Indications and diagnosis for spine fusion surgery
The most common type of spine fusion surgery is performed
for mechanical low back pain. This type of mechanical
lower back pain occurs with increased activities and
an often times is associated with degenerative changes
in the discs (such as degenerative disc disease). At
other times it may be due to a low-grade slippage of
the spine (such as degenerative spondylolisthesis and
isthmic spondylolisthesis). The most important factor
in treatment of these types of low back pain is making
a specific and appropriate anatomic diagnosis.
When considering the indications for lumbar spine
fusion surgery, low back pain that lasts for more than
six months is the most general indication. The indications
for fusing the low back occur primarily in situations
where there may is a large deformity or, more commonly,
for back pain that does not get better with time or
non-surgical treatment, such as:
Determining where the pain arises is the greatest
challenge in fusion of the low back. The steps involved
in evaluating the source of pain include:
-
Patient history
A patient history entails reviewing when the
pain occurs, where it is located, how it began, the
previous treatment and the extent to which it limits
the patient's activities. Additionally, the physician
will try to determine if other factors (such as depression)
may be contributing to the patient's back pain. An
individual's general health can influence the role
of spine surgery (e.g. heart or lung disease).
-
Physical exam
A physical examination is done to determine whether
there is evidence for any neurologic (nerve-related)
injury.
-
Diagnostic studies
There are a number of diagnostic studies that
are available to investigate the etiology (medical
cause) of the pain. The most common study is an
x-ray of the low back, which can show if there
is any instability or deformity to the spine. It
can also image such things as a fracture, or in
advanced stages, it can show tumors of the spine.
Although done frequently, they usually fail to
demonstrate the cause of the back pain. For
more subtle lesions (injuries) in the spine, additional
studies are often needed.
The gold standard is to follow x-rays with magnetic
resonance imaging (MRI scan). An MRI scan provides
very precise anatomic information about the health
of the discs as well as presence of any tumors or compression on the nerves.
The difficulty with this study, as with many others, is that "abnormalities" that
show up on an MRI scan may not be the cause of the pain. Most often the
disc degeneration identified on an MRI is a normal finding, secondary to
aging, which occurs in more than 50% of people in their 40's.
For a small percentage of people an MRI scan cannot be safely performed,
e.g., if the patient has a pacemaker. In these cases a CT scan with
myelogram may be done. The anatomic information from a CT scan with myelogram
is very similar to that of an MRI scan. A CT myelogram is also sometimes
ordered as an adjunctive study to a MRI scan as it can show very subtle
nerve root compression and also images out in the foramen better.
A discogram, which is a more controversial study,
may also be performed before spine fusion surgery.
This study involves inserting a needle into the
disc and injecting dye. If this process causes
the patient's normal pain to occur, it is presumed
that the specific disc is the anatomic cause for
the pain. The difficulty with discography is that
it is not entirely objective, and its effectiveness
is quite dependent upon the person doing the discogram.
Also, it is clearly an unpleasant test to undergo. Currently, however,
it probably is the most reliable test available
to add anatomic precision to the diagnosis of mechanical
low back pain. Many factors can result in pain
production during a dicograms, not only the true
anatomic source of the problem. A discogram is
a test to confirm the pathology, rather
than one to " find
the cause of the pain." When done properly, a painless "control" level
should be performed.
Other studies may also be performed before a spine fusion surgery,
such as an electromyography (EMG), particularly in situations where
there is a large amount of leg pain. This study involves placing
needles within the legs to determine whether the nerves are working
properly and to help identify which nerve is compromised. Another
study to try to determine the specific nerve that is a problem is
a procedure to block that specific nerve. A selective nerve root
block (SNRB) can be quite helpful, particularly in situations where
there is evidence on other studies of compression of many nerves.
Piecing together all of the indications to determine
the potential need for a spine fusion surgery is obviously
quite complex. It involves compiling results from history,
physical exam and diagnostic studies. While the information
does not always produce a clear indication for spine
fusion surgery, certainly the best opportunity for
improvement with a spine fusion occurs when all the
pieces of the puzzle fit neatly together.
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