Bone is a specialized type of connective tissue consisting of various cell types and an extracellular collagenous matrix, within which is deposited a complex crystalline mineral substance consisting mainly of calcium, phosphate and carbonate in a defined relationship.Bone is not simply hard, relatively inert, framework for body support, but in reality it is a complex, highly organized metabolically active tissue. In addition to providing a gravity resistant structure, the skeleton also acts as an extracellular reservoir for calcium and phosphorus.However, there are many disorders either specifically of bone or more generally of mineral metabolism in which there is major involvement of bone.