ENHANCED HEALING OF LARGE CRANIAL DEFECTS BY AN OSTEOINDUCTIVE PROTEIN IN RABBITS

Two experimental bone-graft substitutes, one composed of a porous hydr oxyapatite plus an osteoinductive protein and the other composed of la ctomer beads (copolymers of polylactic acid and polyglycolic acid) plu s an osteoinductive protein, were evaluated as a means of reconstructi ng a large cranial defect model created in the rabbit. Twenty-five rab bits underwent a 16 x 20 x 1.5 mm full-thickness (extradural) excision of the parietal bone, were divided into different groups of five rabb its each, and were reconstructed by (1) hydroxyapatite, (2) hydroxyapa tite plus protein, (3) lactomer beads, and (4) lactomer beads plus pro tein, and (5) one group consisted of nonreconstructed controls. The im plants were harvested at 12 weeks and analyzed for percentage of bone ingrowth by histologic examination of decalcified midcoronal sections stained with hematoxylin and eosin. The groups reconstructed with prot ein-treated implants demonstrated significantly greater amounts of ing rowth than those with untreated implants. Both protein-treated hydroxy apatite and lactomer bead groups had more than twice the amount of bon e ingrowth than their respective untreated groups (29.0 versus 12.8 pe rcent, p < 0.005, and 27.0 versus 10.0 percent, p < 0.001, respectivel y). The new bone found in the protein-treated and untreated implants w as quite different: lamellar and woven, respectively. The results stro ngly suggest a clinical role for the combination of the mechanisms of osteoconduction and osteoinduction in the treatment of bone defects.