Bone, a highly specialized supporting framework of the body, is characterized by its rigidity and hardness and is endowed with the power of regeneration and repair. Its formation is carried out by osteoprogenitor cells powered by Wnt pathway by two important methods, namely, intramembranous ossification, wherein bone is laid down into the primitive connective tissue (mesenchyme) resulting in the formation of bones as seen in skull, clavicle, and mandible, while endochondral ossification is characterized by a cartilage model which acts as a precursor as in femur, tibia, humerus, and radius. To meet the requirements of skeletal growth and mechanical function, bone undergoes dynamic remodeling by a coupled process of bone resorption by osteoclasts and reformation by osteoblasts.

Bone metabolism is under constant regulation by a host of hormonal and local factors. The calcitropic hormones, namely, parathyroid hormone, vitamin D, and calcitonin, affect the bone metabolism the most in addition to other hormones like insulin, growth hormone, gonadal hormones, cytokines, and growth factors.

The bone metabolism can be monitored by markers such as alkaline phosphatase and urinary hydroxyproline. Other markers include products associated with bone formation, such as osteocalcin, osteonectin, and N- and C-terminal pro-peptides of type I collagen, or with bone resorption, namely, acid phosphatase, free gamma-carboxyglutamate, and hydroxylysine glycosides, especially galactosyl hydroxylysine.