Polylactide membranes in the treatment of segmental diaphyseal defects: Animal model experiments in the rabbit radius, sheep tibia, Yucatan minipig radius, and goat tibia

Resorbable polymeric membranes have many potential applications in the treatment of bone loss. A resorbable membrane can be fabricated to have: (1) a custom in vivo life span, (2) specific mechanical attributes, (3) an optimal micro or macro porosity for nutritional diffusion or vascular ingrowth, and (4) carrier properties for the timed delivery of drugs, organic compounds, or inorganic substances, or cells. Because the polylactide class of polymers has a proven record of human biocompatibility as well as a wide range of synthetic characteristics, polylactide membranes have been studied for their utility in regenerating diaphyseal bone defects. Using a variety of animal models, the basic mechanism of bone regeneration has been elucidated. A resorbable membrane functions by: (1) exclusion of nonosseous tissues, (2) maintenance of an intramedullary canal, and (3) the provision of an extralumenal scaffold for periosteum regeneration and revascularization. Microporous membranes have been studied in small defects which do not require stabilization-the rabbit and minipig radius models where the ulna is left intact (1-4 cm diaphyseal defects). Larger defects (4-7 cm middiaphysis) have been studied in the sheep and goat tibia where intramedullary (IM) nailing or double plate stabilization was used. So far the parameters of polylac tide composition, biocompatibility, porosity, adjunctive internal fixation, and the suitability of membranes as chemical delivery devices have been investigated in these animal models. Large defects successfully treated with polylactide membranes suggest that the optimum construct will be a perforated, thin, microporous membrane used to span an appropiately stabilized defect.