Extra Weight Brings Hip Replacement Woes

GENEVA, March 2 -- Complications after hip replacement are more common for obese patients, particularly women, researchers here found.

Obese patients had a fourfold higher incidence of infection and twice as many dislocations as nonobese patients after hip replacement, according to a study in the March issue of Arthritis Care & Research.

Although total hip arthroplasty is still a successful intervention for obese patients, surgeons should alert these patients about the higher risk, said Anne Lbbeke, M.D., M.Sc., of the University Hospital of Geneva, and colleagues.

"In addition, participating in a weight-loss program prior to surgery might be beneficial for such patients," they suggested.

The prospective cohort study included all 2,186 patients (1,217 women, 508 obese) who had a hip replacement at a single center from 1996 to 2005. Acute hip fracture was excluded as were patients without height and weight information. A body mass index 30 kg/m² or more defined obesity.

After about 40.5 to 42 person-months of follow-up, 91 complications had occurred, including 17 deep infections, 53 dislocations, and 21 surgical revisions. The adjusted findings were:

• The infection rate was 4.4 times higher among obese patients (95% confidence interval 1.8 to 10.8) with a crude incidence of 1.7% versus 0.4%.
• The dislocation rate was 2.4 times higher among obese patients (95% CI 1.4 to 4.2) with a crude incidence of 3.7% versus 1.6%.
• The surgical revision rate was 2.0 times higher for obese patients (95% CI 0.9 to 4.8), particularly due to septic loosening of the joint (rate ratio 4.3 95% CI 1 to 19) with a crude incidence of 0.68% versus 0.16%).

Obese women were particularly at risk. The researchers reported:

• Obesity substantially increased the infection rate ratio among women (16.1, 95% CI 3.4 to 75.7) but not men (1.0, 95% CI 0.2 to 5.3),
• Dislocation was more common among men overall but obesity increased the rate more for women than men (rate ratio 3.0 versus 1.8).
• The rate ratio for revisions also increased more with obesity for women than men (2.3 versus 1.7).

At five years, obesity was associated with slightly lower functional outcomes (good to excellent 77% versus 58% for women and 85% versus 81% for men) and satisfaction (86% versus 77% for women and 86% versus 87% for men).

"In terms of clinical significance, the difference can be considered moderate," Dr. Lbbeke and colleagues wrote.

Reasons for the differences between sexes may include body fat distribution, metabolic response, and lower peripheral muscle strength.

Treatment characteristics were similar between obese and nonobese patients including the percentage who underwent bilateral replacement, choice of prosthesis, surgical approach, and rehabilitation although operation time was nine minutes shorter on average among nonobese patients.