Does Body Mass Index Decrease One Year Following Total Joint Arthroplasty?

Background: Obesity is prevalent in patients undergoing total joint arthroplasty (TJA) and is associated with multiple preoperative comorbidities and postoperative complications. Patients often suggest that obesity is due to the immobility imposed by painful osteoarthritis, and that weight loss would be facilitated by pain relief and improved function afforded by TJA. Recent evidence suggests that this may not be the case.

Purpose: To determine the trends in weight change in patients after TJA.

Hypothesis: Body Mass Index (BMI) will not significantly change after TJA.

Methods: This study was a retrospective review of prospectively gathered data. Patients who underwent primary total knee arthroplasty (TKA) and total hip arthroplasty (THA) by a single surgeon at a single center between 06/2014 and 05/2015 were included. Records were queried for age, sex, height and weight preoperatively and at 12.0±3.9 months postoperatively.

Results: 238 patients were screened for eligibility. Patients with missing data were excluded. 209 patients (92 males and 117 females) with mean ages of 65.4 and 69.6 years respectively were included. 27 males and 29 females underwent THA, 65 males and 87 females underwent TKA. Mean BMI preoperatively was 29.7±5.0 for males (mean height 187.1±9.1cm and weight 93.3±17.9kg) and 29.2±5.6 for females (mean height 161.0±7.9cm and weight 75.3±15.1kg). Mean BMI for males at follow-up was 30.7±5.0, corresponding to an average increase of 0.83 compared to preoperatively (p=0.455, 95% CI [-2.4,1.1]). Mean BMI for females at follow-up was 29.9±5.5, corresponding to an average increase of 0.39 compared to preoperatively (p=0.644, 95% CI [-2.1;1.3]). There were no significant differences between the BMI changes in the TKA and THA groups (p=0.612).

Conclusion: BMI should not be expected to change significantly in the first year following TJA. This finding is important to consider during preoperative counseling of patients as well as for postoperative management.

Figure 1: Preoperative and postoperative body mass index (BMI) in male and female total joint arthroplasty patients