Mobi-C for cervical disc replacement

Study component

Description

Objectives/hypotheses

To critically assess the available literature on CDA with the Mobi‑C prosthesis, with a focus on 2‑level CDA.

Study design

Systematic review.

Setting

Search date: September 1, 2014.

Inclusion/exclusion criteria

Any studies (randomised controlled, retrospective, and prospective studies) that presented clinical results associated with the Mobi‑C cervical disc prosthesis were included. Exclusion criteria: biomechanical studies, radiographic studies, animal studies and articles dealing with nucleus replacement.

Primary outcomes

Complications and/or adverse outcomes assessed included HO, ASDG (defined radiographically), adjacent segment disease (defined clinically by symptoms), or other, such as dysphagia or reoperation.

Statistical methods

Results were not combined statistically but presented as a narrative and in tables.

Patients included

Fifteen studies were included: 1 RCT, 5 prospective studies and 9 retrospective studies, involving a total of 1,319 people receiving Mobi‑C.

Results

All included studies showed non‑inferiority of 1‑level Mobi‑C CDA to 1‑level ACDF. In comparison with other cervical disc prostheses, the Mobi‑C prosthesis is associated with high rates of HO.

In the 1 RCT identified (Davis et al. 2013; n=330), 225 patients underwent 2‑level CDA, and 105 underwent 2‑level ACDF. Both groups experienced statistically significant improvements in NDI and VAS arm/neck scores versus preoperative values. The Mobi‑C group experienced significantly greater improvement in NDI score than the ACDF cohort (p<0.05). ROM was maintained at both treated segments. The reoperation rate was significantly higher with ACDF (11.4%) versus Mobi‑C (3.1%). Lower adverse events were reported with Mobi‑C. ASDG occurred in 16% with Mobi‑C and 51% with ACDF (p<0.03). The authors provided only the Grade IV HO rate for Mobi‑C at 2 years (4.9%, 11 patients). Overall study success rates were superior with CDA cohort versus ACDF (69.7% vs 37.4%; p<0.01).

Conclusions

One‑level Mobi‑C CDA is non‑inferior, but not superior, to 1‑level ACDF for patients with cervical degenerative disc disease. Mobi‑C is also associated with high rates of HO. Two‑level Mobi‑C CDA may be superior to 2‑level ACDF however, insufficient evidence exists.

Abbreviations: ACDF, anterior cervical discectomy and fusion; ASDG, adjacent segment degeneration; CDA, cervical disc arthroplasty; HO, heterotopic ossification; NDI, Neck Disability Index; RCT, randomised controlled trial; ROM, range of motion; VAS, visual analogue scale.

Study component

Description

Objectives/hypotheses

To evaluate the safety and effectiveness of 2‑level TDR using Mobi‑C at 48 months' follow‑up.

Study design

RCT. This is a follow‑up to the Davis et al. 2013 study described in Alvin et al. (2014).

Setting

24 centres in the US. Patients underwent surgery between April 2006 and March 2008. This paper reports outcomes at 48 months.

Inclusion/exclusion criteria

Inclusion: people aged 18–69 years with a diagnosis of degenerative disc disease with radiculopathy or myeloradiculopathy at 2 contiguous levels from C3 to C7 that was unresponsive to non‑operative treatment for at least 6 weeks or demonstrated progressive symptoms calling for immediate surgery. Other inclusion criteria included: NDI score ≥30, physically and mentally able, signed informed consent and willingness to discontinue all use of NSAIDs from 1 week before surgery until 3 months after surgery.

Exclusion included: more than 2 vertebral levels requiring treatment, any prior spine surgery, metabolic bone disease, marked cervical instability, diseases that would preclude accurate clinical evaluation, use of high‑dose steroids, use of other investigational drug or medical device within 30 days before surgery, pending personal litigation relating to spinal injury, smoking >1 pack of cigarettes per day, reported to have mental illness.

Primary outcomes

The primary endpoint was "overall success", that is a composite endpoint including: 1) ≥30‑point improvement for patients with baseline NDI ≥60 or 50% improvement for patients with baseline NDI <60; 2) no subsequent surgical intervention at either treated level; 3) no AEs assessed as major complications; 4) maintenance or improvement in neurological function; and 5) radiographic success.

Other outcome measures included: VAS for neck and arm pain, the SF‑12 MCS and PCS, subsequent surgical intervention, complications, neurological function, return to work, patient satisfaction, ROM, HO, and adjacent‑segment degeneration.

Statistical methods

The study included a non‑inferiority hypothesis of the overall success rate of Mobi‑C compared with that of the control procedure. Non‑inferiority was assessed using an exact 95% 1‑sided confidence bound. A post hoc test was pre‑planned to test for superiority in the event of non‑inferiority. Superiority was assessed using a 97.5% 1‑sided confidence bound in the event a 10% non‑inferiority margin could be excluded. Two‑sided t‑tests were used to determine statistical significance for all continuous outcome measures between groups at each time point. Fisher's exact tests were used to determine success or incident rates. Wilcoxon signed‑rank tests were used to compare the change from baseline within treatment groups. A p value <0.05 was considered significant.

Patients included

225 people received treatment with a Mobi‑C cervical artificial disc and 105 with corticocancellous allograft and an anterior cervical plate using the standard ACDF technique, for disease at 2 levels.

Results

66.0% of the TDR group and 36.0% of the ACDF group achieved 'overall success' (p<0.0001).

Conclusions

The authors concluded that 4‑year results support TDR as a safe, effective, and statistically superior alternative to ACDF for the treatment of degenerative disc disease at 2 contiguous cervical levels.

Abbreviations: ACDF, anterior cervical discectomy and fusion; BMI, body mass index; CI, confidence interval; HO, heterotopic ossification; MCS, Mental Component Summary; n, number of patients; NDI, Neck Disability Index; NSAID, nonsteroidal anti‑inflammatory drug; PCS, Physical Component Summary; RCT, randomised controlled trial; ROM, range of motion; SF‑12, 12‑item Short Form Health Survey; TDR, total disc replacement; VAS, visual analogue scales.

Mobi‑C cervical artificial disc

ACDF

Analysis

Randomised

n=225

n=105

Efficacy

n=200

n=85

Primary outcome: overall success at 4 years

66.0% (132/200)

36.0% (31/85)

p<0.0001

Selected secondary outcomes:

Improvement in NDI score at 4 years (Mean±SD)

36.5±21.3

28.5±18.3

p=0.0048

Improvement in VAS neck pain score from baseline at 4 years (Mean±SD)

53±30

48±29

NS

SF‑12 MCS score improvement at 4 years (Mean±SD)

11±12

10±12

NS

SF‑12 PCS score improvement at 4 years (Mean±SD)

13±12

10±12

p<0.05

Time to return to work (for those working; mean±SD)

46±101 days (n=191)

67±113 days (n=86)

NS

Very satisfied or somewhat satisfied with treatment

96.4%

89.0%

p=0.03329

Safety

n=234

n=105

Neurological deterioration at 4 years

6.2%

7.6%

NS

Major complications at 4 years

4.0%

7.6%

NS

Subsequent surgical intervention

4.0% (9 of 225 patients, having a total of 10 surgeries).

15.2% (16 of 105 patients, having a total of 18 surgeries).

p<0.0001

Problems identified radiographically at 4 years

Clinically relevant HO (grades III and IV): 25.6%; includes 10.2% at grade IV.

Failed fusion in 14.8% (12 of the 81 patients with available radiographs; 7.8% of treated levels).

N/A

Adjacent‑segment degeneration at 4 years

41.5%

85.9%

p<0.0001

Abbreviations: ACDF, anterior cervical discectomy and fusion; HO, heterotopic ossification; MCS, Mental Component Summary; n, number of patients; NDI, Neck Disability Index; N/A, not applicable; NS, non‑significance; PCS, Physical Component Summary; ROM, range of motion; SF‑12, 12‑item Short Form Health Survey; TDR, total disc replacement; VAS, visual analogue scales.

Study component

Description

Objectives/hypotheses

To compare clinical outcomes 5 years after TDR surgery using Mobi‑C or ACDF to treatment single‑level symptomatic disc degeneration.

Study design

RCT. This is a follow‑up to the Hisey et al. 2014 study.

Setting

Surgery was performed between April 2006 and March 2008; this paper reports results at 5 years.

Inclusion/exclusion criteria

Symptomatic DDD with radiculopathy or myeloradiculopathy at 1 level from C3 to C7, disc height of at least 3 mm, not osteoporotic, no previous cervical fusion, and failure of at least 6 weeks of non‑operative care.

Primary outcomes

The primary outcome measure was a composite endpoint that required patients to meet all of the following criteria: 1) minimum 30/100 point improvement in NDI scores compared to baseline; 2) no device‑related subsequent surgery; 3) no AEs classified as possibly or probably device‑related by an independent CEC; 4) no neurological deterioration; 5) no intraoperative changes in treatment if randomised to Mobi‑C.

Statistical methods

This study was designed as a non‑inferiority trial with the primary study hypothesis testing the non‑inferiority of TDR with Mobi‑C against ACDF using a 10% margin with respect to patient success at 60 months. Non‑inferiority in the overall success rate was assessed using an exact 95% 1‑sided confidence bound. Statistical significance in success criteria and incidence rates was determined using Fisher's exact test. Statistical significance of continuous outcome measures was assessed by 2‑sided t‑tests at each time point. Changes from baseline within treatment groups were evaluated by Wilcoxon signed‑rank test to determine significance. Statistical significance was indicated by a p‑value less than 0.05.

Patients included

People with single‑level symptomatic cervical disc degeneration; Mobi‑C (n=164) or ACDF (n=81).

Results

The composite overall success was 61.9% with Mobi‑C compared with 52.2% for ACDF, demonstrating statistical non‑inferiority.

Conclusions

Five‑year results demonstrate the safety and efficacy of TDR with Mobi‑C as a viable alternative to ACDF in the treatment of 1‑level symptomatic cervical disc degeneration, with the potential advantage of lower rates of re‑operation and adjacent segment degeneration.

Abbreviations: ACDF, anterior cervical discectomy and fusion; AE, adverse event; CEC, Clinical Events Committee; DDD, degenerative disc disease; n, number of patients; NDI, Neck Disability Index; TDR, total disc replacement.

Mobi‑C

ACDF

Analysis

Randomised

n=164

n=81

Efficacy

n=140

n=64

Primary outcome: overall success at 5 years

61.9%

52.2%

NS

Selected secondary outcomes:

SF‑12 PCS final score at 5 years

47.6

48.3

NS

Subsequent surgery within 5 years

8 people

(4.9%)

14 people (17.3%)

p<0.01

Patient satisfaction (very satisfied)

92.0%

83.9%

Not stated

Safety

n=179

n=81

Failure based on radiographic evaluation

5.5%

3.7%

NS

Adjacent segment degeneration at the superior level

37.1%

54.7%

p<0.03

Abbreviations: ACDF, anterior cervical discectomy and fusion; AE, adverse event; CEC, Clinical Events Committee; DDD, degenerative disc disease; n, number of patients; NDI, Neck Disability Index; NS, non‑significance; SF‑12 PCS, Short Form‑12 Health Survey Physical Component Score.

Study component

Description

Objectives/hypotheses

To compare cervical disc replacement using Mobi‑C disc prostheses with ACDF.

Study design

RCT.

Setting

11 separate medical institutions across China; participants enrolled from February 2008 to November 2009.

Inclusion/exclusion criteria

Patients aged 18–68 years with a diagnosis of degenerative cervical spondylosis of 1 segmental level, supported by clinical symptoms and imaging data and with no significant improvement after conservative treatment for at least 3 months. Patients were excluded if they had multi‑segmental‑level cervical diseases, severe facet‑joint degeneration, osteoporosis, cervical instability, spinal‑canal stenosis, ossification of the posterior longitudinal ligament, tumour, infection or metal allergies.

Primary outcomes

Clinical and neurological outcome was determined by measuring the JOA scores, VAS and NDI. Static and dynamic radiographs were obtained of the cervical curvature, the FSU angle and ROM of the cervical spine, FSU angle and treated and adjacent segments.

Statistical methods

Statistical analysis was determined using a single‑factor analysis of variance with Bonferroni's post hoc tests for multiple comparisons of baseline within the treatment groups at each follow‑up time‑point. For between‑treatment group comparisons, paired t tests were performed.

Patients included

111 patients with single‑level symptomatic cervical spondylosis were included; n=55 with Mobi‑C disc replacement and n=56 with ACDF using plate/cage.

Results

JOA, VAS and NDI showed statistically significant improvements 48 months after surgery (p<0.05). ROM, FSU angle, treated segment and adjacent segments in the Mobi‑C group were not significantly different before and after replacement (p>0.05). ROM in the ACDF group was significantly reduced at 1 month and remained so throughout the follow‑up. By 48 months, more ACDF patients required secondary surgery (4 of 56 patients).

Conclusions

The authors concluded that although ACDF may increase the risk of additional surgery, clinical outcomes indicated that both Mobi‑C artificial cervical disc replacement and ACDF were reliable. Radiographic data showed that ROM of the cervical spine, FSU angle and treated and adjacent segments were relatively better reconstructed and maintained in the Mobi‑C group compared with those in the ACDF group.

Abbreviations: ACDF, anterior cervical discectomy and fusion; CI, confidence interval; FSU, functional spinal unit; JOA, Japanese Orthopaedic Association; n, number of patients; NDI, Neck Disability Index; ROM, range of motion; VAS, visual analogue scale.

Mobi‑C

ACDF

Analysis

Randomised

n=55

n=56

Efficacy

n=55

n=56

JOA score

Before surgery: 10.86

7 days: 12.80

1 month: 13.86

3 months: 14.58

Before surgery: 10.84

7 days: 12.54

1 month: 13.64

3 months: 14.44

NS

VAS score

Before surgery: 6.72

7 days: 4.20

3 months: 2.04

Before surgery: 6.64

7 days: 4.44

3 months: 2.24

NS

NDI score 48 months post‑operation

19.60

20.10

NS

ROM

Around 60° (shown graphically)

Around 50° (shown graphically)

p<0.0005

Safety

n=55

n=56

Number of patients with post‑operative pharyngeal discomfort or hoarseness

15

13

NR

Other complications at 4 years

33% (18/55) had HO at 4 years

Pseudarthrosis rates in treated segments were 10.7 % (6/56) at the 6‑month follow‑up and 1.8 % (1/56) at 48‑month follow‑up.

NR

Adjacent‑segment reoperations

0

7.1% (4/56)

NR

Abbreviations: ACDF, anterior cervical discectomy and fusion; CI, confidence interval; FSU, functional spinal unit; HO, heterotopic ossification; JOA, Japanese Orthopaedic Association; n, number of patients; NDI, Neck Disability Index; NR, not reported; NS, non‑significance; ROM, range of motion; VAS, visual analogue scale.