334

ORIGINAL
A comparison of reoperation rates after single-level anteriorcervical discectomy and fusion (ACDF) between theprocedures with and without anterior plate fixation
Nobuaki Tadokoro1, Katsuhito Kiyasu1, Naoki Aoyama1, Shuhei Mizobuchi1, Masahiko Ikeuchi1, Kazunobu Kida2,
Toshikazu Tani2, and Yusuke Kasai31

Department of Orthopaedic Surgery, Kochi University, Kochi, Japan, 2Department of Orthopaedic Surgery, Kubokawa Hospital, Kochi, Japan,
Department of Orthopaedic Surgery, Kochi Prefectural Hata Kenmin Hospital, Kochi, Japan

3

Abstract : Introduction : The plate fixation for anterior cervical discectomy and fusion (ACDF) has become increasingly widespread for facilitating early mobilization and improving fusion rate. However, apart from multilevel operations, there is still some controversy over its use for single-level ACDF. This retrospective study hascompared the reoperation rates after single-level ACDFs performed at our institution between the procedureswith and without plate fixation. Methods : This retrospective study included a total of 131 patients with ≥ 1-yearof follow-up after a single-level ACDF, consisting of 100 patients without plating (conventional ACDF) and 31 patients with plate fixation (plated ACDF). Results : Eleven patients (8.4% of all patients) : four conventional ACDFs(4% of the conventional ACDFs) and seven plated ACDFs (22.6% of the plated ACDFs), had reoperation surgeries. The incidence of reoperation was significantly higher in the plated ACDFs than in the conventional ACDFs(P = 0.0037). The log-rank test revealed a significant difference (P = 0.00003) in 5-year reoperation-free survival
rates between the conventional (96.9%) and the plated groups (68.3%). Conclusion : Anterior cervical plating may
have a negative impact on the adjacent segment integrity, resulting in an increased reoperation rate after a single-level ACDF at relatively shorter postoperative time points. J. Med. Invest. 70 : 334-342, August, 2023
Keywords : Anterior cervical discectomy and fusion, adjacent segment disease, reoperation, anterior cervical plate, interbody cage

INTRODUCTION
Anterior cervical discectomy and fusion (ACDF) represents
an established surgical treatment for degenerative cervical spinediseases. The technique conventionally involved autologous
bicortical or tricortical iliac crest bone graft (ICBG) without
plating and postoperative external immobilization. A negative
aspect of this procedure includes the possibility of graft-related
complications such as subsidence, collapse, and extrusion as well
as bone harvest site morbidity (1). To reduce these limitations
and eliminate the need for postoperative external immobilization, spine surgeons have increasingly employed non-autologous
bone materials such as allograft or various synthetic interbody
cages in combination with an anterior cervical plate (2). According to the studies on multilevel ACDFs (3-5), the use ofanterior cervical plate helped provide immediate stability andfacilitate fusion. In contrast, another study (6) on single-level
ACDFs showed that the plate fixation had no benefit in fusion
rate or clinical outcome, but rather 9.7% of the patients withplated ACDF required reoperation. In addition, whether anterior cervical plate accelerates adjacent segment degeneration or
not still remains a matter of controversy (7, 8). This, at times,
results in clinically symptomatic neural compression. We wish toreport our experience on a comparison of reoperation rates after
single-level ACDFs between the procedures with and without
anterior plate fixation.

MATERIALS & METHODS
1. Patients

From January 2000 to December 2020, 168 patients underwent a single-level ACDF at our institution. Of these, we retrospectively studied 131 patients (74 men and 57 women) withmean (range) age 66 (27-91) years, who had a minimum one
year of follow-up evaluations (mean, 70 months ; range, 12-199
months). All patients had radiographic evidence of a solid fusion.
This study divided the 131 patients into those without and thosewith plate fixation : 100 patients who had undergone stand-alone
autologous tricortical ICBG conducted before July 2010 (conventional group) and 31 patients who had had an ACDF witheither an ICBG (3 patients) or an interbody cage packed withcancellous autograft (28 patients) followed by anterior plating(plated group) after July 2010. The clinical diagnoses included
cervical spondylotic myelopathy (CSM) in 75 patients, cervicaldisc herniation (CDH) in 35, ossification of posterior longitudinal
ligament (OPLL) in 9, cervical spondylotic radiculopathy in 7,
cervical spondylotic amyotrophy in 4, and infection in 1. In the
study period, any one of the eight experienced spine surgeons
performed ACDF. This study was approved by the institutional
review board (IRB) at the first author’s institution (approval
number : ERB-108570).

2. Single-Level ACDF Techniques

2.1. ACDF with a stand-alone autologous ICBG (conventional group)
Received for publication December 27, 2022 ; accepted March 9, 2023.
Address correspondence and reprint requests to Nobuaki Tadokoro,
Department of Orthopaedic Surgery, Kochi University, Kohasu,
Oko-chou, Nankoku 783-8505, Japan and E-mail : tadokoro.nobuaki@
kochi-u.ac.jp

After surgical exposure of the anterior aspect of the vertebral
bodies with a standard anterior cervical approach, patients withcervical myelopathy underwent ascending and / or descending
evoked potential (EP) studies as described earlier (9-11). For
this purpose, a series of recording needle electrodes (Dantec
13R23, Dantec Medical, Skovlunde, Denmark) was inserted into

The Journal of Medical Investigation Vol. 70 2023

The Journal of Medical Investigation Vol. 70 August 2023
the intervertebral discs in the midline. This electrodiagnostic
technique carried out during surgery before decompression
procedures served well as a measure for documenting the site of
conduction block and excluding clinically silent cord compression
seen on MRI, allowing for a surgical intervention at the appropriate level responsible for the main functional change. With EP
confirmation of the lesion site (9, 11, 12), a discectomy at a single
appropriate level followed by a partial removal of the adjacentvertebrae above and below with a high-speed carbide-tippedburr created a vertical trench of 10 to 15 mm long and at least
15 mm wide through the center of each vertebra. The trench wasthen deepened with a diamond-tipped burr under the operating
microscope until the posterior vertebral cortex and osteophytes
were completely removed. Finally, a piece of tricortical ICBG wastapped into the intervertebral space distracted by the Casper
cervical distractor (Aesculap, Center Valley, PA).
2.2. ACDF with a plate (plated group)
Unlike the conventional group, the ACDF for this group required preserving the vertebral bodies and their bony endplates
adjacent to the disc space to be decompressed as much as possible
for preventing less-than-ideal plate fixation and cage subsidence.
We managed to thoroughly remove the disc materials and the offending posterior osteophytes through a narrow working corridor
with the help of the operating microscope. For the safe, adequate
decompression, the intervertebral space must be kept distracted
either by spreader forceps or Casper distractor system during
the decompression procedures. Usually, the decompression wascompleted with incision of the posterior longitudinal ligament,
which allowed the dura to bulge anteriorly. An interbody cage
packed with the cancellous bone, which was harvested through asmall cortical window made on top of the anterior iliac crest, wasinserted into the intervertebral space distracted by the Casper
distractor. We used either one of the two interbody cages madeof titanium-coated polyetheretherketone (PEEK) : the CeSpace
cage (Aesculap, Center Valley, PA) for 20 patients and Anatomic
PEEK PTC (Medtronic, Sofamor Danek, Memphis, TN) for 8 patients. In the remaining 3 patients, we placed an ICBG insteadof a cage. All plated group patients underwent single-segment
fixation with one of the two dynamic anterior plates with locking
screw mechanisms : 23 patients with an ABC plate (Aesculap,
Center Valley, PA), which allows screw translation and rotation
within the plate and 8 patients with a Zevo plate (Medtronic,
Sofamor Danek, Memphis, TN), which only allows screw rotation within the plate. As we had been concerned about the initialstability of stand-alone PEEK cage use, we also decided to use an
anterior plate to provide supplementary support.
The wound closure in both groups consisted of meticulous
hemostasis, thorough irrigation with saline, repositioning thesubperiosteally dissected flaps of bilateral longus colli muscles
and the anterior longitudinal ligament with a few sutures, theclosed suction drain tube placement, and closing in layers overthe drain.
2.3. Postoperative management
All patients were allowed to ambulate as soon as clinicallypossible with a semirigid cervical collar for additional stability.
We encouraged the patients to continue bracing for at least 3
months for the conventional group and at least 6 weeks for theplated group.

3. Statistical Analysis
We conducted the Fisher’s exact t-test for nominal variables
and Mann Whitney U-test for continuous variables to elucidate
the factors associated with the reoperation between the conventional and plated ACDFs. Log-rank test was used to compare the335

reoperation-free survival rates between the two groups. Because
computed radiography (CR) supplanted film radiography in2010 at our institution, we could access CR data of plated ACDF
patients when we conducted this study. On the other hand, it
was difficult to access radiographic films of conventional ACDF
patients. CRs taken after the initial surgery and before the reoperation or at the last follow-up were evaluated using the following items : cervical alignment (C2-7 angle), intervertebral discheight (DH), plate to disc distance (PDD), and range of motion(ROM). Adjacent cranial and caudal segments of the operated
segment were evaluated for the abovementioned items except for
the C2-7 angle. Wilcoxon signed-rank test was used for paired
comparisons to evaluate degenerative changes after plated
ACDFs. Reoperation cases due to symptomatic adjacent segment
disease (ASD) were also assessed. The Torg-Pavlov ratio at theC5 vertebral body level, calculated by the sagittal diameter of the
midpoint of the posterior surface of the C5 vertebral body to theclosest point of the C5 lamina / sagittal diameter of C5 vertebral
body measured between the midpoints of anterior and posterior
surfaces, was also measured in 31 plated patients after the initial surgery to evaluate the bony spinal canal stenosis.
All statistical analyses were performed with EZR (13) (Saitama Medical Center, Jichi Medical University, Saitama, Japan),which is a graphical user interface for R (The R Foundation for
Statistical Computing, Vienna, Austria) . P < 0.05 was considered statistically significant.

RESULTS
Table 1 summarizes a comparison between the dataof conventional and plated groups at initial ACDF. The twogroups showed no significant differences in age (averaged
65.5 vs 67.6 years ; p = 0.39) and gender ratio (M / F) (57 / 43 vs
17 / 14 ; p = 0.84), but the conventional group had a significantly
longer follow-up evaluation than the plated group (averaged 78
vs 44 months ; p = 0.00029). Compared with the conventionalgroup, the plated group included CSM patients at a lower rate
(63.0% vs 38.7%) and CDH patients at a higher rate (21.0% vs
45.2%), resulting in a significantly different frequency distribution (p = 0.026) of the diagnoses at initial surgery between
the two groups. In contrast, the frequency distribution of the
ACDF levels showed no significant difference between thegroups (p = 0.38). As mentioned in the Methods section above, weused different types of interbody graft between the two groups(P < 0.00001) : the ICBG for all conventional group patients andthe PEEK cage for all except 3 plated group patients (Table 1).
A total of 11 patients (8.4% of all patients) had reoperations
either earlier than 1 month (early reoperation) (4 patients) orlater than 1 year (late reoperation) (7 patients) postoperatively(Table. 2). Of the 4 patients (3.1% of all patients) with an “earlyreoperation”, 2 patients each initially had undergone the conventional and the plated ACDFs. Their “early reoperation” resulted
from neurological worsening secondary to epidural hematoma
needing revision : reoperation for the same site of primary surgery (3 patients) or cage subsidence due to host bone osteoporosis(1 patient). The 3 patients with epidural hematoma underwent
evacuation of the hematoma within three days after initialsurgery. Another patient with cage subsidence and cervicalsagittal alignment change required an additional laminoplasty
for recurrent cord compression. Of the 7 patients (5.3% of all patients) with “late reoperation”, 2 patients initially had undergone
conventional ACDFs and 5, plated ACDFs. The late reoperation
resulted from ASD in 6 patients (4.6% of all patients) and a
cervical spine infection at the level different from the initial
surgical intervention in 1 patient. All ASD patients underwent

N. Tadokoro, et al. The reoperation rate after single-level ACDFs

336

Table 1. Patient demographic data
Conventional ACDF

Plated ACDF

Number of patients

100

31

Age (years old), mean [range]

65.5 [29-90]

67.6 [28-91]

0.39

Gender ratio : male / female

57/43

17/14

0.84

Length of follow-up (months), mean [range]

78 [12-199]

44.4 [12-113]

0.00029

CSM

63

12

CDH

21

14

C-OPLL

9

0

CSR

4

3

CSA

3

1

Infection

1

0

C3-4

31

6

C4-5

34

12

C5-6

28

7

C6-7

5

4

C7-Th1

2

1

Diagnosis

P-value

0.026

Surgical level

0.38interbody graft<0.00001

auto iliac bone100

3

PEEK cage

028

CSM : Cervical Spondylotic Myelopathy, CDH : Cervical Disc Herniation, C-OPLL : Cervical Ossification of Posterior Longitudinal Ligament, CSR : Cervical Spondylotic Radiculopathy, CSA : Cervical Spondylotic Amyotrophy
Fisher’s exact t-test and Mann-Whitney U-test were used for the nominal and continuous variables, respectively.
P < 0.05 was considered to be significant.

Table 2. Demographic data of patients who underwent reoperation
Patient no.

Age

GenderDiagnosis

Surgical level

Plate

Cage

Early / lateTime after initial surgery

Reason for reoperation

1

46

male

CSM

C3-4

no

no

early

0 day (12 hours)

hematoma237

female

CDH

C5-6

no

no

early

1 day

hematoma

367

female

CDH

C4-5

no

no

late

25 months

ASD

4

49

female

CDH

C5-6

no

no

late

175 months

ASD

5

85

male

CSM

C4-5

yes

yes

early

3 dayshematoma

669

female

CSM

C4-5

yes

yes

early

3 weeks

cage subsidence

7

71

male

CDH

C5-6

yes

yes

late

12 months

ASD

8

76

female

CSM

C3-4

yes

yes

late

22 months

ASD

9

75

male

CSR

C4-5

yes

yes

late

54 months

ASD

10

69

male

CDH

C4-5

yes

no

late

58 months

ASD

11

65

male

CSM

C4-5

yes

yes

late

99 months

infection

CSM : Cervical Spondylotic Myelopathy, CDH : Cervical Disc Herniation, CSR : Cervical Spondylotic Radiculopathy, ASD : adjacent segment disease
early : reoperation within a month after the initial surgery, late : reoperation over a year after the initial surgery

337

The Journal of Medical Investigation Vol. 70 August 2023
a reoperation of laminoplasty and / or laminectomy for recurrent
myelopathy.
The incidence of “overall reoperation” surgery was significantly higher in the plated ACDFs than in the conventional ACDFs(P = 0.0037). The PEEK cage, which was used together with theanterior plate, was also associated with a higher incidence of“overall reoperation” surgery than the ICBG (P = 0.012). Otherrisk factors were excluded from the reoperation-related factors(P > 0.05) (Table 3).
For all 11 reoperations, the intervals between initial andreoperations averaged 50.0 months in the conventional groupand 35.1 months in the plated group. The corresponding values
for 6 reoperations as a result of new myelopathy averaged 100
and 36.5 months, respectively (Table 2). The log-rank test revealed a significant difference (P = 0.00003) in reoperation-freesurvival rates at 5 years after initial surgery between the twogroups ; 96.9% (95%CI, 90.6-99.0) for the conventional group vs
68.3% (95%CI, 37.3-86.3) for the plated group (Figure 1).

Table 4 showed changes of C2-7 angle, DH, PDD, ROM fromafter the initial surgery to last follow-up or before the reoperation. PDDs at adjacent cranial and caudal segment had significantly reduced at the final follow-up or before reoperationcompared to after the initial operation (P = 0.0008 and 0.0004).
ROM at both cranio-caudal segments increased during two time
points (P = 0.005 and 0.049). C2-7 angle and DH showed no significant changes (P > 0.05).
There was a similar trend of PDD and ROM changes in four
reoperation cases due to ASD, with the abovementioned overallchange. We did not conduct statistical analysis due to the small
sample number. PDD changes at adjacent cranial and caudal
segments between two time points were -0.7{-1.9 to 0.0} and-1.0{-2.6 to 0.0}, respectively. Similarly, ROM changes at two segments were 8.8{2 to 19} and 1.8{-1 to 7}. The Torg-Pavlov ratio offour reoperation cases was 0.7{0.6 to 0.8} and that of all 31 plated
patients was 0.7{0.5 to 1.2}.

Table 3. P-values in univariate analysis of potential risk factors forreoperation
Overall reoperation
conventional or anterior cervical plate use

0.0037*

auto iliac bone or PEEK cage0.012*

surgical level

0.69

diagnosis

0.52

gender ratio : male/female

1surgery year

0.32

age of patients

0.6

follow-up period

0.19

Fisher’s exact t-test and Mann-Whitney U-test were used for thenominal and continuous variables, respectively. P < 0.05, marked
as *, was considered to be significant.

Figure 1. Two Kaplan-Meier survival curves comparing thereoperation-free survival probabilities of conventional (non-plated)versus plated ACDF group patients.
The log-rank test revealed a significant difference (p = 0.00003) in
5-year reoperation-free survival probabilities between the conventional(96.9%) and the plated group patients (68.3%).

Table 4. Radiographic data of plated ACDF patients : all plated ACDF patients and reoperation cases due to ASD
All plated ACDF patients (N = 31)

C2-7 angle

Reoperation cases due to ASD (N = 4)

Final follow-up/ before reoperation

P-value

12.3 [-24 to 35]

9.6 [-19 to 35]

0.3

17.3 [3 to 28]

16.8 [4 to 23]NA

6.4 [4.1 to 8.8]

6.5 [4.4 to 8.7]

0.8

6.9 [5.4 to 8.7]

6.6 [5.3 to 8.7]

NA

After initial
operation

After initial
operation

P-value
Final follow-up/ before reoperationDH

at adjacent cranial segment
at adjacent caudal segment

5.5 [2.2 to 9.2]

5.5 [2.2 to 9.2]

0.1

4.6 [2.2 to 7.3]

4.6 [2.2 to 7.3]

NA

PDD

at adjacent cranial segment

3.3 [-2.3 to 6.7]

2.6 [-2.7 to 6.1]

0.0008*3.8 [1.0 to 5.3]

3.1 [1 to 5]

NA

ROM

at adjacent caudal segment

4.6 [0 to 9.2]

3.9 [0 to 9.4]

0.0004*4.4 [1.4 to 7.8]

3.4 [1.4 to 5.2]

NA

at adjacent cranial segment

6.7 [0 to 22]

9.8 [0 to 21]

0.005*

3.5 [1 to 7]

9.8 [7 to 13]

NAat adjacent caudal segment

4.2 [0 to 15]

6.6 [0 to 16]

0.049*

4.5 [1 to 12]

6.3 [0 to 12]NANA

0.7 [0.6 to 0.8]

Torg-Pavlov ratio at C5 vertebral body level

0.7 [0.5 to 1.2]

NA

Data were expressed as mean[range]. Wilcoxon’s signed rank-test was used for paired continuous variables. P < 0.05, marked as *, wasconsidered to be significant.
ACDF : anterior discectomy and fusion, ASD : adjacent segment disease, DH : intervertebral disc height, PDD : plate to disc distance,
ROM : range of motion, NA : not applicable338

N. Tadokoro, et al. The reoperation rate after single-level ACDFs

Case Presentation 1. (patient no. 4 in Table 2)
A 49-year-old woman suffered from progressive spastic limb
paresis with disc herniation at C5-6, where the intraoperative
EP studies uncovered conduction block with normal conduction
at the other levels. She underwent the conventional C5-6 ACDF
(Figure 2a and 2b), resulting in a good functional outcome.
However, she experienced a recurrence of spastic limb paresis
14 years after the initial surgery with radiographic evidence ofC6-7 degenerative changes, anterior osteophyte formation anddisc space narrowing, and MRI evidence of mild to moderate
spinal cord compression at C4-5 and C6-7 (Figure 2c and 2d).
She underwent a reoperation with combined laminectomies andlaminoplasties, which yielded clinical improvement to the point
where she was ambulatory on her own.
Case Presentation 2 (Patient no. 9 in Table 2)
A 75-year-old man presented with intractable right arm painwith weakness of the deltoid and the biceps muscles. Temporary
pain relief after selective right C5 nerve root block together withthe electromyographic (EMG) evidence of denervation in the deltoid and the biceps on the right confirmed the diagnosis of rightC5 radiculopathy. He underwent C4-5 ACDF with a PEEK cage
and a dynamic anterior cervical plate, resulting in a successful
outcome. MRIs 6 months after the initial surgery demonstrated,
although clinically silent, mild to moderate cord compressions at
C3-4 and C6-7 adjacent to the initial ACDF level (Figure 3a and3b). MRIs 4 years after the initial surgery, when he developed
difficulty walking, showed increased segmental motion at C3-4
with kyphotic alignment change at the lower cervical spine andincreased spinal cord compressions both at C3-4 and C6-7 levels(Figure. 3c and 3d). As a result, he underwent a reoperation
with selective laminectomies at C3-4 and C6-7, which improved
myelopathy, restoring ambulation.

Figure 2a. Follow-up computed radiograph (CR) studies at 4 years after initial ACDF without plate fixation.
CRs showed cervical lordotic alignment with preserved cervical motion without instability.

Figure 2b. Follow-up MRI studies at 4 years after initial ACDF without plate fixation.
The T2-weighted images showed an adequate decompression and solid fusion at C5-6 with only a mild
asymptomatic ASD at C6-7.

The Journal of Medical Investigation Vol. 70 August 2023

Figure 2c. CR studies at 14 years postoperatively.

Anterior osteophyte formation and disc space narrowing at C6-7 were observed. Decreased cervical lordosis
with preserved cervical ROM were also noted.

Figure 2d. MRI studies at 14 years postoperatively.
Reflecting the recurrence of spastic limb paresis, the T2-weighted images showed an increase in cord
compression at C6-7 adjacent to the level of initial ACDF.

Figure 3a. Follow-up CR studies at 6 months after initial ACDF at C4-5.
CRs showed intervertebral disc height reduction at the lower cervical spine with C3-4 disc height sparing. C3-4
segmental motion was three degrees.

339

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N. Tadokoro, et al. The reoperation rate after single-level ACDFs

Figure 3b. Follow-up MRI studies at 6 months after initial ACDF at C4-5.
Although the initial operation at C4-5 improved C5 radiculopathy, a clinically silent, mild cord compression
had developed at the adjacent C3-4 level.

Figure 3c. CR studies at 4 years after the initial ACDF at C4-5.

CRs showed C3-4 disc height reduction and advanced degeneration at the lower cervical spine. C3-4
compensatory increased motion (10 degrees) and kyphotic alignment changes at the lower cervical spine due tosevere disc degeneration were also noted.

Figure 3d. MRI studies at 4 years after the initial ACDF at C4-5.
Reflecting the development of spastic limb paresis, the MRIs showed marked cord compression with highintensity T2 signals within the cord at C3-4 adjacent to the previous ACDF level.

The Journal of Medical Investigation Vol. 70 August 2023
DISCUSSION
While this area still remains controversial, this single-center,retrospective cohort study has suggested that plate fixation for
single-level ACDFs increased the rate of reoperation, although
the instrumentation provides immediate stability at the fusionlevel and eliminates the bone harvest site morbidity.
Consistent with a previous large database study (14), which
reported a reoperation rate within 90 days after a single-level
ACDF of 3.4%, our early reoperation rate was similar at 3.1%
(4 out of 131 patients). As with another previous report (15),the early reoperations in our study most commonly resulted
from postoperative epidural hematoma with nearly the same
incidence in both the conventional group (two cases, 2%) and theplated group (one case, 3%).
Any single-level ACDF carries the inherent risk of developing
late ASD generally known as postoperative ASD (16). The current study has shown that ASD requiring reoperation developed
earlier in the plated group than in the conventional group, as
evidenced by a significantly lower reoperation-free rate at 5
years (68.3% vs 96.9%). Consistent with our data, one long-term
follow-up study after Robinson ACDF for radiculopathy reported
a reoperation rate of 7% (9 out of 122 patients) (17), while anothertwo studies on single-level ACDFs with plate fixation showed
higher reoperation rates ; one study at 15% (18) and the other at
28% (19). Although the PEEK cage was associated with a higher
incidence of “overall reoperation” surgery than the ICBG (P =0.012), this statistically significant difference was explainedby the fact that all PEEK cages were concomitantly used withanterior plates due to concerns over the stability of stand-alone
PEEK cage use. The current study, therefore, has provided further evidence on the adverse effect of the use of anterior plate forsingle-level ACDFs based on a comparison between the conventional and the plated ACDFs conducted at the same institution.
One previous study showed that the plate-to-disc distance(PDD) of < 5 mm at the time of surgery adversely affected thedevelopment of adjacent-level ossification (20). Our plated grouppatients who required reoperation, in fact, showed that all endsof the anterior plates except one end lay in close proximity to
the adjacent discs with PDD ≤ 5 mm at the time of reoperation.
In our series, however, many plated group patients who did not
require reoperation also showed PDD < 5 mm at the final follow-up evaluations. Therefore, the need for a reoperation after
plated ACDF depends, in addition to plate fixation with a short
PDD, on other factors such as developmentally-narrowed canal(the normal Torg-Pavlov ratio is about 0.8 (21) and reoperation
cases were 0.8 or less) and compensatory hypermobility after the
initial surgery.
Widely used dynamic anterior cervical plates, developed in
an attempt to improve the biomechanical deficiencies of static
plates, allow themselves to settle through longitudinal translation by screw translation or screw rotation within the plate overtime. This longitudinal settling of the plate-screw construct renders the ends of the plate closer to the adjacent disc spaces. Thus,
one must bear in mind this possibility in attempting to employ
dynamic anterior cervical plate fixation. The countermeasures
to be taken include the following : (1) preservation of the subchondral bone of the vertebral endplates adjacent to the discspace(s) to be decompressed, which minimizes the cage subsidence, thereby limiting longitudinal translation of the plate-screw
construct ; (2) the use of the widest possible cage to maximize thesupport at the endplate-cage interface ; (3) the use of the shortest
possible plate positioned as far as possible from the adjacentdisc spaces, which, at times, may require lateral fluoroscopic
control. These technical considerations would help minimize the
ASD-related reoperation rate not only in single-level ACDFs, as341

suggested by the current study, but also possibly in multilevel
ACDFs.

STUDY LIMITATIONS
The current study has several limitations. Firstly, we analyzed a small number of patients who required “reoperation”(n = 11) after single-level ACDFs to identify the potential risk
factors for the reoperations. The limited number of events prevented the further multivariate analysis to adjust confounding
factors including the PEEK cage use and the detailed analysis
about the association between the timing of the reoperation : either “early” or “late,” and anterior plate use. It was also difficult
to compare ICBG or PEEK cage with or without anterior plate
due to the small sample size. Secondly, the current series was
not randomized, but all the conventional ACDFs were conductedprior to July 2010 during a 21-year study period from January
2000 to December 2020. Thirdly, any one of the 8 experienced
spine surgeons, but not a single surgeon, performed conventionaland / or plated ACDFs in the study period, which may have affected the consistency in surgeons’ familiarity with ACDFs andthe treatment decision-making trends. A senior spine surgeon
and younger spine surgeon thus operated together (as surgeon
and assistant) for better clinical outcomes and improved patient
safety. Fourthly, some missing imaging data from past decades
prevented us from further assessing the additional factors thatmight be found in the initial radiographs and MRIs. Fifthly, thecurrent retrospective study relied on 131 patients who had hada single-level ACDF and a minimum of 1-year of postoperative
follow-up. The follow-up rate was 78% (131 of 168 patients), in
which 22% loss to follow-up may have led biased effects in thecohort study. Racial difference should be considered because
only Japanese patients were enrolled in this study. This study
nonetheless contributes to the documentation of further evidence
that a single-level ACDF with plate fixation may increase the reoperation rate possibly resulting from an earlier development ofadjacent segment diseases as compared to conventional ACDFs.

CONCLUSIONS
A reoperation rate comparison between single-level ACDFs
with and without anterior plate fixation has shown that the platefixation may adversely affect the adjacent segment integrity.
The incidence of “reoperation” was significantly higher in theplated ACDFs than in the conventional ACDFs (P = 0.0037). The
log-rank test revealed a significantly lower (p = 0.00003) reoperation-free survival rate at 5 years in the plated group (68.3%)
than in the conventional group (96.9%).

CONFLICTS OF INTEREST
The authors report no conflict of interest in this study.

SOURCE OF FUNDING
No funds were received in support of this study.

AUTHOR CONTRIBUTION
N.T. designed the study ; N.T. analyzed the date ; K.K, N.A.,
S.M., M.I, K.K., T.T., and Y.K. revised the manuscript ; K.K.,

342

N. Tadokoro, et al. The reoperation rate after single-level ACDFs

K.K., and T.T supervised the study ; N.T. wrote the manuscript.

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ETHICAL APPROVALThis study has been approved by the institutional review board (IRB) at the first author’s institution (approval
number : ERB-108570).

INFORMED CONSENT
Informed consent for publication was obtained by all participants in this study.

ACKNOWLEDGMENTS
The authors wish to thank Mr. Hajime Kuroiwa, Ph.D. for his
advice on the statistical analyses.

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