The association between obesity and OA is arguably strongest and most consistent at the knee joint. In 1958, Kellgren and Lawrence found that knee OA was more common in obese people, particularly women. Since then, cross-sectional studies have consistently shown an association between obesity and knee OA, which has been stronger for women than men. Among obese middle-aged females with knee OA, it has been reported that the proportion of the disease attributable to obesity is approx 63% (26).
Longitudinal studies have consistently demonstrated an association between obesity and knee OA. A 35-yr follow-up study demonstrated a strong association between being overweight and the development of OA, particularly in women (27). Likewise, an increased BMI at a young age was a risk factor for knee OA in males (39). Twin studies have also demonstrated that a twin with tibiofemoral and patellofemoral OA is likely to be 3 to 5 kg heavier than the co-twin. Moreover, twin studies have also demonstrated a 14% increased risk of developing tibiofemoral osteophytes and a 32% increased risk of developing patellfemoral osteophytes for every kilogram gain in body weight (35).
Given that the knee is composed of distinct compartments, the association between obesity and knee OA may differ between the different knee compartments. Of the few studies that have examined the association between obesity and compartment OA, one cross-sectional study of middle-aged women demonstrated that obesity was an important risk factor for both medial tibiofemoral and patellofemoral joint disease (35). Another study demonstrated an association between obesity and tibiofemoral OA, but failed to show a relationship at the patellofemoral joint (40). These contrasting results highlight the need to clarify the association between obesity and OA at the different compartments in the knee complex. Nevertheless, the association between obesity and knee OA is unequivocal.
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