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Isthmic Spondylolisthesis
|
 Spondylolisthesis
refers to the relative translation of adjacent Vertebra
in the spine. Anteriorlisthesis means forward translation
of the upper vertebra. Although spondylolisthesis can
be caused by various pathologic states in the spine,
Isthmic Spondylolisthesis is produced when bones (pars
interarticularis) connecting the facet joints in the
posterior spine are fractured causing anteriolisthesis
of the vertebra. The pars serves as a checkrein for translation
movement of the vertebra and when fractured, the vertebra
are allowed to move past each other producing symptoms
ranging from mild low back ache to severe neurologic
deficits. Although L5-S1 is most commonly affected, isthmic
spondylolisthesis has been found at every lumbar level.
Why the pars fractures is incompletely
understood, but research has revealed some telling
facts. Approximately 5-8% of the ambulatory (walking)
population older than age 5 has pars fractures. Pars
fractures interestingly have not been found in two
populations of humans: fetuses and patients who have
been paralyzed and non-ambulatory from birth. Moreover,
pars fractures are found in increased frequency in
athletes who hyperextend their spine such as gymnasts
and football inside lineman. These facts taken together
indicate that pars fractures are in fact stress fractures
produced when the predisposed, weakened pars interarticulars
is subjected to repetitive hyperextension forces. Why
certain patients become variably symptomatic is unknown.
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 The
magnitude of symptoms caused by spondylolisthesis
does correlate with the degree of anteriolisthesis
of the vertebra. A grading system has been defined
to characterize the degree of slip: the full front-back
depth of the vertebra is divided into fourths and
a spondylolisthesis is graded 1-4 based on the quarter
percentage of slip. For example, a grade 2 slip is
defined as the upper vertebra moving 50% on the lower
vertebra. A grade 5 slip means that the vertebra
has completely dislocated off the lower vertebra.
In general, grade 4 slips may present with more low
back pain and neurological problems than a grade
1 slip, although this rule does have exceptions.
One study has suggested that 2/3rds of grade 2 slips
could be treated non-operatively, while larger slips
uniformly needed treatment including surgery. In
general though, approximately 50% of individuals
with Isthmic spondylolisthesis will seek treatment
for low back pain at sometime during their life. |
Low back
pain and nerve compression symptoms are found in patients
with isthmic spondylolisthesis. For the same reason that
the vertebra translate relative to each other, the pars
fracture permits abnormal vertebral motion creating low
back pain. Chronic tearing and degeneration of the disc
may actually be the pain  generator,
but this has never been proven. This chronic abnormal
motion (sometimes referred to as instability) also creates
a situation where the pars fracture cannot heal. New
bone forms around the fracture and may actually compress
the nerves which pass in proximity. This compression,
plus the nerve stretch caused by the forward motion of
the vertebra, is responsible for the nerve irritation
and leg pain.
Treatment is designed to stop either
the progression of the slip or the abnormal motion
which creates pain. As with most spinal problems, children
are treated for different reasons than adults. In children,
low back pain and associated nerve irritation causing
leg pain and hamstring tightness can initially be treated
by rest and cessation of athletic activity. In some
cases, bracing may be attempted. Documented progression
of the slip and pain refractory to conservative measures
are indications for surgery.
Adults should initially be treated
with rest, anti-inflammatories, and physical therapy
as symptoms subside. Slippage does not usually progress
in adults. Studies have shown that subtle neurological
deficits can exist in 18% of patients without surgery,
but that severe neurological deficits are rare. It
is for this reason that serial neurological examinations
should be performed during the course of conservative
treatment. Patients with symptoms refractory to conservative
treatment may be candidates for surgery. |
The
current state of the art is fusion surgery for isthmic
spondylolisthesis. To view an animation of the surgery,
click on the projector below.
How this fusion will be done depends on multiple
factors. As the vertebra translates, it also tilts
producing the characteristic slip angle. The slip angle
produces kyphosis in the lumbar spine which may need
to be corrected if severe. It is generally held that
if correction of the spondylolisthesis is attempted,
that it is more important to correct the slip angle
than translation. These factors might determine whether
a fusion surgery can be effectively done from the back
only versus a front and back operation. In my hands
it is impossible to correct slip angle without a front
operation. The rate of fusion failure (pseudarthrosis)
for posterior-only fusion is 25% meaning that only
75 out of 100 patients will obtain a solid fusion with
this technique. In my practice, in approximately 300
patients with front and back surgery for spondylolisthesis,
none required revision surgery for failure of fusion.
Unequivocally, Isthmic Spondylolisthesis should not
be treated with decompression surgery only. Anterior-only
surgery for spondylolisthesis is risky because the
potential instability created by the pars fractures
does not lend itself to correction by the placement
of dowel grafts or cages primarily. Each patient should
be individualized and a specific operative strategy
implemented. |
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| In most cases the instrumentation
and fusion for Isthmic Spondylolisthesis is done from L4
to S1.
After 25 years of clinical experience, I am convinced that stopping a fusion
at L5-S1 in an adult significantly increases the possibility of L4-5 adjacent
segment degeneration.
This
is because the instrumentation from the L5 pedicle screws
are very close to the L4-5 facet joints, changing their
mechanics. Moreover, the L5-S1 inner spondylolisthesis
is in kyphosis and there is a junctional hyperlordosis
so that compensation can occur. This hyperextension causes
significant alterations of facet contact structure and
change of the IAR (instaneous axis of rotation) and constant
pressure. Moreover, the connection of the L4 to L5 ligaments
is incomplete because of the bilateral pars fracture and
the Gill fragment being a free-floating entity. There,
the adjacent segment normal tethering mechanisms are not
intact. The L4-5 disk space is still under a significant
amount of shear and because it is already predestined to
degeneration because of its MR view, most adults are fused
L4-S1. For more information, you can read this research
study that Dr. Pashman participated in: In
Vivo Analysis Of Canine Intervertebral And Facet Motion. |
Related
links:
ASF/PSF
Improves Lumbar Sagittal Alignment in Multi-level
Fusions for Isthmic Spondylisthesis
Spondylolisthesis
cases performed by Dr. Pashman
Posterior Spinal Fusion
Degenerative
Spondylolisthesis
Spinal Balance
Anterior Lumbar
Fusion
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