Keywords
anterior cervical discectomy and fusion (ACDF) - anterior cervical plate - adjacent
segment degeneration - stand-alone cage
Introduction
Anterior cervical discectomy and fusion (ACDF) is one of the most commonly used techniques
for treating degenerative cervical radiculopathy and cervical myelopathy.[1] The proposed procedure provides both neural decompression at the symptomatic level
and segmental stability. Cervical cages have been widely used as a fusion tool in
this procedure. They are biocompatible and composed of diverse materials, such as
carbon, titanium, and polyetheretherketone, which can be filled with different types
of synthetic bone grafts.[1]
[2]
There have been controversies about the superiority of augmentation with anterior
cervical plate fixation over stand-alone cage placement. Placing a titanium plate
can provide additional stability to the operated segment, preventing the collapse
of the interbody fusion device.[3] However, ACDF augmented with anterior cervical plate (ACDF-CPA) alters the normal
biomechanical state of the cervical spine, leading to motion obliteration at the fused
segment, increasing the stress on the adjacent segment, and increasing abnormal activities,
accelerating adjacent segment degeneration.[4] Yet, there is a wide diversity of implant choices. Several surgeons adopt ACDF with
a stand-alone cage (ACDF-SA), while others use anterior cervical plate augmentation,
aiming for better outcomes and fewer complications.[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
Our study primarily aimed to compare the radiological outcomes between ACDF-SA and
ACDF-CPA in single-level cervical degenerative disc disease. The secondary objective
was to assess the associations between patient characteristics and radiological outcomes.
Methods
Study Design and Ethical Approval
This retrospective cohort study was conducted following approval from the institutional
review board of our local medical research center (approval number MRC-01–21–136),
with a waiver for informed consent due to the nature of the research.
Patient Selection
The study included all adult patients (>18 years old) with cervical radiculopathy
or myelopathy resulting from single-level cervical degenerative disc disease who had
failed conservative treatment and underwent ACDF with either a tantalum stand-alone
cage (ACDF-SA) or a cage augmented with an anterior titanium cervical plate (ACDF-CPA)
between January 2011 and December 2019. All procedures were performed by attending
physicians from the orthopaedic or neurosurgery departments at the same academic institution.
The stand-alone cage devices used were nonlocking tantalum cages, while the anterior
plate instrumentation consisted of low-profile titanium. The devices were secured
to the cervical vertebrae with two cranial screws and two caudal screws. Patients
with a history of systemic infection, trauma, malignancy, inadequate radiographs,
or less than 12 months of follow-up were excluded from the study.
Data Collection and Radiological Evaluation
Retrospective data collection was performed using medical records. Patient demographics,
including age, gender, comorbidities, operating surgeon (orthopaedics or neurosurgery),
and the level of operation, were recorded. Radiological data were reviewed by two
senior orthopaedic spine fellows, supervised by a senior spine surgeon. Cervical radiographs
were taken immediately postoperatively, at 6 months, and at 12 months. Radiological
cage subsidence on lateral cervical spine plain radiographs was defined as a ≥2 mm
loss of intervertebral height by comparing postoperative intervertebral heights with
those at the last follow-up. The total decrease in intervertebral height was measured
between the midpoint of the lower margin of the upper vertebra and the upper margin
of the lower vertebra at the fusion site as shown in [Fig. 1].
Fig. 1 Lateral X-ray of the cervical spine with stand-alone cage, the blue line indicating
the midpoint of the lower margin of the upper vertebra and the upper margin of the
lower vertebra at the fusion site for which the cage subsidence is measured.
Intervertebral fusion was assessed using the Oshina criteria, which defines fusion
by the presence of bridging trabecular bone between the endplates. Flexion–extension
radiographs were evaluated, with less than 1 mm of motion between spinous processes
being considered confirmation of successful fusion.[15] Adjacent segment degeneration was assessed 12 months postoperatively using the Hilibrand
criteria, including disc space narrowing (>25%), new or enlarged osteophytes, anterior
or posterior longitudinal ligament calcification, endplate sclerosis, and magnetic
resonance imaging evidence of new disease in the adjacent segment.[16] All radiological outcomes were assessed and measured using the FUJI PACS (Picture
Archiving and Communication System) at our institution.
Statistical Analysis
All statistical analyses were conducted using Stata 17.0 (College Station, Texas,
United States). Descriptive statistics were used to summarize demographic and radiological
measures. Continuous data were assessed using histograms; normally distributed data
were summarized as means and standard deviations, while skewed data were summarized
as medians and interquartile ranges. Categorical variables were summarized as numbers
and percentages. The chi-square test and Fisher's exact test were used to compare
categorical variables. The two-sample t-test was used to compare normally distributed continuous data, and the Wilcoxon rank-sum
test was applied to skewed data. Adjusted risk ratios (ARRs) were used to compare
the radiological outcomes of ACDF-SA and ACDF-CPA, as well as to assess the association
between patient characteristics and radiological outcomes. Adjustment was done for
age and gender only. The method for estimating ARRs was based on the approach reported
by Norton et al.[17]
Results
Patient Demographics and Operative Characteristics
The demographic and operative characteristics of the included patients are detailed
in [Table 1]. A total of 43 patients were included in the study, with 58% undergoing surgery
with a stand-alone cage, while 42% had the procedure augmented with an anterior cervical
plate. The mean age was 49.5 years (standard deviation [SD]: 11.5), with 40% of patients
aged between 41 and 50 years. Males comprised 53% of the cohort, and orthopaedic surgeons
performed the majority of the surgeries (74%). The most commonly treated spinal level
was C5–C6 (49%), followed by C6–C7 (33%), with an average operative time of 147.2 minutes
(SD: 38.6). In terms of comorbidities, 21% of the patients were smokers, and 23% had
diabetes. Baseline characteristics were generally similar between the two groups,
except for diabetes, which was more prevalent in the cage and plate group (39%) compared
with the stand-alone cage group (12%).
Table 1
Demographic and operative characteristics of included patients
|
Variable
|
ACDF-SA
|
ACDF-CPA
|
Overall
|
p-Value
|
|
N
|
25
|
18
|
43
|
|
|
Age, mean (SD)
|
47.0 (9.6)
|
52.9 (13.1)
|
49.5 (11.5)
|
0.092
|
|
Gender
|
|
Male
|
12 (48%)
|
11 (61%)
|
23 (53%)
|
0.4
|
|
Female
|
13 (52%)
|
7 (39%)
|
20 (47%)
|
|
Operating surgeon
|
|
Orthopaedics
|
18 (72%)
|
14 (78%)
|
32 (74%)
|
0.74
|
|
Neurosurgery
|
7 (28%)
|
4 (22%)
|
11 (26%)
|
|
Operated level
|
|
C3–C4
|
2 (8%)
|
3 (17%)
|
5 (12%)
|
0.24
|
|
C4–C5
|
1 (4%)
|
1 (6%)
|
2 (5%)
|
|
C5–C6
|
11 (44%)
|
10 (56%)
|
21 (49%)
|
|
C6–C7
|
11 (44%)
|
3 (17%)
|
14 (33%)
|
|
C7–T1
|
0 (0%)
|
1 (6%)
|
1 (2%)
|
|
Smoking status
|
7 (28%)
|
2 (11%)
|
9 (21%)
|
0.26
|
|
Cortisone use
|
1 (4%)
|
0 (0%)
|
1 (2%)
|
1
|
|
Diabetes
|
3 (12%)
|
7 (39%)
|
10 (23%)
|
0.067
|
|
Operation time, mean (SD)
|
143.2 (39.2)
|
152.8 (38.0)
|
147.2 (38.6)
|
0.42
|
Abbreviations: ACDF-CPA, anterior cervical decompression and fusion-cervical plate
augmentation; ACDF-SA, anterior cervical decompression and fusion-stand-alone cage;
ASD, adjacent segment disease.
Fusion Outcomes, Subsidence, and Adjacent Segment Degeneration
As shown in [Table 2], the overall fusion rate at 6 months was 77%, with the stand-alone cage group achieving
a higher fusion rate of 88% compared with 61% in the cage and plate group. By 12 months,
the overall fusion rate increased to 81%, with similar rates between the stand-alone
cage group (88%) and the cage and plate group (72%). Regarding subsidence, 44% of
patients experienced cage subsidence at 6 months, rising to 60% by 12 months, with
no notable difference between the groups at either time points. Additionally, 74%
of patients showed signs of adjacent segment degeneration by 12 months, with 76% in
the stand-alone cage group and 72% in the cage and plate group. Importantly, none
of the patients required revision surgery during the follow-up period.
Table 2
Comparison of radiological and clinical outcomes between ACDF-SA and ACDF-CPA
|
Factor
|
Level
|
ACDF-SA
|
ACDF-CPA
|
Overall
|
p-Value
|
|
N
|
|
25
|
18
|
43
|
|
|
Subsidence at 6 months
|
No
|
15 (60%)
|
9 (50%)
|
24 (56%)
|
0.51
|
|
Yes
|
10 (40%)
|
9 (50%)
|
19 (44%)
|
|
Subsidence at 12 months
|
No
|
10 (40%)
|
7 (39%)
|
17 (40%)
|
0.94
|
|
Yes
|
15 (60%)
|
11 (61%)
|
26 (60%)
|
|
Fusion at 6 months
|
No
|
3 (12%)
|
7 (39%)
|
10 (23%)
|
0.067
|
|
Yes
|
22 (88%)
|
11 (61%)
|
33 (77%)
|
|
Fusion 12 months
|
No
|
3 (12%)
|
5 (28%)
|
8 (19%)
|
0.25
|
|
Yes
|
22 (88%)
|
13 (72%)
|
35 (81%)
|
|
ASD at 12 months
|
No
|
6 (24%)
|
5 (28%)
|
11 (26%)
|
0.78
|
|
Yes
|
19 (76%)
|
13 (72%)
|
32 (74%)
|
|
Subsidence
|
None
|
9 (36%)
|
7 (39%)
|
16 (37%)
|
0.66
|
|
6 months
|
10 (40%)
|
9 (50%)
|
19 (44%)
|
|
12 months
|
6 (24%)
|
2 (11%)
|
8 (19%)
|
|
Fusion
|
None
|
3 (12%)
|
5 (28%)
|
8 (19%)
|
0.098
|
|
6 months
|
22 (88%)
|
11 (61%)
|
33 (77%)
|
|
12 months
|
0 (0%)
|
2 (11%)
|
2 (5%)
|
|
Reoperation
|
No
|
25 (100%)
|
18 (100%)
|
43 (100%)
|
|
Abbreviations: ACDF-CPA, anterior cervical decompression and fusion-cervical plate
augmentation; ACDF-SA, anterior cervical decompression and fusion-stand-alone cage;
ASD, adjacent segment disease.
Comparison of Radiological Outcomes between ACDF-SA and ACDF-CPA
[Table 3] compares the adjusted relative risks (RRs) for radiological outcomes between ACDF-SA
and ACDF-CPA, with the latter as the reference group. At 6 months, patients in the
ACDF-SA group had a 50% higher probability of achieving fusion compared with the ACDF-CPA
group, with strong evidence against the model hypothesis at this sample size (RR:
1.50, 95% confidence interval [CI]: 1.01–2.22, p = 0.021). By 12 months, there was a 22% increase in probability of fusion in the
ACDF-SA group compared with the ACDF-CPA group, however with weak evidence against
the model hypothesis (RR: 1.22, 95% CI: 0.90–1.64, p = 0.174).
Table 3
Association between ACDF-SA and ACDF-CPA in radiological outcomes
|
Outcome
|
Adjusted RR
|
Lower 95% CI
|
Upper 95% CI
|
p-Value
|
Reference group
|
|
Fusion at 6 months
|
1.50
|
1.01
|
2.22
|
0.021
|
ACDF-CPA
|
|
Fusion at 12 months
|
1.22
|
0.90
|
1.64
|
0.174
|
ACDF-CPA
|
|
Subsidence at 6 months
|
0.59
|
0.33
|
1.06
|
0.071
|
ACDF-CPA
|
|
Subsidence at 12 months
|
0.90
|
0.57
|
1.42
|
0.660
|
ACDF-CPA
|
|
ASD at 12 months
|
1.20
|
0.82
|
1.76
|
0.333
|
ACDF-CPA
|
Abbreviations: ACDF-CPA, anterior cervical decompression and fusion-cervical plate
augmentation; ACDF-SA, anterior cervical decompression and fusion-stand-alone cage;
ASD, adjacent segment disease; CI, confidence interval.
For subsidence, there was a 41% reduction in the risk of subsidence at 6 months in
the ACDF-SA group compared with ACDF-CPA (RR: 0.59, 95% CI: 0.33–1.06, p = 0.071), with some evidence against the null hypothesis. By 12 months, the risk
of subsidence was comparable between the two groups, with little difference between
the groups (RR: 0.90, 95% CI: 0.57–1.42, p = 0.660). Similarly, for adjacent segment disease at 12 months, the ACDF-SA group
had a 20% higher risk, but with weak evidence against the model hypothesis at this
sample size (RR: 1.20, 95% CI: 0.82–1.76, p = 0.333).
Associations between Patient Characteristics and Radiological Outcomes
[Table 4] demonstrates the associations between various exposure variables and radiological
outcomes. Female gender was associated with a 52% increased probability of achieving
fusion at 6 months (RR: 1.52, 95% CI: 1.05–2.19, p = 0.010) and a 45% increased probability at 12 months (RR: 1.45, 95% CI: 1.05–2.01,
p = 0.009), with strong evidence against the null hypothesis at this sample size. Females
also had a 51% lower risk of subsidence at 12 months (RR: 0.49, 95% CI: 0.28–0.86,
p = 0.002), again with strong evidence against the null hypothesis.
Table 4
Association between patient characteristics and radiological outcomes
|
Exposure variable
|
Fusion 6 months
|
Fusion 12 months
|
Subsidence 6 months
|
Subsidence 12 months
|
ASD 12 months
|
|
Gender
|
|
Male
|
Reference
|
|
|
|
|
|
Female
|
1.52 (1.05–2.19), 0.010[a]
|
1.45 (1.05–2.01), 0.009[a]
|
0.91 (0.48–1.73), 0.782
|
0.49 (0.28–0.86), 0.002[a]
|
0.87 (0.60–1.26), 0.461
|
|
Age group, years
|
|
30–40
|
Reference
|
|
|
|
|
|
41–50
|
0.93 (0.54–1.60), 0.800
|
1.14 (0.68–1.89), 0.612
|
0.79 (0.42–1.49), 0.477
|
0.94 (0.62–1.43), 0.780
|
1.23 (0.67–2.29), 0.482
|
|
51–60
|
1.22 (0.75–1.98), 0.404
|
1.25 (0.76–2.04), 0.351
|
0.52 (0.20–1.36), 0.146
|
0.73 (0.40–1.34), 0.294
|
1.54 (0.85–2.81), 0.104
|
|
> 60
|
1.25 (0.76–2.07), 0.352
|
1.28 (0.77–2.13), 0.302
|
–
|
0.32 (0.10–1.09), 0.008[a]
|
1.38 (0.68–2.82), 0.367
|
|
Smoking
|
1.02 (0.69–1.51), 0.939
|
1.11 (0.84–1.47), 0.470
|
1.26 (0.59–2.69), 0.573
|
1.05 (0.53–2.08), 0.891
|
0.73 (0.37–1.43), 0.300
|
|
Diabetes
|
1.05 (0.74–1.50), 0.769
|
0.96 (0.68–1.36), 0.822
|
1.52 (0.85–2.71), 0.183
|
1.33 (0.85–2.06), 0.231
|
0.97 (0.62–1.54), 0.912
|
|
Operated level
|
|
C3–C4
|
Reference
|
|
|
|
|
|
C4–C5
|
0.67 (0.15–2.99), 0.556
|
0.78 (0.23–2.62), 0.674
|
–
|
–
|
0.41 (0.07–2.56), 0.263
|
|
C5–C6
|
1.24 (0.60–2.58), 0.529
|
1.24 (0.62–2.48), 0.510
|
0.70 (0.21–2.36), 0.611
|
1.59 (0.40–6.27), 0.417
|
1.21 (0.51–2.87), 0.638
|
|
C6–C7
|
1.16 (0.53–2.51), 0.700
|
1.34 (0.67–2.67), 0.352
|
0.97 (0.29–3.20), 0.961
|
1.84 (0.43–7.85), 0.312
|
1.44 (0.61–3.41), 0.336
|
Abbreviations: ASD, adjacent segment disease.
Note: Cells displayed as RR (95% CI), p-value.
a Statistically significant p-values.
Age categories did not show strong associations with fusion or subsidence, except
for patients over 60, who had a 68% reduced risk of subsidence at 12 months (RR: 0.32,
95% CI: 0.10–1.09, p = 0.008), with strong evidence against the null hypothesis. Smoking and diabetes
were not associated with any of the radiological outcomes, with weak evidence observed
across all variables. Regarding the operated level, no clear associations were found
with fusion or subsidence, though the C5–C6 level showed a 59% increase in the risk
of subsidence at 12 months (RR: 1.59, 95% CI: 0.40–6.27, p = 0.417), but this result had weak supporting evidence.
Discussion
Disc height following ACDF typically increases in the immediate postoperative period
but gradually returns to preoperative levels, or slightly above or below them.[1]
[18] Studies report variable rates of cage subsidence with stand-alone cages, ranging
from 8 to 32%, typically occurring within the first 3 months after surgery without
further progression.[2]
[18]
[19]
[20]
[21]
[22] In contrast, anterior cervical plate augmentation has been associated with a reduction
in cage subsidence rate.[2]
[21]
[23] However, recent meta-analyses have shown no significant difference in subsidence
rates between the two groups, indicating that the stand-alone cage does not increase
the risk of cage subsidence in mono-segmental ACDF, even in long-term outcomes.[24]
[25]
[26] Our findings were consistent with this, showing no significant association between
type of fixation and cage subsidence at 12-month follow-up.
In our study, the fusion rates at 12 months were similar across the two groups. However,
signs of fusion appeared earlier in ACDF-SA when compared with the ACDF-CPA group
with a higher probability of fusion at 6 months. This may be related to the continued
micro-motions at the fusion site with ACDF-SA, which are minimized by anterior cervical
plate augmentation. Moreover, the application of a plate requires a greater disruption
to the soft tissues, microvasculature, and periosteal layer. Overall, our results
align with previous literature, which reports satisfactory arthrodesis rate regardless
of plating status.[4]
[27]
[28] Furthermore, Zhu et al found similar fusion rates in multilevel ACDF in both groups
at 3-year follow-up.[29]
Adjacent segment degeneration is a common complication following ACDF, affecting up
to 47% of the patients.[30]
[31] Biomechanical studies suggest that the use of titanium plates increases stress on
adjacent disc spaces, potentially accelerating adjacent segment degeneration.[32]
[33] Zhou et al reported a higher postoperative risk of adjacent segment disease in patients
with ACDF-CPA compared with ACDF-SA, and Zhang et al found similar results in mono-segmental
ACDF.[25] However, in our study, there was no significant difference in the incidence of adjacent
segment degeneration between the two groups at 12-month follow-up.
Limitations
There are some limitations in our study. First, the retrospective design limited the
range of variables that could be assessed. Although CT scans are ideal for providing
more detailed information on fusion and other outcomes, we relied on X-rays due to
the constraints of the study's retrospective nature. The small sample size resulted
in wide CIs, affecting the precision of our estimates and limiting the robustness
of our conclusions. Additionally, the procedures were performed by different surgeons,
potentially contributing to variability in surgical techniques and outcomes. Lastly,
the short-term follow-up may not fully capture long-term complications or outcomes,
particularly for conditions like adjacent segment disease or late-onset subsidence.
Conclusion
Augmentation with the anterior cervical plate in ACDF did not show superiority to
the conventional stand-alone cage in mono-segmental ACDF at 12 months. Our study showed
similar outcomes regarding cage subsidence, adjacent segment disease, and fusion rates
at 12 months. However, the stand-alone cage achieved faster fusion at 6 months compared
with the plate group. Future studies are needed to compare the results of ACDF-SA
and ACDF-CPA groups prospectively.
