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body mass index (BMI) of 30 kg/m2 1 year postoperatively. T0time of surgery, T11 year after surgery. Body Weight Change per BMI Category BMI Group kg Preoperatively Postoperatively 1 year Postoperatively 4.5 years 120 100 80 60 Figure 4. Body weight changes 1 and 4.5 years after total hip arthroplasty. *Significant change compared with baseline (P.05); shown are mean and standard error. BMIbody mass index (kg/m2 ). Changes in Body Weight After Total Hip Arthroplasty 684 f Physical Therapy Volume 92 Number 5 May 2012 in 1 year, whereas in our study, the obese group lost 3.2 kg in 1 year. The proportion of men and women in the Dowsey et al study sample was comparable to ours; therefore, it provides no explanation for the differences in results. The contradictions in weight change in both studies could be explained by the different numbers of patients who were morbidly obese and the way they were categorized. In our study, the percentage of patients who were morbidly obese was only 1.6%, so we did not categorize this specific group separately, whereas in the Dowsey et al study, 8% were morbidly obese. Vincent and colleagues stated that patients who are morbidly obese need far more time and effort for rehabilitation and subsequently to achieve physical improvements than patients who have less body mass,27 which can have an effect on losing weight. Aderinto et al19 examined a longterm (3-year) effect of THA surgery on body weight change. They categorized their study group of 140 patients into nonobese (BMI 30 kg/m2 ) and obese (BMI 30 kg/ m2 ) groups. Their obese group (n 59) showed an increase in body weight of 4 kg in 3 years. Again, this finding is in sharp contrast to our results of losing 6 kg after 4.5 years in the obese group (n31). Cultural, sex (in Aderinto and colleagues’ study, 55% were women; in our study, 67% were women), and group size differences aside, we have no explanation for this contrast. In a study by Middleton and Boardman,12 all patients had an increase in body weight, unlike the outcomes of our study. Middleton and Boardman examined the change of BMI, instead of body weight, 2 years after a THA surgery. It was not stated clearly, however, what had been the indication for surgery (OA, fracture, or other reasons) or whether there were comorbidities at the time of surgery, both of which could influence the outcome of the hip arthroplasty and subsequently a possible change in weight. The finding in our study that sex and age at the time of surgery were not confounders or effect modifiers is in agreement with the findings of Aderinto et al19 and Dowsey et al.20 They showed that neither age nor sex predicted weight change after a primary THA. However, Dowsey et al concluded that comorbidities had no association with weight change after a primary THA either. This finding is in contrast to our finding that patients with a preoperative ASA score of 3, indicating severe systemic disease, presented a different course of weight change than patients with normal weight and obesity. For patients who were obese, the smaller decrease in body weight was not unexpected, as being obese and having severe systemic disease at the same time probably makes losing weight more difficult. In the patients who were of normal weight, there was a decrease in body weight, which was not expected and certainly not aimed for in this subcategory. An explanation of this difference in outcome between our study and the study by Dowsey et al may lie in how comorbidities were measured and defined. Dowsey et al categorized the comorbidities as diabetic, cardiovascular, or respiratory types.20 No information about the severity of these comorbidities at the time of surgery was provided. More research would be advisable, especially among patients of normal weight and comorbidities at the time of surgery, to gain insight into determinants of this phenomenon and to avoid undesirable weight loss. Strengths and Limitations The large study group and the long-term follow-up of 4.5 years were major strengths of this study. Because of the difficulties in explaining why weight gain or weight loss occur in this type of research, we also consider it a strength to have taken the baseline BMI and comorbidities into account when analyzing our results. Another strength was the sourcing of patients from 3 different types of hospitals, which limits the risk of selection bias and improves generalizability of results. Effect Modification in Patients With BMI ANN MARIE SCHMIDT ’83, MELANIE JAY ’00, AND BRIAN ELBEL, PHD, ARE USING DATA AND TECHNOLOGY TO CONNECT RESEARCH IN BASIC SCIENCE, CLINICAL MEDICINE, AND POPULATION HEALTH. by jen swetzoff A nn Marie Schmidt ’83 has never forgotten the patients she saw as a resident in internal medicine at Bellevue more than 30 years ago. Back then, blood tests for type 2 diabetes, the most common kind of diabetes and the one most often associated with obesity, had only recently emerged. Insulin pumps were just becoming available. Many of her patients worked two or more jobs, unable to monitor their insulin levels regularly or compute a daily step count. There was no affordable diabetes drug to prescribe. “Those patients in the clinic had so many stresses and complications related to diabetes, including blindness, plus a lot of economic challenges,”
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