Normal joints move easily because healthy cartilage cushions the bones as they move against each other. In spinal osteoarthritis, the cartilage lining the facet joints (vertebral joints) wears out, allowing the bones to rub together. Osteophytes (small bony growths also known as bone spurs) form on facet joints and around vertebrae in an attempt to return stability to the joint. Gradually, the spine stiffens and loses flexibility. Osteophytes sometimes become large enough to cause narrowing of the spinal canal or foramen, irritating or entrapping nerves passing through them (spinal stenosis and foraminal stenosis). Stenosis, while related to osteoarthritis, is a separate medical condition. Osteoarthritis can also be confused with degenerative disk disease, a gradual deterioration of disks between the vertebrae, but is a separate medical condition. Osteoarthritis occurs as a person ages but is not a direct result of aging. It may result from repetitive use, high mechanical stress, injury, joint infection, obesity, ligament damage, hormonal problems, pregnancy, and other conditions. Heredity also plays a role.