The effect of body mass index on 30-day complications after total hip arthroplasty.

BACKGROUND

Evaluating body mass index (BMI) as a continuous variable eliminates the potential pitfalls of only considering BMI as a binary or categorical variable, as most studies do when correlating BMI and total hip arthroplasty (THA) outcomes. Therefore, the objective of this study was to correlate the effect of continuous BMI on 30-day complications post-THA. Specifically, we correlated BMI to: (1) 30-day readmissions and reoperations; (2) medical complications; and (3) surgical complications in: (a) normal-weight; (b) over-weight; (c) obese; and (d) morbidly obese patients.

METHODS

Using the NSQIP database, 93,598 primary THAs were identified. 30-day rates of readmissions, reoperations, and medical/surgical complications as well as patient BMI data were extrapolated. A comparative analysis using univariate, multivariate, and spline regression models adjusting for demographics and comorbidities were created to study the continuous effect of BMI on different outcomes.

RESULTS

Readmission ( 0.001), reoperation ( 0.007), superficial infection ( 0.003), prosthetic joint infection ( 0.001), and sepsis ( 0.026) had a J-shaped relationship with BMI, with the lowest rates seen in patients with BMI around 28 kg/m. The risks of mortality ( 0.007) and transfusion ( 0.001) had a reverse J-shaped relationship, with the risk steadily decreasing for BMIs in the normal weight and overweight range, and then flattening afterwards.

CONCLUSION

This data proposes a multifactorial effect of BMI on post-THA complications. Considering BMI as a continuous variable allows for a better assessment when considering the interplay between modifiable risk factors, such as smoking or alcohol use, as well as multiple comorbidities.