[ relationship between serum level of osteoprotegerin and post-laminectomy epidural fibrosis in rabbit]

Epidural fibrosis [EF] is part of natural physiological tissue response to laminctomy and it may be an important cause of failed back surgery syndrome [FBSS]. There is still no effective medical or surgical therapy for EF. Osteoprotegerin [OPG] is a soluble member of the tumor necrosis factor receptor family that might play a role in postoperative EF. The objective of this study was to evaluate the relationship between serum OPG level and EF after laminectomy. Sixty rabbits were employed and divided randomly into two groups. Group A contained 20 rabbits as controls and group B contained 40 rabbits that underwent bilateral laminecyomy at L4 and L5 lumbar levels under an approved surgical protocol. Serum sample was obtained after 8 weeks from all rabbits and then the animals in group B were killed in accordance with the guidelines for euthanasia. The spine segment from L3 to L6 was removed en bloc. The amount of scar tissue at the laminectomy defect was scored on an ordinal score from 0 to 3 with a scoring system similar to that of He et al. According to the amount of scar the rabbits in group B, were divided into two groups: B1 with low fibrosis [grade 0, 1] and B2 with high fibrosis [grade 2, 3]. The serum OPG level of groups A, B1 and B2 were determined using ELISA method. The one way ANOVA was used to assess significant difference among groups. Serum OPG level ranged from 0-4 Pmol/l with a median of 1.5 Pmol/l in group A, 0-6 Pmol/l with a median of 2.42 Pmol/l n group B1 and 0-6 Pmol/l with a median of 2.15 Pmol/l in group B2. There was not any significant difference in OPG levels among these 3 groups. This study showed no relation between OPG level and existence of postlaminectomy EF after 8 weeks