Increased Body Mass Index is Associated With Increased Cost for Primary Total Knee Arthroplasty Exclusive of Readmissions and Complications

Background

Surgeons participating in alternative payment models may encounter financial disincentives in caring for high-cost patients. While prior studies have shown a relationship between body mass index (BMI) and cost in total knee arthroplasty (TKA), this question has not been examined using recent data in a nationally-representative dataset. We sought to use recent data to assess the relationship between BMI and cost in TKA.

Methods

We queried the 2016-2022 PINC AI Healthcare Dataset for primary TKAs identified by the Current Procedural Terminology code 27447. Baseline patient demographics, characteristics, and outcomes were gathered. Patient costs included index and 90-day period costs starting from the surgical encounter. A multivariate generalized linear model estimated patient costs across eight BMI categories (WHO BMI categories, with BMI >40 grouped into BMI 40-45, BMI 45-50, and BMI >50), and a linear regression model assessed the effect of BMI on costs. Both models controlled for age, sex, payer, race, ethnicity, and Elixhauser Comorbidity Index.

Results

A total of 24,064 primary TKAs were included. Patient characteristics were age (mean 68 years, SE 0.06), sex (62.3% female), payer (63.8% Medicare), race (88.6% white), ethnicity (3.1% Hispanic), and Elixhauser Comorbidity Index (mean 2.07, SE 0.01). The mean BMI was 32.0 (SE 0.1), with mean index and 90-day costs of $14,051 ± $32.6 and $17,377 ± 107.3, respectively. Predicted patient index and 90-day costs were both highest in the BMI >50.0 category at $15,555 and $20,716, respectively. Predicted index and 90-day costs were lowest in the 25.0-29.9 ($13,765) and <18.5 ($16,403) categories, respectively. The multivariate analysis showed that patient index and 90-day costs increased by $23.20 (P < .001) and $48.10 (P < .01), respectively, per one-point increase in BMI.

Conclusions

Higher patient BMI is associated with increased index and 90-day episodic costs for primary TKA. Stakeholders may consider incorporating this information in bundled payment models and other value-based reimbursement models.