Osteoarthritis is the most common form of arthritis and is characterised by joint pain accompanied by varying degrees of functional limitation and reduced quality of life. Pain is usually in the large weight bearing joints such as the knees and hips. It also affects the joints of the thumb and fingers. Hand osteoarthritis has a good prognosis with most cases becoming asymptomatic after a few years. Involvement of the thumb base may have a worse prognosis. Knee osteoarthritis is very variable in its outcome. Over a period of several years about a third of cases improve, a third stay much the same and the remaining third develop progressive symptomatic disease. Hip osteoarthritis probably has the worst overall outcome of the three major sites though some hips heal spontaneously.
Osteoarthritis is a complex disorder caused by a combination of genetic predisposition and environmental factors. Environmental factors include lifestyle factors such as being overweight, a sedentary occupation, repetitive use of joints and history of trauma to affected joints.
The genes that predispose to Osteoarthritis remain to be clarified. Many studies have pointed to different HLA class I and II associations, perhaps indicating the heterogeneity of the condition. Several studies on generalized Osteoarthritis have revealed an association with HLA-B8. Linkage of HLA-B8 on the HLA-A1, B8, DR17 haplotype makes it difficult to be certain the association is actually with HLA-B8 and not with some other gene on the haplotype. A Japanese study showed an association with HLA-Cw4. Other studies have indicated associations with HLA-B35, B40, DR2 and DQ1 but again linkage disequilibrium makes it difficult to be certain what the true disease susceptibility gene is.
Diagnosis of Osteoarthritis is on the basis of persistent joint pain that is worse with use, age 45 years old and over and morning stiffness lasting no more than half an hour, rather than on genetic testing. The main value of genetic testing in Osteoarthritis is to provide insights into the mechanism of the disease, thereby potentially suggesting strategies for prevention and treatment, rather than as a diagnostic tool.
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