No influence from BMI found on primary THA efficacy at one year

Patients with a BMI over 35 have an increased risk of complications and need for skilled nursing care.

CHICAGO — Despite increased complications and longer hospital stays, new research shows no clinically significant differences in outcomes at one year between the highly obese and normal-weight total hip arthroplasty patients.

Thomas R. Turgeon, MD, FRCSC, an orthopedist at the University of Manitoba in Winnipeg, Manitoba, and colleagues prospectively evaluated 1343 total hip arthroplasty (THA) patients divided into four groups according to body mass index (BMI), as follows:

normal, BMI of 18.5 to 25;
overweight, BMI of 25 to 30;
low obesity, BMI of 30 to 35; and
high obesity, BMI of 35 or higher.

The researchers found that preoperative and one-year postop modified Harris Hip Scores (HHS) averaged a 3.5-point difference between the heaviest patients and those with normal BMI. However, patients with the highest BMI encountered more difficulties.

“In the BMI category of greater than 35, the odds of a complication occurring while in the hospital were 2.4-times increased, the odds of staying greater than five days was 2.3-times increased and the odds of skilled nursing facility usage were 2.6-times increased than those in the normal BMI category,” said Turgeon, who presented the study results here at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting.

The researchers also found that low obesity patients had slightly higher intraoperative blood loss. “They were slightly less likely to receive a blood transfusion and yet, despite this, had on average a slightly higher than average hematocrit discharge than the normal BMI group,” Turgeon said.

“The same trend was also seen in the greater than 35 BMI group, however it was not statistically significant. This was felt to be due to a relationship between body mass and circulatory volume, which makes a heavier patient slightly more tolerant to the blood loss,” he said.

Unilateral THA patients

The study included adult patients who received primary, unilateral THA at two San Diego centers. Researchers collected preoperative HHS, patient demographics and mental assessments. “In the perioperative period, we included transfusions, complications, the length of stay in the hospital and the use of a skilled nursing facility after,” Turgeon said. The researchers also gathered one-year postoperative complication rates and the modified HHS for pain and for functional assessments only.

Initially, the study included two high obesity patient groups — patients with a BMI of 35 to 40 and those with a BMI over 40. However, the researchers combined these two BMI classes due to a lack of patients with a BMI over 40. Similarly, they also excluded an underweight patient cohort because of limited numbers.

“We controlled for the comfounding variables we identified as gender, the number of comorbidities and a higher than average preop Harris Hip Score,” Turgeon said. “What we found was that for each of the three elevated BMI categories, their scores were relatively reduced compared to the normal BMI group. However, the absolute value of the differences was really quite small.”

Compared to normal-weight patients, Harris Hip Scores dropped by 2.4 points among overweight patients (P=.001), by 2 points among low obese patients (P=.02) and by 3.5 points among high obese patients (P=.002), according to the abstract.

Despite comparable clinical outcomes at one-year, patients with the highest BMI faired the worst in the study. This group had an increased risk for intraoperative complications, a greater need for skilled nursing care and longer hospital stays compared to normal BMI patients.

Researchers found no increases regarding these factors for the overweight and low obesity groups, Turgeon said, noting patient age did not affect the results.

For more information:
Turgeon TR, Santore RF, Coutts RD. Influence of obesity on outcome following primary hip replacement. #10. Presented at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. March 22-26, 2006. Chicago.