Reconstruction of large segmental defects in the sheep tibia using polylactide membranes. A clinical and radiographic report

Reconstruction of large segmental defects with conventional cancellous bone graft only is not recommended because the graft undergoes severe resorption even in a well vascularized muscular soft tissue envelope. The purpose of this study was to evaluate the ability of polylactide membranes to improve the healing process in a large diaphyseal defect which heals neither spontaneously nor after conventional bone grafting. A previously described and established 7 cm defect in the sheep tibia was reconstructed with resorbable membranes from poly(L/DL-lactide). Membranes with similar microstructure (15-50 mum pore size) but different macrostructure (non-perforated or perforated, 800-900 mum perforation size) where implanted in four animal groups. In group A, a non-perforated membrane was implanted without bone graft. In group B, a nonperforated membrane was combined with autologous cancellous bone graft. A perforated membrane in combination with autologous cancellous bone graft was used in group C. In group D a vascularized osteoperiosteal flap was wrapped over a perforated membrane and no graft was used. After an observation time of 16 weeks, stable defect reconstitution had occurred in groups C and D, whereas the defect remained empty in group A and the bone graft became necrotic in group B. There were no inflammations or sterile cysts in any animals and in group D the membranes were completely embedded in newly formed bone. We conclude that polymeric membranes of adequate composition and pore/perforation size in combination with autologous bone graft or vascularized periosteum allow for rapid and stable defect regeneration in the sheep model.