Bone morphogenetic protein-2 increases the rate of callus formation after fracture of the rabbit tibia

The effects of human recombinant bone morphogenetic protein-2 (rhBMP-2) on rabbit fractures healing under both stable and unstable mechanical conditio ns were investigated. rhBMP-2 was administered (1) on bioerodible particles , (2) in a collagen gel, and (3) by injection. rhBMP-2 on bioerodible parti cles has no effect as the particles prevent the migration of cells that pro duce the callus. The collagen gel is resorbed more rapidly; the development of the callus of mechanically unstable fractures is similar to controls at 14 days. When rhBMP-2 is injected, the callus of mechanically unstable fra ctures develops more rapidly so that cortical union occurs by 21 days, as c ompared with 28 days in control fractures. The effects on fractures healing under stable mechanical conditions are minimal. It is argued that mechanic al factors influence the size of the callus of normally healing fractures a nd, although BMP-2 accelerates the rate of development of the callus and co rtical union, it does not affect the amounts of bone and cartilage produced .