Study rationale
Anterior cervical decompression and fusion is considered a gold standard for the treatment
of symptomatic spondylosis following failure of appropriate nonsurgical care. Favorable
clinical outcomes following anterior cervical discectomy and fusion (ACDF) have been
attributed to successful healing / fusion of the interbody graft [1]
[2]. Anterior fixation with plate and screw devices have been recommended for patients
requiring multilevel fusions and may play a beneficial role in maintaining or restoring
physiologic alignment of an operated neck while assuring a best possible fusion rate,
especially when nonautologous structural bone-graft sources are used. Studies have
investigated various factors that may enhance fusion rates, including the use of anterior
plating [1]
[2]
[3]
[4]. Rigid plate and screw implants had been a mainstay of fixation. Questions, however,
have been raised whether these implant designs may adversely affect bone healing due
to stress shielding and prevention of settling, as has been shown in biomechanical
cadaveric studies [5]
[6]. These concerns have led to the development of implants with the stated goal of
enhancing fusion rates by providing improved load sharing through the anterior interbody
grafts and the anterior spinal column. A variety of implant designs have been introduced,
some with angulating screws, others with intrinsic mechanisms to allow for compression
of structural grafts across the anterior spinal column. These types of implants, however,
are invariably more complex and expensive than more conventional rigid locking plates.
These „dynamic” implants have been called into question due to their potential to
allow for an unwanted collapse and the potential for implant migration. Can the theoretical
advantages of dynamization of plates be substantiated in the clinical setting based
on radiographic findings? Do „dynamic loading plates” have improved fusion rates and
radiographic outcomes compared with conventional rigid locking plates?
Objective
To compare the difference in fusion rates, time to fusion, subsidence levels, complication
rates between 1) a static, 2) a dynamic angulation, and 3) a dynamic translation plate
and between dynamized plates in general and statically locked plates.
Methods
Study design:
Randomized controlled trial.
Inclusion criteria:
Patients with symptomatic degenerative conditions resulting in radiculopathy or myelopathy
who would benefit from a two-level anterior cervical discectomy and fusion (ACDF)
with anterior plating.
Exclusion criteria:
Exclusion criteria included trauma to the cervical spine, corpectomy, revision surgery,
or previous posterior cervical surgery.
Patient population and interventions compared (Figure [1])
-
Of 97 patients who were assessed for eligibility, 61 did not meet inclusion criteria
or were excluded as described above. None were lost to follow-up, however, one patient's
x-rays could not be adequately measured due to the patient's morbid obesity, leaving
35 patients available for a follow-up rate of 97% at 12 months.
-
All surgeries were performed using the same technique and postoperative regimen by
the same surgeon, including use of the same intervertebral allograft cage without
use of supplemental graft materials.
-
Patients were randomly assigned to one of three plate designs: the cervical spine
locking plate (CSLP, Synthes) or the Atlantis (Medtronic); or the Premier (Medtronic).
The CSLP plate is a static locked plate that theoretically does not allow settling.
The Atlantis and the Premier provided controlled settling.
-
Patients were randomized in blinded fashion where the assistant nurse selected a folded
paper which contained the name of the plate from an envelope, without the knowledge
of the surgeon.
Outcomes:
-
At follow-up, patients' charts were analyzed for age and gender, smoking status and
litigation. If chart data were insufficient, patients were contacted individually
and interviewed via telephone and asked to obtain one last x-ray.
-
Only radiographic criteria and measurements were evaluated, as the main purpose of
this study was the effect of the plate on radiographic outcome and not clinical outcome.
X-rays were evaluated by observers blinded to patient history at 0 and 6 weeks, 3,
6, and 12 months, and at the time of most recent follow-up. X-rays were graded as
fused or not fused. Criteria for fusion included the presence of bridging trabeculae
across the graft site and the lack of radiolucency between the graft and the adjacent
vertebral body.
-
Standardized radiographic measurements for settling, plate migration, subsidence and
linear translation were used (see web appendix for details). Three independent observers
provided the measurements and graded fusion by assessing incorporation of the graft
as „healed” or „unclear or not healed”. These observers were also asked to asses implant
integrity and hardware loosening.
Analysis:
-
Measurements were made from each lateral radiograph to assess 1) fusion rates, 2)
time to fusion, 3) subsidence, 4) linear translation, and 5) angular variation [7]
(Figure [2]).
-
After comparison between the three groups was completed, patients with dynamic plates
were grouped together (Premier and Atlantis), and compared with the patients with
the static plate (CSLP patients).
-
Statistical analysis was performed using ANOVA for three-way comparison for the different
type of plates. Unpaired Student t-tests were used when the two dynamic plates were
grouped and compared against the static plate for the variable values, while chi-square
tests were used for categorical values. Results were considered statistically significant
when P < .05.
Additional detail regarding methods can be found in the web appendix at www.aospine.org / ebsj.
