OSTEOARTHRITIS (OA) is the most common arthritis in the world, affecting approximately 20% of the population.

In Malaysia, a survey carried out over 10 years ago found that 9.3% of Malaysians in the study population complained of knee pain. Over the age of 55, the proportion of people with knee pain increased to 23%, and to 39% over the age of 65 [1]. By the age of 60, over 50% of people will have OA.

The most common site for OA in Malaysians is in the knee joint [2]. However, other weight-bearing joints such as the hip and lumbar spine can be affected, as well as the hands.

OA is a disease of the cartilage and also of the underlying bone. Cartilage lines the ends of the bone in a joint and provides a smooth surface, so that the bones in the joint can move smoothly over each other. Also, cartilage spreads out the load stress on the joint, preventing concentration of stresses, so that the bones do not shatter when the joint is loaded. The main load on the cartilage is produced by the contraction of the muscles that stabilise or move the joint.

Why it starts

OA starts with thinning of the cartilage surface as well as softening of the cartilage. The integrity of the surface is breached and clefts start to appear in the cartilage. There is an attempt by the body to repair the damage, but the repair tissue is inferior to the original cartilage, with less elasticity to withstand the mechanical stresses.

The repaired cartilage has fewer cells (hypocellular) and is therefore less able to repair itself when it starts getting damaged. Thus a vicious circle is set up, with further gradual thinning of the cartilage. In addition, the underlying bone can be affected, leading to new bone growth, called osteophytes.

However, thinning of the cartilage itself does not necessarily lead to symptoms and the correlation between cartilage loss and pain is poor. When OA becomes symptomatic, patients will usually notice pain and stiffness of the joint.

Thankfully, the progression of OA is typically slow, taking many, many years before the symptoms become disabling.

Risk factors

The main risk factors for the development of OA include increasing age, female sex, race (Chinese get less hip OA compared to the Caucasians), major joint trauma, repetitive stresses, obesity and previous inflammatory arthritis (for example, rheumatoid arthritis) [3].

Whilst we cannot change our age, sex or race, we will look at some of the modifiable risk factors with a view to preventing OA.

An ancient English proverb states that "an ounce of prevention is worth a pound of cure". With regards to the link between OA and weight, this is very true!

With increasing weight, there is an increased risk of developing knee OA over the next few decades. It has been estimated that each 1lb increase in weight will increase the force through the each knee while walking by 2-3lb [3].

In a study, those in the top 20% of body mass index had an increased relative risk of developing severe knee OA over the next 36 years of 1.9 in men and 3.2 in women [4]. Furthermore, those patients who are obese but not yet developed OA can reduce their risk: a weight loss of 5kg was associated with a 50% reduction in the odds of developing symptomatic knee OA over the next 10 years [5].

Therefore, maintenance of an ideal body weight would reduce the future risk of OA.

Muscle power

When the muscles contract and move the joint, a force is applied through the joint. When the muscles are weak, there will be more stress on the joint/cartilage during movement, compared to when the muscles are strong. Stronger muscles can take more load off the joint.

For the knee, an important muscle is the front thigh muscle called the quadriceps muscle. Quadriceps muscle weakness is associated with disability from OA [3]. Strengthening the quadriceps muscle can reduce pain and disability in knee OA.

Physical support

In addition, there are other methods of reducing joint loading. For example, patients with hip or knee OA should avoid prolonged standing, kneeling or squatting. A stick, cane or walker may be helpful in reducing joint pain when walking in patients with unilateral hip or knee OA.

Joint trauma can lead to cartilage loss and thus lead to OA. Commonly, this would be due to sporting injuries. Footballers with knee injuries would be more prone to knee OA later in life. It has been shown there are higher rates of ankle OA in ballet dancers, elbow OA in baseball pitchers and metacarpophalangeal joint (knuckles) OA in boxers; sites of OA which are uncommon in the general population.

Nonetheless, in the general population, there are no convincing data that link specific sporting activities to arthritis, if major trauma is excluded. For example, jogging has not been shown to cause OA [3].

Other types of arthritis can also lead to secondary OA. For example, in rheumatoid arthritis, there is destruction of the cartilage as a result of the underlying inflammation in the disease, leading to secondary OA. Tight control of the inflammation and arthritis would reduce the risk, so patients are advised to seek early treatment for their arthritis.

In conclusion, OA is common, but (usually) progresses very slowly. One of the important modifiable risk factors in the development of OA is obesity. Maintenance of a normal body mass index would be a useful general measure to reduce the risk of future OA.

References:

1. Veerapen K et al. J Rheumatol 2007; 34: 207-13.

2. Clinical Practice Guidelines in the Management of Osteoarthritis 2002. Downloaded from www.msr.org.my/html/Bookleta.pdf (25 June 2008)

3. Felson DT et al. Ann Intern Med 2000; 133: 635-46.

4. Anderson JJ, Felson DT. Am J Epidemiol 1988; 128: 179-89.

5. Felson DT et al. Ann Intern Med 1992; 116; 535-9.

Dr Yeap Swan Sim is a consultant rheumatologist. This article is contributed by The Star Health & Ageing Panel, which comprises a group of panellists who are not just opinion leaders in their respective fields of medical expertise, but have wide experience in medical health education for the public.

The members of the panel include: Datuk Prof Dr Tan Hui Meng, consultant urologist; Dr Yap Piang Kian, consultant endocrinologist; Datuk Dr Azhari Rosman, consultant cardiologist; A/Prof Dr Philip Poi, consultant geriatrician; Dr Hew Fen Lee, consultant endocrinologist; Prof Dr Low Wah Yun, psychologist; Datuk Dr Nor Ashikin Mokhtar, consultant obstetrician and gynaecologist; Dr Lee Moon Keen, consultant neurologist; Dr Ting Hoon Chin, consultant dermatologist; Prof Khoo Ee Ming, primary care physician; Dr Ng Soo Chin, consultant haematologist. For more information, e-mail starhealth@thestar.com.my. The Star Health & Ageing Advisory Panel provides this information for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader's own medical care.

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