Significance of the mass-compression effect of postlaminectomy/laminotomy fibrosis on histological changes on the dura mater and nerve root of the cauda equina: an experimental study in rats

Purpose The precise mechanism and pathological role of postlaminectomy/laminotomy fibrosis (PLF) in postoperative neurological deficits have not been established. Many studies use magnetic resonance imaging (MRI) to prove that there is no consistent correlation between PLF and postoperative neurological deficits and back pain (PNDBP). Therefore, we assumed that the direct-compression effect may not be the only factor but that other neurological deficits associated with pathological mechanisms should exist and need more investigation. The purpose of this study was to compare over time the differences and changes in histopathological properties of PLF in rats.Methods We used a rat model with walking-track analysis for neurologic evaluation, grading scale to evaluate PLF, histomorphometric measurements of dura sac diameter, and histological tissue reactions (dura mater and spinal rootlets) juxtaposed to the postlaminectomy/laminotomy defect. The 54 adult Sprague–Dawley rats were divided into laminotomy (n = 18), laminectomy (n = 18), and sham-operation groups (n = 18). All groups were subdivided into three equal subgroups based on different postoperative time points (1, 2, and 3 months). All sections of vertebral column were stained with hematoxylin and eosin and with Masson’s trichrome.Results The results showed that only a slight compression effect reflected by nonsignificant changes in the maximum anterior-posterior diameters within the dura sac, in the walking tract test, and increased grades of PLF over time. In addition, significant pathological inflammatory changes, such as thickening of the dura mater, axonal swelling, and neovascularization, were found in the post-laminectomy/laminotomy groups at each time point.Conclusion Laminectomy-/laminotomy-related inflammation may lead to PLF, and these pathological changes may be the main cause of postoperative neurological deficits. These findings show that research on preventing PLF should include perioperative modulation of inflammatory reactions induced by laminectomy/laminotomy.