Osteoarthritis: How does physical activity keep joints healthy?

Each year in the UK, over 2 million people consult their GP because of osteoarthritis.(1)(2) Many have painful, stiff joints that severely reduce their quality of life. There is no cure. In most cases, we don't even know why people develop osteoarthritis. Researchers are investigating how physical activity affects the joints. They hope that their findings will help in the development of new treatments.

What's the problem and who does it affect?

Pain, stiffness and disability

Osteoarthritis most commonly attacks the hips, knees or hands of older people. Pain and stiffness in the joints can cause significant disability.

Osteoarthritis is the biggest cause of joint pain and the single most common cause of disability in older adults.(3) The condition affects an estimated 5 million people in the UK, with numbers rising fast because of our ageing population.(1)(4)

There is no cure for osteoarthritis. We don't even know what causes it in most cases. Many people are prescribed painkillers or other drugs, such as steroids, which can relieve some of the symptoms of the disease, but cannot cure it. Osteoarthritis is also the leading reason for joint replacement surgery.(5) More than 44,000 hip replacements and 35,000 knee replacements were performed in the UK in 2000, at a cost of £405 million.(1)

Sadly, when everyday tasks like getting in and out of a car become increasingly difficult, and walking becomes painful and laboured, some people with osteoarthritis become reluctant to go out of the house. For all too many, depression and anxiety set in, because of failing health and increasing levels of pain.

What is the project trying to achieve?

How does physical activity affect the make-up of joints?

The main function of our joints is mechanical - they enable us to move. All the tissues in joints - the bone, cartilage, ligaments, muscle and so on - respond to mechanical factors. If we exercise they get stronger, if we stop exercising they waste away. The research team is trying to understand how the cells within our joints sense the loads they are being subjected to, and how they respond by strengthening the tissue.

The researchers hope that understanding how the joints usually respond to loads will shed some light on why the make-up of joints changes in osteoarthritis - why cartilage, which provides a smooth bearing surface, is destroyed and why the underlying bone thickens. They are focusing on the role of two recently discovered molecules - called FGF18 and Wnt16.

The researchers are performing laboratory studies using joint tissue obtained from people who are undergoing surgery for osteoarthritis or fractures. They are studying the effects of mechanical loads similar to those experienced when walking.

What are the researchers' credentials?

The Project Leader, Professor Richard Aspden has a long track record of research into osteoarthritis and other joint disorders. He has developed a number of novel approaches, including new imaging methods for assessment of disease and new analyses of how the hip and the spine carry loads, and identified new signalling molecules which may play a significant part in controlling how these tissues respond to mechanical loads. He has published over 100 peer-reviewed papers on these subjects in scientific journals and served as a reviewer for most of the leading agencies that fund research.

Professor Aspden is based at the University of Aberdeen, one of the leading centres in the world for the study of bone and musculoskeletal disorders. The centre has thriving collaborations between basic scientists, including biologists, geneticists, imaging scientists and engineers, right through to clinicians, such as rheumatologists and orthopaedic surgeons, who see patients on a day-to-day basis. 'Bedside to bench and back again,' describes the centre's approach.

The team has made some unique suggestions about what is going wrong in osteoarthritis and is developing novel ways to assess the disease.

Who stands to benefit from this research and how?

An important stepping stone on the road to new treatments

The ultimate goal of the researchers working on this project is to help find a cure for osteoarthritis. They hope this study will prove to be an important stepping stone along the way.

The team aims to boost our understanding of how physical activity enables our joints to stay healthy, and help explain what goes wrong in osteoarthritis. Once they have that information, they will begin to look at ways of intervening, with potential new drugs.

It would be an enormous blessing to people with osteoarthritis if they could maintain their mobility, free from pain, for as long as possible. The condition can make all sorts of important everyday activities difficult - walking, getting in and out of chairs or beds, opening jars, writing, turning keys, and even sleeping, for example.

An effective treatment could also bring colossal cost savings, by reducing healthcare spending and allowing people to keep working. A massive 36 million working days were lost because of osteoarthritis in 1999-2000 in Great Britain - equivalent to a loss of production of £3.197 billion.(1)(6)

References

1. Arthritis Research Campaign. 'Arthritis: The Big Picture', 2002.

2. McCormick A, Fleming D, Charlton J. Morbidity statistics from general practice. 4th national study 1991-1992. London, HMSO (1995)

3. Peat G, McCarney R, and Croft P. Knee pain and osteoarthritis in older adults: a review of community burden and current use of primary health care. Ann Rheum Dis 60 (2):91-97, 2001.

4. Maurer K. Basic data on arthritis knee, hip and sacro-iliac joints in adults aged 25-74 years, United States 1971-5 Vital Health Statistics. (NHANES I) Series 11, Number 213, USDHEW, 1979

5. Felson DT, Lawrence RC, Dieppe PA, Hirsch R, Helmick CG, Jordan JM, Kington RS, Lane NE, Nevitt MC, Zhang Y, Sowers M, McAlindon T, Spector TD, Poole AR, Yanovski SZ, Ateshian G, Sharma L, Buckwalter JA, Brandt KD, and Fries JF. Osteoarthritis: New Insights. Part 1: The Disease and Its Risk Factors. Ann.Intern.Med. 133 (8):635-646, 2000.

6. Department for Work and Pensions. Analytical Services Division. www.dwp.gov.uk