SYMPOSIUM: CURRENT CONCEPTS IN CERVICAL SPINE SURGERY
A New Zero-profile Implant for Stand-alone Anterior Cervical
M. Scholz MD, K. J. Schnake MD, A. Pingel MD,
R. Hoffmann MD, F. Kandziora MD
Published online: 30 September 2010
? The Association of Bone and Joint Surgeons1 2010
higher with anterior cervical discectomy and fusion pro-
cedures if supplemented with a plate. However, plates may
be associated with higher postoperative morbidity and
higher rates of dysphagia. This led to the development of a
cervical stand-alone cage with integrated fixation for zero-
profile segmental stabilization.
We asked whether this new implant
would be associated with a low rate of dysphagia and other
short-term complications in patients having anterior cer-
vical discectomy and fusion and would be able to achieve
solid fusion and maintain postoperative reduction in pain.
We prospectively followed 38 patients with
radiculopathy/myelopathy undergoing anterior cervical
Several studies suggest fusion rates are
parameters, clinical features (Neck Pain Disability Index,
visual analog scale score for neck/arm pain, Odom’s crite-
ria), and dysphagia scores were recorded. Radiographs were
taken to assess implant failure. Thirty-four patients had a
minimum 6 months’ followup (mean, 8 months; range,
Three patients at 6 weeks and one patient at
symptoms. There was no hardware failure recordable and
all patients had evidence of fusion. Compared to preoper-
atively, visual analog scale pain score and Neck Pain
Disability Index were reduced at 6 weeks’ followup with-
out change during further followup.
The new cervical stand-alone anterior fusion
device allows decompression and fusion with low com-
plication rates. The incidence of chronic postoperative
dysphagia was infrequent in comparison to published
data. Prospective randomized trials with more patients
and longer followup are necessary to confirm these
Level of Evidence
Level IV, therapeutic study. See
Guidelines for Authors for a complete description of levels
Degenerative conditions of the cervical spine (eg, degen-
erative disc disease or cervical spondylotic myelopathy)
are a major cause of radicular arm pain with or without
neurologic deficits. When nonoperative treatment fails,
surgery may be considered. There are two different phi-
losophies to treat a diseased motion segment after cervical
spine anterior decompression: an interbody fusion [13, 19]
or a disc prosthesis . Anterior cervical discectomy and
The authors (MS, FK) certify they have or may receive payments or
benefits from a commercial entity (Synthes GmbH Switzerland,
Oberdorf, Switzerland) related to this work.
Each author certifies that his or her institution approved the human
protocol for this investigation and that all investigations were
conducted in conformity with ethical principles of research.
M. Scholz, K. J. Schnake, A. Pingel, F. Kandziora (&)
Center for Spinal Surgery and Neurotraumatology,
Berufsgenossenschaftliche Unfallklinik Frankfurt am Main,
Friedberger Landstraße 430, 60389 Frankfurt am Main,
Department for Trauma and Orthopaedic Surgery,
Berufsgenossenschaftliche Unfallklinik Frankfurt am Main,
Frankfurt am Main, Germany
Clin Orthop Relat Res (2011) 469:666–673
fusion (ACDF) is considered the ‘‘gold standard’’ surgical
treatment for elderly patients or for patients with contra-
indications for the use of a cervical disc prosthesis .
Many surgeons prefer to add an anterior plate in fusion
procedures for enhancing stabilizing properties, as several
studies suggest this leads to increased fusion rates and
reduced failure rates, particularly in multilevel procedures
[5, 14, 32].
The addition of a plate is, however, not without side
effects. Although the profile of current anterior plates is
thinner than that of earlier designs, the plates are still
somewhat bulky. In the early postoperative period, 2% to
67% of the patients may complain of dysphagia .
Mostly these symptoms disappear during the first 3 months
after surgery [3, 18], but not all patients recover completely
from swallowing problems. The incidence of chronic dys-
phagia-related symptoms after ACDF ranges from 3% to
21% in the current literature [10, 15, 24, 38], whereas the
pathophysiologic cause still remains unclear. Additionally,
the screw-plate interface might lead to postoperative
complications. Cases of migrating screws and subsequent
soft tissue damage are reported [6, 25]. Further, Park et al.
 demonstrated a higher incidence of adjacent-level
degenerations if an additional plate was used. The authors
stated this finding is consistent with inappropriate sized or
misaligned plates interfering with the adjacent-level disc
space. Yang et al.  supported this thesis, demonstrating
lower rates of adjacent-level degeneration performing
ACDF without plates.
Based on these results, a radiolucent implant (Fig. 1) for
stand-alone anterior interbody fusion procedures of the
cervical spine (Zero-P; Synthes GmbH Switzerland,
Oberdorf, Switzerland) was developed to potentially avoid
these complications. This implant was based on an anterior
stand-alone stabilization implant of the lumbar spine
described previously [7, 29]. One in vitro biomechanical
study  showed similar stability using the cervical
implant with integrated screws in comparison to already
established cervical cage and plate constructs. In 2007 the
implant received the CE mark. In February 2008, the US
Food and Drug Administration approved the clinical use of
this implant for degenerative cervical spine conditions.
We asked (1) whether this new implant is associated
with a low rate of dysphagia and other short-term com-
plications in patients having ACDF; (2) whether this
implant is able to achieve solid fusion; (3) whether this
implant is able to maintain the postoperative reduction in
pain; and (4) whether a learning curve using the implant is
Patients and Methods
We enrolled 38 selected patients (24 male, 14 female) who
underwent ACDF between May 2008 and May 2009. All
patients had symptomatic cervical spine disc disease
between C3/C4 and C7/Th1 and failed nonoperative
treatment. The indications for surgery were radicular arm
pain with or without neck pain and/or functional/neuro-
logic deficit confirmed by MRI or CT. The displayed
patient example shows a typical two segmental cervical
spinal stenosis in sagittal MRI (Fig. 2A). Axial MRI plain
revealed that the spinal canal stenosis was caused by
(Fig. 2B) soft disc stenosis C4/C5 and (Fig. 2C) C5/C6
resulting in (Fig. 2D) radiculopathy of C5 and C6 and
myelopathic changes in C5/C6. Patient selection was based
on inclusion and exclusion criteria (Table 1). We operated
on 15 patients with monosegmental, 20 patients with
bisegmental, and three patients with trisegmental disease
(Table 2). All 38 selected patients were treated by anterior
decompression and stabilization with the Zero-P device in
the target levels, with a total of 64 levels operated on.
In the operation theater, patients were placed with a
head extension in supine position. To obtain the target disc
space, a standard left side approach to the cervical spine
was performed. After anterior decompression, trial spacers
were used to determine which implant shape would be
used. After the trial spacer was correctly fitted into the
disc space, a corresponding Zero-P implant filled with
b-tricalcium phosphate (chronOS cylinder; Synthes GmbH,
Oberdorf, Switzerland) was inserted with an implant
holder/aiming device. Correct position of the cage was
controlled by using an image intensifier in lateral and AP
views. The device should be placed 2 mm behind the
anterior column in the lateral view (Fig. 2E) and in the
center of the disc space in the AP view (Fig. 2F). The three
different implant configurations offered are with a parallel-
shaped endplate (Fig. 3A), a convex-shaped endplate
Fig. 1 An image shows the Zero-P implant. Reprinted with permis-
sion from Synthes GmbH Switzerland (Oberdorf, Switzerland).
Volume 469, Number 3, March 2011Zero-P for Cervical Interbody Fusion667
(Fig. 3B), and a lordotic-shaped endplate (Fig. 3C). The
Zero-P device contains a polyether ether ketone body with
tantalum markers to control the position during insertion.
Included is a small plate containing four holes with internal
screw treads. After drilling the pilot hole through the
aiming device, the first locking screw was inserted. The
implant system contains screws of 14- and 16-mm lengths.
In most of the cases described in this report, screws of
16-mm length were used. Subsequently, the other three
holes were drilled using the guidance of the aiming device.
The aiming device was then removed and the three
remaining screws were inserted using torque limitation
(1.2 Nm). When the Zero-P implant is completely inserted,
its zero-profile characteristic can be seen (Fig. 4). Angled
instruments for drilling and inserting screws in the upper
(C3/C4) and lower (C6/C7/Th1) cervical spine are also
To assess a potential learning curve with the implant, the
operation time and radiation time were recorded. The
average operation time for a monosegmental decompres-
sion and stabilization lasted 114 ± 24 minutes and the
radiation time was calculated as 88 ± 54 seconds. For the
increased by 31% to 150 ± 30 minutes and the average
radiation time increased by 21% to 107 ± 77 seconds. In
comparison to a monosegmental operation, the average
operation time of a trisegmental stabilization increased by
68% to 192 ± 50 minutes and the average radiation time
by 92% to 169 ± 56 seconds.
Postoperatively, we used no collars regardless of the
number of operated levels. All patients received standard-
ized pain medication containing metamizole and an oral
muscle relaxant. Supervised by a physiotherapist, the
patients were mobilized on the first day after the operation
and received physical treatment with heat and/or massages
for the dorsal neck. No active physiotherapy for the neck
was allowed within 6 weeks postoperatively. The average
hospitalization time was 6 days (range, 4–11 days).
Fig. 2A–F (A) T2-weighted MRI in sagittal plain, (B) MRI in axial
plain of C4/5, (C) MRI in axial plain of C5/6 and (D) CT in 2D-sagittal
reconstruction show a cervical spinal stenosis C4/C5 + C5/C6
resulting in radiculopathy of C5 and C6 and myelopathic changes in
C5/C6. (E) Lateral and (F) AP plain radiographs show the patient
6 months after decompression and fusion with Zero-P.
668 Scholz et al. Clinical Orthopaedics and Related Research1
During followup, clinical and radiographic data were
collected on the last day of hospital stay, at 6 weeks, at
3 months, and at 6 months. Complications were recorded
as implant-related, surgery-related, or general (not directly
implant or surgery related). Four of the 38 patients (11%)
did not appear for one of the followup examinations. These
patients were excluded from the study. The remaining
34 patients were included in the clinical and radiographic
evaluations at each followup time. The minimum followup
was 6 months (mean, 8 months; range, 6–11 months).
Clinical examination included measurement of neck and
radicular arm pain on a visual analog scale (VAS) of 0 to
100, with 0 representing no pain and 100 representing
severe pain [4, 8], and assessment of functional outcome
using the validated German translation of the Neck Pain
and Disability Scale (NPAD-D), expressed as a percentage
ranging between 0% and 100% [12, 28]. Dysphagia-related
symptoms were graded by the physician depending on the
patient’s state as none (no episodes of swallowing prob-
lems), mild (rare episodes of dysphagia), moderate
(occasional swallowing difficulty with specific food), and
severe (frequent difficult swallowing with majority of food)
according to Bazaz et al. . Additionally, the amount of
pain (VAS 0–100) and the duration of dysphagia-related
symptoms were recorded.
Three of us (MS, AP, FK) independently evaluated all
images including plain radiographs and lateral flexion/
extension radiographs. At the day of discharge and at each
followup visit, plain radiographs (AP and lateral views)
were used to detect implant failure, including segmental
collapse, caused by implant subsidence. An implant pene-
tration into the adjacent endplates of more than 2 mm was
defined as segmental collapse . According to Pitzen
et al. , fusion was defined as an absence of radiolu-
cencies, absence of bone sclerosis, and evidence of
bridging trabecular bone within the fusion area.
We computed means and SDs for continuous data (VAS,
NPAD-D scores). We determined differences in VAS and
NPAD-D scores between preoperative and postoperative
time points and during further followup using the t test for
paired samples if a normality test was passed or a
Wilcoxon signed-rank test if a normality test was failed.
Intraobserver variability for radiographic evaluation was
determined using kappa statistics. SPSS1software (Ver-
sion 15.0; SPSS Inc, Chicago, IL) was used for all analyses.
Table 2. Preoperative patient data and operated level(s)
Variable All patients
(n = 38)
(n = 15)
(n = 20)
(n = 3)
Age (years)*53.7 ± 9 52.8 ± 854.2 ± 10 55.7 ± 3.5
Number of women15582
Number of men2310 121
NPAD-D (%)*55.8 ± 18.3 49.6 ± 19.159.5 ± 18.9 64.1 ± 12.3
Total implants64 15409
* Values are expressed as mean ± SD; ACDF = anterior cervical discectomy and fusion; NPAD-D = German translation of the Neck Pain and
Table 1. Patient selection criteria
Age 18–70 years
Symptomatic cervical disc disease between C3/C4 and C7/Th1 with
Neck or arm (radicular) pain and/or
Functional/neurologic deficit confirmed by imaging (CT or MRI)
Previous surgery at the index level
Fused level adjacent to the index level
Patients having no contraindication for total disc replacement and
wanting to be treated with total disc replacement after informed
Systemic or local infection
Active rheumatoid arthritis, noncontrolled diabetes mellitus, or any
other medical condition(s) that would represent an increase in
surgical risk or interfere with normal healing
Known history of osteoporosis
Previous known allergy to the materials contained in the device,
such as polyether ether ketone or titanium alloy
History of any invasive malignancy (except nonmelanoma skin
cancer) unless treated with curative intent and there has been no
clinical signs or symptoms of the malignancy for more than 5 years
Pregnant or planning to become pregnant during study period
Volume 469, Number 3, March 2011 Zero-P for Cervical Interbody Fusion669
Before surgery, four of 38 patients complained of minor
dysphagia (VAS score, 1.7 ± 0.9). In the early postoper-
ative period, 21 of 34 patients (62%) complained about
minor dysphagia (VAS score, 2.1 ± 1.2) with symptom
duration of 21 ± 16 days. At 6 weeks’ followup, the
number of patients complaining of minor dysphagia was
reduced to three of 34 patients. Only one female patient
complained about minor dysphagia (VAS score, 1.6) at 3
and 6 months followup (Fig. 5). According to the Bazaz
score , there was no moderate or severe dysphagia
detectable during followup.
Intraobserver agreement for radiographic evaluation was
almost perfect. We observed no implant subsidence or
segmental collapse by 6 months; there were no radiolucent
lines or detectable implant/screw loosening. All patients
showed evidence of fusion in each operated segment
according to the criteria of Pitzen et al. . We observed
no implant-related complications. In two patients, a tem-
porarily swelling of the neck without airway problems
caused by a prevertebral hematoma occurred. No patient
had revision surgery. One patient developed an allergy to
All patients had a reduction in VAS neck pain
(p\0.001) (Fig. 6), VAS radicular arm pain (p\0.001)
(Fig. 6), and NPAD-D (p\0.001) (Fig. 7) within the first
3 months. We observed no change in VAS neck pain
Fig. 3A–C Imagesshow different implant configurations:(A) parallel-
shaped endplate, (B) convex-shaped endplate, and (C) lordotic-shaped
endplate. Reprinted with permission from Synthes GmbH Switzerland
Fig. 4A–B (A) Lateral and (B) AP views show the zero-profile of the
Zero-P device implanted in a cadaveric specimen.
Fig. 5 A graph shows incidence (percentage) and duration of
670 Scholz et al.Clinical Orthopaedics and Related Research1
(p = 0.306), VAS radicular arm pain (p = 0.889), and
NPAD-D score (p = 0.189) comparing 3 and 6 months’
Comparing the duration of the monosegmental opera-
tions, related to a supposed learning curve, there was a
longer operation time for the first three monosegmental
operations (143 ± 15 minutes) than for the last three
monosegmental operations (93 ± 11 minutes) recordable.
If nonoperative treatment of cervical spine disc disease
fails, ACDF or cervical arthroplasty are two possible
operative techniques [20, 27, 36]. There are more potential
candidates for a cervical total disc arthroplasty than a
lumbar total disc arthroplasty, but according to the retro-
spective study of Auerbach et al. , only 43% of patients
met their inclusion criteria and were candidates for cervical
total disc arthroplasty. If there are contraindications for
using an artificial disc, ACDF is still the gold standard for
surgical treatment. In cases where ACDF was performed,
numerous reports have documented the effective use of
additional plating to treat degenerative spine conditions
and avoid pseudarthrosis, especially in multilevel proce-
dures [1, 11, 32, 34]. However, the use of an additional
anterior plate is associated with various intraoperative and
postoperative complications. In this study, we described
the first clinical and radiographic results of a new ACDF
technique using a cage with an integrated zero-profile plate
and angle-stable screws. We asked whether this new
implant would be associated with a low rate of dysphagia
and other short-term complications in patients having this
ACDF procedure, would be able to achieve solid fusion
and maintain postoperative reduction in pain, and is asso-
ciated with a learning curve.
We note several limitations to this study. First, the study
was performed as an observational study without a control
group. Second, the number of patients was small, and third,
the followup time was short at only 6 months. Due to the
short-term followup, we were not able to compare adja-
cent-segment degenerations using the zero-profile implant
with those of cage and plate constructs.
Chronic dysphagia is a well-known phenomenon after
ACDF and plating, with a wide variability from 3% up to
21% [15, 24, 26, 33, 35]. For the early postoperative per-
iod, the rate of dysphagia in our study is similar to that in
the current literature [3, 18, 38]. However, in comparison
to published data [3, 18, 38], the incidence of chronic
dysphagia in our patients was low (Table 3). Only one of
34 patients complained about mild symptoms of dysphagia.
According to Fountas et al. , postoperative soft tissue
Fig. 7 A graph shows Neck Pain and Disability Scale (NPAD-D)
preoperatively and during follow-up. *p\0.001 versus preoperative
Table 3. Comparison of dysphagia rates in the current literature
Dysphagia short term
Dysphagia medium term
Dysphagia long term
Bazaz et al.  249 50.2% 17.8% (4.8% moderate–severe)12.5%
Lee et al.  31054.0% 18.6% 15.2%
Smith-Hammond et al. 3847.0% 23.0%
Yue et al.  7435.1%
Scholz et al. [current study]3462.0% 2.9%
Fig. 6 A graph shows neck pain and radicular arm pain (0–100 VAS
score) preoperatively and during followup. *p\0.001 versus preop-
erative time point.
Volume 469, Number 3, March 2011Zero-P for Cervical Interbody Fusion671
edema, esophageal injury, postoperative hematoma, and
adhesive formations around implanted cervical plates
might be possible explanations for dysphagia-related
symptoms, although the exact pathophysiologic mecha-
nism remains unknown. According to Lee et al. , there
is a correlation between plate thickness and dysphagia rate,
with decreased dysphagia incidence when thinner plates
were used. Several patients with isolated anterior cervical
hyperostosis or ‘‘diffuse idiopathic skeletal hyperostosis’’
have revealed symptoms of chronic dysphagia after ante-
rior osteophyte resection [9, 21, 24]. This might suggest
why plates are sometimes associated with chronic dys-
phagia. The zero-profile design of Zero-P avoids an
implant contact to the soft tissue in front of the cervical
spine. This might avoid any mechanical irritation of the
esophagus and may explain the low dysphagia rate in our
Regardless of the number of operated levels in this
study, there were no implant-related complications during
followup. This finding is contrary to literature data where,
especially for multilevel plate reconstructions, a failure rate
of up to 71% was reported . In a recent literature
review, Vaccaro et al.  reported an incidence of screw
and plate loosening between 0% and 15.4%, screw break-
age between 0% and 13.3%, plate breakage between 0%
and 6.7%, plate and graft displacement (with or without
graft fracture) between 0% and 21.4%, and implant mal-
position (screws in discs, plating of unfused segments, etc)
between 0% and 12.5% for long segmental anterior plate
fixation. Newer implants are designed with different screw-
locking mechanisms to avoid these mechanical complica-
tions. It should be noted balancing between preferably
small plate dimensions (low profile) and the necessity of
thicker plates to have a secure constrained screw fixation is
challenging from an engineering standpoint. Nevertheless,
the problem of screw and plate malposition during surgery
still exists. Specifically, the lack of implant migration or
screw loosening in this study might be related to the design
of the locking plate-screw interface. The plate with an
internal screw thread engages with the outer screw thread
located in the head of the screw providing a safe, con-
strained, and angle-stable screw fixation.
Zero-P was able to maintain the postoperative reached
level of VAS and NPAD-D pain scores. Comparing these
outcome data (VAS and NPAD-D) to those of previously
described outcome data of cage and plate constructs [1, 11,
14, 16, 20, 23, 27], no differences could be detected. Due to
the short-term followup and the lack of CT evaluation,
which is necessary to grade the fusion status, we were not
able to compare fusion results with those in the literature.
Using the Zero-P device, especially in the upper and
lower cervical spine, was associated with a learning curve.
In the first cases, a longer operation time was recorded.
It was easy to use the implant in the levels C4/C5, C5/C6,
and C6/C7. Below and above, especially in patients with a
short neck or high sternum, the screw insertion might be
challenging due to the angulation of the screws.
Our observations suggest this new cervical stand-alone
anterior fusion device with integrated screw fixation allows
anterior cervical decompression and stabilization with low
rates of dysphagia. No implant-related complications were
observed. We believe the incidence of chronic postopera-
tive dysphagia was infrequent in comparison to published
data owing to the ‘‘zero’’ implant profile. A randomized
trial with longer followup, comparing the zero-profile
fusion technique with established fusion techniques, should
be performed to confirm our observations.
menting the patients.
We thank Kirsten Stangenberg-Gliss for docu-
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