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

https://doi.org/10.1016/S0749-3797(03)00218-6Get rights and content

Abstract

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/m2 (total hip: OR=9.37, 95% confidence interval [CI] 2.64–33.31; total knee: OR=16.40; 95% CI 5, 19–51.86). In females, the highest OR was for those weighing ≥40 kg/m2 (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.

Introduction

O steoarthritis (OA) is the most common form of arthritis, with about 5% of the U.S. population having hip or knee OA. Among adults aged ≥62 years, the prevalence of knee OA has been estimated at 9.5%.1 OA is severely debilitating in many cases and frequently leads to joint replacement surgery. More than 70% of total hip and knee joint replacements are due to OA.1

Body mass index (BMI), a relative measure of weight, has been associated with OA of the knee in a number of cohort,2, 3, 4, 5 case-control,6, 7 and cross-sectional studies,8, 9, 10 but the data relating obesity and hip OA are inconsistent. Although a few studies have found an association between obesity and hip OA,11, 12, 13 other studies have found no association.14, 15 The effect of BMI on OA is a rising concern as obesity rates in the United States continue to climb. According to 1999 national statistics, 61% of the U.S. adult population is either overweight (BMI 25 kg/m2 to 29.9 kg/m2) or obese (BMI >30 kg/m2).16

We hypothesized that those overweight and obese are more likely to develop generalized OA17, 18, 19 that leads to OA of both the hip and knee joints, which will be associated with elevated risks for joint replacement surgeries. It was also hypothesized that obesity is a risk for partial hip replacements and revisions of the hip and knee joint replacement surgeries, although we are unaware of any previous studies of those outcomes. A large case-control study was designed to estimate the risk of increasing BMI on knee and hip replacement surgeries.

Section snippets

Methods

The University of Utah's Institutional Review Board approved this study.

Results

The relationship between increasing BMI and total hip replacement surgery appears stronger in males than females (see Table 3). However, there is a fairly consistent relationship in both genders. Statistical significance was achieved in the BMI groups 30.00 to 32.49 kg/m2 and above in males and in the BMI groups 27.50 to 29.99 kg/m2 and above in females. The chi-square linear test for trend in both males and females was highly significant (p<0.0001). The interaction term from the regression

Discussion

The relationship between increasing BMI and total hip replacement surgeries in this study is strong in contrast with some prior reports.11, 12, 13, 14, 15 This study confirmed other findings of strong associations for knee replacement surgery.2, 3, 4, 5, 6, 7, 8, 9, 10 The compelling OR concerning the total knee procedure lends greater evidence that being overweight, not just obese, is a risk factor for developing OA. There was also a relationship between increasing BMI and hip revision and

Acknowledgements

This study was partially supported by a grant from the Centers for Disease Control and Prevention/National Institute for Occupational Safety and Health (Training Grant T42/CCT810426-06-1). This study was also partially funded by the Prostate Lung Colorectal and Ovarian Cancer Screening Trial, University of Utah (contract N01-CN25524).

We are grateful for the help of Dr. Brent James and Abe Lindemen from Intermountain Health Care for helping obtain the data. We are also grateful to Dr. Saundra S.

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