Today's News

Saturday, February 15, 1997

Obese patients have good hip replacement outcomes

Obese patients obtain a similar benefit from total hip arthroplasty as nonobese counterparts and do not have an increased of operative risk or complications due to their obesity.

Clinical assessment was performed preoperatively and postoperatively on 47 obese patients and 47 nonobese patients who had total hip arthroplasty. The postoperative assessment was at three, six and 12 months and then on an annual basis for two to five years.

The results, reported in scientific paper 246 Friday, showed that postoperatively both groups had dramatic improvement in reported pain, walking distance and range of motion. The obese patients had a significantly lower postoperative walking distance than nonobese patients.

There were no statistically significant differences between the groups for either intraoperative or long-term complications, said co-author of the study, Mark M. Harrison, MD, division of orthopaedic surgery, St. Michael's Hospital, University of Toronto, Canada.

There were no significant differences between the groups for operative time or intraoperative blood loss. The incidence of dislocation, intraoperative fracture, trochanteric nonunion, infection and DVT/pulmonary embolus was the same in both groups.
The obese group had a trend towards more trochanteric fractures and nonunion of the trochanter, but this did not reach statistical significance, Dr. Harrison said. There were no cases of infection in the nonobese group and one case of infection requiring revision in the obese group.

Radiographic assessment of the femoral component showed excellent bone ingrowth for both groups. There was very little evidence of femoral osteolysis. There was radiographic evidence of acetabular loosening in five hips in the nonobese group and one hip in the obese group. The obese and nonobese group did not differ in terms of the incidence of acetabular loosening, the amount of radiolucency surrounding the acetabular component nor the degree of acetabular migration.

A major concern with obese patients is material failure of the polyethylene liner due to the high loads placed on it. The study indicates that obese patients are not at increased risk of failure, Dr. Harrison said.

"The trend for obese patients to have less acetabular loosening may be related to differences in acetabular density," Dr. Harrison said. "Obesity may be protective through a hormonally mediated mechanism. Alternately, obese patients may have less polyethylene wear than their nonobese controls. Obese patients have a documented decrease in activity level. If polyethylene wear particle production is mainly caused by the number of cycles of loading, then the lesser activity level would be protective. Although the obese patient loads the cup more with each step, there are fewer cycles of wear and hence overall less production of polyethylene wear debris."

Co-authors of the study are Emil H. Schemitsch, MD; Delan Jinaprya; Jane Morton, RN; and James P. Waddell, MD, all of the division of orthopaedic surgery, St. Michael's hospital.