1. In a meta-analysis of 14 prospective studies, increased body mass index (BMI) was a significant risk factor for knee osteoarthritis (OA).
2. BMI was found to be an independent predictor of knee OA, regardless of gender, sex, age, country, or duration of follow-up.
Evidence Rating Level: 2 (Good)
Study Rundown: OA is a degenerative disease which is characterized tenderness, joint pain, stiffness, limited mobility, joint deformities, and swelling. Currently, it is the most common form of arthritis in the knee and affects 20 million people in the United States. Obesity has been previously associated with an increased risk of developing knee OA. However, previous meta-analysis included both cohort and case-control studies, which may limit the accuracy of the true effect size of increased obesity on OA. The purpose of this study was to clarify this association.
The authors performed a meta-analysis on 14 prospective trials on obesity and knee OA. At the conclusion of the study, increased BMI was associated with a significant increase in knee OA. In terms of effect size, the risk of OA increased by 35% for every 5 kg/m2 increase in BMI. Additionally, subgroups analyses demonstrated that the increased risk persisted regardless of gender, sex, age, country, or duration of follow-up. The results of the study suggest that it is important for physicians to consider obesity as one of the most crucial factors for development of OA. Although the limitations of this study was that it was performed with a small sample size of participants within a small number of studies, random-effect models were applied to the data to avoid overstating the level of precision.
Relevant Reading: Obesity and Knee Osteoarthritis: The Framingham Study
In-Depth [ meta-analysis]: The meta-analysis identified 14 prospective studies from English-language journals published before August 2014. All studies calculated BMI according to the World Health Organization categorization (overweight: 25.0-29.9 kg/m2; obese over 30.0 kg/m2). The quality of studies were assessed by the Newcastle-Ottawa-Scale (NOS). Each study was reviewed by two independent investigators. At the conclusion of the trial, the relative risk of knee OA for patients who are overweight and obese were 2.45 (95% CI 1.88 to 3.20, p<0.001) and 4.55 (95% CI 2.90 to 7.13, p<0.001), respectively. Furthermore, for every 5 kg/m2 incremental increase of BMI, the risk of knee OA increased by 35%. In subgroup analysis, the increased risk of knee OA in overweight and obese patients remained regardless of study country, duration of follow-up, or gender.
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