Patients lose weight after a total knee arthroplasty: myth or reality?

Obesity is one of most discussed factors when assessing prosthetic knee surgery outcomes. Prior to the procedure, most patients perceive that their excessive weight is secondary to the low level of activity due to limiting knee pain.

The main objective of this study was to assess whether patients undergoing total knee arthroplasty (TKA) lose weight after the procedure. The secondary objective was to correlate weight loss with post-operative knee function.

A prospective observational study was designed including 247 patients who undergone TKA from January 2018 to January 2019. A significant change in weight was considered anything above or below 5% of the pre-operative weight. Three groups were established based on a change in weight: loss of more than 5%, those who did not pass above or below 5% of their initial weight and increase of more than 5%. Follow-up was carried out at 12 months after the intervention assessing patient's BMI (kg/m²), functional level (KSS), weight loss expectations, and range of motion.

Among the total population, 17 (6.9%) lost weight, 168 (68%) did not have a change, and 62 (25.1%) increased weight at one year follow-up. The mean pre-operative BMI was 31.5 kg/m², and mean postoperative BMI was 31.98 kg/m². Furthermore, obese patients were more likely to present weight reduction than non-obese (p = 0.01). When comparing functional results between groups, no differences were observed in terms of KSS-K and KSS-F.

Patients who undergo TKA do not lose weight one year after surgery. When correlating weight loss with post-operative outcomes, no differences were observed between groups.