Cervical spinal instrumentation
Cervical spinal instrumentation is often used to help
provide considerable stability for the spine after
surgery.
Common types of instrumentation include:
A small plate can be applied to the front of the
spine
(Figure
1). This relatively simple procedure can add considerable
stability to the spinal construct.
Anterior plates were developed in the 1980’s
and their use was initially restricted to long fusions
(multi-level fusions). Now more surgeons are also
using them for single level procedures.
The addition of an anterior cervical plate during
surgery to protect the bone graft and add extra stability
to the spine does not add that much to a cervical
fusion procedure. The plates are expensive but help
provide for earlier return to normal functioning
after surgery. It has become much more commonplace
for surgeons to use a plate as a routine addition
to a cervical fusion.
The technique is fairly simple. The plate
is placed over the front of the cervical spine and
bridges the level/s being fused. Following application
of the plate, two small screws are placed through
the plate and into the vertebral body above and below
the fusion. Usually, intraoperative fluoroscopy (live
time x-ray) is used to watch the screws and assure
their correct placement.
Risks with putting in the plate include:
-
Screw failure or loosening
-
Added risk of infection
-
The screws can be misplaced into the disc space
above or below the fusion.
-
The screws can be misplaced into the vertebral
artery that runs on the side of the spine, which
can lead to excessive bleeding or a stroke.
Intraoperative or postoperative complications of
plating should be rare.
To add stability to the spine, a posterior cervical
plate can be placed on the side of the spine (over
the facet joints) and attached to the spine using screws.
The screws are angled out into the bone, away from
the canal, into what is known as the lateral mass.
Placement of the screws involves some risk to the vertebral artery and the exiting
nerve root, so there is added risk (versus wiring procedures), but better fixation
of the spine is achieved.
A new procedure and posterior instrumentation system
can be used in lieu of a cervical plate. It involves
small screws that are then connected by a small rod.
It is a more flexible system and is technically easier
to apply than a cervical plate, yet still provides
excellent posterior fixation and is quite rigid.
Before plates and rods had been developed, the
only fixation system available was wiring. In the lower
cervical spine, wiring alone for fixation is rarely
done as the newer system is easy to apply and more
rigid. Wiring is still done to fuse the upper cervical
vertebral segments (C1 to C2). Wiring at this level,
if the posterior cervical elements are intact, can
provide quite a rigid construct.
Although wiring can be used to fixate the C1-C2 level
in most situations, sometimes a posterior facet screw
(Magerl screw) is necessary in cases with significant
instability. Cases of tumor, fracture, or rheumatoid
arthritis can cause such instability. It can also be
used if the posterior elements are not intact, or if
a patient has already had a failed fixation with posterior
wiring.
Interbody
cages can be used in the cervical interbody space to
obtain a fusion. There are different
varieties (impactable vs. threaded), and they can be
made of different substances (carbon fiber, PEEK (polyethylethylketone),
or titanium).
There currently is some growing interest on the part
of surgeons to stabilize the intervertebral joint without
using either allograft or autograft bone. These
synthetic cages can be filled with synthetic bone graft
substitutes or bone morphogenic protein. In some
cases, enough stability can be obtained with the use
of an interbody cage that supplemental fixation with
a cervical plate may not be necessary.
Because of its relatively small size, the cervical
spine is well suited for postoperative bracing. The
extent of the surgery typically determines the length
of time a collar is recommended after surgery.
Many surgeons will ask patients to wear a collar for:
Unfortunately, there is no definitive evidence in
the medical literature that points to exactly how long
a cervical collar is necessary, or if it is necessary
at all.
With fixation techniques (such as anterior plates)
it is probably reasonable to use collars mainly for
pain control in the initial postoperative period (since
most of the actual stability of the spine is from the
bone graft and plate). Postoperative bracing
for a one level fusion with instrumentation is probably
not necessary, and increasingly surgeons are limiting
the use of a postoperative brace or even eliminating
its use.
By: Peter
F. Ullrich, Jr., MD
October 7, 2005 (article originally published
September 8, 1999)
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