The three most common forms of arthritis to affect the knees are osteoarthritis, rheumatoid arthritis and post-traumatic arthritis (see below). Although most people affected by arthritis of the knee are older, there are some types that can affect younger people and children.
Arthritis describes an inflammatory condition which affects a joint in the body, and the knee joint is one of the most commonly affected.
Although there are many forms of arthritis that can affect the knee, the following three are the most common:
Osteoarthritis ('OA') develops when the cartilage (also referred to as the 'meniscus'), which acts as a form of 'shock absorber' and sits between the joint components, starts to deteriorate and wear away. This condition is regarded as a type of degenerative disease and is much more common in patients over 50 years of age.
Rheumatoid arthritis is an auto-immune condition, which is where the body's own immune system attacks healthy body tissue. Where rheumatoid arthritis is present in the knee joint affected tissue includes bone tissue, cartilage tissue, ligament tissue and the membrane that surrounds the joint (the 'synovial membrane'). If rheumatoid arthritis is present, it generally affects more than one joint in the body and sometimes only affects joints on one side of the body.
This form of arthritis is caused by some kind of damage or trauma to the knee or knee joint. Sometimes damage is to one specific part of the knee joint such as the cartilage, the bone or the muscles and ligaments and in other cases a number of these are affected. Arthritis often does not appear immediately after the trauma, but develops a long time afterwards.
Risk factors for developing arthritis of the knee include;
- Body weight – a higher body weight increases the risk of developing the condition.
- Sex – women are more affected than men.
- Repetitive stress injuries – most commonly caused by specific types of work activity or some sports (for example soccer, tennis and running).
The following symptoms may indicate arthritis of the knee:
- Pain / stiffness in the knee (often most apparent just after getting out of bed, after sitting down for an extended period, while walking or kneeling down or going up or down stairs).
- A feeling that the knee may give way (also referred to as 'knee instability').
- Swelling of the knee.
- Restricted range of movement (i.e.: it becomes difficult to bend or straighten the knee).
- 'Locking' of the knee and accompanying sensations and noises, such as clicking or popping noises or 'crepitus' – a grinding noise when moving the knee.
Although most symptoms appear and then worsen over a period of time, in rare cases they can appear quite suddenly. The weather can also affect symptoms, with wet weather often making symptoms worse.
People who are overweight or obese will experience more severe symptoms than people of normal weight, and symptoms often reduce or even disappear when some weight is lost.
Tests / Diagnosis
Diagnosis of knee arthritis generally involves an initial physical examination and a review of the patient's medical history. The range of motion of the knee joint(s) will also be assessed. After the physical examination, x-rays may be required to determine if any bone spurs ('osteophytes') are present and if there has been any change to bone structure.
In some cases, an MRI and / or CT scan will help assess bone density and look at soft tissue in the joint. A blood test may also be required to determine whether rheumatoid arthritis or osteoarthritis is present, or if another condition is causing symptoms.
Non-surgical treatment for knee arthritis can include weight loss (if overweight), following a moderate exercise regime and using pain medication and / or anti-inflammatory medication. Support braces as well as physiotherapy can also help alleviate symptoms. Where these treatments do not have the desired effect, knee replacement surgery may be an option.