We don't fully understand how osteoarthrtis is caused but there are a number of significant risk factors which increase the chances of somebody developing this condition-
Age.
The risk is known to increase with age. Symptoms usually appear in middle age. We don't know why there is such a strong correlation with aging although it is thought that this may be to do with muscles becoming weaker, increased body weight and the fact that the body is less able to heal itself.
Gender.
Over the age of 55 osteoarthritis is more common and severe in women. Studies have indicated that women who are users of oestregen replacement therapy for longer than five years are less likely to develop OA of the knee.
Genetics.
Genetics is a major factor in nodal osteoarthritis which usually affects the hands of women in middle age.The Arthritis Foundation states that "twin and familial studies have shown OA to be a multigenic trait, with several genes involved". Heredity plays a significant role in knee and hip osteoarthritis.
Obesity.
Being overweight increases the risk of affecting the load bearing joints (especially the knees). Studies have shown that obese men are 4.8 times more likely to develop OA of the knee whereas obese women are almost 4 times as likely. Reducing weight also reduces your chances of developing OA of the knee. There is some rather patchy evidence that being overweight is a risk factor in OA of the hip.
Previous injury or condition.
Having joint abnormalities as a child can lead to osteoarthritis in later life.
A major injury or operation on a joint may also lead to osteoarthritis in later life.
The Arthritis Research Campaign states that "people with rheumatoid arthritis can develop 'secondary' osteoarthritis in those joints in which the rheumatoid inflammation has largely burnt out but where the joint remains damaged by the disease".
Occupation.
Farmers are more likely to have affected hips, professional footballers are more like to have osteoarthritis of the knee.
Diet.
Low intake of vitamin D and vitamin C increases the risk of osteoarthritis of the knee progressing.
Strength.
Having weak thigh muscles is known to increase the chance of OA of the knee developing and progressing.
