The association of obesity with osteoarthritis of the hand and knee in women: a twin study.

OBJECTIVE: To examine the association of obesity and osteoarthritis (OA) at various sites in middle aged women and to estimate the magnitude of the weight difference associated with OA.
METHODS: A co-twin control study was performed within a population based twin study of women aged 48-70. OA was defined radiologically using site specific features and a standard atlas. Twin pairs discordant for OA disease traits were analyzed.
RESULTS: The mean weight differences (95% CI) within twin pairs discordant for different OA traits were: tibiofemoral osteophytes 3.75 (1.29, 6.21) kg; patellofemoral osteophytes 3.05 (0.96, 5.15) kg; carpometacarpal (CMC) osteophytes 3.06 (0.83, 5.28) kg. There was no significant difference in weight within twin pairs discordant for osteophytes at the distal interphalangeal (DIP) or proximal interphalangeal (PIP) joints or for joint space narrowing at all sites examined except the patellofemoral joint, 4.73 (1.61, 7.84) kg. For each kg increase in weight the increased likelihood of developing different OA traits [OR (95% CI)] was: tibiofemoral osteophytes 1.14 (1.01-1.28), patellofemoral osteophytes 1.32 (1.09-1.59), patellofemoral narrowing 1.15 (1.01-1.30), and CMC osteophytes 1.09 (1.02-1.17).
CONCLUSION: Obesity is an important risk factor for development of OA at the tibiofemoral and patellofemoral joints of the knee and CMC joints of the hands, with significant increases of 9-13% in risk of OA per kg increase in body weight. This emphasizes the potential importance of even minor weight reduction as a preventive health measure for OA.