Calvarial Reconstruction with Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2)/Absorbable Collagen Sponge (ACS) Implant: Initial Results in 8 Children

Acquired skull defect are common as a result of trauma, infection, and calvarial expansion. Traditional techniques available to repair these defects have included a variety of foreign body implant or bone grafting from proximal or distal sites. Such methods have well-known associated problems including: bioimcompatibility, breakdown, infection, donor site morbidity, and prolonged operating time.

Bony calvarial defect in 8 children ranging from 8 months to 15 years were repaired using rhBMP-2/ACS implant. These defects resulted from trauma (3), calvarial expansion (3), and infection (2). Reconstructive technique varied with the size and geometry of the defect. Defects ranged in size from 10 cm2 to the entire frontal bone. Results of the repair were judged by physical examination and 3D CT scan.

8 patients were followed for at least 6 months. Calvarial ossification was complete in 6 cases, with a small residual defect 2 cm2 in the first case of the series. The frontal reconstruction was carried out in two stages with 75% of the defect repaired at the first intervention and the remainder at the second stage.

The mesenchymal source for calvarial bone resides in stem cells of both dura and periosteum. Dura is formed exclusively from neural crest cells, all of which bear membrane bound receptors for bone morphogenetic protein. The parietal, the occiput and the skull base arise from paraxial mesoderm but can be reproduced with the same rhBMP-2 stimulus. The mechanism by which such bone is synthesized is referred to as osteoinduction and the surgical technique is called in situ osteogenesis (ISO). Rconstruction using rhBMP-2/ACS implants shows great promise for repair of significant calvarial defects by activating local stem cells to form osteoblasts, thus producing bone native to the environment. Reduction in morbidity and operative risk by avoiding foreign body implants or bone graft donor sites is of significant advantage to patient and surgeon alike.