Conversion total knee arthroplasty: A case complexity between primary and revision total knee arthroplasty.

BACKGROUND Conversion total knee arthroplasty (TKA) may represent a more complex procedure compared with primary TKA. The purpose of this study was to compare 30-day complications between conversion TKA and primary, non-conversion TKA as well as between conversion TKA and revision TKA on a national scale using a multi-center surgical registry. METHODS Adult patients undergoing conversion TKA from 2006 to 2018 were identified in the National Surgical Quality Improvement Program database and were compared with patients who underwent primary TKA and aseptic revision TKA. In this analysis, 30-day complications were assessed. Bivariate analyses, including chi-squared and analysis of variance, and multivariate logistic regressions were performed. RESULTS Of 299,065 total patients undergoing knee arthroplasty, 1,310 (0.4%) underwent conversion TKA, 275,470 (92.1%) underwent primary TKA, and 22,285 (7.5%) underwent revision TKA. Following adjustment, patients who underwent conversion TKA were more likely to have increased risks of any complications (P < 0.001), mortality (P = 0.021), wound complications (P < 0.001), cardiac issues (P = 0.018), bleeding requiring transfusion (P < 0.001), and reoperation (P = 0.002) relative to primary TKA patients. Compared with patients who underwent revision TKA, conversion TKA patients were less likely to have septic complications (P = 0.009). CONCLUSION Conversion TKA is associated with significantly higher rates of complications compared with primary, non-conversion TKA, but less risk of sepsis compared with revision TKA. Because current reimbursement classifications do not account for the case complexity of a conversion TKA, new classifications should be implemented with reimbursements for conversion TKA approximating reimbursements for revision TKA.