HETEROTOPIC OSTEOINDUCTION IN A RAT MEMBRANE-ISOLATED LATISSIMUS-DORSI ISLAND FLAP - A PILOT-STUDY

Applying our knowledge of heterotopic osteoinduction by bone morphogen etic protein (BMP) and demineralized bone matrix (DBM), we sought to i nduce ossification of membrane-isolated latissimus dorsi flaps in the rat. Our aim was to produce an animal model for a versatile ''custom-m ade'' bone island flap which could be used as a substitute for bone. T en 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, Goretex(TM) Or OpSite(TM) membranes. We applied 3-9 mg partially purified bovine B MP or 0,1 . 0,25mg BMP bound covalently to type IV collagen with 15mg DBM inside the flaps. We had five animals with eight implants of BMP a nd DBM in latissimus muscle pouches as rat bioassay controls. The resu lts were evaluated after a period of three weeks using soft X-ray radi ography and histology with hematoxylineosin-azure II and Alcian blue s tains. Positive radiological results were observed in 10/10 flaps (100 %), in controls in 7/8 (87,5 %). Positive histological results compri sed 8/10 (80 %) and in controls 7/8 (87,5 %). Two flaps (20 %) showed partial necrosis. These did not lower the percentage of either positiv e histological or radiological findings, but exemplified some of the p roblems which are faced in this kind of tissue engineering.