Primary[edit]

A number of studies have shown that there is a greater prevalence of the disease among siblings and especially identical twins, indicating a hereditary basis.^[14] Although a single factor is not generally sufficient to cause the disease, about half of the variation in susceptibility has been assigned to genetic factors.^[15]

As early human ancestors evolved into bipeds, changes occurred in the pelvis, hip joint and spine which increased the risk of osteoarthritis.^[16] Additionally genetic variations that increase the risk were likely not selected against because usually problems only occur after reproductive success.^[17]

The development of OA is correlated with a history of previous joint injury and with obesity, especially with respect to knees.^[18] Since the correlation with obesity has been observed not only for knees but also for non-weight bearing joints and the loss of body fat is more closely related to symptom relief than the loss of body weight, it has been suggested that there may be a metabolic link to body fat as opposed to just mechanical loading.^[19]

Changes in sex hormone levels may play a role in the development of OA as it is more prevalent among post-menopausal women than among men of the same age.^[20][21] A study of mice found natural female hormones to be protective while injections of the male hormone dihydrotestosterone reduced protection.^[22]

Secondary[edit]

lateral

front

Secondary osteoarthritis (due to an old injury with fracture) of the ankle in a woman of 82 years old

This type of osteoarthritis is caused by other factors but the resulting pathology is the same as for primary osteoarthritis:

• Alkaptonuria
• Congenital disorders of joints
• Diabetes doubles the risk of having a joint replacement due to OA and people with diabetes have joint replacements at a younger age than those without diabetes.^[23]
• Ehlers-Danlos Syndrome
• Hemochromatosis and Wilson's disease
• Inflammatory diseases (such as Perthes' disease), (Lyme disease), and all chronic forms of arthritis (e.g., costochondritis,gout, and rheumatoid arthritis). In gout, uric acid crystals cause the cartilage to degenerate at a faster pace.
• Injury to joints or ligaments (such as the ACL), as a result of an accident or orthopedic operations.
• Ligamentous deterioration or instability may be a factor.
• Marfan syndrome
• Obesity
• Joint infection