Should Medical Severity-Diagnosis Related Group Classification Be Utilized for Reimbursement? An Analysis of Elixhauser Comorbidities and Cost of Care

The Center for Medicare and Medicaid Services (CMS) classifies reimbursement for total hip arthroplasty (THA) and total knee arthroplasty (TKA) based on Medical Severity-Diagnosis Related Groups (MS-DRGs) 469 (with major complication/comorbidity) and 470 (without major complication/comorbidity). The validated Elixhauser comorbidity index includes 31 variables that may be associated with MS-DRG 469. However, we hypothesized that these comorbidities may not be the most predictive of increased cost of care.

Elixhauser comorbidities were retrospectively examined for 1243 TKAs and 897 THAs from 2013 to 2017 at a single center. Comorbidities were investigated in univariable analysis and significant variables associated with MS-DRG 469, and cost of care was further investigated in a multivariable regression to determine which were most predictive of the increased complexity classification assigned by CMS vs true increased cost of care.

Thirty-nine patients (1.8%) were classified as MS-DRG 469. Univariable and multivariable logistic analysis revealed that coagulopathy, electrolyte disorders, neurodegenerative disorders, and psychosis were significantly associated with an increased complexity classification. These 4 comorbidities were also associated with increased cost of care; however, 13 additional comorbidities were also predictive of increased cost but not MS-DRG classification.

Patient comorbidities have been shown to increase complications and cost of care for arthroplasty patients. To date, however, the only risk adjustment provided has been the 469 DRG code. This study demonstrates little correlation to the current system with the most expensive diagnoses. Consequently, an expansion of the current risk adjustment system for THA and TKA provided by CMS appears greatly needed.