STUDY RATIONALE AND CONTEXT
Several prospective, randomized, controlled clinical trials regarding cervical artificial
disc replacement (C-ADR) have been published. However, the number of C-ADR patients
with long-term follow-up for more than 4 years is still sparse. The purpose of this
systematic review is to provide a summary of the available literature reporting long-term
follow-up of C-ADR and to elucidate whether the favorable outcomes seen in the short-term
continue after 4 to 5 years.
CLINICAL QUESTION
Does single-level unconstrained, semiconstrained, or fully constrained C-ADR improve
health outcomes compared with single-level ACDF in the long-term?
RESULTS
Two randomized, multicenter FDA trials comparing outcomes following C-ADR and ACDF
with follow-up > 48 months were found ([Fig 1 ]). Inclusion and exclusion criteria and demographic information for each study are
listed in [Table 1 ]. Overall, a total of 1004 adult patients (47% male) with a mean age of 44 years
were included. All patients were diagnosed with single-level degenerative disc disease
between C3 and C7 and had failed a minimum of 6 weeks conservative treatment.
Function, pain, and health-related quality of life (
[Table 2 ]
)
At 48 months in the Bryan trial, patients in the C-ADR group showed significantly
greater mean improvement in NDI, VAS neck and arm pain, and SF-36 PCS measured at
48 months compared with patients in the ACDF group.
At 60 months in the Prestige trial, only mean improvement in NDI scores was significantly
greater in the C-ADR group (38.4 vs 34.1, P =.022); however, for the remaining three outcomes, mean improvements were slighter
greater following C-ADR versus fusion.
Success, ASD, and return to work (
[Table 3 ]
)
At 48 months in the Bryan trial, overall success and NDI success, were achieved in
a significantly greater proportion of C-ADR patients compared with ACDF patients (P = .004 and .003, respectively).
At both 48 months in the Bryan trial and 60 months in the Prestige trial, more patients
achieved overall neurological success (maintenance or improvement) and were working
following C-ADR compared with ACDF, although these differences were not significant.
The rate of ASD at 48 months in the Bryan trial was identical between groups (4.1%);
at 60 months in the Prestige trial the rate was 2.9% in the C-ADR group versus 4.9%
in the ACDF group, however these differences were not statistically significant.
Range of motion
Subsequent operations (
[Table 4 ]
)
No significant differences between groups were reported for rates of revisions, hardware
removal, supplemental fixation, use of bone growth stimulators, or reoperation at
48 months postoperatively in the Bryan trial.
At 60 months, a significant difference was seen between the Prestige C-ADR and ACDF
groups, respectively, in revisions (0% vs 1.9%; P = .028), supplemental fixation (0% vs 1.9%; P = .028), and the use of external bone growth stimulator (0% vs 2.6%; P = .007).
Adverse events
The Bryan study only reported more severe WHO grade 3 or 4 events that occurred after
24 months and up to 48 months follow-up in the C-ADR and ACDF groups, respectively:
any, 24.3% vs 26.1%; severe arm and neck pain, 1.7% vs 3.6%; and new neurological
deficits, 0% vs 1.4%.
In patients with complete radiographic follow-up at 60 months in the Prestige trial,
subsidence (loss of > than 2 mm in functional spinal unit height) was seen in 2.8%
and 1.4% of patients in the C-ADR and ACDF groups, respectively; bridging bone was
reported in 3.2% of the C-ADR patients.
Clinical guidelines
One guideline was found, published by the North American Spine Society (NASS) in 2010,
entitled “Diagnosis and treatment of cervical radiculopathy from degenerative disorders.”
Among the major recommendations listed were the following statements relevant to the
topic of this review:
“ACDF and total disc arthroplasty (TDA) are suggested as comparable treatments, resulting
in similarly successful short term outcomes, for single level degenerative cervical
radiculopathy.” (grade: B; fair evidence–level II or III studies)
“Surgery is an option for the treatment of single level degenerative cervical radiculopathy
to produce and maintain favourable long term (> 4 years) outcomes.” (grade C; poor
quality evidence–level IV or V studies)
Fig 1
Results of literature search.
Table 1
Inclusion and exclusion criteria and demographics for the two included FDA trials
providing long-term follow-up data.*
* FDA indicates US Food and Drug Administration; DDD, degenerative disc disease; NDI,
Neck Disability Index; VAS, Visual Analog Scale; CT, computed tomography; and MRI,
magnetic resonance scan.
Table 2
Function, pain, and health-related quality of life outcomes following C-ADR versus
fusion from two FDA trials with follow-up of 48 months or more.*
* C-ADR indicates cervical artificial disc replacement; FDA, US Food and Drug Administration;
NDI, Neck Disability Index; SF-36, Short-Form 36 Questionnaire; and PCS, Physical
Component Score.
†
P values compare the mean improvement in scores from baseline to each follow-up time-point
between C-ADR and fusion.
Table 3
Success, return to work, and ASD rate following C-ADR versus fusion from two FDA
trials with follow-up of 48 months or more.*
* ASD indicates adjacent segment disease; C-ADR, cervical artificial disc replacement;
FDA, US Food and Drug Administration; NDI, Neck Disability Index; and NS, not statistically
significant.
† Composite measure in which patients had to achieve all the following: an improvement
of ≥15 points on NDI, neurological improvement, no serious (WHO grade 3 or 4) adverse
events related to the implant or surgical implantation procedure, and no subsequent
surgery or intervention that would be classified as treatment failure.
‡ Improvement of ≥15 points in NDI from baseline.
§ Defined as maintenance or improvement of all three neurological parameters (motor
and sensory function, and reflexes).
Table 4
Subsequent operations following C-ADR versus fusion from two FDA trials with follow-up
of 48 months or more.*
* C-ADR indicates cervical artificial disc replacement; FDA, US Food and Drug Administration;
and NS, not statistically significant.
CASE STUDY
A 43-year-old woman presented with cervical myelo-radiculopathy that did not respond
to medical treatment for 6 weeks. The magnetic resonance images demonstrated a large
herniated disc at the level of C5/6, eccentric to the right side ([Fig 2 ]). She then underwent cervical C-ADR at C5/6. Her symptoms improved significantly
after surgery and x-rays taken 2 years postoperatively demonstrated very good range
of motion at the index level ([Fig 3 ]). Her VAS arm pain score improved from a preoperative score of 8 to a postoperative
score of 1 at 2-year follow-up.
Fig 2
Preoperative axial (A) and sagittal (B) magnetic resonance images of a 43-year-old
woman with myeloradiculopathy due to a C5/6 disc herniation.
Fig 3
Postoperative flexion (A) and extension (B) x-rays of the patient 24 months after
surgery. Her VAS arm pain score improved from 8 preoperatively to 1 postoperatively.
