Inhibition of epidural scar formation after lumbar laminectomy in the rat.

Abstract

An animal model of laminectomy in rats was used to study scar tissue formation around the spinal cord. Dexamethasone, in controlled-release form, was tested in this system for its ability to decrease fibrous tissue formation. The results were evaluated to determine whether dexamethasone in a biodegradable controlled-release vehicle could be used to limit scar tissue formation around the spinal cord after laminectomy. Steroids can delay the formation of scar tissue. Continued treatment with dexamethasone results in various unacceptable side effects. Use of biodegradable controlled-release vehicles to deliver drugs may allow for prolonged low-dose treatment, concentrated at the surgical site, thereby avoiding side effects. Forty-four Sprague Dawley rats underwent laminectomies and were treated with dexamethasone in one of two controlled-release vehicles or with vehicle alone. After 4 weeks, the rats were killed and histologic sections prepared from the spines were examined and graded by a pathologist. In addition, the dexamethasone preparations were introduced into Hunt-Schilling wound chambers, which were implanted in rats. Four weeks after implantation, the wound chambers were removed and the tissue inside was assayed for DNA and protein content. Dexamethasone acetate (Decadron, MSD, West Point, PA) significantly reduced the density of the scar tissue undermining the laminas. Steroids embedded in polymer did not change the scar formation in the back, but did decrease protein and DNA values in wound chamber tissues. Long-term release of small amounts of steroid from the polymer poly-carboxy-phenoxypropane does not appear to reduce scar at laminectomy sites but does decrease the protein:DNA ratio in wound chambers. In contrast, Decadron does not significantly alter the biochemistry of wound chamber tissue but does reduce scar in the back.