Bone regeneration with resorbable polymeric membranes. III. Effect of poly(L-lactide) membrane pore size on the bone healing process in large defects.

Poly(L-lactide) membranes of various pore sizes: microporous, medium pore size (10-20 microns), and large pore size (20-200 microns) were implanted in 15 mature New Zealand female rabbits to cover a 10-mm diaphyseal defect created in the radius. Five rabbits were implanted with each membrane. No internal fixation was used, as it was assumed that the intact ulna splints the radius adequately. Postoperative radiographs revealed the formation of hematoma within the bone defect. At the 2nd week after surgery, the hematoma was resorbed and the formation of new bone was noted radiologically either at the ends of the bone fragments or as osteophytes on the proximal and distal edges of the membrane. At 4 weeks, the newly formed bone was growing centripetally from the fragment ends. The bone regeneration took place in the majority of the cases under investigation, regardless of the pore size of the polymeric membranes used. There were, however, some differences in the intensity of the bone regeneration process. Although at 2 weeks after surgery bone formation was seen radiographically in all animals, at 6 months five rabbits of five, four rabbits of five, and three rabbits of five implanted respectively with microporous membrane, medium pore-size membrane, and large pore-size membrane showed complete regeneration of bone within the defects. It is suggested that the primary function of the membrane used to cover bone defects is to preserve the osteogenic components present in the space under the membrane from escaping and support the growth of cells within the "medullary cavity" formed by the tubular implant.