The different types of arthritis are: Osteoarthritis – The most common form, this arthritis results when joint tissues deteriorate, causing bones to rub against each other. Knees are commonly affected by osteoarthritis; Rheumatoid arthritis – A less common form, this arthritis is an inflammatory disease in which the body’s immune system attacks the joints, causing them to become damaged; Infectious arthritis – Arthritis that is caused by an infection in the joint itself; Juvenile arthritis – Arthritis that affects those age 16 or younger; Psoriatic arthritis – A form of arthritis that is associated with psoriasis, a skin disease; Reactive arthritis – A chronic form of the disease that results from a gastrointestinal, genital, or urinary infection. Other diseases that can cause knee pain include gout, Lyme disease, or lupus.
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