Causes of osteoarthritis
What causes osteoarthritis?
Osteoarthritis is the wear-and-tear form of arthritis that is more common as people get older.
During a person's lifetime, damage to the joints is repaired by the body, but eventually joint problems can develop.
This process can be caused by damage to ligaments or tendons, inflammation in and around the joint, or damage to the cartilage that protects the surface of the joints.
Ageing and osteoarthritis
With ageing, the water content of the cartilage increases and the protein make-up of cartilage degenerates. Repetitive use of the joints over the years irritates and inflames the cartilage, causing joint pain and swelling. Eventually cartilage begins to degenerate by flaking or forming tiny crevasses. In advanced cases there is a total loss of the cartilage cushion between the bones of the joints. Loss of cartilage cushion causes friction between the bones, leading to pain and limitation of joint mobility. Inflammation of the cartilage can also stimulate new bone outgrowths (spurs) to form around the joints. Osteoarthritis occasionally can be found in multiple members of the same family, implying an inherited basis for this condition. Rarely some of these inherited cases of osteoarthritis are caused by defects in collagen, which is an important component of cartilage.
Secondary osteoarthritis is caused by another disease or condition. Conditions that can lead to secondary osteoarthritis include obesity, repeated trauma or surgery to the joint structures, abnormal joints at birth (congenital abnormalities), gout, diabetes and other hormone disorders.
Obesity causes osteoarthritis by increasing the mechanical stress on the cartilage. In fact next to ageing, obesity is the greatest risk factor for osteoarthritis of the knees. The early development of osteoarthritis of the knees among weight lifters is believed to be in part due to their high body weight. Repeated trauma to joint tissues (ligaments, bones and cartilage) is believed to lead to early osteoarthritis of the knees in football players. Interestingly recent studies have not found an increased risk of osteoarthritis in long-distance runners.
In gout and pseudogout, crystal deposits can cause cartilage degeneration. This is a separate type of arthritis but can also accelerate the degenerative changes seen in osteoarthritis. Uric acid crystals cause arthritis in gout, while calcium pyrophosphate crystals cause arthritis in pseudogout (or false-gout).
Some people are born with abnormally formed joints (congenital abnormalities) that are vulnerable to mechanical wear, causing early degeneration and loss of joint cartilage. Osteoarthritis of the hip joints is commonly related to structural abnormalities of these joints that have been present since birth, which leads to abnormal stresses when the ball at the top of the femur (leg bone) moves within the hip socket.
Hormone disturbances such as diabetes and growth hormone disorders are also associated with early cartilage wear and secondary osteoarthritis.