The properties of inducible membranes in animals and humans

Membranes form around spacers used in large bone defects. We studied the effect of the spacer material on the ability of the membrane to promote osteogenesis in an animal model and the gene expression patterns of membranes obtained from humans. Critical-sized osseous defects were created in the ulnae of 12 rabbits. Stainless steel (SS) or polymethymethacrylate (PMMA) spacers were inserted into the defects, and the animals healed for four or eight weeks. After sacrifice, samples of the membrane were grown in cell culture. Human membrane samples were collected for gene expression analyses. Cultures of rabbit membranes with bone marrow cells showed significantly greater alkaline phosphatase activity (PMMA) and mineral deposition (SS) than bone marrow cells alone. All membranes had elevated expression of osteoblast-related genes. Inducible membranes around orthopaedic implants likely contain active cells of the OB lineage and the spacer material may influence the healing properties of the membrane.