Incorporation of polylactide-polyglycolide in a cortical defect: neoosteogenesis in a bone chamber

One hundred-micron-thick threads of 40-kDa copolymer polylactide:polyglycolide (PLGA) in a 50:50 molar ratio in bone chambers were implanted in rabbit tibias. Weekly intravital microscopic observations were used to assess trabecular ingrowth and PLGA absorption, processes referred to as incorporation. Nineteen rabbits were observed from the 3rd (W3) to the 10th or 12th (W10/W12) week postimplantation. Analysis of digitally processed video images obtained weekly showed that PLGA absorption was completed in about 8-10 weeks and trabecular ingrowth delayed to about 1 week slower than its control value. Four of the bone chambers showed PLGA unraveled by week 3, no trabecular ingrowth, and significantly reduced neovascularization. No such apparent inhibitory effects were observed in bone chambers that displayed PLGA absorption. No causal link could be established between the rate of neoosteogenesis and the rate of PLGA absorption, but it was clear that incorporation slowed and rapid degradation inhibited bone regeneration. It was concluded that copolymer synthesis and postsynthesis processing must result in a synthetic with a predictable micro- and macro-molecular structure before one can predict its incorporability in a given reconstruction or fixation site.