SURGICAL MANAGEMENT OF DEGENERATIVE SCOLIOSIS

Mild to moderate degrees of degenerative scoliosis may
not progress, and they may not be symptomatic. With more advanced
disease, axial pain and neurogenic claudication are typical symptoms.
As with any degenerative spine disease, facet hypertrophy, diffuse disc
bulges, disc degeneration, and narrowing and redundant ligamentum
flavum can result in spinal stenosis and produce symptoms of neurogenic
claudication and radiculopathy (25). The degree
of compression can be aggravated in the presence of lateral listhesis
or spondylolisthesis, by traction on the nerve roots.

Lateral listhesis, where slippage of one vertebra upon
another occurs in the coronal plane, appears to correlate with a
greater risk of curve progression (25,27).
Significant lateral listhesis, particularly when it occurs at multiple
adjacent levels, can result in significant truncal imbalance with
resultant pain and fatigue. In many patients, these symptoms can be
managed conservatively with anti-inflammatories, physical therapy, and
epidural steroids. With progression of the patient’s curvature,
however, failure to respond to conservative measures or significant
compromise of the patient’s quality of life may call for consideration
of surgical intervention.

Curve progress is variable, but among those who progress, it has been reported to average 3° a year (25).
Risk factors for curve progression include curve magnitude greater than
30°, osteoporosis, and lateral listhesis or rotatory spondylolisthesis (9,14).
Prior decompressive surgery, such as a laminectomy, can increase curve
progression as well, sometimes secondary to development of a
postsurgical fracture of the pars interarticularis and
spondylolisthesis. Rapid progression of scoliosis in a patient with a
prior laminectomy is highly suspect for a pars fracture, which should
be sought in the workup of such a patient.

Asymmetric disc space collapse can result in spinal deformity, as can rotatory spondylolisthesis or lateral listhesis. Compression fractures
with a lateral wedge component may aggravate or cause development of
scoliosis. These patients may have a relative loss of lumbar lordosis
as well. Patients with lateral listhesis appear to be at greater risk for curve progression (25,27),
and, in addition, they are subject to traction on their nerve roots at
the involved levels. Asymmetric wear on the facet joints may contribute
to facet arthropathy, leading to central or foraminal stenosis.
Although most patients present with pain secondary to nerve root
compression, others present with weakness. Pain and weakness may be
particularly intractable from severe disc space collapse, with or
without listhesis, and decreasing space between the adjacent pedicles
results in foraminal stenosis. Patients with stenosis secondary to
degenerative scoliosis suffer a similar pathophysiology as a cause of
their neurogenic claudication—namely, a vascular insufficiency to the
neural elements secondary to the stenosis, which is generally worsened
by lumbar extension.

Clearly, vascular claudication and neurogenic
claudication occur in similar patient populations, and it is important
to distinguish the true cause of the patient’s leg pain. A careful
history, palpation of distal pulses, examination of feet and skin, and,
if indicated, referral to a vascular specialist may be needed. In
general, neurogenic claudication is improved by forward flexion of the
spine, including sitting, and it may be worse going downhill because
hyperextension is necessary (see Chapter 147).
However, at least some patients with stenosis secondary to degenerative
scoliosis have reported that their extremity symptoms are not reliably
relieved by forward flexion (11).

Patients with degenerative scoliosis can be managed
according to the conditions that cause the most symptoms. For example,
the patient with more back pain secondary to the degenerative disease
can be managed successfully using nonsteroidal anti-inflammatories,
rest, physical therapy, cardiovascular conditioning, and, occasionally,
bracing. Patients with neurogenic claudication may respond to any of
these measures but may receive relief from epidural cortisone
injections. Bracing can be used on occasion for the patient with mild
degenerative scoliosis with back pain only. Rigid bracing has not been
shown to prevent progression in adults with scoliosis. However, bracing
may be a reasonable alternative for a patient who has a degenerative
scoliosis with mild to moderate progression, but who is medically
unable to tolerate a major reconstructive procedure.

Bracing may need to include a rigid molded thoracolumbar
orthosis for more severe scoliosis or kyphosis, or it may simply be a
lightweight, corset-type brace for milder curves. However, since
symptom improvement is the primary goal, rather than curve control,
results with a specific patient will be the final determining factor.

As for adult idiopathic scoliosis, pain, curve, and
neurologic deterioration are the main indications for surgical
intervention. In general, bracing in adults is discouraged because it
does not halt progression and may result in patient dependence on the
brace and associated trunk deconditioning. However, in certain cases,
such as an elderly patient who is too ill to tolerate a major surgical
procedure, or a patient whose severely osteoporotic bone is too weak to
support instrumentation, bracing may slow progression or attenuate the
pain symptoms.

Determining whether a patient’s back pain can be
improved by stabilization and fusion of her degenerative scoliosis can
be difficult. Once surgery has been deemed likely to help such a
patient, however, choice of the fusion levels requires consideration of
curve pattern, sagittal and coronal balance, pain locale, levels
needing decompression, and the presence of degenerated or listhetic
levels, as well as patient expectations and activity levels. Facet
blocks, discography, and nerve root blocks may be helpful in
determining symptomatic levels, although their predictive value for
fusion surgery has not been proven. Grubb et al. (12)
used provocative discography to help determine fusion levels in adult
scoliosis patients (degenerative and idiopathic) and felt that this
aided them in their surgical planning. However, in their study, all
positive discograms were at morphologically abnormal levels, and it is
not clear whether they might have included such levels based on
radiographic or magnetic resonance imaging (MRI)–determined
degenerative levels. Fortunately, fusion for back pain secondary to
scoliosis appears more predictable than fusion for back pain secondary
to degenerative disc disease without deformity. We do not routinely
perform discography in these patients, because it

has not proven of benefit in predicting the outcome of fusion surgery.

Patients with degenerative scoliosis and neurogenic
claudication should have their stenosis decompressed concurrently with
stabilization of the curvature. In most patients, an MRI will give
adequate information for localization of stenotic levels; in some
patients, however, the lateral deformity or rotatory component
precludes clear delineation of the anatomy. In these cases, computed
tomography (CT) or myelography is indicated for preoperative planning.

For patients with limited regions of spinal stenosis,
neurogenic claudication, and only mild degrees of scoliosis, it may be
reasonable to address the compressive symptoms with laminotomy,
laminectomy, or foraminotomy as needed. Aggressive decompression can
result in curve progression; this isolated procedure should be reserved
for milder cases in which limited decompression can be expected to help
the patient. Be sure the patient understands the possibility of curve
progression and recurrence of symptoms.

For patients with limited disease, a posterior fusion
alone may be sufficient. The majority of patients with degenerative
scoliosis will require instrumentation and grafting to achieve fusion
over multiple segments that require stabilization. Because of the
increased pseudarthrosis rate with multiple-level fusions, it is rare
to have a patient who can be managed without instrumentation. However,
certain older patients, particularly the medically fragile, may better
tolerate laminectomy and limited uninstrumented fusion (i.e., at the
level where there is a degenerative spondylolisthesis). In some
patients, moderate to severe osteoporosis may preclude fixation, but,
as with laminectomy alone, there is a risk of curve progression and
recurrence of symptoms. Therefore, this approach is limited to patients
who clearly understand the limitations of what surgery can accomplish
for them and are willing to risk recurrent symptoms. In general, we
have not found age or osteopenia to be a contraindication for fusion
with instrumentation.

Selection of fusion levels should take into account
several factors. The levels that should be fused should include at
least the entirety of the symptomatic curve, but often additional
levels must be included to address symptomatic degenerative levels and
permit maintenance or restoration of coronal and sagittal balance.
Generally, preoperative bending films can help predict the amount of
correction that can be obtained after exposure, facetectomy, and
application of appropriate corrective forces. The end vertebra,
particularly distally, should be a vertebra that is level on side
bending. Sagittal balance is exceedingly important to consider,
particularly because many of these patients have osteoporosis. Most
degenerative curves are kyphotic; if the kyphosis is not flexible, a
combined anterior–posterior approach may be indicated to achieve
sagittal realignment and successful arthrodesis. It is also important
not to end the fusion at a kyphotic segment. Many of these patients
have lumbar or thoracolumbar curvatures, and including only the major
curve often can result in ending the fusion at the mid or lower
thoracic spine—in the middle of the kyphosis. Such patients are at
considerable risk for development of progressive junctional kyphosis,
and in general it is best to include the minor compensatory thoracic
curve and end the fusion at the end vertebra of the kyphosis (usually
T-4 or T-5).

Only in patients with acceptable bone quality and a
nonkyphotic thoracolumbar junction can the fusion safely stop at the
thoracolumbar junction. Choosing the distal end vertebra can be
difficult in the patient with degenerative scoliosis and low back pain.
Deciding whether L-4–L-5 and/or L-5–S-1 is symptomatic is crucial
because long fusions to the sacrum generally necessitate combined
anterior and posterior surgery and have a higher rate of complications.
Not including a symptomatic level will result in limited pain relief,
however, and thus it will decrease the success of the surgery. In
addition, fusions ending at L-4 or L-5 are at risk for development of
symptomatic degeneration below the fusion. This development 5–10 years
after the surgery may be acceptable for the older patient, but its
occurrence 2 years or so after the surgery is not. Therefore, consider
whether a more distal fusion is indicated. Involvement of the
lumbosacral region is very common in degenerative scoliosis, and the
majority of these patients require combined anterior and posterior
spinal fusion to the sacrum.

Many patients with degenerative scoliosis also have
spinal stenosis as part of their degenerative process. As part of
preoperative planning, evaluate with an MRI or CT/myelogram any patient
with degenerative scoliosis who notes leg pain or buttock pain. As
previously noted, the MRI is adequate for many patients; with greater
degrees of curvature, however, CT/myelography gives better bony detail
and permits better understanding of the anatomy in the presence of the
curvature. It is important to identify symptomatic levels of stenosis
so that decompression can be performed at the time of posterior fusion.
In most cases, this can be determined anatomically according to
dermatomal levels and nerve root distributions; however, occasionally,
selective nerve root injections may be needed to determine which levels
with mild to moderate degrees of stenosis are the symptomatic ones.

Once laminectomy has been performed for decompression,
pedicle screw instrumentation may be needed to attain fixation.
Generally, fusion rates are improved with instrumentation, particularly
in patients with conditions such as degenerative scoliosis (13).
As with deformity surgery in general, try to visualize the medial wall
of the pedicle before screw placement, to correctly account for spinal
rotation. This is a simple matter after laminotomy or laminectomy has
already been performed. Frazier et al. (8)
reported on patients who underwent decompression for spinal stenosis,
including 19 who had at least 15° of scoliosis preoperatively. The
majority of their patients with scoliosis did not have fusion performed
at the time of decompression. They found that a greater degree of
preoperative scoliosis was associated with less improvement in back
pain. We have not found curve severity to correlate with outcomes of
reconstructive surgery in these patients. We do take a more aggressive
approach, however, preferring to fuse patients with scoliosis who are
undergoing a laminectomy even if the underlying medical condition
permits only limited fusion.

Selection of fusion levels and instrumentation guidelines are otherwise as noted in the prior section.

If they are fairly healthy, the majority of patients
with degenerative scoliosis will require anterior and posterior
procedures to achieve fusion, as well as coronal and sagittal balance.
There are several indications for combined techniques in this complex
patient population.

As with posterior instrumented fusions, segmental
fixation is preferred for combined surgery in this patient population.
Sublaminar wires may be used as a component of the fixation, but use
fixed components (hooks in a claw construct in the mid and upper
thoracic spine, pedicle screws at the thoracolumbar junction) at the
proximal end of the construct to decrease the risk of junctional
kyphosis.

When the patient can tolerate it, perform both
procedures under a single anesthetic to lower overall incidence of
complications, nutritional depletion, and blood loss (5,21,24).
Older patients, particularly those with coexisting medical conditions
or significant osteoporosis, may be less able to tolerate the lengthy
anesthetic, however. Older patients with significantly osteoporotic
bone may experience increased blood loss, which can lead to development
of a coagulopathy during a prolonged procedure.

If the combined procedures in these older patients
cannot be completed in 8–10 hours, then stage the procedure. The
scheduled delay between stages may be 3–7 days, depending on coexisting
medical conditions, the age of the patient, and scheduling issues. The
occurrence of complications, however, may further delay the
second-stage procedure.

Staged spinal surgery can result in nutritional
depletion, which may lead to an increased incidence of infection,
pneumonia, and urinary tract infection (5,21,24). We have shown that, particularly in the older patient population, use of total parenteral nutrition may decrease the

rate of nutritional depletion, which may in turn decrease the risk of complications (15).

Grubb et al. (12) have found an
average of 70% reduction of pain in patients fused for painful
degenerative scoliosis, which is somewhat less than that seen for
patients fused for painful adult idiopathic scoliosis (80% pain relief).

Recent advances in minimally invasive surgery have
suggested that endoscopic surgery, both thoracoscopy and lumbar
endoscopy, may result in lower morbidity and decreased length of
hospital stay (20,26).
Unfortunately, such techniques are difficult to learn and have not yet
been proven to demonstrate comparable fusion rates to that achieved in
open procedures. In general, for degenerative scoliosis, the indicated
anterior procedure is in the lumbar or lumbosacral spine. Currently,
most of the lumbar endoscopic techniques have concentrated on
screw-in–type cages, which are not well suited for degenerative
scoliosis because of the presence of multiplanar deformity.