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longevity.16 With respect to general health, overweight or obesity is considered a risk factor for all kinds of serious illnesses, such as type 2 diabetes and coronary heart disease,17 which is another reason for losing weight after a THA. From the small number of studies presenting change of body weight in patients with hip OA who were overweight, it can be concluded that these patients do not lose weight after hip arthroplasty; some of these studies presented no change, and some showed an increase in body weight. However, there are some points of criticism that can be raised with respect to these past studies, including the fact that some studies used no BMI categories (normal weight, overweight, or obese)18,19; that patients were recruited from one source (eg, university or regional hospital), which might have consequences for the generalizability of results12,18–21; that some studies did not consider the influence of comorbidities or presurgical fitness status (American Society of Anesthesiologists [ASA] status) in their analyses12,18,19,21; and that the effect was determined only 1 year after THA.18,20 The objective of this study, therefore, was to analyze the short-term and long-term effects of THA on body weight, taking into account the aforementioned points of criticism. Method Design and Setting An observational, multicenter cohort study was conducted at the University Medical Center in Groningen (university hospital), Martini Hospital in Groningen (large teaching hospital), and Ro¨pcke-Zweers Hospital in Hardenberg (regional hospital). All hospitals are situated in the northern part of the Netherlands. Recruitment for the study started in 2005, and the last data were collected in 2010. Data Collection Patients’ sex, age at surgery, selfreported height, self-reported body weight, and ASA status were recorded from their medical records. The ASA status is a standard measure of fitness for surgery, scored in this study as 1 (normal, healthy), 2 (mild systemic disease), or 3 (severe systemic disease).22 Postoperative selfreported body mass was obtained through questionnaires, with a mean of 1 year (short-term) and 4.5 years (long-term) postoperatively. These questionnaires also asked whether the patients had had other knee or hip surgery in the follow-up period. Selection Criteria Patients admitted to the orthopedic surgery department in 2005 and 2006 for an elective THA because of primary hip OA were eligible for the study (N848) and invited to participate by a questionnaire sent 1 year after surgery (shortterm effect). A total of 653 patients returned the questionnaire, and their medical records were assembled to collect body weight and height at the time of surgery. A flowchart of the study population is presented in Figure 1. To get an impression of the longterm effect, approximately 20% of the 1-year follow-up group was selected at random. In this draw, the different ratios related to the origin of the patients from the 3 different hospitals were taken into account. In addition, a non-response of 20% was taken into account, which eventually resulted in 150 patients who were sent a questionnaire for the second time. Changes in Body Weight After Total Hip Arthroplasty May 2012 Volume 92 Number 5 Physical Therapy f 681 Height, Body Weight, and Body Mass Index Preoperative height and body weight from the medical records, as well as the postoperative data, were selfreported. Preoperative BMI was calculated by dividing body weight in kilograms by height in square meters. For preoperative BMI, the patients were divided into BMI categories defined as normal weight (BMI 25 kg/m2 ), overweight (BMI between 25 and 30 kg/m2 ), and obese (BMI 30 kg/m2 ).23 Body Weight Change Body weight change was measured per BMI category and considered clinically significant if the loss or gain was at least 5% of the preoperative weight.24 This minimum amount of weight loss is required to induce metabolic and cardiovascular health benefits.25 Data Analysis Descriptive statistics were used to describe the study sample. The baseline characteristics of the short-term follow-up group and the long-term follow-up group were compared for differences using chi-square and independent t-test analyses. Generalized estimating equations (GEEs) were used to investigate the time course of body weight in the patients who had a THA at baseline.26 The GEE adjusts for the correlation between repeated observations taken from the same individual and is able to handle longitudinal data on participants with a varying number of unequally spaced observations. An exchangeable correlation structure was assumed in all analyses. All statistical analyses were performed with PASW Statistics 18 (SPSS Inc, Chicago, Illinois). A significance level of P.05 was considered statistically significant. For effect modification analysis, the variables sex, age at time of surgery, other knee or hip surgery, and ASA status were taken into account, and a Assessed for eligibility (N=848) Non-response (n=195) Included in the study by returning questionnaire (n=653) Analyzed short-term (1 y) (n=618) Lost to follow-up (n=35) - Missing preoperative data Non-response (n=44) - Deceased (5) Assessed for subgroup (n=150) Returned questionnaires (n=106) Lost to follow-up (n=6) - Missing data Analyzed long-term (4.5 y) (n=100)
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