 The receptor activator of NF-kB ligand RANKL system is considered important for bone homeostasis and comprises three important factors. RANKL exist in three isoforms but the predominant function is mediated by the transmembrane ligand that binds to a specific receptor receptor activator of NF-KB RANK on a neighbour cell that subsequently activates NFKB and regulates cell cycle OPG is an endogenous secreted protein that binds RANKL and inhibits its signalling. 