Novel approach to calvarial bone transport using a rabbit model

Calvarial defects sometimes require cranioplasty to protect the brain. Alloplastic materials, such as acrylic resin, hydroxyapatite ceramics, and titanium, involve various problems, such as vulnerability, infection, deformity resulting from growth, and high cost. We devised a new bone transport model in the rabbit based on the distraction osteogenesis theory of Ilizarov. Twelve Japan white rabbits with a mean body weight of 2.5 kg aged 12 weeks were used. Craniectomy (7 x 14 mm) was performed in 12 rabbits. Trapezoid bone osteotomy was performed anterior to the calvarial defect in 10 rabbits. The distraction device (Extension-plates) was fixed between the trapezoid bone island and the skull. Distraction was initiated 5 days postoperatively. The device was activated once every other day, with approximately 0.75 mm or 0.5 mm per activation. Bone distraction was continued until the rod could not be moved. The lengths of distraction were 4 mm in two cases, 5 mm in one case, 6 mm in one case, and 7 mm in two cases, with a mean of 5.5 +/- 0.56 mm. Both radiographic and histological findings showed osteogenesis by intramembranous ossification and trans-chondroid bone formation. Distraction osteogenesis has potential clinical applications in cranioplasty, especially in children because usage of autogenous bone is difficult if not impossible in most cases.