Relationships between body mass indices and surgical replacements of knee and hip joints

Background: Osteoarthritis is both the most common form of arthritis and the most common reason for joint replacement surgery. Obese persons are believed to be more likely to develop generalized osteoarthritis that leads not only to knee but also to hip joint replacement surgeries. We hypothesized that obesity is also a risk for partial joint replacements and surgical revisions. Methods: A frequency matched case-control study was conducted in Utah. Between 1992 and 2000, 840 hip and 911 knee joint replacement surgery patients, aged 55 to 74 years, were included in this study. Cases were randomly matched to 5578 controls, defined as Utah residents enrolled in a cancer screening trial. Odds ratios (ORs) were calculated using ICD-9 (International Classification of Diseases, 9th revision) procedural codes and body mass index (BMI) groups. Results: There was a strong association between increasing BMI and both total hip and knee replacement procedures. In males, the highest OR was for those weighing 37.50 to 39.99 kg/m(2) (total hip: OR = 9.37, 95% confidence interval [CI] 2.64-33.31; total knee: OR = 16.40; 95% Cl 5, 19-51.86). In females, the highest OR was for those weighing greater than or equal to40 kg/m(2) (total hip: OR = 4.47; 95% CI, 2.13-9.37; total knee: OR = 19.05; 95% CI, 9.79-37.08). There were slight gender-specific differences in risk found for partial hip replacement procedures. Unexpectedly, no statistically significant association was found between obesity and the risk for hip or knee revision procedures. Conclusions: While there is an association between obesity and hip and knee joint replacement surgeries, obesity does not appear to confer an independent risk for hip or knee revision procedures.