Most of the time, the cause of osteoarthritis (OA) is unknown. It is primarily related to aging. However, metabolic, genetic, chemical, and mechanical factors can play a role in its development. The symptoms of osteoarthritis usually appear in middle age and are present in almost everyone by the age of 70. Before the age of 55, the condition occurs equally in both sexes. However, after 55 it is more common in women. The cartilage of the affected joint becomes rough and wears down (degenerates). As the disease gets worse, the cartilage disappears and the bone rubs on bone. Bony spurs usually develop around the joint. OA is classified as primary or secondary. Primary OA occurs without any type of injury or identifiable cause. Secondary OA is osteroarthritis due to another disease or underlying condition. The most common causes of secondary OA are metabolic conditions, such as acromegaly, problems with anatomy (for example, being bow-legged), injury, or inflammatory disorders like septic arthritis.
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