Use of a fibrillar polylactic acid homopolymer in sheep cranial defects

Guided tissue regeneration has been shown to permit osteoconduction in otherwise nonhealing cranial defects. The relative importance of preventing the prolapse of soft tissue versus the infiltration of individual connective tissue cells has not been determined. A fibrillar form of polylactic acid (PLA) was tested in 13-mm-diameter defects in the parietal bones of 12 sheep. The polymer was hypothesized to prevent the prolapse of dura and periosteum but allow entrance of individual cells. Control defects in the same sheep were either filled with autogenous bone shavings or left unfilled. The animals were killed at times ranging from 6 to 25 weeks and the defects examined grossly, radiologically, and histologically. The autogenous bone-filled defects were spanned by trabeculated bone by 6 weeks. The unfilled defects demonstrated prolapse of soft tissues into the defect; however, progressive centripetal bone growth was evident. The fibrillar PLA-filled defects were occupied by a full-thickness mixture of fibrous tissue interspersed with PLA. After 19 weeks, small "fingers" of bone were seen to minimally infiltrate the fibrous tissue. Although separation of the dura and periosteum was maintained by the fibrillar PLA, invasion of fibrous tissue restricted osteoconduction.