Abstract
Background and objective: In guided tissue regeneration a membrane is used for defect isolation to protect it against invasion from surrounding tissues and to keep intrinsic healing factors ‘in situ’. This technique has been successfully used in maxillo-facial surgery, but short experience has been reported in long-bone defects, with synthetic membranes and with variable results. In the other hand, calcification and ossification inside the arterial wall have been described. The aim of the study was to evaluate the use of cryopreserved aorta allografts as membranes for guided tissue regeneration in comparison with expanded poly-tetra-fluoro-ethylene (e-PTFE) synthetic membranes.
Methods: Prospective, randomized, blinded study in 15 New-Zeland rabbits. 10 mm mid-diaphyseal defects were created in both radii: 10 defects were covered with a cryopreserved aortic allograft as a tube, 10 with an e-PTFE membrane and 10, with no barrier membrane, served as controls. Animals sacrifice at 6-12-24-30 months. Studies: X-rays, CT, MR, morpho-densitometric analysis, electronic and optical microscopy. Immuno-cytochemistry on tissues and arterial wall cells cultured.
Results: None of the control defects healed. Nine defects covered with an artery completely reconstituted, but only six of those covered with e-PTFE, with a nearly normal cortical-medullar pattern and with progressive increasing in density and thickness of medullar and cortical to values similar to those of the normal bone. Histological studies showed no inflammatory response to the arterial graft, direct union between the artery and the regenerated bone and even mature bone between the elastic laminae of the arterial wall, suggesting superior biocompatibility properties. Immuno-cytochemistry and ultrastructural studies suggest that arterial allografts could act not only as membrane barriers, with additional osteoinductive properties due to trans-differentiation of viable arterial wall cells (endothelial, smooth muscle and/or tissue specific stem cells) towards osteoblastic cells, and also due to ossification secondary to changes in proteins of the arterial extracellular matrix. This could be the application of the process of arterial wall calcification and ossification (usually seen in arteriosclerosis, gender, diabetes or kidney failure) for regeneration of long-bone defects.
Conclusion: Cryopreserved aortic allografts can be used as membrane barriers for guided bone regeneration, with superior results to e-PTFE membranes.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
