The Charlson and Elixhauser Scores Outperform the American Society of Anesthesiologists Score in Assessing 1-year Mortality Risk After Hip Fracture Surgery
Authors: Varady Nathan H. , Gillinov Stephen M. , Yeung Caleb M. , Rudisill Samuel S. , Chen Antonia F. 
Published: April 2021

Abstract

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.