What causes osteoarthritis?

Osteoarthritis is thought to be caused by the breakdown of cartilage - the lining between bones in a joint - along with other changes in different parts of the joint. Our joints are exposed to low-level stress and damage all the time. In osteoarthritis, it seems that something happens which means the body is less likely to be able to protect against, and recover from, these small injuries to joints. Things that are linked to osteoarthritis include age, being overweight or obese, having a joint injury, and overusing the joints.

If you think you may have osteoarthritis find out what to do here. Osteoarthritis is one of the causes of arthritis. See here for more detail.

In this series of articles centred around osteoarthritis you can read about osteoarthritis treatment, osteoarthritis causes, and osteoarthritis symptoms - all written by one of our expert GPs.

The rest of this feature will take an in-depth look at osteoarthritis causes as, at Patient, we know our readers sometimes want to have a deep dive into certain topics.

What causes osteoarthritis?

The diagram shows a joint with changes of osteoarthritis, including damage to the lining of the joint (cartilage) and to the underlying bone.

Osteoarthritis

By Laboratoires Servier, CC BY-SA 3.0, via Wikimedia Commons

In osteoarthritis, the lining of joint is damaged and breaks down. Changes can also develop in the bones as well, including thinning of some areas of bone, and growth of new parts. Other parts of the joint can become affected, such as the ligaments - the connective tissue which joins bones together. In joints which have a meniscus - a type of cushioning cartilage - such as the knee, the menisci can tear or wear away completely.

It's thought that joint damage in osteoarthritis occurs because the body's natural healing process in joints is not working properly. It's not quite as simple as wear and tear alone - all our joints are exposed to low-level damage when we use them, but normally the body can recover and repair from this. In osteoarthritis, the healing process seems to be disrupted, leading to damage, loss of cartilage, and changes in the rest of the joint - it's not entirely clear why this happens.

Another interesting question is how osteoarthritis joint changes lead to pain and stiffness. It's common to see signs of osteoarthritis on an X-ray in some groups of people. For example, around four in ten of over-40s have signs of knee osteoarthritis, but without having any symptoms of osteoarthritis. Again, it's not entirely clear why some people have no symptoms despite having osteoarthritis signs on an MRI or X-ray, and yet other people get pain, swelling, and stiffness.

Things that are thought to be important in osteoarthritis include:

Age

Osteoarthritis is more common in older age. It usually starts after the age of 40. Osteoarthritis typically develops slowly with age. This probably isn't because of wear and tear with time, but may be due to things such as:

• Changes in joint healing, meaning the body isn't able to repair damage as well.

• Muscle weakness, reducing support around the joints.

• Other age-related changes of the joints, like ligament stiffness, which make the joint more vulnerable to damage.

Gender

Osteoarthritis is more common in women. It's possible that differences in joint structure between men and women make women more likely to develop osteoarthritis. It's also thought that hormonal changes around menopause affect joint healing and repair, potentially leading to osteoarthritis.

Overweight and obesity

Osteoarthritis is linked with being overweight or obese. Carrying extra weight puts additional stress on weight-bearing joints, which can lead to more strain and damage of those joints, causing problems like osteoarthritis of the knee and hip. People who are overweight or have obesity often move and exercise less too, which leads to muscle weakness. Muscle weakness reduces support around the joints and makes them more prone to injury.

It's also more common for people who are overweight or have obesity to get osteoarthritis in non-weight-bearing joints, such as the hands. It's thought that extra fat tissue leads to inflammation in the body, which can affect the healing ability of joints and lead to joint pain.

Genetics

Osteoarthritis is more common in people with a family history of the condition. It's thought that having some gene variants - mostly those that affect joint healing and repair - can increase your risk of developing osteoarthritis.

There are also some rare genetic conditions which can lead to osteoarthritis at a young age.

Joint injuries

A major joint injury - such as a break/fracture or dislocation - or joint surgery, can increase the risk of developing osteoarthritis later on. This might be due to damage to the joint from the initial injury, but could also be due to things such as the joint not being correctly aligned, leading to extra strain on parts of the joint.

Joint overuse

It's thought that repeatedly doing very hard or demanding physical activity, can increase the risk of osteoarthritis by causing joint damage. Some jobs may increase the risk of osteoarthritis, such as those involving lots of heavy lifting, climbing, squatting, kneeling and standing.

Normal levels of activity and exercise doesn't seem to cause osteoarthritis. Exercise is an important treatment for osteoarthritis.

Joint problems at birth

Being born with certain joint problems can increase the risk of osteoarthritis, by putting extra strain on the joint. For example, developmental dysplasia of the hip can cause hip osteoarthritis later in life if not treated.

Other conditions

Osteoarthritis can sometimes develop as a result of a different condition. For example, joint damage from rheumatoid arthritis or septic arthritis can lead to osteoarthritis in the affected joints.

Patient picks for Arthritis

Bones, joints and muscles

How to treat arthritis

Arthritis means pain and inflammation in one or more joints of the body. Arthritis causes pain, swelling, and sometimes redness and warmth in affected joints. There are many different causes of arthritis and having it can significantly affect your quality of life. Treatments for arthritis include pain relief and physiotherapy, but differ depending on the type of arthritis.

by Dr Doug McKechnie, MRCGP

Bones, joints and muscles

Calcium pyrophosphate deposition

Calcium pyrophosphate is a substance produced in the cartilages of the joints. It can become deposited as crystals on joint tissues. This is called calcium pyrophosphate deposition. Calcium pyrophosphate deposition can cause a number of problems of which the most well known is pseudogout. This is almost identical to gout, causing attacks of pain and swelling in one or more joints. Some people develop damage to the joint, causing a type of long-term arthritis. Calcium pyrophosphate deposition may cause no symptoms and is sometimes picked up on an X-ray done for an unrelated condition. Unlike gout, there is no special treatment for pseudogout. Rest, ice packs and anti-inflammatory medicines are the main forms of treatment.

by Dr Hayley Willacy, FRCGP

How common is osteoarthritis?

Osteoarthritis is common. Around one in 10 men, and two in 10 women over the age of 60 are thought to have it. Around 8.5 million people in the UK are thought to be affected by osteoarthritis.

What causes osteoarthritis flare-ups?

People with osteoarthritis can get flare-ups of pain, swelling, and stiffness. These can last for days to weeks. Although people with osteoarthritis have known about flare-ups for a long time, they have only recently been studied in medical research, so there's not a lot of clear evidence about the causes of flares. Some possible causes are:

• Overuse of a joint - for example, doing an intense physical activity such as prolonged kneeling, lifting, moving heavy objects, or squatting.

• Poor mental health - for example, feeling low in mood, anxious, stressed, or depressed.

• Poor sleep.

• Injury to a joint.

• Weather changes, such as temperature and pressure changes - these have long been reported as triggers for symptoms by people with osteoarthritis. It's difficult to find clear evidence for this in research, though.

Risk factors for osteoarthritis

Risk factors for developing osteoarthritis include:

• Age. This is the strongest risk factor for osteoarthritis. Osteoarthritis usually develops after age 40, and becomes more common in older age.

• Females. Osteoarthritis is more common in women.

• Obesity and overweight. This is the strongest modifiable risk - one that we can change - factor for osteoarthritis. It's estimated that the risk of developing osteoarthritis is about three times greater in people with obesity, compared to those of a healthy weight. Osteoarthritis also progresses faster in people with obesity.

• Family history and genetics. Osteoarthritis is more common in people who have a family history of osteoarthritis.

• Bone density. High bone density has been linked with an increased risk of osteoarthritis, whereas low bone density (osteoporosis) has been linked with more rapidly worsening osteoarthritis.

• Joint injuries. Having joint damage from a prior injury, surgery, or another condition (like rheumatoid arthritis) can increase the risk of osteoarthritis.

• Joint alignment problems. Joints that are not properly aligned - in the correct position - can increase the risk of osteoarthritis. For example, developmental dysplasia of the hip can lead to osteoarthritis if not treated. Some people are born with other problems, like having legs that are of a different length, which can put extra stress on certain joints.

• Heavy repetitive exercise. For example, some groups of elite sportspeople, like professional footballers, are at higher risk of later developing osteoarthritis. Moderate, recreational exercise, however, does not seem to increase the risk of osteoarthritis, and has lots of other health benefits.

• Certain types of job. Jobs that involve repeated squatting, bending, kneeling, heavy lifting or prolonged standing may be linked to an increased risk of osteoarthritis.

How to prevent osteoarthritis

It's not possible to prevent osteoarthritis fully. However, there are things you can do that reduce the risk of osteoarthritis, help to treat it if it does occur, and have other health benefits too. These include:

• Maintaining a healthy weight. Losing weight - if overweight or obese - reduces stress on weight-bearing joints, and has lots of other health benefits too.

• Exercising regularly. Regular exercise has lots of health benefits, including helping to stay a healthy weight. Exercise helps to strengthen the muscles around joints, supporting them when in use:

  • Although high-intensity exercise - such as elite sport - has been linked to a higher risk of osteoarthritis, this doesn't appear to be the case with moderate-intensity recreational sport. This is probably because elite sportspeople are more likely to suffer joint injuries, rather than the effects of their exercise alone.

  • Low-impact exercises, like cycling, yoga, swimming and Pilates are often recommended, because these put less strain on the joints. However, high-impact exercises - like running and weightlifting - don't seem to be linked with osteoarthritis, unless done intensively, such as in professional or elite sport.

  • Exercise is also an important part of osteoarthritis treatment, as it can reduce pain and stiffness, and improve quality of life.

• Maintaining good posture helps to avoid unbalanced loads on the joints.

• Avoiding injuries during sport. Some types of exercises - including warm-up exercises - can help to prevent injuries. Advice from a physiotherapist or sports therapist can be helpful.

Further reading

• Versus Arthritis.

• The State of Musculoskeletal Health 2021 - Arthritis and other musculoskeletal conditions in numbers; Versus Arthritis.

• Osteoarthritis; NICE CKS, August 2022 (UK access only).

• Roos EM, Arden NK; Strategies for the prevention of knee osteoarthritis. Nat Rev Rheumatol. 2016 Feb;12(2):92-101. doi: 10.1038/nrrheum.2015.135. Epub 2015 Oct 6.

• Driban JB, Hootman JM, Sitler MR, et al; Is Participation in Certain Sports Associated With Knee Osteoarthritis? A Systematic Review. J Athl Train. 2017 Jun 2;52(6):497-506. doi: 10.4085/1062-6050-50.2.08. Epub 2015 Jan 9.