The relationship between the American Society Of Anesthesiologists physical rating and outcome following total hip and knee arthroplasty: an analysis of theNew Zealand Joint Registry.
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 &lt; 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 &lt; 0.001) following hip arthroplasty compared with knee arthroplasty. A significant difference (p &lt; 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.


METHODS
Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
Department of Orthopaedic Surgery and Musculoskeletal Medicine, Christchurch School of Medicine and Health Sciences, University of Otago, Private Bag, Christchurch, 8140 New Zealand. gary.hooper@otago.ac.nz
Gary J
GJ
Hooper
Alastair G
AG
Rothwell
Nikki M
NM
Hooper
Chris
C
Frampton
D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000401:mortality*; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000401:mortality*; D015331:Cohort Studies; D005260:Female; D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D020127:Recovery of Function; D012042:Registries; D012086:Reoperation; D016896:Treatment Outcome