Update
on minimally invasive spinal fusion surgery
Introduction to minimally invasive fusion
A spine fusion is aimed at alleviating pain that is
believed to originate from a motion segment in the
spine. For some patients, it may be recommended to
have a spine fusion surgery performed in both the front
and back of the spine in an effort to provide extra
stability for the painful motion segment. There is
some new evidence about these types of procedures,
and the use of a minimally invasive spinal fusion system
may sometimes be considered.
At the time of this article, minimally invasive spine
fusion technology is still in the early stages of development.
This type of procedure uses a needle, which is inserted
through small incisions in the back, and radiographic
magnified images of the spine are projected onto television
screens in the operating room. Narrow surgical instruments
are then inserted into the small (1 to 1 ½ cm)
incisions to complete the operation. See Figure
1, Figure
2,
and Figure
3.
The goals of minimally invasive spine fusion surgery
systems include:
At the time of this article, minimally invasive spinal
fusion technology is still new, and none of the above
benefits have been definitively proven. Some spine
surgeons have anecdotal evidence from their own practice
indicating that patients have better outcomes with
using a minimally invasive spine surgery system, and
other surgeons have anecdotal evidence from their practice
that patients have better outcomes with techniques
associated with traditional (open) approaches to spine
fusion surgery.
Use of a minimally invasive spine fusion surgery system
is best suited for patients with degenerative disc
disease or spondylolisthesis. The technique does not
allow the spine surgeon to do a central decompression.
Foraminal decompression can be achieved by interbody
distraction and grafting. If there is any central stenosis
an open incision still needs to be made. Due to the
limited visualization at the time of surgery, it is
a difficult and possibly dangerous technique to use
in patients with a severe deformity.
Spine fusion surgery background information
Initial spinal fusion surgery attempts were performed
with the placement of posterior lateral (on the side)
and posterior (in the back of the spine) bone grafts.
With the advent of internal fixation, these spine fusions
were performed with the addition of posterior instrumentation
(pedicle screws), with fusion rates approaching 80
to 90%.
Surgeons sometimes perform an anterior lumbar interbody
fusion (ALIF) in addition to the posterior lateral
bone grafting and posterior instrumentation. An ALIF
is considered effective due to the large surface area
in the front of the spine, as well as studies reporting
two thirds of the loads are transmitted through the
anterior column (front of the spine). When both an
ALIF and a posterior lateral bone grafting and posterior
instrumentation are performed it is commonly referred
to as a 360-degree spine fusion or a circumferential
spine fusion.
Although associated with high spine fusion rates and
a high level of patient satisfaction, follow-up radiographs
of 360-degree fusions demonstrated inconsistent fusion
of the posterior lateral bone mass, suggesting that
the anterior lumbar interbody fusion (front of the
spine) is the more structural component.
It was theorized that the placement of the anterior
graft altered the biomechanics of the spine such that
the posterior lateral bone graft did not consolidate.
This raises the question: Is there a need for posterior
lateral bone graft in the setting of an ALIF with posterior
instrumentation?
This question was answered in a prospective randomized
study by Schofferman et al. that compared 360-degree
fusions versus an ALIF plus posterior instrumentation
(270-degree fusions). Their results showed that both
procedures were successful in alleviating pain with
no clinical differences among the two; however the
270-degree fusions had less blood loss and shorter
hospital stays.
Minimally invasive spine fusion surgery approach
Performing a 270-degree spine fusion by traditional
surgical techniques requires an open procedure exposing
the lamina, pars, facets, and transverse processes
of the levels to be instrumented. This approach permits
excellent visualization of the spine, and access to
the portions of the spine to place the implants. Depending
on the spine surgeon's technique, however, the muscle
retraction and disruption of the posterior muscles
and ligaments may lead to some degree of scar formation
and damage. In turn, this is potentially associated
with unwanted postoperative effects (sometimes referred
to as "fusion disease").
Depending on the spine surgeon's technique and other
factors, a traditional open spine fusion procedure
may include a risk of:
-
Disruption of the supraspinous and interspinous
ligaments, which has been implicated in decreased
flexion strength and delayed spinal instability.
-
Sihoven et al. demonstrated local denervation atrophy
of paraspinal muscles postoperatively from dissection
and lateral muscle retraction. This was associated
with a loss of support and stability potentially
leading to continued pain after surgery (failed back
surgery syndrome).
-
Styf et al. also showed that retracting muscle
during the surgical procedure can lead to regional
ischemia (deprivation of oxygen), and EMG studies
have demonstrated chronic denervation of paraspinal
muscles following some types of open surgery.
Since previous studies demonstrated that posterior
lateral bone grafting was not necessary for
a successful spine fusion surgery, efforts have been
made to perform a 270-degree fusion with anterior lumbar
interbody fusion and minimally invasive, percutaneous
posterior instrumentation. The hope is that this will
allow for a 270-degree spine fusion without the complications
potentially associated with open procedures.
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