Patients successfully lose body weight after primary total knee arthroplasty but not more than a matched general population.

High BMI is associated with increased risk for knee osteoarthritis, ultimately necessitating total knee arthroplasty (TKA). The aim of this retrospective study was to (1) analyse the amount of postoperative long-term weight loss as reflected by BMI change in TKA patients, (2) identify factors associated with increased change in BMI, and to (3) compare changes with BMI trends of a general population. Overall, 298 TKA patients [198 females; mean age: 65.1 ± 7.9 years, median follow-up 8.8 (interquartile range: 5.9-10.8 years)] were included in the final evaluation and compared with an age group-matched control group from the general population regarding weight trends between 2006 and 2014. Main variable of interest in both cohorts was body mass index (BMI). Linear regression analyses were performed to assess changes in weight and BMI over time between TKA patients and the general population. Furthermore, mixed linear-effects models were constructed to analyse the potential change in BMI independent from age and gender. In TKA patients, a significant drop in BMI by 0.8 ± 3.2 points from postoperative to final follow-up was observed (p < 0.001), with reduction being significant independently from age (p = 0.382), gender (p = 0.310), or revision surgery (p = 0.195). In the general population, likewise a significant BMI-decrease by 0.7 ± 6.1 points was observed between 2006 and 2014, with younger people (p = 0.004) and females (p < 0.001) being more likely to reduce BMI. Yet, BMI-decrease between TKA patients and the general population over time was comparable (p = 0.734). Notably, patients with initially higher BMI were significantly more likely to lose weight postoperatively than normal-weight patients (p < 0.001). Our results point against the notion that TKA patients lose a considerable amount of weight in comparison to the general population as soon as improved joint function and pain relief have been achieved. Thus, individualized patient education programmes should be reinforced, promoting a healthy lifestyle.

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