Guided bone growth in sheep: a model for tissue-engineered bone flaps

The emerging field of tissue engineering is yielding a variety of new strategies for bone replacement. In vivo assessment of candidate bone substitutes to demonstrate biocompatibility, degradability, and the ability to produce meaningful quantities of bone is essential prior to clinical use. We present results of a large animal model using formed plastic chambers implanted adjacent to the rib periosteum in sheep to fabricate vascularized bone flaps of different shapes. Chambers packed with morcellized corticocancellous bone graft, representing the most favorable natural circumstances for bone formation, were compared to empty chambers, representing the least favorable. Implants containing bone chips yielded formed blocks of vascularized bone after 6 weeks with evidence of remodeling after 13 weeks. Histomorphometric analysis demonstrated that there was full bone penetration into shallow (5 mm) chambers and 8.8 mm (+/-0.6) penetration into deep (10 mm) implants after 6 weeks. Molded bone segments failed to grow in empty chambers. This model presents a quantifiable range of bone forming potential to which different bone substitutes may be compared for usefulness in creating tissue engineered bone flaps for reconstructive surgery.