Heterotopic osteoinduction in a rat membrane-isolated latissimus dorsi island flap. A pilot study

Applying our knowledge of heterotopic osteoinduction by bone morphogenetic protein (BMP) and demineralized bone matrix (DBM), we sought to induce ossification of membrane-isolated latissimus dorsi flaps in the rat. Our aim was to produce an animal model for a versatile "custom-made" bone island flap which could be used as a substitute for bone. Ten latissimus dorsi island flaps in nine Wistar rats, 5-6 weeks of age, were prepared using microsurgical techniques in aseptic conditions. The flaps were isolated from other tissues with silicone, Gortex or OpSite membranes. We applied 3-9 mg partially purified bovine BMP or 0.1 -0.25mg BMP bound covalently to type IV collagen with 15mg DBM inside the flaps. We have five animals with eight implants of BMP and DBM in latissimus muscle pouches as rat bioassay controls. The results were evaluated after a period of three weeks using soft X-ray radiography and histology with hematoxylin-eosin-azure II and Alcian blue stains. Positive radiological results were observed in 10/10 flaps (100%), in controls in 7/8 (87.5%). Positive histological results comprised 8/10 (80%) and in controls 7/8 (87.5%). Two flaps (20%) showed partial necrosis. These did not lower the percentage of either positive histological or radiological findings, but exemplified some of the problems which are faced in this kind of tissue engineering.