Healing of critical-size segmental bone defects in the sheep tibiae using bioresorbable polylactide membranes

Bioresorbable polylactide membranes were used to treat critical-size segmental defects in the sheep tibiae. Six different experimental groups (3 animals in each) were investigated. These included defects treated with polylactide membranes with or without perforations, single- or double-tube membrane designs, and were treated with or without cancellous bone grafting. Defect healing was assessed radiographically (plain radiography, CT) and histologically at 16 weeks post implantation. In all animals with bone defects treated with membranes without bone grafting, a non union developed and persisted until 16 weeks. Defect healing was only observed in the animals in which autogenous bone graft was used along with perforated membranes. The presence of perforations improved bone graft reconstitution as compared with historical controls (bone graft in combination with non perforated membranes). There was more bone formed in the defects covered with the double membranes (tube-in-tube) than in those covered with the single tube, despite higher graft volume used in the latter. In the defects covered with tube-in-tube membranes, new bone was formed preferentially within the space between the tubes resulting in a radiographically and histologically denser appearance. The thickness of new bone between the tubes had a thickness corresponding to that of the intact cortex. The study demonstrates that the tube-in-tube membrane is superior to the single membrane design with regard to the nature and extent of defect healing. The perforated polylactide membranes seem to enhance reconstitution of the bone graft within the defect. Further studies are required to better understand the mechanisms of bone graft reconstitution in the critical-size segmental bone defects and the role of perforated polylactide membranes in this process.