This is followed by thickening of the bone and destruction of the joint surface. This results in pain and stiffness of the joint and increasing deformation. In the late stage, the joint cartilage in the affected area is not only damaged, but completely worn away and has disappeared. The exposed bone now rubs directly on the bone of the opposite joint and in the final stage, the joint may turn completely into bone (ossification). Although this process can be delayed by various means, the ultimate treatment is surgical joint replacement.

The risk of osteoarthritis increases with age. Whereas only 4 per cent of 20-year-olds have osteoarthritis, it is present in 70 per cent of the over 70s. Women are affected more than men.

Certain joints are particularly susceptible:

• Joints at the finger tips (Heberden's arthritis)
• Middle joints of the fingers (Bouchard's arthritis)
• Joint at the base of the thumb (rhizarthritis)
• Knee joints (gonarthritis): the commonest form of osteoarthritis, is age-related and affects almost everybody at some time.
• Hip joints (coxarthritis)

Arthritis of the small joints of the spine (vertebral facet joints): often in combination with other degenerative diseases of the spine such as disc problems, disc degeneration (spondylosis), a forward shift of one vertebra over another (spondylolisthesis), stenosis (narrowing) of the spinal canal etc.