Peridural fibrosis (or scarring) after spine surgery may be associated
with persistant leg and low back pain, the so-called failed back syndrome.
The relationship between peridural fibrosis and symptoms has been a
matter of some debate. A recent prospective study using Magnetic Resonance
Imaging (MRI) to evaluate patients after routine diskectomy identified
a strong correlation between peridural scar formation and recurrent
sciatica.5 In addition, reoperation on patients who have undergone previous
laminectomy is clearly hindered by the presence of extensive epidural
fibrosis adherent to the underlying dura mater. Dissection through this
dense scar tissue is associated with an increased risk of complications
including dural tears, nerve root injury, and bleeding.
Various
strategies have been devised to limit the development of peridural fibrosis
following spine surgery including modifications in surgical technique;
biochemical and pharmaceutical interventions to control the inflammatory
and wound repair processes; and the use of interposed material to serve
as a mechanical barrier between the dura mater and overlying paraspinal
tissue.
The most favorable results thus far have been generated through use
of various mechanical barriers. Gelfoam, silastic, and sodium hyaluronate
have all been used successfully but with inconsistent results. Interposed
free fat graft remains the most commonly used strategy, however numerous
complications have been reported including seroma formation, scar dimpling,
and difficulty in harvesting sufficient quantity of graft in thin patients,
particularly in the face of large laminectomy defects. Of even more
concern, fat graft migration has been identified as the cause of several
cases of cauda equina syndrome.6
We are
in the process of studying the efficacy of a new class of material known
as elastomeric polypeptide matrices in limiting the development of peridural
fibrosis and adhesions. Preliminary results from a recently completed
phase I study are promising and indicate that specific formulations
of these matrices create an effective barrier between the dura mater
and overlying paraspinal tissues, thereby preventing the formation of
tethering adhesions.
A rabbit
laminectomy model was designed in which two different polymers were
tested in both membrane and gel form. The material was randomly placed
at either L5 or L6 with the other site serving as an internal control.
Animals were sacrificed at 8 weeks and subjected to gross pathologic
and histologic analysis. Histological sections were assessed using an
optical microscope, and the relative contact surface of fibrotic tissue
adherent to the dura was estimated using computer-assisted image analysis.
Two animals were additionally evaluated with serial MRI utilizing an
experimental 4.2 T magnet and custom-designed surface coil. At 8 weeks
overlying muscle and repair tissue was less adherent to the dural membrane
where the elastomeric polymers were used. In addition, the 2 MRIs appeared
to accurately identify epidural fibrosis.
The need
for safe and reliable prevention of epidural adhesions following spinal
laminectomy makes the positive preliminary results from this study quite
compelling. A phase II grant has been obtained to study this material
in a sheep model. Detailed anatomical descriptions of the sheep spine
have already been published and the larger size of the sheep spine will
allow direct mechanical testing and potentially clearer radiographic
imaging of the postsurgical specimens.
