REGENERATION OF DIAPHYSEAL BONE DEFECTS USING RESORBABLE POLY(L DL-LACTIDE) AND POLY(D-LACTIDE) MEMBRANES IN THE YUCATAN PIG MODEL/

Objectives: To determine the effects of tubular resorbable polymer mem branes on the healing of a segmental diaphyseal bone defect. Design: A randomized prospective study using the minipig model. Animals were ev aluated with in vivo roentgenograms on a biweekly basis until explante d at twelve weeks. Setting: After surgery, animals were allowed unrest ricted activity and weight bearing between twenty-four and forty-eight hours. Animals: Fifteen yearling Yucatan minipigs. Intervention: A 2. 5- to 3.0-centimeter mid-diaphyseal defect was created in the middle t hird of the radius. Animals were assigned in groups of three to receiv e the following implants: (a) poly(L/DL-lactide), (b) poly(L/DL-lactid e)-CaCO3, (c) poly(D-lactide), (d) poly(D-lactide)-CaCO3, and (e) an u ntreated defect. No adjunctive internal or external fixation was used as the ulna was left intact. Main Outcome Measures: The limbs were stu died with in vivo anterior-posterior and lateral radiographs at biweek ly intervals for the presence and pattern of bone formation. All limbs were explanted at twelve weeks postimplantation for methylmethacrylat e embedding and histologic and microradiographic study. Results: The b one defects covered with membranes were completely reconstituted by si x to eight weeks. Untreated defects healed with less bone formation an d in a more disorganized pattern. Histologic evaluation of the implant s demonstrated that the entire lumen of the implant was filled with bo ne, with some periosteal bone formation occurring on the outer surface of the membrane. There was direct apposition of bone onto the membran e surface or minimal fibrous tissue interposition between membrane and new bone. There was no foreign body or adverse reaction to the membra ne. Untreated defects showed woven bone formation with clefts and irre gularly shaped margins occupied by fibrous tissues or surrounding musc le tissues. Conclusions: This study supports the concept that a membra ne enhances bone defect healing by excluding nonosseous tissues from a defect and providing structural scaffolding for periosteal and endost eal bone regeneration.