Prevention of epidural fibrosis after laminectomy: 3-week and 8-week study using a barrier sheet and hyaluronan gel

Abstract

Purpose of study: Epidural fibrosis contributes to failed back surgeries. Previously, many methods were used to reduce postlaminectomy scar with mixed results. The purpose of this study is to: 1) compare the effect of a thin barrier (Macropore) sheet and a hyaluronan (HA) gel using a control laminectomy model; 2) to examine the incisional wound integrity after treatment; and 3) to compare long-term and short-term results.Methods used: Bilateral laminectomies (L5 and L6) and a disc injury (L5–L6) were performed in 80 male adult Sprague-Dawley rats. There were four groups: 1) normal controls without surgery; 2) laminectomy without treatment; 3) HA gel and 4) a Macropore barrier sheet. The animals were sacrificed at 3 and 8 weeks for analysis. Sixty-six specimens were analyzed biochemically to determine the amount of total collagen from hydroxyproline content in the dura and the L5 nerve roots. Fourteen specimens were prepared and stained with Masson-Goldner Trichrome to assess collagen distribution. Twenty-seven healing surgical incisions were analyzed by uniaxial tensile testing to determine ultimate force, strain and prefailure stiffness. Statistics were performed using analysis of variance.of findings: Gross appearance and histology show that the untreated laminectomy scar becomes more adherent to the dorsum of the dura mater with time, whereas the barrier sheet and the HA gel prevented scar attachment to the dural sleeve in both the 3-week and 8-week study. The treatment groups showed significant (p<.0001 to .03) reduction of total collagen content in the laminectomy site in both time periods. However, the 8-week untreated group showed a significant (p=.0216) increase in total collagen content compared with the 3-week results. The HA and the Macropore barrier sheet each appeared to reduce scar around the nerve roots on histological sections, and the nerve roots were not as adherent to the adjacent pedicle grossly. However, biochemically the collagen content was not significantly different. The mechanical properties of incisional wounds increased significantly (p<.0001) between 3 weeks and 8 weeks. The ultimate strength, stress, strain and stiffness of untreated, HA and Macropore wounds were similar within each time point.Relationship between findings and existing knowledge: Wound healing experiments using HA are based on the concept of fetal healing. Fetal wounds heal without scar during the first two trimesters of gestation. Application of HA has been shown to decrease cutaneous scar formation in various models. Thus, HA represents a possible candidate for reduction of postlaminectomy scar formation. The barrier sheet, by walling off the overlying muscle may be effective in reducing cellular trafficking and vascular ingrowth into postlaminectomy defect. Because the barrier is a confined substrate, it should not interfere with normal posterior incisional wound healing. The current study confirmed the hypothesis that postlaminectomy scar formation can be attenuated by application of HA or placement of a particular barrier sheet. Furthermore, we show the antifibrotic agent used did not interfere with the incisional wound healing.Overall significance of findings: HA and Macropore barrier sheet treatment significantly reduced postlaminectomy peridural scar formation in this model without affecting the integrity of incisional wound healing. Furthermore, our results suggest untreated postlaminectomy scar is maturing with time, as indicated by increase collagen content and improvement of incisional mechanical properties.Disclosures: Device or drug: Healon. Status: approved. Device or drug: Macropore (70:30 absorbable poly L-lactide-co-D and Poly L-lactide). Status: approved.Conflict of interest: Jennifer Massie, grant research support: VA Merit Grant.