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Could OA Be Recategorised As More Than One Disease?

24th January 2019

Traditionally, osteoarthritis has been considered to be a single disease with the same cause and course of treatment. However, recent evidence has emerged which suggests that it is not a single disease and this may have implications when it comes to treatment options.

What is osteoarthritis?

Osteoarthritis is also sometimes called degenerative joint disease or degenerative arthritis. It is known as a wear and tear condition which predominantly affects older people, although if a person has suffered a joint injury then they may be more susceptible. It is also more common in obese people as supporting additional weight puts extra strain on joints. It is caused when the cartilage in joints gets worn away so that bones rub against each other, resulting in pain and inflammation. OA can affect any joint but the knees, hips and lower back are most commonly affected.

In normal joints, the end of each bone is covered by cartilage which is a firm, rubbery material. It provides a surface which allows bones to glide smoothly against each other. Over time OA can become worse as wear and tear may cause the bones to break down and develop spurs. The body then responds with an inflammatory process whereby proteins are produced which damage the cartilage further.

Diagnosis of osteoarthritis

The first step for diagnosing osteoarthritis is a physical examination and discussion of symptoms with a doctor. The doctor will check any affected joints for tenderness, redness and swelling and also look at the range of motion.

Depending on how the initial examination goes, the doctor may well order imaging tests to determine how badly affected the joints are. X-ray images cannot show cartilage, but if there is a narrow space between bones then this can suggest that the cartilage has been worn away. In addition, an x-ray can show if there are any bone spurs in the joint. It may be possible for osteoarthritis to be identified in joints before a patient starts to show any symptoms.

Magnetic resonance imaging (MRI) uses radio waves and a magnetic field to create pictures of joints. The detailed images produced can show bone and soft tissue, including cartilage. MRIs are not typically needed in order to diagnose osteoarthritis, but they can provide more information about complex cases or conditions.

In addition to ordering imaging, the doctor may also order lab tests of blood or joint fluid samples. There are no blood tests for diagnosing osteoarthritis, but it can be used to eliminate other potential causes of joint pain such as rheumatoid arthritis. Analysing a sample of joint fluid can confirm whether there is inflammation and if there may be gout or an infection causing joint pain.

Current treatments for osteoarthritis

There is currently no way in which to reverse the process of osteoarthritis, but there are several options available to treat the symptoms. First and foremost, weight loss and exercise often have the largest impact but there are also medical, physical and surgical options available.

Several drugs have been shown to reduce the pain of osteoarthritis and some may also have an effect on reducing inflammation. These are commonly taken by patients with arthritis, but they can cause serious side effects including liver and kidney damage, stomach upsets and bleeding problems.

Physical therapy can be very effective at relieving osteoarthritis pain, as specific exercises can strengthen the muscles around affected joints and increase the range of motion. Occupational therapy can also help as professional therapists can educate patients on ways to carry out everyday tasks without putting extra stress on painful joints.

If arthritis is severe then there are also some injections and surgical procedures that could be considered. Injecting cortisone into the space within the joint can reduce the pain for an extended period, but these injections cannot be carried out too often as they can worsen joint damage. Injecting hyaluronic acid into the joint can also relieve pain as it adds extra cushioning between the bones, although there is some evidence that the injections are no more effective than a placebo.

The last resort is to replace an arthritic joint with an artificial replacement. Surgeons can remove damaged joint surfaces and replace them with parts made from plastic or metal. Surgery can have serious risks and side effects so the decision to operate is not one which is taken lightly.

What are the different types of osteoarthritis?

Research has been carried out by the University of Manchester, funded by Versus Arthritis, which found that there may be two distinct disease groups within OA. The two groups have different disease activity patterns and the researchers suggested that it might be more effective to work on developing separate treatments for the two types, rather than continuing to try and develop a single treatment which would work for everyone.

Researchers carried out an analysis of thousands of genes which are expressed in cartilage. They looked at the results from 60 different patients and separated samples based upon the level of metabolic activity in the affected joints. From the analysis, two distinct groups of patients emerged which had key genetic differences. The team also developed a list of biomarkers which could be used to distinguish to which group a patient belonged, using a sample of synovial fluid. This fluid is found in the cavities of joints.

The researchers hypothesised that the differences found between the two categories of patients may explain why treating OA as a single condition has not proved successful.

How could this new research affect treatment?

Researchers from the study suggested that by determining into which group a patient fits, it may be possible to predict how they may respond to treatments. In the future, it may even be possible to develop new drugs and treatments which are specifically targeted to the group profiles. The genetic profile of patients could also be used to tailor recruitment into new drug trials so that treatments are tested on groups where there is a realistic chance success.

What are the experts saying?

Professor Tim Hardingham from the Wellcome Trust Centre for Cell-Matrix Research and Division of Cell Matrix Biology and Regenerative Medicine at the University of Manchester described this research as a significant step forward in the understanding of osteoarthritis. He highlighted that osteoarthritis is a condition with a major socioeconomic impact and it is a complex and debilitating disease. Although this research is an encouraging first step, the road to developing new drugs and treatment options still has a long way to go.

The research liaison manager at Versus Arthritis, Dr Devi Sagar, also highlighted the challenges faced by patients with osteoarthritis due to the daily pain, stiffness and fatigue they experience. These symptoms can have a significant impact on a person's ability to dress themselves, carry out a job, or negotiate stairs. Dr Sagar considered this latest research to be good news for patients since it expands the understanding of the condition. The findings of this study may start to explain why people who have similar symptoms from what is apparently the same disease respond to treatments in very different ways.

Dr Sagar says that more research like this study is needed if better diagnosis and targeted treatments are going to be developed. The ultimate aim is for people with arthritis to be able to live a life free of pain and without the associated stiffness and limitations to their mobility.

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