Background: The purpose of this study was to review the results of the first four years of use of the American Society of Anesthesiologists (ASA) physical status rating system in the New Zealand Joint Registry. Our hypothesis was that patients with a higher ASA score would have an increased mortality rate, an increased early revision arthroplasty rate, and poorer clinical outcomes at six months after total hip or knee arthroplasty.
Methods: We prospectively evaluated the preoperative ASA classes for all patients in the registry who underwent primary total hip or knee arthroplasty from 2005 to 2008 with regard to the six-month mortality rate and the Oxford Hip and Knee Scores at six months. Survival curves were constructed with use of revision joint replacement as the end point.
Results: Twenty-two thousand six hundred patients who underwent total hip arthroplasties and 18,434 patients who underwent total knee arthroplasties were recorded in the New Zealand Joint Registry. The six-month mortality rate was 0.77% following hip arthroplasty and 0.40% following knee arthroplasty. Significant differences were observed in the mortality rate between all ASA classes following hip arthroplasty (p < 0.001). Similarly, significant differences were observed in the mortality rate between ASA classes after knee arthroplasty, except between ASA classes 1 and 2 and between ASA classes 3 and 4. The mortality rate was significantly higher (p < 0.001) following hip arthroplasty compared with knee arthroplasty. A significant difference (p < 0.001) in Oxford scores was observed when ASA class 1 and ASA class 2 were compared with ASA class 3 and ASA class 4, independent of age and sex, following both hip or knee arthroplasty. A significant difference was observed in the rate of early revision (revision less than two years after the index procedure) following total hip arthroplasty when ASA class 1 (hazard ratio, 1.39 [95% confidence interval (CI), 1.04 to 1.95]; p = 0.015) and ASA class 2 (hazard ratio, 1.24 [95% CI, 1.02 to 1.55]; p = 0.030) were compared with ASA class 3, which was independent of age and sex. No significant difference was observed in the rate of early revision after total knee arthroplasty.
Conclusions: The ASA physical status score can be used as a predictor of postoperative mortality and functional status following both hip and knee arthroplasty and may predict early failure of total hip arthroplasty necessitating revision.
Level of Evidence: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
Investigation performed at the University of Otago, Christchurch, New Zealand
A commentary by Edward Y. Cheng, MD, is linked to the online version of this article at jbjs.org.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. One or more of the authors has had another relationship, or has engaged in another activity, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
- Copyright © 2012 by The Journal of Bone and Joint Surgery, Incorporated
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