Maximum lifetime body mass index is the appropriate predictor of knee and hip osteoarthritis.

INTRODUCTION: In light of inconsistencies in the literature, this study aimed to investigate the relationship between obesity (current and historic) and osteoarthritis (OA) of the knee or hip.

MATERIALS AND METHODS: We examined 99 people (knee OA, hip OA and controls), age > 50 years, in a case-control study. The current weight, height and waist circumference were measured on site, and detailed weight changes over their lifetime were based on questionnaires and standardized interviews. We used binomial logistic regression to determine the predictive value for an osteoarthritis group membership of each derived indicator.

RESULTS: An increase in 'maximum-BMI' increased the odds ratio for both knee OA (OR 1.2; CI 1.1-1.4; p = 0.005; R 2  = 0.36) and hip OA (OR 1.2; CI 1.0-1.3; p = 0.027; R 2  = 0.16). Current BMI was significantly associated with knee OA but not with hip OA. A high "minimum-BMI" (over the age of 18 years) had the highest odds ratio of all calculated indicators for both osteoarthritis groups.

CONCLUSIONS: Based on our findings, it is concluded that the maximum BMI over one's lifespan is a better predictor of OA of the hip or the knee than the current BMI. The knee joint seems to be more sensitive to obesity as current BMI was associated only with knee OA but not with hip OA.