Some theories on how this response may contribute to osteoarthritis involve overproduction of enzymes called matrix metalloproteinases or MMPs (also called collagenases). In large amounts they break down collagen, the building blocks of cartilage. Some studies suggest that immune factors called vascular endothelial growth factor (VEGF) are overproduced during the inflammatory response and in turn increase production of MMPs.
Another theory suggests that the inflammatory response is triggered by the changes and injuries in the bone that occur during osteoarthritis. According to this theory, immune factors released in this process diffuse into the cartilage, where they suppress cartilage cell growth and activate MMPs.
Injuries
Joint injuries are the starting point in the disease process. Osteoarthritis sometimes develops years after a single traumatic injury to or near a joint. One large study found that by age 65, osteoarthritis developed in almost 14% of those who had joint injuries as young adults, compared to just 6% in those without earlier injuries. Patients with knee injuries were five times more likely to have osteoarthritis in the injured knee than those without injuries, and patients with hip injuries were more than three times more likely to develop arthritis in the injured hip. Proper treatment of injuries, such as surgical repair of ligament tears in the knee with a strong rehabilitation approach, may help to prevent the development of osteoarthritis.
Other Medical Conditions that Can Cause Osteoarthritis
Other causes of osteoarthritis include:
- Bleeding disorders such as hemophilia that cause bleeding to occur in the joint
- Disorders such as avascular necrosis that block the blood supply near the joint
- Complications of persistent, inflammatory arthritic conditions, particularly chronic gout, pseudogout, or rheumatoid arthritis
- Conditions that cause iron build-up in the joints such as hemochromatosis
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