BONE REGENERATION WITH RESORBABLE POLYMERIC MEMBRANES .3. EFFECT OF POLY(L-LACTIDE) MEMBRANE PORE-SIZE ON THE BONE HEALING-PROCESS IN LARGEDEFECTS

Poly(L-lactide) membranes of various pore sizes: microporous, medium p ore size (10-20 mu m), and large pore size (20-200 mu m) were implante d in 15 mature New Zealand female rabbits to cover a 10-mm diaphyseal defect created in the radius. Five rabbits were implanted with each me mbrane. No internal fixation was used, as it was assumed that the inta ct ulna splints the radius adequately. Postoperative radiographs revea led 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 fragme nt ends. The bone regeneration took place in the majority of the cases under investigation, regardless of the pore size of the polymeric mem branes 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 impla nted respectively with microporous membrane, medium pore-size membrane , and large pore-size membrane showed complete regeneration of bone wi thin the defects. It is suggested that the primary function of the mem brane used to cover bone defects is to preserve the osteogenic compone nts present in the space under the membrane from escaping and support the growth of cells within the ''medullary cavity'' formed by the tubu lar implant. (C) 1996 John Wiley & Sons, Inc.