Experimental myositis ossificans: cartilage and bone formation in muscle in response to a diffusible bone matrix-derived morphogen.

Bone matrix gelatin, prepared by chemical extraction of soluble noncollagenous proteins, was half digested with a chromatographically purified collagenase. The residue was placed on one side and autologous muscle on the other side of cellulose acetate membranes in diffusion chambers and tissue cultures. In this avascular system, the muscle septa connective tissue proliferated and differentiated into cartilage. Muscle tissue cultured in media conditioned with matrix residues and then transferred into a vascularized muscle pouch differentiated into cartilage and bone. These observations form the basis for a working hypothesis that myositis ossificans is a response of new populations of proliferating intramuscular connective tissue cells to a bone matrix-derived diffusible molecule.