Osteoarthritis of the knee (degenerative arthritis of the knee)

While age is a major risk factor for osteoarthritis of the knee, young people can get it too. For some individuals it may be hereditary. For others osteoarthritis of the knee can result from injury or infection or even from being overweight. Here are answers to your questions about knee osteoarthritis including how it's treated and managed.

What is osteoarthritis?

Osteoarthritis is a condition in which the natural cushioning between joints - cartilage - degenerates. Microtrauma (injury at a microscopic level) within the joint triggers an immune reaction, which - in an ill-fated attempt to repair the damage - causes inflammation that leads to a breaking down of cartilage tissue causing pain, swelling and deformity.

Cartilage is a firm rubbery material that covers the ends of bones in normal joints. It is primarily made up of water and proteins. The main function of cartilage is to reduce friction in the joints and serve as a "shock absorber". The shock-absorbing quality of normal cartilage comes from its ability to change shape when compressed. It can do this because of its high water content.

When the cartilage is damaged - for example in a joint stressed by abnormal weight bearing loads - attempts by the immune system to repair the damaged cartilage cause it to swell. The cartilage becomes thin, soft and cracked, exposing the bone beneath and leading to the formation of small cysts and new outgrowths of bone called osteophytes, which further disrupt the way the joint works and aggravate the problem. The joint space becomes narrowed, further altering the mechanics and adding to the stresses within the joint. Other tissues in the joint such as the surrounding membrane (the synovium) ligaments and tendons may also be affected. This degeneration is a gradual process that may go on over many years, although there are occasional exceptions.

Who gets osteoarthritis of the knee?

The charity Arthritis Research Campaign says more than 6 million people in the UK have painful osteoarthritis in one or both knees. The numbers rise with age: one in five adults between 50 and 59 years old to almost one in every two adults over 80 years old.

What causes osteoarthritis of the knee?

Osteoarthritis of the knee may happen as a result of injury or infection but often there is no obvious precipitating cause. Some of the following risk factors may play a part in the developing of osteoarthritis of the knee:

• Heredity. This includes the possibility of genetic mutations that might make a person more likely to develop osteoarthritis of the knee.
• Age. The ability of cartilage to heal decreases as a person gets older.
• Gender. Women who are 50 years old and over are more likely than men to develop osteoarthritis of the knee.
• Repetitive stress injuries. These are usually a result of the type of job a person has. Certain occupations that include a lot of walking (over 3.2km/2 miles per day), kneeling, squatting or lifting heavy weights (25kg/55lb or more) have higher incidences of osteoarthritis of the knee because of the constant pressure on the joint.
• Weight. Weight increases pressure on all the joints including the knees.
• Athletics. Athletes involved in football, tennis or long-distance running are at higher risk for developing osteoarthritis of the knee.
• Other illnesses. This includes gout and certain metabolic disorders.