Osteoarthritis occurs when the cartilage that cushions the ends of bones in your joints starts to deteriorate gradually. Cartilage is a firm, connective tissue that enables nearly frictionless joint motion. Eventually, if the cartilage wears down completely, your bones will begin to rub on bone, often referred to as bone on bone.
Besides the breakdown of cartilage, Osteoarthritis can affect the entire joint. It will change the bone and cause deterioration of the connective tissue. It may also cause inflammation in the joint lining.