 patients with symptomatic degenerative disc disease enrolled to receive 1- or 2-level treatment with either TDR or ACDF

Age, 18–69 yrs
Symptomatic cervical degenerative disc disease in 1 or 2 levels btwn C-3 and C-7 w/any of the following:
  Neck and/or arm pain
  Decreased muscle strength
  Abnormal sensation and/or abnormal reflexes
Deficit confirmed by imaging (CT, MRI, or radiograph)
NDI score ≥30
Unresponsive to nonoperative, conservative treatment for at least 6 wks or presence of progressive symptoms or signs of nerve root/spinal cord compression despite continued nonoperative treatment
No prior surgery at the operative level and no prior cervical fusion procedure at any level
Physically and mentally able and willing to comply w/the protocol
Signed informed consent
Willingness to discontinue all use of NSAIDs from 1 wk before surgery to 3 mos after surgery
TABLE 2.

Exclusion criteria for 599 patients with symptomatic degenerative disc disease enrolled to receive 1- or 2-level treatment with either TDR or ACDF

>2 vertebral levels requiring treatment/immobile levels btwn C-1 & C-7 from any cause
Any prior spine surgery at operative level or any prior cervical fusion at any level
Disc height <3 mm
T score < −1.5 (osteoporosis evaluation)
Paget's disease, osteomalacia, or any metabolic bone disease other than osteoporosis
Active systemic infection of surgical site or history of/anticipated treatment for systemic infection including HIV & hepatitis C
Active malignancy, i.e., a history of any invasive malignancy (except nonmelanoma skin cancer), unless treated w/curative intent and w/o any clinical signs or symptoms of the malignancy for >5 yrs
Marked cervical instability on resting lateral or flexion-extension radiographs
Known allergy to cobalt, chromium, molybdenum, or polyethylene
Segmental angulation >11° at treatment or adjacent levels
Rheumatoid arthritis, lupus, or other autoimmune disease
Any diseases or conditions that would preclude accurate clinical evaluation
Daily, high-dose oral and/or inhaled steroids or a history of chronic use of high-dose steroids
Body mass index >40
Use of any other investigational drug or medical device w/in 30 days prior to surgery
Pending personal litigation relating to spinal injury (workers' compensation not included)
Smoking >1 pack of cigarettes per day
Reported to have mental illness or belong to a vulnerable population

Study Interventions

The investigational device is the Mobi-C Cervical Disc Prosthesis (LDR Medical). The implant is composed of an ultra-high-molecular-weight polyethylene (UHMWPE per ISO 5834–2) mobile insert between 2 endplates (Fig. 1). The control device is ACDF, using either the Slim-Loc Anterior Cervical Plate System (DePuy Spine) or the Sofamor Danek Atlantis or Atlantis Vision Anterior Cervical Plate Systems (Medtronic) with corticocancellous allograft. Postoperative care for both groups was left to the discretion of the treating surgeon.

FIG. 1.
FIG. 1.

Mobi-C Cervical Disc Prosthesis (LDR Medical). Copyright LDR Holding Corporation. Published with permission. Figure is available in color online only.

Study Outcomes

The intent of this study was to assess subsequent surgery rates of patients treated at 1 or 2 contiguous levels with a TDR or an ACDF. A subsequent surgery was considered to be any operation that occurred at the initial treatment level or at adjacent levels after the primary operation. Subsequent surgeries were categorized by 4 methods based on the levels involved during the subsequent surgery: only index-level surgeries, only adjacent-level surgeries, index-and adjacent-level surgeries, and index-level surgeries leading to study failure. Subsequent surgical interventions leading to study failure were considered to be any secondary surgery at an index-level segment that was classified as a removal, revision, supplemental fixation, or reoperation according to the FDA IDE study protocol. Index-level surgeries leading to study failure would be duplicated in 1 of the other categories. Index-level surgeries that did not indicate study failure were also included in the analysis. In the instance of multiple subsequent surgeries, only the first subsequent surgery was used to determine the subsequent surgery rates. Operations at C7–T1 were included in the calculation of adjacent-level surgery rates.

Statistical Analysis

Fisher's exact tests were used to assess subsequent surgery rates. Statistical significance was determined by a p value > 0.05.

Results

For both the 1- and 2-level arms, a total of 599 patients were treated with the investigational or control device. For the 1-level arm, 179 patients received TDR and 81 received ACDF treatment. For the 2-level arm, 234 patients received TDR and 105 received ACDF treatment. No significant differences were found between the demographic profiles of the investigational and control groups. The 60-month follow-up rate was 85.5% (TDR) and 78.9% (ACDF) for the 1-level group and 90.7% (TDR) and 86.7% (ACDF) for the 2-level group.

A subsequent surgery was considered to be any operation that occurred at the initial treatment level or at adjacent levels after the primary operation. All TDR and ACDF subsequent surgery cases are listed in Tables 3 and 4.

TABLE 3.

Subsequent surgical procedures in 1-level arm (in ascending order by time to surgery)

Case No.Index LevelDeviceTime to SurgeryReasonDescriptionTreated SegmentsStudy Failure
1C3–4ACDF5 daysHematomaEvacuation of hematomaC3–4No
2C4–5TDR3 mosRadiculopathyCervical laminectomy at index level (C4–5)C4–5Yes
3C5–6ACDF5 mos1) Neck pain; 2) radiculopathy; 3) foraminal stenosis; 4) pseudarthrosisPosterior fusion (C5–6) w/instrumentationC5–6Yes
4C4–5TDR5 mos1) Radiculopathy; 2) spondylosisRemoval of Mobi-C, fusion of index level (C4–5)C4–5Yes
5C5–6ACDF11.5 mos1) Radiculopathy; 2) pseudarthrosisRemoval of instrumentation, redo C5–6 fusion w/iliac crest bone graftC5–6Yes
6C4–5ACDF12.5 mos1) Neck pain; 2) muscle spasms; 3) numbness; 4) malpositioned screwsRemoval of instrumentation, fusion of inferior adjacent level (C5–6)C4–6Yes
4*C4–5TDR13 mos1) Neck pain; 2) spondylosisFusion of C3–4, C5–6, & C6–7C3–4, C5–6, C6–7NA
7C5–6ACDF14 mos1) Neck pain; 2) radiculopathy; 3) herniated disc at adjacent level; 4) pseudarthrosis (1 & 2 resulted from trauma after rock climbing fall)Removal of instrumentation, fusion of index & superior adjacent level, & extended superiorly (C3–6)C3–6Yes
8C5–6ACDF15.5 mos1) Radiculopathy; 2) pseudarthrosisPosterior fusion (C5–6) w/instrumentationC5–6Yes
9C5–6TDR19 mos1) Neck pain; 2) radiculopathy; 3) herniated disc at superior adjacent levelFusion of superior adjacent level (C4–5)C4–5No
10C5–6ACDF20 mos1) Neck pain; 2) herniated disc at inferior adjacent levelFusion of inferior adjacent level (C6–7)C6–7No
11C5–6TDR25 mos1) Neck pain; 2) headache; 3) numbness w/loss of motionRemoval of Mobi-C, fusion of index level (C5–6)C5–6Yes
8*C5–6ACDF26 mos1) Radiculopathy; 2) cervical stenosisRemoval of previous posterior fusion instrumentation (C5–6), posterior fusion (C3–6)C3–6NA
12C6–7ACDF27 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosisPosterior fusion (C6–7) w/instrumentationC6–7Yes
13C5–6TDR32 mos1) Radiculopathy; 2) cervicalgia; 3) device malpositioning causing kyphosisRemoval of Mobi-C, fusion of index level (C5–6)C5–6Yes
14C3–4ACDF34 mos1) Numbness; 2) herniated discs at both adjacent levelsRemoval of instrumentation, fusion of inferior adjacent level C4–5 through C-7C3–7Yes
15C5–6TDR38 mos1) Neck pain; 2) radiculopathy; 3) adjacent-level diseaseRemoval of Mobi-C, fusion of index & inferior adjacent level (C5–7)C5–7Yes
16C6–7ACDF42 mos1) Neck pain; 2) radiculopathy; 3) cervical stenosisRemoval of instrumentation, fusion of index & superior adjacent level (C5–7)C5–7Yes
17C6–7ACDF49.5 mos1) Neck pain; 2) radiculopathy; 3) herniated disc at inferior adjacent levelDecompression & discectomy at inferior adjacent level (C7–T1)C7–T1No
18C6–7TDR52 mos1) Neck pain; 2) headaches; 3) radiculopathy; 4) cervical spondylosis at superior adjacent levelFusion of superior adjacent level (C5–6)C5–6No
19C5–6ACDF52 mos1) Neck pain; 2) radiculopathy; 3) herniated disc at inferior adjacent levelFusion of inferior adjacent level (C6–7)C6–7No
20C4–5TDR52 mos1) Radiculopathy; 2) herniated disc at inferior adjacent levelRemoval of anterior osteophytes at index level, fusion of inferior adjacent level (C5–6)C4–6No
15*C5–6TDR55 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosisRedo fusion at index level, fusion of inferior adjacent level (C5–7) (was previously replaced as a fusion)C5–7NA
21C6–7ACDF57 mos1) Neck pain; 2) adjacent-level degeneration at superior level, w/posterior annular tearRemoval of instrumentation, ProDisc-C implanted at superior adjacent level (C5–6)C5–7Yes
22C5–6ACDF59 mos1) Radiculopathy; 2) herniated disc at adjacent levelFusion of inferior adjacent level (C6–7)C6–7No

NA = not applicable.

Indicates a third surgical intervention.

TABLE 4.

Subsequent surgical procedures in 2-level arm (in ascending order by time to surgery)

Case No.Index LevelDeviceTime to SurgeryReasonDescriptionTreated SegmentsStudy Failure
1C4–6TDRIntraoperativeHematomaEvacuation of hematomaC4–6No
2C5–7ACDF3 daysHematomaEvacuation of hematomaC5–7No
3C4–6ACDF4 daysHematomaEvacuation of hematomaC4–6No
4C5–7TDR7 daysHematomaEvacuation of hematoma, TDR was repositioned by a tap from the surgeonC5–7Yes
5C4–6TDR2.5 mosPosterior migration of inferior endplate of the inferior index levelRemoval of Mobi-C at inferior index level (C5–6), repeat w/fusionC5–6Yes
6C4–6TDR8 mosRadiculopathyPosterior foraminotomy at inferior index level & both adjacent levelsC5–7Yes
7C5–7TDR8 mosCervical painImplantation of Medtronic spinal cord stimulatorC3–7No
8C5–7ACDF9 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosisBilateral hemilaminectomy & posterior fusion at both index levels (C5–7)C5–7Yes
9C5–7ACDF10 mos1) Neck pain; 2) pseudarthrosisPosterior fusion at index levels (C5–7) w/instrumentationC5–7Yes
10C4–6ACDF10 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosisRemoval of instrumentation at both index levels, revise fusion at inferior index level (C5–6)C5–6Yes
11C4–6ACDF10 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosisRemoval of instrumentation at both index levels (C4–6), revise fusion at inferior index level, & discectomy at superior adjacent level (C3–6)C3–6Yes
12C4–6TDR11 mos1) Neck pain; 2) radiculopathy; 3) poor attachment of deviceRemoval of Mobi-C at both index levels (C4–6), repeat w/2-level fusionC4–6Yes
13C5–7ACDF14 mos1) Radiculopathy; 2) cervical spondylosis; 3) pseudarthrosisPosterior foraminotomy & repeat fusion at superior index level (C5–6)C5–6Yes
14C4–6ACDF14 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosisPosterior fusion of inferior index level (C5–6)C5–6Yes
15C4–6TDR15 mos1) Radiculopathy; 2) adjacent-level degeneration, inferior adjacent levelTDR at inferior adjacent level (C6–7)C6–7No
16C5–7ACDF15 mos1) Radiculopathy; 2) pseudarthrosisPosterior fusion of both index levels (C5–7)C5–6, C6–7Yes
17C5–7ACDF16 mos1) Radiculopathy; 2) muscle spasmsPosterior foraminotomy for both index levels (C5–7)C5–7Yes
18C5–7TDR16 mos1) Radiculopathy; 2) herniated disc at superior adjacent levelFusion at superior adjacent level (C4–5)C4–5No
19C4–6TDR19 mos1) Headaches; 2) radiculopathyRemoval of Mobi-C at both index levels (C4–6), revised to fusionC4–6Yes
20C5–7ACDF20 mos1) Radiculopathy; 2) pseudarthrosisBilateral laminal foraminotomy, medial facetectomy, & posterior fusion at inferior index levelC6–7Yes
21C5–7TDR20 mosNeck painFacet rhizotomy at superior adjacent level & nonadjacent superior levelC3–5No
22C5–7ACDF20 mos1) Neck pain; 2) headaches; 3) herniated disc at superior adjacent levelRemoval of instrumentation, fusion of superior adjacent level C4–5C4–5, C5–6, C6–7Yes
12*C4–6TDR20 mos1) Neck pain; 2) headaches; 3) pseudarthrosis360° cervical fusion at both index levels (C4–6)C4–6NA
23C4–6ACDF20 mos1) Neck pain; 2) radiculopathy; 3) pseudarthrosis; 4) subsidence reversing normal lordosisRemoval of instrumentation at index levels (C4–6), revise anterior plating, posterior instrumentation (C4–7)C4–7Yes
24C3–5ACDF22 mos1) Neck pain; 2) radiculopathy; 3) adjacent-level degeneration, inferior levelRemoval of instrumentation at both index levels (C3–5), artificial disc implanted at inferior adjacent level (C5–6)C3–6Yes
25C5–7TDR22 mos1) Neck pain; 2) radiculopathy; 3) C5–7 facet spondylosisPosterior fusion w/instrumentation at both index levels (C5–7)C5–7Yes
11*C4–6ACDF22 mos1) Pain; 2) adjacent-level disease, superior adjacent level; 3) pseudarthrosisRemoval of instrumentation, bilateral posteriorlateral fusion w/instrumentation (C3–6)C3–6NA
26C4–6TDR23 mos1) Neck pain; 2) radiculopathyRemoval of Mobi-C at inferior index level (C5–6), revised to fusionC5–6Yes
27C5–7ACDF27 mos1) Neck pain; 2) radiculopathy; 3) herniated disc at inferior adjacent levelFusion at inferior adjacent level (C7–T1)C7–T1No
11C4–6ACDF29 mosNeck painRemoval of posterior instrumentation at superior adjacent & both index levels (C3–6)C3–6NA
26*C4–6TDR30 mosNeck painRemoval of Mobi-C at superior index level (C4–5), revised to fusionC4–5NA
28C5–7ACDF31 mos1) Neck pain; 2) facet syndrome; 3) spondylosisRemoval of instrumentation at both index levels (C5–7), fusion at inferior adjacent level (C7–T1)C5–T1Yes
9*C5–7ACDF32 mos1) Neck swelling; 2) cervical spondylosis at C3–4Prestige disc implanted at superior nonadjacent level (C3–4)C3–4NA
29C5–7ACDF33 mos1) Radiculopathy; 2) herniated disc at superior adjacent levelFusion at superior adjacent level (C4–5)C4–5No
30C4–6ACDF36 mos1) Radiculopathy; 2) herniated disc at inferior adjacent levelRemoval of instrumentation, fusion at inferior adjacent level (C6–7)C6–7Yes
31C5–7TDR36 mos1) Neck pain; 2) radiculopathy; 3) headaches; 4) herniated disc at superior adjacent levelFusion at superior adjacent level (C4–5)C4–5No
32C5–7ACDF39 mos1) Neck pain; 2) radiculopathy; 3) herniated disc at both adjacent levelsRemoval of instrumentation, disc replacement at superior adjacent level (C4–5), & fusion at inferior adjacent level (C7–T1)C4–T1Yes
33C5–7ACDF40 mosTrauma (motor vehicle accident)Decompression & stabilizing fusion at both index levels and inferior adjacent (C5–T1), fusion inferior nonadjacent (T1–2)C5–T1Yes
9C5–7ACDF41 mos1) Neck pain at cervicothoracic junction; 2) instability of cervical & thoracic spineRemoval of posterior instrumentation, posterior fusion at both index & inferior adjacent level (C5–T2)C5–T2NA
34C5–7TDR41 mos1) RadiculopathyForaminotomy at inferior adjacent level (C7–T1)C7–T1Yes
35C4–6TDR41 mos1) Radiculopathy; 2) adjacent-level disease, inferior adjacent levelFusion at inferior adjacent level (C6–7)C6–7Yes
36C4–6TDR46 mos1) Neck pain; 2) radiculopathy; 3) foraminal stenosis C4–5Foraminotomy at superior index level (C4–5)C4–5Yes
37C5–7TDR52 mos1) Neck pain following a head injury from fall; 2) cervical stenosis w/spondylolisthesisRemoval of Mobi-C at inferior index level (C6–7), fusion of inferior index levelC6–7Yes
24*C3–5ACDF52 mos1) Neck pain; 2) artificial disc looseningRemoval of artificial disc at inferior adjacent level (C5–6), revised to fusionC5–6NA
38C4–6ACDF54 mos1) Neck pain; 2) radiculopathy; 3) adjacent-level disease; 4) adjacent-level spondylosisRemoval of instrumentation at index levels (C4–6), fusion of both adjacent levels (C3–4, C6–7)C3–7Yes
39C4–6ACDF60 mos1) Neck pain; 2) herniated disc at inferior adjacent levelFusion at inferior adjacent level (C6–7)C6–7No

NA = not applicable.

Indicates a third surgical intervention.

Indicates a fourth surgical intervention.

For the 1-level ACDF group, 14 of 81 patients underwent subsequent surgeries and 1 patient required multiple subsequent surgeries. In the 1-level TDR group, 8 of 179 patients underwent subsequent surgeries and 2 patients required multiple subsequent surgeries. The number of 1-level patients receiving subsequent surgeries was significantly higher for ACDF at 60 months (TDR 4.5% vs ACDF 17.3%; p = 0.0012).

For the 2-level ACDF group, 22 of 105 patients underwent subsequent surgeries and 3 patients required multiple subsequent surgeries. In the 2-level TDR group, 17 of 234 patients underwent subsequent surgeries and 2 patients required multiple subsequent surgeries at the 60-month follow-up point. The percentage of 2-level ACDF patients receiving subsequent surgery was significantly higher than that of 2-level TDR patients at 60 months (TDR 7.3% vs ACDF 21.0%; p = 0.0007).

Subsequent surgeries were classified by operative level as an index- and/or adjacent-level surgery (Fig. 2). For the 1-level arm at 60 months, there were a total of 8 TDR (4 index, 2 adjacent, 2 index and adjacent) and 14 ACDF (5 index, 4 adjacent, 5 index and adjacent) subsequent surgeries classified by operative level. For the 2-level arm, there were a total of 17 TDR (9 index, 6 adjacent, 2 index and adjacent) and 22 ACDF (10 index, 3 adjacent, 9 index and adjacent) subsequent surgeries classified by operative level at the 60-month follow-up.

FIG. 2.
FIG. 2.

Subsequent surgery classification by operative levels.

Surgeries Involving an Index Level

At 60 months, the rate of subsequent surgeries that involved the index level for the 1-level arm was significantly different at 3.4% (6/179) for TDR and 12.3% (10/81) for ACDF (p = 0.0097). Of the 10 1-level ACDF surgeries involving an index level, 7 ACDF surgeries were a result of index-level indications and 3 surgeries resulted from removal of the anterior plate when treating adjacent-level disease. When censoring patients undergoing plate removal due to adjacent-level indications only, the ACDF group retained a substantially higher subsequent surgery rate, although this difference lost significance (3.4% vs 8.6%; p = 0.1194). The difference in index-level subsequent surgeries was also significant in the 2-level arm, at 4.7% (11/234) for TDR and 18.1% (19/105) for ACDF. Of the 19 2-level ACDF surgeries involving an index level, 13 surgeries were due to index-level indications and 6 surgeries were due to hardware removal for adjacent-level disease. When censoring patients undergoing plate removal due to adjacent-level indications only, the ACDF group maintained a higher rate of subsequent surgeries (4.7% vs 12.4%; p = 0.0197).

Of these subsequent surgeries involving the index level at 1 level, 2.8% (5/179) TDR and 11.1% (9/81) ACDF patients (p = 0.014) failed to meet the primary end point criteria due to subsequent surgical intervention. Similarly, at 2 levels, 3.8% (9/234) TDR and 16.2% (17/105) ACDF patients (p = 0.0002) did not meet the study's primary end point criteria (Fig. 3). There was no statistically significant difference within treatment types between 1- and 2-level rates. The most prevalent reasons for subsequent surgeries at the index level for 1- and 2-level ACDF were radiculopathy, neck pain, and pseudarthrosis. Radiculopathy was the most common indication for subsequent surgery among TDR patients.

FIG. 3.
FIG. 3.

Subsequent surgery at index level leading to study failure. *p= 0.014; **p = 0.0002.

Surgeries Involving an Adjacent Level

The rate of subsequent surgeries involving an adjacent level was calculated at 60 months for both 1- and 2-level arms (Fig. 4). The involvement of adjacent level could overlap with a subsequent surgery at the index level. For the 1-level arm at 60 months, the rate of adjacent-level subsequent surgery was significantly higher for ACDF patients, at 11.1% (9/81), than for TDR patients, at 2.2% (4/179) (p = 0.0043). For the 2-level arm at 60 months, the ACDF group also demonstrated a significantly higher rate of adjacent-level subsequent surgical intervention (TDR 3.4% [8/234] vs ACDF 11.4% [12/105]; p = 0.0059). There was no statistically significant difference observed within treatment groups between 1- and 2-level treatments.

FIG. 4.
FIG. 4.

Subsequent surgery at adjacent level. *p = 0.0043; **p = 0.0059.

The most common reasons for adjacent-level ACDF surgeries were adjacent-level disease and neck pain. Radiculopathy and adjacent-level disease were the most frequent indications for subsequent surgery among TDR patients. Adjacent-level disease was an indication for surgical intervention for 8 of 9 ACDF and 4 of 4 TDR 1-level patients. For 2-level patients, adjacent-level surgery was initiated by adjacent-level disease for 11 of 12 ACDF and 5 of 8 TDR surgeries. The average time from diagnosis of adjacent-level disease to surgery was 35.8 months for ACDF patients and 32.1 months for TDR patients.

Multiple Surgeries

Several patients underwent more than 1 subsequent surgery. In the 1-level TDR group, 1 patient initially had the TDR device removed (C4–5) and replaced with an ACDF at 5 months postsurgery due to worsening radiculopathy and spondylosis, possibly due to an oversized implant. Eight months later, the patient underwent surgery again, with an ACDF at 3 adjacent levels (C3–4, C5–7) due to symptomatic adjacent-level disease. Another patient in the 1-level TDR group had the device removed 38 months postsurgery and underwent fusion at the index level (C5–6) and the inferior adjacent level (C6–7) after experiencing neck pain, radiculopathy, and adjacent-level disease following an injury. Seventeen months later, the patient underwent a revision fusion with supplemental fixation due to pseudarthrosis at C5–6 and foraminal stenosis at C6–7.

In the 1-level ACDF group, 1 patient had a subsequent surgery at 15 months postoperatively for symptomatic pseudarthrosis with radiculopathy, undergoing a posterior foraminotomy and medial facetectomy plus posterior fusion with instrumentation (C5–6). Due to worsening dysesthesia and spinal cord changes, the subject underwent posterior decompression and fusion with allograft at C3–6, as well as removal of the posterior hardware at C5–6 at 26 months postoperatively.

In the 2-level arm, 1 patient with a TDR device continued to experience neck and arm pain following the primary surgery, which was attributed to poor device stability (Fig. 5). The patient underwent removal of both prostheses and received a fusion at both index levels (C4–6) approximately 11 months postsurgery. Nine months later, the patient presented with symptomatic pseudarthrosis at both levels and underwent another anterior and posterior fusion procedure. A second patient in the TDR group had the inferior prosthesis (C5–6) removed after experiencing multiple motor vehicle accidents with concurrent neck pain 23 months postsurgery. The patient had a surgery to remove the superior prosthesis (C4–5) 7 months later at a noninvestigational site and chose not to release their medical records to the investigator.

FIG. 5.
FIG. 5.

TDR failure requiring removal and multiple subsequent fusions.

In the 2-level ACDF group, 3 patients had multiple subsequent surgeries. One patient had a subsequent surgery at 10 months postoperatively due to continuing neck and arm pain (Fig. 6). The patient underwent removal of the index-level (C4–6) hardware and underwent ACDF at an adjacent level (C3–4). A nonunion (C5–6) was detected intraoperatively, and a redo fusion takedown with decompression was performed. One year later, the subject presented with disabling neck pain and was admitted. This patient underwent removal of hardware C3–6 anteriorly; exploration of fusion with a finding of nonunion at C5–6; reinstrumentation of C3–6 with a plate and screw system; and C3–4, C4–5, and C5–6 bilateral posterior-lateral fusion with instrumentation using a posterior cervical fixation system. Seven months later, the patient returned with complaints of recurrent neck pain and underwent removal of hardware from C3–6 and exploration of the fusion, which showed solid union.

FIG. 6.
FIG. 6.

ACDF nonunion and development of adjacent-level disease leading to subsequent fusion surgeries.

A second 2-level ACDF subject, who was initially treated at C5–7, developed pseudarthrosis with neck pain 10 months postoperatively. The subject underwent a C5–6 posterior arthrodesis with lateral mass screws and local autologous graft. After the patient reported swelling in her neck 22 months later, it was revealed by MRI that the patient had a large posterior disc protrusion at C3–4 with cord indentation and bilateral foraminal narrowing. The subject underwent anterior cervical discectomy and C3–4 arthroplasty. After presenting with severe cervical and thoracic instability 11 months later, the patient underwent C5–T2 posterior fusion.

A third patient in the 2-level ACDF group treated at C3–5 underwent an additional surgery for adjacent-level disease at C5–6, 22 months after the primary surgery. The patient was treated with discectomy and TDR at C5–6 and removal of the initial hardware at C3–5. Thirty months later, the patient presented with persistent and worsening neck pain, and radiographs showed loosening of the TDR. The subject then underwent removal of the TDR, corpectomy, and anterior cervical fusion.

Discussion

The safety and effectiveness of TDR has been validated across a number of studies at many different follow-up periods.3,5,15,22,23,27–29,33 Overall, TDR has demonstrated an advantage over ACDF with regard to motion preservation. The nature of ACDF eliminates motion at treated levels, whereas TDR has been shown to preserve segment mobility with high success.3,22,28 Both short- and long-term results have trended toward similar or greater improvements in NDI, neck pain, and arm pain visual analog scale scores in TDR populations when compared with ACDF, although the significance of these results remains controversial.5,11,12,14,22,24,27–29

The results of many single-level TDR clinical trials suggest that TDR may also result in a lower incidence of secondary operations.5,7,9,12,15,22,23,28,29 Sasso et al. reported a 2-fold increase in secondary surgery rates in patients with 1-level ACDF compared with Bryan cervical disc replacement counterparts after 2 years (TDR 2/56 vs ACDF 4/59).28 Garrido et al. reported a 4-fold increase in subsequent surgical intervention in patients with 1-level ACDF compared with Bryan cervical disc replacement at 4 years (TDR 1/23 vs ACDF 5/26).12 In a 5-year study on secondary surgery rates, Delamarter and Zigler reported a significant decrease in secondary surgery rates in patients who received a ProDisc-C artificial cervical disc (2.9%) versus ACDF (14.5%).9

The intent of this study was to further demonstrate the benefits of TDR in terms of subsequent surgical intervention rates. In agreement with previous studies, we found that patients with 1-level ACDF who received a TDR device had a significantly lower occurrence of subsequent surgical intervention at the treated level compared with ACDF-treated patients (2.8% TDR vs 11.1% ACDF; p < 0.05). Patients with 2-level ACDF who received a TDR device also demonstrated significantly fewer index-level surgeries at 60 months (3.8% TDR vs 16.2% ACDF; p < 0.001).

Several authors have hypothesized that TDR may reduce the incidence of adjacent-segment degeneration compared with ACDF as a consequence of maintaining segmental motion and stress profiles.16,20,25,31 For our 1-level arm at 60 months, we found that 4 times fewer TDR patients required a subsequent operation at adjacent levels (2.2% TDR vs 11.1% ACDF; p < 0.05). Similar results were shown in the 2-level arm for adjacent-level surgeries (3.4% TDR vs 11.4% ACDF; p < 0.05). These results are in agreement with the findings of other investigators and suggest an elevated rate of adjacent-segment degeneration in the ACDF population.

In a retrospective review of anterior cervical decompression and stabilization, patients with a maximum follow-up of 21 years (range 2–21 years), including patients without cervical instrumentation, Hilibrand and Robbins17 cite studies by Bohlman et al.,4 Gore and Sepic,13 and Williams et al.32 when analyzing rates of adjacent-segment disease among ACDF patients, with an average follow-up of 4.5 years.17 From these studies, the annual incidence of adjacent-segment disease requiring additional surgery was 1.5%–4%,17 equating to 7.5%–20% at 5 years. In a long-term TDR study with the Prestige artificial cervical disc, Burkus et al. showed a lower rate of secondary surgeries involving adjacent segments in their TDR population compared with ACDF controls (TDR 2.9% vs ACDF 4.9%).5 Mummaneni et al. also reported a statistically significant decrease in secondary operations involving adjacent segments in their TDR population (TDR 2/276 vs ACDF 9/265).22 Davis et al. reported a significantly greater rate of adjacent-segment degeneration at both the inferior and superior index levels for 2-level ACDF compared with TDR at 4 years.8 Interestingly, the rate of adjacent-level operations was similar between the 1- and 2-level ACDF or TDR groups, and does not reflect the expectation that multilevel ACDF causes a greater amount of adjacent-level disease than single-level ACDF. However, this study was not powered or designed for intratreatment comparisons, and these results are suggestive, not conclusive.

Limitations of this study include the inability to blind surgeons and patients to treatment, which opens the results to the potential of confirmation bias. Although the control group in this study was limited to anterior plating with allograft, other fusion procedures and devices (e.g., standalone devices and the use of autograft) are viable treatment options. The comparative results between the control and investigational groups are limited to anterior plate and allograft and may not be consistent with those of other surgical alternatives for cervical fusion. Additionally, the control group consisted of patients receiving 3 different cervical plate systems, based on surgeon preference. This heterogeneity represents a study limitation because ACDF failures may not have been equally distributed across the 3 fusion systems implanted.

All authors were investigators for the Mobi-C IDE clinical trial, which was sponsored by LDR Spine USA, Inc. Some surgeons received compensation for their participation in the trial or have equity in LDR Spine. To ensure that these potential conflicts of interest have not affected study outcomes, an analysis was performed to compare the subsequent surgery rates between sites with and without financial interests. A site was considered financially interested if an investigator received any payment from the manufacturer or if the investigator held company equity during the study period. At 60 months, the financially interested and nonfinancially interested sites had statistically similar subsequent surgery rates within treatment groups for both treatment arms, with no trend observed. Additionally, 45.9% of patients had subsequent surgeries performed by surgeons not participating in the IDE trial.

Conclusions

The results from this clinical trial suggest that TDR may provide a substantial benefit over ACDF in providing a lower risk for subsequent surgical intervention. Furthermore, a lower rate of subsequent adjacent-level surgical procedures in patients who received TDR devices provides indirect evidence that motion preservation may lead to a lower rate of adjacent-level disease than an anterior fusion approach.

Acknowledgments

LDR Spine USA, Inc. sponsored the FDA IDE clinical trial. We would like to thank the other principal investigators for their contributions to the study, who are as follows: Guy Danielson III, MD; Charlie Gordon, MD; Daniel Peterson, MD; John Stokes, MD; Arnold Schwartz, MD; Ali Araghi, MD; David Tahernia, MD; Hazem Eltahawy, MD; Reginald Tall, MD; Douglas Wong, MD; Gerald Schell, MD; Michael Ramsey, MD; B. Christoph Meyer, MD; Robert McLain, MD; Jon Park, MD; Ed Simmons, MD; Mark Stern, MD; and Phillip S. Yuan, MD.

References

  • 1

    Auerbach JDAnakwenze OAMilby AHLonner BSBalderston RA: Segmental contribution toward total cervical range of motion: a comparison of cervical disc arthroplasty and fusion. Spine (Phila Pa 1976) 36:E1593E15992011

  • 2

    Bae HWKim KDNunley PDJackson RJHisey MSDavis RJ: Comparison of clinical outcomes of 1- and 2-level total disc replacement: four-year results from a prospective, randomized, controlled, multicenter IDE clinical trial. Spine (Phila Pa 1976) 40:7597662015

  • 3

    Beaurain JBernard PDufour TFuentes JMHovorka IHuppert J: Intermediate clinical and radiological results of cervical TDR (Mobi-C) with up to 2 years of follow-up. Eur Spine J 18:8418502009

  • 4

    Bohlman HHEmery SEGoodfellow DBJones PK: Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am 75:129813071993

  • 5

    Burkus JKHaid RWTraynelis VCMummaneni 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 13:3083182010

  • 6

    Bydon MXu RMacki MDe la Garza-Ramos RSciubba DMWolinsky JP: Adjacent segment disease after anterior cervical discectomy and fusion in a large series. Neurosurgery 74:1391462014

  • 7

    Davis RJKim KDHisey MSHoffman GABae HWGaede SE: Cervical total disc replacement with the Mobi-C cervical artificial disc compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled multicenter clinical trial: clinical article. J Neurosurg Spine 19:5325452013

  • 8

    Davis RJNunley PDKim KDHisey MSJackson RJBae HW: Two-level total disc replacement with Mobi-C cervical artificial disc versus anterior discectomy and fusion: a prospective, randomized, controlled multicenter clinical trial with 4-year follow-up results. J Neurosurg Spine 22:15252015

  • 9

    Delamarter RBZigler J: Five-year reoperation rates, cervical total disc replacement versus fusion, results of a prospective randomized clinical trial. Spine (Phila Pa 1976) 38:7117172013

  • 10

    Elsawaf AMastronardi LRoperto RBozzao ACaroli MFerrante L: Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages. Neurosurg Rev 32:2152242009

  • 11

    Fay LYHuang WCTsai TYWu JCKo CCTu TH: Differences between arthroplasty and anterior cervical fusion in two-level cervical degenerative disc disease. Eur Spine J 23:6276342014

  • 12

    Garrido BJTaha TASasso RC: Clinical outcomes of Bryan cervical disc arthroplasty a prospective, randomized, controlled, single site trial with 48-month follow-up. J Spinal Disord Tech 23:3673712010

  • 13

    Gore DRSepic SB: Anterior cervical fusion for degenerated or protruded discs. A review of one hundred forty-six patients. Spine (Phila Pa 1976) 9:6676711984

  • 14

    Hacker FMBabcock RMHacker RJ: Very late complications of cervical arthroplasty: results of 2 controlled randomized prospective studies from a single investigator site. Spine (Phila Pa 1976) 38:222322262013

  • 15

    Heller JGSasso RCPapadopoulos SMAnderson PAFessler RGHacker RJ: Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine (Phila Pa 1976) 34:1011072009

  • 16

    Hilibrand ASCarlson GDPalumbo MAJones PKBohlman HH: Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 81:5195281999

  • 17

    Hilibrand ASRobbins M: Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion?. Spine J 4:6 Suppl190S194S2004

  • 18

    Hisey MSBae HDavis RGaede SHoffman GKim K: Multi-center, prospective, randomized, controlled investigational device exemption clinical trial comparing Mobi C Cervical Artificial Disc to anterior discectomy and fusion in the treatment of symptomatic degenerative disc disease in the cervical spine. Int J Spine Surg 8:72014

  • 19

    Khong PBogduk NGhahreman ADavies M: Cervical disc arthroplasty for the treatment of spondylotic myelopathy and radiculopathy. J Clin Neurosci 20:141114162013

  • 20

    Kim SWLimson MAKim SBArbatin JJChang KYPark MS: Comparison of radiographic changes after ACDF versus Bryan disc arthroplasty in single and bi-level cases. Eur Spine J 18:2182312009

  • 21

    Matsunaga SKabayama SYamamoto TYone KSakou TNakanishi K: Strain on intervertebral discs after anterior cervical decompression and fusion. Spine (Phila Pa 1976) 24:6706751999

  • 22

    Mummaneni PVBurkus JKHaid RWTraynelis VCZdeblick TA: Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine 6:1982092007

  • 23

    Murrey DJanssen MDelamarter RGoldstein JZigler JTay B: Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 9:2752862009

  • 24

    Ren CSong YXue YYang X: Mid- to long-term outcomes after cervical disc arthroplasty compared with anterior discectomy and fusion: a systematic review and meta-analysis of randomized controlled trials. Eur Spine J 23:111511232014

  • 25

    Robertson JTPapadopoulos SMTraynelis VC: Assessment of adjacent-segment disease in patients treated with cervical fusion or arthroplasty: a prospective 2-year study. J Neurosurg Spine 3:4174232005

  • 26

    Robinson RAWalker AEFerlic DCWiecking DK: The results of anterior interbody fusion of the cervical spine. J Bone Joint Surg Am 44:156915871962

  • 27

    Sasso RCAnderson PARiew KDHeller JG: Results of cervical arthroplasty compared with anterior discectomy and fusion: four-year clinical outcomes in a prospective, randomized controlled trial. J Bone Joint Surg Am 93:168416922011

  • 28

    Sasso RCSmucker JDHacker RJHeller JG: Artificial disc versus fusion: a prospective, randomized study with 2-year follow-up on 99 patients. Spine (Phila Pa 1976) 32:293329422007

  • 29

    Upadhyaya CDWu J-CTrost GHaid RWTraynelis VCTay B: Analysis of the three United States Food and Drug Administration investigational device exemption cervical arthroplasty trials. J Neurosurg Spine 16:2162282012

  • 30

    Vaccaro ABeutler WPeppelman WMarzluff JMHighsmith JMugglin A: Clinical outcomes with selectively constrained SECURE-C cervical disc arthroplasty: two-year results from a prospective, randomized, controlled, multi-center investigational device exemption study. Spine (Phila Pa 1976) 38:222722392013

  • 31

    Wigfield CGill SNelson RLangdon IMetcalf NRobertson J: Influence of an artificial cervical joint compared with fusion on adjacent-level motion in the treatment of degenerative cervical disc disease. J Neurosurg 96:1 Suppl17212002

  • 32

    Williams JLAllen MB JrHarkess JW: Late results of cervical discectomy and interbody fusion: some factors influencing the results. J Bone Joint Surg Am 50:2772861968

  • 33

    Zhang ZGu BZhu WWang QZhang W: Clinical and radiographic results of Bryan cervical total disc replacement: 4-year outcomes in a prospective study. Arch Orthop Trauma Surg 133:106110662013

Disclosures

Dr. Nunley has direct stock ownership in Amedica, Paradigm Spine, Safewire, and Spineology; serves as a consultant to Amedica, Vertiflex, LDR, and K2M; and is a patent holder for LDR, K2M, and Osprey. Dr. Hisey is a member of the faculty for LDR clinical courses. Dr. Gaede performed statistical analysis for the study/writing or editorial assistance on the manuscript on behalf of LDR. Dr. Jackson serves as a consultant for LDR. Dr. Bae has direct stock ownership in LDR, serves as a consultant, and receives royalties. Dr. Davis received research support during the trial. Dr. Kim has ownership in Molecular Matrix and Globus, serves as a consultant to FzioMed, and has speaking/teaching arrangements with Precision Spine, LDR, and Globus. Dr. Hoffmann has ownership in Path4/LDR.

Author Contributions

Conception and design: Jackson. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Drafting the article: Jackson, Davis. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Jackson. Administrative/technical/material support: Jackson. Study supervision: Jackson, Bae, Kim, Nunley.

Supplemental Information

Previous Presentations

Portions of this work were presented at the 29th Annual Meeting of North American Spine Society, San Francisco, California, November 12–15, 2014.

If the inline PDF is not rendering correctly, you can download the PDF file here.

Article Information

INCLUDE WHEN CITING Published online January 22, 2016; DOI: 10.3171/2015.8.SPINE15219.

Correspondence Robert J. Jackson, Orange County Neurosurgical Associates, 23961 Calle Magdalena, Ste. 504, Laguna Hills, CA 92653. email: rjocna@gmail.com.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Mobi-C Cervical Disc Prosthesis (LDR Medical). Copyright LDR Holding Corporation. Published with permission. Figure is available in color online only.

  • View in gallery

    Subsequent surgery classification by operative levels.

  • View in gallery

    Subsequent surgery at index level leading to study failure. *p= 0.014; **p = 0.0002.

  • View in gallery

    Subsequent surgery at adjacent level. *p = 0.0043; **p = 0.0059.

  • View in gallery

    TDR failure requiring removal and multiple subsequent fusions.

  • View in gallery

    ACDF nonunion and development of adjacent-level disease leading to subsequent fusion surgeries.

References

  • 1

    Auerbach JDAnakwenze OAMilby AHLonner BSBalderston RA: Segmental contribution toward total cervical range of motion: a comparison of cervical disc arthroplasty and fusion. Spine (Phila Pa 1976) 36:E1593E15992011

  • 2

    Bae HWKim KDNunley PDJackson RJHisey MSDavis RJ: Comparison of clinical outcomes of 1- and 2-level total disc replacement: four-year results from a prospective, randomized, controlled, multicenter IDE clinical trial. Spine (Phila Pa 1976) 40:7597662015

  • 3

    Beaurain JBernard PDufour TFuentes JMHovorka IHuppert J: Intermediate clinical and radiological results of cervical TDR (Mobi-C) with up to 2 years of follow-up. Eur Spine J 18:8418502009

  • 4

    Bohlman HHEmery SEGoodfellow DBJones PK: Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am 75:129813071993

  • 5

    Burkus JKHaid RWTraynelis VCMummaneni 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 13:3083182010

  • 6

    Bydon MXu RMacki MDe la Garza-Ramos RSciubba DMWolinsky JP: Adjacent segment disease after anterior cervical discectomy and fusion in a large series. Neurosurgery 74:1391462014

  • 7

    Davis RJKim KDHisey MSHoffman GABae HWGaede SE: Cervical total disc replacement with the Mobi-C cervical artificial disc compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled multicenter clinical trial: clinical article. J Neurosurg Spine 19:5325452013

  • 8

    Davis RJNunley PDKim KDHisey MSJackson RJBae HW: Two-level total disc replacement with Mobi-C cervical artificial disc versus anterior discectomy and fusion: a prospective, randomized, controlled multicenter clinical trial with 4-year follow-up results. J Neurosurg Spine 22:15252015

  • 9

    Delamarter RBZigler J: Five-year reoperation rates, cervical total disc replacement versus fusion, results of a prospective randomized clinical trial. Spine (Phila Pa 1976) 38:7117172013

  • 10

    Elsawaf AMastronardi LRoperto RBozzao ACaroli MFerrante L: Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages. Neurosurg Rev 32:2152242009

  • 11

    Fay LYHuang WCTsai TYWu JCKo CCTu TH: Differences between arthroplasty and anterior cervical fusion in two-level cervical degenerative disc disease. Eur Spine J 23:6276342014

  • 12

    Garrido BJTaha TASasso RC: Clinical outcomes of Bryan cervical disc arthroplasty a prospective, randomized, controlled, single site trial with 48-month follow-up. J Spinal Disord Tech 23:3673712010

  • 13

    Gore DRSepic SB: Anterior cervical fusion for degenerated or protruded discs. A review of one hundred forty-six patients. Spine (Phila Pa 1976) 9:6676711984

  • 14

    Hacker FMBabcock RMHacker RJ: Very late complications of cervical arthroplasty: results of 2 controlled randomized prospective studies from a single investigator site. Spine (Phila Pa 1976) 38:222322262013

  • 15

    Heller JGSasso RCPapadopoulos SMAnderson PAFessler RGHacker RJ: Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine (Phila Pa 1976) 34:1011072009

  • 16

    Hilibrand ASCarlson GDPalumbo MAJones PKBohlman HH: Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 81:5195281999

  • 17

    Hilibrand ASRobbins M: Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion?. Spine J 4:6 Suppl190S194S2004

  • 18

    Hisey MSBae HDavis RGaede SHoffman GKim K: Multi-center, prospective, randomized, controlled investigational device exemption clinical trial comparing Mobi C Cervical Artificial Disc to anterior discectomy and fusion in the treatment of symptomatic degenerative disc disease in the cervical spine. Int J Spine Surg 8:72014

  • 19

    Khong PBogduk NGhahreman ADavies M: Cervical disc arthroplasty for the treatment of spondylotic myelopathy and radiculopathy. J Clin Neurosci 20:141114162013

  • 20

    Kim SWLimson MAKim SBArbatin JJChang KYPark MS: Comparison of radiographic changes after ACDF versus Bryan disc arthroplasty in single and bi-level cases. Eur Spine J 18:2182312009

  • 21

    Matsunaga SKabayama SYamamoto TYone KSakou TNakanishi K: Strain on intervertebral discs after anterior cervical decompression and fusion. Spine (Phila Pa 1976) 24:6706751999

  • 22

    Mummaneni PVBurkus JKHaid RWTraynelis VCZdeblick TA: Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine 6:1982092007

  • 23

    Murrey DJanssen MDelamarter RGoldstein JZigler JTay B: Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 9:2752862009

  • 24

    Ren CSong YXue YYang X: Mid- to long-term outcomes after cervical disc arthroplasty compared with anterior discectomy and fusion: a systematic review and meta-analysis of randomized controlled trials. Eur Spine J 23:111511232014

  • 25

    Robertson JTPapadopoulos SMTraynelis VC: Assessment of adjacent-segment disease in patients treated with cervical fusion or arthroplasty: a prospective 2-year study. J Neurosurg Spine 3:4174232005

  • 26

    Robinson RAWalker AEFerlic DCWiecking DK: The results of anterior interbody fusion of the cervical spine. J Bone Joint Surg Am 44:156915871962

  • 27

    Sasso RCAnderson PARiew KDHeller JG: Results of cervical arthroplasty compared with anterior discectomy and fusion: four-year clinical outcomes in a prospective, randomized controlled trial. J Bone Joint Surg Am 93:168416922011

  • 28

    Sasso RCSmucker JDHacker RJHeller JG: Artificial disc versus fusion: a prospective, randomized study with 2-year follow-up on 99 patients. Spine (Phila Pa 1976) 32:293329422007

  • 29

    Upadhyaya CDWu J-CTrost GHaid RWTraynelis VCTay B: Analysis of the three United States Food and Drug Administration investigational device exemption cervical arthroplasty trials. J Neurosurg Spine 16:2162282012

  • 30

    Vaccaro ABeutler WPeppelman WMarzluff JMHighsmith JMugglin A: Clinical outcomes with selectively constrained SECURE-C cervical disc arthroplasty: two-year results from a prospective, randomized, controlled, multi-center investigational device exemption study. Spine (Phila Pa 1976) 38:222722392013

  • 31

    Wigfield CGill SNelson RLangdon IMetcalf NRobertson J: Influence of an artificial cervical joint compared with fusion on adjacent-level motion in the treatment of degenerative cervical disc disease. J Neurosurg 96:1 Suppl17212002

  • 32

    Williams JLAllen MB JrHarkess JW: Late results of cervical discectomy and interbody fusion: some factors influencing the results. J Bone Joint Surg Am 50:2772861968

  • 33

    Zhang ZGu BZhu WWang QZhang W: Clinical and radiographic results of Bryan cervical total disc replacement: 4-year outcomes in a prospective study. Arch Orthop Trauma Surg 133:106110662013

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