PREVENTING POSTLAMINECTOMY ADHESION - A NEW EXPERIMENTAL-MODEL

Study Design. The efficacy of various interpositional membranes for prevention of extradural adhesion was investigated by a new animal model that quantified the biomechanical effect of scar formation. Twenty-one dogs were treated with autologous free fat graft, hyaluronic acid or no interpositional membrane after undergoing two-level laminotomy, nerve root exploration, and disk injury. An additional 11 dogs that did not undergo spine surgeries served as control animals. Objectives. Inter-animal variability in inherent propensity to form scar was first measured before any spine surgery. Twelve weeks after spine surgery, the lumbosacral spine of each dog was harvested en bloc for biomechanical testing of extradural adhesion ultimate load. Scar stiffness coefficient was also calculated. Summary of Background Data. Adhesion ultimate load was significantly less in the nonoperative control group when compared with the fat graft and no interpositional membrane group, but not when compared with the hyaluronic acid group. A beneficial effect of hyaluronic acid in lowering adhesion ultimate load was demonstrated, although a statistically significant difference from the fat graft and no interpositional membrane groups was not reached. No difference in scar stiffness coefficient was found between the four groups. Methods. A new experimental model allowing objective biomechanical quantification of the effect of postop-erative scar was described. Ultimate load of adhesions to both nerve roots and dura was measured. A biochemical assay that determined collagen content was also used to assess inter-animal propensity to form scar after a standardized surgical insult. Results were compared with other relevant studies. Results. Findings suggest a beneficial effect of hyaluronic acid in decreasing the biomechanical strength of extradural adhesions following laminotomy, nerve root exploration, and disk injury when compared with use of fat graft or no interpositional membrane. These results support other recent investigations that study the use of hyaluronic acid treatment in a laminectomy model. The adverse consequence of intraoperative epidural bleeding was also demonstrated. Conclusions. The new experimental model described in the current study was reproducible and permitted objective quantification of the effect of postoperative adhesion rather than measuring its mere presence. A beneficial effect of hyaluronic acid treatment and a lack of such beneficial effect of free fat graft interpositional membrane was suggested. The importance of avoiding active epidural bleeding was also evident.