BONE REGENERATION WITH RESORBABLE POLYMERIC MEMBRANES - TREATMENT OF DIAPHYSEAL BONE DEFECTS IN THE RABBIT RADIUS WITH POLY(L-LACTIDE) MEMBRANE - A PILOT-STUDY

Tubular poly(L-lactide) membranes with a pore size of 5-15 mu m and a molecular weight of 70,000 Daltons were implanted into 24 New Zealand skeletally mature rabbits to cover 10-mm mid-diaphyseal defects of the radius of the forelimb. An identical defect on the contralateral limb was not treated with the membrane and served as a control. The animal s were killed at 1, 2, 4, 8, 12, 24, 36, and 64 weeks after implantati on, and radiographic and microscopic studies were conducted. The canal s of the polymeric tubes were initially filled with blood. At 2 weeks, there was direct woven bone formation within the polymeric tube in co ntinuity with the fragment cortices and its medullary canal. The forma tion of woven bone across the defect progressed until reconstruction o f the defect had occurred at 6-8 weeks. The bone continued to remodel throughout the observation period of 64 weeks. By 12 weeks, bone withi n the lumen of the implant consisted of cancellous bone and cortical b one lining the membrane walls. At 24, 36, and 64 weeks, the implants w ere filled with cancellous bone and cortical bone in direct apposition to the polymer membrane. For one implant, the newly formed woven bone had only incompletely filled the defect at 8 weeks. This resulted in a nonunion with a residual gap of 0.5 mm and the appearance of mature bone. There was extensive bone formation along the intraosseous membra ne in both control and implanted defects, although the untreated defec ts were rapidly filled with overlying muscle and soft tissues. The oss eous activity of the untreated defects appeared confined to the bone e nds by the interposed muscle and fibrous soft-tissue margins. The untr eated defects resulted in radial-ulnar synostosis along the intraosseo us membrane with cortical bone caps at the bone ends. The poly(L-lacti de) membrane remained intact throughout the 64-week period without evi dence of significant degradation. The membranes were encapsulated in a thin fibrous tissue. There was no histological evidence of acute or c hronic inflammation associated with the implants.