The Charlson and Elixhauser Scores Outperform the American Society of Anesthesiologists Score in Assessing 1-year Mortality Risk After Hip Fracture Surgery.

BACKGROUND: Risk adjustment has implications across orthopaedics, including informing clinical care, improving payment models, and enabling observational orthopaedic research. Although comorbidity indices (such as the American Society of Anesthesiologists [ASA] classification, Charlson comorbidity index [CCI], and Elixhauser comorbidity index [ECI]) have been examined extensively in the immediate perioperative period, there is a dearth of data on their three-way comparative effectiveness and long-term performance. Moreover, the discriminative ability of the CCI and ECI after orthopaedic surgery has not been validated in the ICD-10 era, despite new diagnosis codes from which they are calculated. QUESTION/
PURPOSE: Which comorbidity index (ASA, CCI, or ECI) is associated with the greatest accuracy on receiver operating curve (ROC) analysis with respect to the endpoint of death at 90 days and 1 year after hip fracture surgery in the ICD-10 era?
METHODS: A retrospective study was conducted on all patients undergoing surgical fixation of primary hip fractures at two Level I trauma centers and three community hospitals from October 2016 to May 2019. This time frame allowed for a 1-year baseline period of ICD-10 data to assess comorbidities and at least a 1-year follow-up period to assess mortality. Initially 1516 patients were identified using Common Procedural Terminology and ICD codes, of whom 4% (60 of 1516) were excluded after manual review; namely, those with pathologic fractures (n = 38), periprosthetic fractures (n = 12), and age younger than 18 years (n = 10). Of the patients who were studied, 69% (998 of 1456) were women and the mean ± SD age was 77 ± 14 years; 45% (656 of 1456) were treated with intramedullary nails, 32% (464 of 1456) underwent hemiarthroplasties, 10% (149 of 1456) underwent THAs, 7% (104 of 1456) underwent percutaneous fixations, and 6% (83 of 1456) were treated with plates and screws. The mean ± SD ASA score was 2.8 ± 0.6, CCI was 3.1 ± 3.2, and ECI was 5.2 ± 3.5. Hip fracture fixation was chosen as the operation of interest given the high incidence of this injury, the well-documented effects of comorbidities on complications, and the critical importance of risk stratification and perioperative medical management for these patients. Demographics, comorbidities, surgical details, as well as 90-day and 1-year mortality were collected. Logistic regressions with ROC curves were used to determine the accuracy and comparative effectiveness of the three measures. The 90-day mortality rate was 7.4%, and the 1-year mortality rate was 15.0%.
RESULTS: The accuracy (area under the curve [AUC]) for 1-year mortality was 0.685 (95% CI 0.656 to 0.714) for the ASA, 0.755 (95% CI 0.722 to 0.788) for the ECI, and 0.769 (95% CI 0.739 to 0.800) for the CCI. The CCI and ECI were more accurate than ASA (p < 0.001 for both), while the CCI and ECI did not differ (p = 0.30). The ECI (AUC 0.756 [95% CI 0.712 to 0.800]) was more accurate for 90-day mortality than the ASA (AUC 0.703 [95% CI 0.663 to 0.744]; p = 0.04), while CCI (AUC 0.742 [95% CI 0.698 to 0.785]) with ASA (p = 0.17) and CCI with ECI (p = 0.46) did not differ at 90 days.
CONCLUSION: Performance measures and research results may vary depending on what comorbidity index is used. We found that the CCI and ECI were more accurate than the ASA score for 1-year mortality after hip fracture surgery. Moreover, these data validate that the CCI and ECI can perform reliably in the ICD-10 era. If other studies from additional practice settings confirm these findings, as would be expected because of the objective nature of these indices, the CCI or ECI may be a useful preoperative measure for surgeons to assess 1-year mortality for hip fracture patients and should likely be used for institutional orthopaedic research involving outcomes 90 days and beyond. LEVEL OF EVIDENCE: Level III, diagnostic study.