Hospital-Specific Total Joint Arthroplasty Casemix and Patient Flows in the Era of Payment Reform: Impact on Resource Utilization Among New York State Hospitals

Background: Bundled payment models may lead to selection of healthier total joint arthroplasty (TJA) candidates resulting in comorbid patients being taken care of in fewer hospitals. We aimed to (1) evaluate hospital-specific TJA comorbidity burden (“casemix”) over time and (2) associations with resource utilization. Methods: This retrospective cohort study used 2011 and 2016 New York State data (n = 36,078 hip/knee arthroplasties). Comorbidity burden was estimated by the Charlson-Deyo Index; main outcomes were hospitalization cost and nonhome discharge. Hospitals were categorized into those with a decreased, stable (with a 5% buffer), or increased percentage of comorbidity-free patients (Charlson-Deyo = 0) between 2011 and 2016. Mixed-effects models measured the association between Charlson-Deyo Index category and outcomes, by hospital casemix categorization. Odds ratios and 95% confidence intervals (CIs) are reported. Results: Overall, 29 (n = 8810), 37 (n = 16,297), and 46 (n = 10,971) hospitals were categorized into the decreased, stable, and increased Charlson-Deyo = 0 categories, respectively, with median annual TJA volumes of 499, 814, and 393 (P < .0001). Multivariable models demonstrated that—in hospitals with a stable patient casemix—increased patient comorbidity was associated with increased hospitalization costs (maximum 21.8%, CI 18.9-24.9, P < .0001). However, this effect was moderated (maximum 11.1%, CI 8.0-14.2) in hospitals that took on a more comorbid patient casemix. Similar patterns were observed for nonhome discharge. Conclusion: Most studied hospitals show an increase in comorbidity-free TJA patients, suggestive of patient selection. This redistribution of comorbid patients to select hospitals may not necessarily be a negative development as our results suggest more efficient resource utilization for comorbid patients in such hospitals.