Devitalized extracts from cultured human osteosarcoma cells (Saos-2) can induce ectopic bone formation. The ability of an extract from Saos-2 cells to stimulate healing of an operatively created four-millimeter defect in the femoral diaphyses of rats was compared with that of collagen and that of autogenous bone graft. Forty adult rats were randomized into four groups of ten each. In Group 1 (controls), no material was placed in the defect; in Group 2, the defect was filled with pure bovine collagen; in Group 3, it was filled with autogenous graft obtained by morseling of the resected segment of the femur; and in Group 4, it was filled with ten milligrams of extract from Saos-2 cells that was mixed with an equal amount of bovine collagen.Five rats from each group were killed at four weeks and the remaining five, at eight weeks. Each femoral defect was analyzed radiographically and histologically for osseous healing. There was no evidence of healing at either four or eight weeks in Groups 1 and 2. Although there was some new-bone formation in Group 3, none of the defects had united at eight weeks. There was early, almost complete union in all five four-week specimens in Group 4 and complete healing of the defect in four of the five rats assessed at eight weeks. The Saos-2 cell extract was found to be the most effective agent, promoting union by mature lamellar bone within eight weeks.CLINICAL RELEVANCE: Potential clinical applications of Saos-2-cell bone-inducing extract include the promotion of bone growth in fracture non-unions, in large operatively created defects, and in spinal arthrodeses. It is possible that a bone-inducing extract could enhance osteointegration of porous prosthetic implants.