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Flowchart of the study population. Changes in Body Weight After Total Hip Arthroplasty 682 f Physical Therapy Volume 92 Number 5 May 2012 significance level of P.01 was considered statistically significant. Results A total of 653 patients (77%) returned the questionnaire 1 year after surgery. The response rates for the 3 hospitals were 61% (university hospital), 74% (large teaching hospital), and 95% (regional hospital). In 35 medical records, preoperative weight or height could not be found. As a result, 618 patients were included in the 1-year followup. In the 5-year follow-up group, 106 patients (71%) returned the questionnaire. The response rates for the three hospitals were 60% (university hospital), 81% (large teaching hospital), and 73% (regional hospital). For 6 patients, data were incomplete, which led to the inclusion of 100 patients. The mean follow-up time of the long-term follow-up group was 4.5 years. Demographic Characteristics The Table shows the demographic characteristics and the BMI and ASA classification of the short-term (1-year) and long-term (4.5-year) follow-up groups at baseline. In both groups, most patients were overweight and had mild systemic disease at the time of surgery. The representativeness of this longterm follow-up group also was analyzed. To that end, the demographic characteristics and baseline BMI and ASA scores of the short-term and long-term follow-up groups were compared. Short-term Effect of THA on Body Weight In Figure 2 the mean standard error) body weight of patients is shown per BMI category preoperatively and 1 year postoperatively. The GEE analysis showed a significant increase in body weight of 0.7 kg in the group with normal weight (95% confidence interval [CI]0.1 to 1.4), which corresponds to a 1.1% weight gain; a significant decrease in body weight of 0.8 kg (95% CI1.2 to 0.3) in the group with overweight, which corresponds to a 1.0% weight loss; and a significant decrease in body weight of 3.2 kg (95% CI4.2 to 2.2) in the group with obesity, which corresponds to a 3.4% weight loss. The GEE analysis showed no confounding or effect modification by sex, other knee or hip surgery, or age at the time of surgery for the change of body weight in time (data not shown). The ASA score did not affect the change of body weight over time (no confounding or effect modification) for any patients except those who were obese and had an ASA score of 3. In this particular group, no confounding was shown, but effect Preoperatively Postoperatively 1 year Body Weight Change per BMI D) unless otherwise indicated. BMIbody mass index (kg/m2 ), ASAAmerican Society of Anesthesiologists. Changes in Body Weight After Total Hip Arthroplasty May 2012 Volume 92 Number 5 Physical Therapy f 683 modification was significant (95% CI2.2 to 8.2), resulting in a smaller decrease in body weight compared with patients with an ASA score of 1 standard error) body weight of patients preoperatively and 1 year and 4.5 years postoperatively by BMI category. The GEE analysis of the long-term effect of THA on body weight showed no change in body weight in the group of patients who were of normal weight and the group of patients who were overweight, but a significant decrease of 6.2 kg of body weight for those patients who were obese (95% CI9.0 to 3.5), which corresponds to a 6.4% weight loss. The GEE analysis showed no confounding or effect modification by sex or age at the time of surgery for the change of body weight over time (data not shown). The ASA score did not affect the change of body weight over time (no confounding or effect modification) for any patients except those who had a normal weight and an ASA score of 3. In this particular group, no confounding was shown, but effect modification was significant (95% CI8.2 to 2.4), resulting in a prominent decrease in body weight compared with those who had a normal weight and an ASA score of 1 (Fig. 5). Discussion The results of this study showed that 1 year (short term) as well as 4.5 years (long term) after THA, there was no (5%) clinically relevant reduction in body weight compared with preoperative body weight, except for patients with obesity in the long-term group. In addition, body weight change was influenced by an ASA 3 status, which led to a more apparent decrease after 1 year in patients who were obese compared with patients with an ASA 1 status who were obese. The same pattern in body weight was seen in patients with normal weight and an ASA 3 status in the long-term group compared with patients with an ASA 1 status who were of normal weight. The results of our study are in line with existing literature about weight change after THA surgery, which shows an increase or no change at all.12,18–21 Although weight reductions were found in our research, they were small and considered not clinically relevant, with the exception of the patients with obesity in the long-term follow-up group. This latter finding is not seen in the study by Dowsey et al,20 which categorized a study population of 471 patients into nonobese (BMI 30 kg/m2 ), obese (BMI 30–40 kg/m2 ), and morbidly obese (BMI 40 kg/m2 ) groups. In that study, the obese group gained 0.7 kg Effect Modification in Patients With BMI >30 kg/m2 Effect modification of American Society of Anesthesiologists (ASA) score for patients with
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