CALLUS

, also spelled Callous, in osteology, bony and cartilaginous material forming a connecting bridge across a bone fracture during repair. Within one to two days after injury, a provisional callus forms, enveloping the fracture site. Bone-forming cells in the periosteum (the bone layer where new bone is produced) proliferate rapidly, forming collars around the ends of the fracture, which grow toward each other to unite the fragments. The definitive callus forms slowly as the cartilage becomes ossified. Two to three weeks after injury, strong bony extensions (trabeculae) join the fractured bone ends, and the organized aspect of bone gradually recurs. The callus is resorbed over a period of months. also spelled Callous, in dermatology, small area of thickened skin, caused by continued friction, pressure, or other physical or chemical irritants. In response to mild but repeated injury, the cells of the epidermis, the outermost horny layer of the skin, become more active, giving rise to a localized increase in horny tissue on the surface of the skin. Calluses are most frequently seen on the hands and feet. They are usually yellowish white, flat, and painless. When a callus is conical in shape, penetrating into the deeper layer of the skin and causing pain when pressed, it is called a corn.