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Causes and incidence of OA

OA is the commonest cause of joint disability in developed world, and listed in the top 10 of the global disease burden according to the World Health Organisation.

In white North Americans and North Europeans, about one-third of adults between 25 to 74 years have signs of OA on their x-rays in at least one joint. In the US, 6% of those over 30 and 12% over 65 have a troublesome OA knee.

Most common areas to be affected by OA are the hands, followed by feet, knees and hips. See development of OA for a more technical account of the condition.

Risk factors for OA

Genetic factors
OA appears to be strongly genetically linked.

• Sex - more common in females
• Inherited disorders of type 2 collagen (a main component of joints, ligaments, skin).An example is Stickler’s syndrome
• Genetic mutations of the type 2 collagen gene
• Other inherited joint or bone disorders
• Race and ethnic origin

Non-genetic factors

• Increasing age
• Being overweight
• Reduction in female sex hormones (eg after menopause) - this is not clear
• Developmental diseases of bones and joints, and any acquired during life.
• Knee trauma is a significant risk factor, such as anterior cruciate, meniscal and ligamentous injuries.
• Previous joint surgery such as “cartilage”(properly called menisci) removal from knees
• Race and ethnic origin

Environmental factors

• Occupations and physical effort of work
• Excessive repetitive joint use
• Major accidents/injuries to joints
• Leisure and sports activities

Risk factors are complex and may vary both from joint to joint and even within certain areas of one joint.

Age

Age is the strongest risk factor for OA and the rates of arthritis for all joints rises with increasing age. Why age is important in OA is not clear. Aging joint cartilage may undergo chemical changes which render it vulnerable to the development of OA but there is no good evidence for this.

Women

Women are at higher risk of developing OA than men, especially after the menopause but the reasons for this are complex and not well understood.

Weight

Obesity is strongly associated with knee (and to a lesser extent hip) OA, perhaps due to the increase in stress put through the joint when the person is overweight. However, systemic factors may be involved because obesity is linked to hand OA too.

Jobs

Occupations and sport are also associated with developing OA. Jobs which involve kneeling, squatting and stair climbing are connected with higher rates of knee arthritis. Heavy repetitive joint use appears to increase OA risk.

Jobs involving repetitive heavy lifting (eg farming) show higher rates of hip arthritis.

Sport

Sport participation is connected with lower limb arthritis. Jogging, however, does not seem to increase the risk of OA if the person’s joints are normal.

Other risks

Joint deformities, knee mal-alignment, joint laxity (loose ligaments), changes in walking pattern and quadriceps muscle weakness are all associated with OA knee.