OA occurs as a result of mechanical breakdown in the structures affecting the joints.
In healthy joints, cartilage – a shiny gristly material –acts as a shock absorber and provides a smooth surface between the bones to allow easy movement. When a joint develops osteoarthritis the cartilage thins and becomes rough. In some cases the cartilage breaks down, leaving the bones unprotected.
As a result the joint loses its ability to move smoothly. The bones lose shape and thicken at the end, producing bony spurs. Pieces of cartilage may break off and float around in the joint. This can disturb other soft tissue in the joint, causing pain and swelling.
Osteoarthritis progresses slowly and develops over many years. In most cases there are only small changes that affect parts of the joint. However sometimes osteoarthritis can be more severe and extensive.