Fillingham Y, Zachwieja E, Rondon AJ, et al. - This study was carried out to assess the additional costs associated with individual medical comorbidities and demographic variables. Between 2015 and 2016, researchers examined a consecutive series of primary total hip and knee arthroplasty patients at our institution using claims data from Medicare and a single private insurer. Demographic data and medical comorbidities for all patients were collected. To control for confounding variables, a stepwise multivariate regression was conducted to ascertain the independent effect of medical comorbidities and demographics on 90-day episode-of-care costs.They identified 6,537 consecutive patients (4,835 Medicare and 1,702 private payer patients). In alternative payment models, providers participating should be aware of factors (cardiac history, age, and elevated BMI) associated with increased costs. A future trial is required to ascertain if risk adjustment in alternative payment models can prevent problems with access to care for these high-risk patients.