Summary

Overweight is already known to increase the risk of knee osteoarthritis. Now a study on Icelandic men and women who had had either knee or hip joint replacement surgery shows that excess weight is a factor in needing a hip replacement for men, but not for women. Overweight increased the risk of needing a knee replacement among both sexes.

Introduction

The link between body mass index (BMI) and knee osteoarthritis is well known. A high BMI increases the risk of getting arthritis in the first place and makes it worse once it is established. Rather less is known about the relationship between high BMI and hip osteoarthritis. Since both conditions are painful and disabling, it is worth finding out more about the role excess weight plays - given this is a risk factor than can be modified by lifestyle changes focused on diet and exercise.

What was done

Researchers in Sweden and Iceland compared a group of 1473 Icelandic patients who had undergone hip or knee replacement with age-matched relatives who had not had a joint replacement. There were 601 men and 872 women in the patient group. They filled in a questionnaire, providing information about their weight and height, from which BMI was calculated. The BMI data was verified by checking it against a health database that covers the Icelandic population.

What was found

Men who were overweight, with a BMI between 25 and 30, were more ten percent likely to have had a hip replacement than men of normal weight. Men who were obese, with a BMI of more than 30, were 70 percent more likely to have had a hip replacement. Women who were overweight or obese did not have an increased risk of having had a hip replacement, however.

When it came to need for a knee replacement, overweight and obese men and women were both at risk. Obese men were five times more likely to need a knee replacement, obese women four times more likely.

What this study means

The findings on excess weight and the need for knee replacement confirm what is already known, but the findings for hip replacement, with the differences between men and women, are new. The differences could be due to anatomical differences between men and women. Although joint replacements do improve mobility and quality of life, it is clearly better not to need them in the first place. Keeping to a healthy weight is clearly one was in which this particular procedure might be avoided.