Key-words: Anterior cervical discectomy and fusion - cervical disc arthroplasty - cervical arthrodesis
- cervical arthroplasty - cervical degenerative disc disease - polyether ketone
Introduction
Anterior cervical discectomy and fusion (ACDF) and cervical disc arthroplasty (CDA)
are both acknowledged as equally effective treatments for patients of cervical degenerative
disc disease (CDDD). However, there are very few randomized controlled trials (RCTs)
in literature comparing the two modalities. Both procedures have their own set of
advantages and disadvantages. The common complications of ACDF include screw backout,
dysphagia, and plate fracture and development of adjacent-level disc degeneration.
On the other hand, CDA which may prevent the complications of anterior cervical plating
and cervical immobilization has its own side effects of implant migration or subsidence,
and heterotopic ossification, though the more recent implants show fewer complications.[[1 ]],[[2 ]],[[3 ]],[[4 ]]
While several studies have compared the immediate and short-term clinical and radiological
outcomes of both these procedures, however, to the best of our knowledge, there have
been few studies comparing long-term clinical and radiological outcomes of these patients.
In this study, we compare the long-term clinical and radiologic outcomes of patients
who underwent ACDF with polyether ether ketone (PEEK) implant versus CDA with Artificial
cervical Disc (CDA) in single and bilevel CDDD.
Subjects and Methods
Study setting, patient population, and indication for surgery
This study was carried out from 2010 to 2019 in the Neurosurgery department of a tertiary
care hospital attached to a medical college in India. Patients with prolapsed cervical
intervertebral disc requiring decompression, between the age group of 18–65 years,
admitted to the center constituted the study population. The inclusion criteria were
(i) CDDD requiring surgical treatment at one level or two levels from C3-T1 for symptoms
or signs of cervical radiculopathy and/or myelopathy, with or without axial neck pain
and (ii) failed conservative treatment lasting at least 6 weeks for disc herniation
with a radiculopathy or disc herniation with myelopathy or compressive lesion confirmed
by magnetic resonance imaging (MRI). The exclusion criteria were postlaminectomy with
kyphotic deformity, translational instability, ankylosing spondylitis, rheumatoid
arthritis, ossification of the posterior longitudinal ligament or diffuse hyperostosis,
patients with insulin-dependent diabetes miletus, pregnancy, metabolic bone disease,
and nondiscogenic pain sources. The included patients were randomly allocated to Arthroplasty
(AD) or Anterior cervical discectomy and fusion with PEEK implant group. All patients
signed informed consent and agreed to participate in this study.
Randomization
A total of 60 patients were included in the study and randomized into the two groups
in a one-to-one fashion. Allocation concealment was ensured by using sealed envelope
for allocating treatment group to the selected study participants. Though patients
could not be masked about type of surgery, outcome was measured by independent trained
observers and data analysts were blinded to the type of surgery undergone by the patients.
Five patients were lost to follow-up in each group and finally, 25 patients in each
group were included in the final analysis. The patients were followed up at fixed
intervals postsurgery and continued to be in follow-up and final evaluation was done
5-year postsurgery. In this present study, we evaluate the clinical and radiological
findings preoperatively and at final follow-up (5-year postsurgery).
Clinical and radiological evaluation
Relevant clinical and radiological evaluation was done for all patients before surgery
and also at fixed intervals postoperatively and last follow-up examination was done
5-year postsurgery. Visual Analogue Pain Scale (VAPS) was used to measure pain intensity
and Neck disability Index (NDI) was used to measure neck-specific disability both
preoperatively and thereafter at routine follow-up. cervical range of motion (CROM)
goniometer was used to record active CROM. Preoperative evaluation was done to rule
out cardiac, hepatic, renal, and respiratory disease and to grade the patient's fitness
for surgery.
Radiological evaluation (radiography, MRI) was done to confirm the diagnosis and extent/level
of involvement. Thereafter postsurgery lateral cervical spine radiograph with flexion
and extension views was used at each follow-up and finally at 5 years to compare long-term
radiological outcome in both the groups.
Surgical procedure
All procedures were performed by a single surgeon and were completed through a transverse
skin incision made on the right side of the neck. Under general anesthesia, ACDF with
PEEK implant (filled with autogenous bone) without anterior cervical plating or implantation
or the Prestige® artificial disc prosthesis was performed. Patients in the PEEK group
were given a soft/hard neck collar for 6-week postsurgery.
Statistical analysis
Numerical variables were summarized by median and inter-quartile range and categorical
variables were summarized by proportions. Wilcoxon signed-rank test was used to compare
preoperative and follow-uP values of numerical variables. Median of differences between
preoperative and follow-up values with 95% confidence intervals were also calculated.
The difference in change in numerical variables between two groups-CDA and PEEK were
compared by Mann Whitney U Test. Categorical variables were compared by Fisher's exact
test. Two-tailed tests were used and P < 0.05 was considered to be statistically significant.
R-3.6.0 software version (Windows) was used for statistical analysis.
Results
Baseline characteristics and clinical scores
There were no significant differences in demographic factors or the presence of myelopathy
between the two groups. The mean age of patients in the CDA group was 34 years (29.25–39.50)
while those in the PEEK group were 41 years (33–57 years). There were 6 females and
19 males in the CDA group while the PEEK group had 04 females and 21 males. In our
study, 32% of the patients in the CDA group and 28% in the PEEK group had myelopathy
[[Table 1 ]].
Table 1: Baseline characteristics in the two groups
The median preoperative VAS scores were 8.3 and 8.0 for CDA and PEEK groups, respectively.
At the last follow-up (5 years postsurgery), the median VAS scores decreased to 3.6
in the CDA group and 3.9 in the PEEK group (P < 0.001). The median VAS scores at 5-year
follow-up were significantly lower compared to the preoperative VAS scores in both
groups. Though the reduction in scores was more for the CDA group than the PEEK group,
however, this difference was not significant (P = 0.203) [[Table 2 ]].
Table 2: Comparison of clinical findings in the cervical disc arthroplasty and polyether ether
ketone group
The mean preoperative NDI scores were 26 for both the CDA and PEEK groups, and this
reduced to 07 for both the groups when assessed at the last follow-up. While both
groups demonstrated a significant difference in the follow-up scores when compared
to their preoperative scores (P < 0.05) [[Table 2 ]], however, the difference between the groups was not significant.
The CROM for cervical, lateral flexion, and rotational motion has been compared in
[[Table 3 ]] and [[Figure 1 ]]. The median range of motion (ROM) increased postoperatively in the CDA group for
all forms of ROM. This increase was found to be statistically significant (P < 0.0001).
However, in the PEEK group, a significant decrease in motion was observed in all forms/types
of ROM at 5 years of follow-up. The change between the two groups was also found to
be significant in all the forms of ROM.
Figure 1: Comparison of range of motion in the two groups
Table 3: Comparison of cervical range of motion in cervical disc arthroplasty and polyether
ether ketone group
Radiological outcomes
Sagittal ROM was compared preoperatively and at follow-up both within the two groups
and between the groups [[Table 4 ]] and [[Figure 2 ]]. The preoperative median sagittal ROM in the CDA group was 9.10, 8.80, and 12.60
in the three levels, namely upper, lower, and implanted level ROM, and it increased
to 9.90,9.30 and 13.0, respectively. This change was found to be statistically significant
in all three levels. However, in the PEEK group, a reduction in the sagittal ROM values
was noted at the final follow-up in all three levels. This change between the two
groups was found to be highly significant (P < 0.0001).
Figure 2: Comparison of sagittal range of motion in cervical disc arthroplasty and polyether
ether ketone group
Table 4: Comparison of radiological findings in cervical disc arthroplasty and polyether ether
ketone groups
Median functional spinal unit (FSU) values decreased postoperatively in both groups
[[Table 5 ]], however, the decrease was significantly more in the PEEK group. The FSU flexion
reduced from 8.20 to 6.60 in the CDA group, FSU range of movement also decreased from
14.10 to 11.20 in the FSU range of movement for the CDA group. A larger reduction
in the FSU was noticed in the PEEK group.
Table 5: Comparison of functional spinal unit in cervical disc arthroplasty and polyether
ether ketone groups
We assessed overall cervical alignment (OCA) in both the groups [[Table 6 ]]. The median OCA flexion, extension, and ROM values preoperatively in the CDA group
were 25.40, −25.10, and 50.70. On follow-up, these increased for both flexion and
ROM (26.20 and 52.30, respectively) and only showed a decline (−26) for OCA extension.
The changes in all three planes were significant. However, in the PEEK group, there
was a significant decrease in the follow-up median OCA values for flexion and ROM.
The difference in OCA between the two groups was also found to be statistically significant.
Table 6: Comparison of overall cervical alignment in cervical disc arthroplasty and polyether
ether ketone group
The disc height between the two groups is compared in [[Table 7 ]]. In the CDA group, we noticed that the disc height was maintained at all the levels
measured (Posterior intervertebral height at the Implanted level and lower level and
Anterior Intervertebral height at the upper and lower level) while in the PEEK group
there was a significant decrease in the disc heights at all the levels measured.
Table 7: Comparison of disc height in cervical disc arthroplasty and polyether ether ketone
group
Discussion
A meta-analysis of published RCTs which compared CDA with ACDF for patients with CDDD
found that CDA was an effective and safe surgical procedure for the treatment of one-level
CDDD, and CDA group had significantly better ROM and rate of neurological success,
significantly lower neck pain scores, and lower arm pain scores at 24 months postoperatively
than the ACDF group.[[5 ]] A similar study by Rao et al., which also included two level CDDD, reported similar
findings.[[6 ]]
Our study compares the long-term clinical and radiological outcomes of CDA versus
PEEK in patients with cervical disc degenerative disease. While the VAS and NDI scores
improved in both subsets of patients, however, no difference could be observed between
the two groups for both these scores. Similar findings were reported from China by
Xinlin Gao et al. and Shi J S et al. However, in another similar study by Zeng et
al., better improvement in NDI scores was reported in the CDA group as compared to
the ACDF group.[[4 ]],[[7 ]],[[8 ]]
When we compared the CROM in the two groups of patients, we found significantly better
ROM in patients undergoing CDA as compared to those in the PEEK group. A similar result
was reported by Xinlin Gao et al. with preservation of ROM of the C2-C7 level in the
CDA group, whereas in the ACDF group decrease in ROM was noted postoperatively. Several
RCTs comparing the ROM in these two groups have also reported similar findings.[[9 ]],[[10 ]],[[11 ]]
When the sagittal ROM was compared between the two groups, the PEEK group showed a
reduction in the sagittal ROM, while an increase in the sagittal ROM in all planes
was noticed in the CDA group. Similar results have been reported by Parish JM et al.
from Spain, Radcliff K et al. from China, and also by Janssen ME et al. in a published
meta-analysis of RCTs comparing ACDF versus CDA for two contiguous levels of cervical
disc degenerative disease.[[9 ]],[[11 ]],[[12 ]]
The FSU showed a steeper decline in the PEEK group as compared to the CDA group. Similar
findings have been reported in RCTs from China and Korea.[[13 ]],[[14 ]] We also report a significant decrease in OCA in the measured planes for the PEEK
group, while the CDA group shows showed an increase in both planes. Several other
authors have also reported an improvement in the cervical lordosis in patients who
underwent CDA as compared to ACDF.[[7 ]],[[8 ]] This assumes importance due to the correlation reported by authors between restoration
of cervical lordosis and delay/prevention in anterior segmental pathology.[[15 ]]
When we compared the disc height between the two groups, we observed that the disc
height was more or less maintained in the CDA group, while those in the PEEK group
demonstrated a significant decrease in the disc height. Several other authors have
also reported similar findings, underlining the better long-term radiological outcome
in patients who undergo CDA for cervical disc disease.[[8 ]],[[13 ]],[[16 ]],[[17 ]]
Our study has the advantage of being one of the few long-term follow-up studies in
patients undergoing CDA and ACDF in India. Further being a closely monitored group
of patients, there were no dropouts among the subjects which could have affected the
results of our study.
However, we acknowledge that possible limitations of our study include a small sample
size in each group, a single observer for interpreting the results of the two groups,
and the confounding factor of heterogeneity of single and bilevel cases of CDDD in
both the groups.
Conclusions
We conclude that although there was no long-term significant difference in the VAPS
and NDI between the two groups, CDA offers better results in terms of cervical kinematics
and radiological outcomes as compared to ACDF in patients of CDDD. We thus feel that
CDA may be a more close to physiological state than ACDF in regard to preserving ROM
and maintaining disc height, thus preventing adjacent segment disease in the future
in patients with uni and bilevel CDDD.
