In late 2017, the American Academy of Orthopaedic Surgeons (AAOS) published an appropriateness classification system using the RAND/University of California, Los Angeles (UCLA) approach for patients with hip osteoarthritis (OA). We determined the contribution of predictor variables in the system to final classification, rated as "appropriate," "may be appropriate," or "rarely appropriate" for hip arthroplasty.
An AAOS-appointed expert panel developed 270 clinical vignettes incorporating all permutations of 5 evidence-driven indication variables associated with hip arthroplasty outcome or need. Indication variables were age, function-limiting pain severity, radiographic hip OA severity, hip motion, and presence of modifiable prognostic risk factors. Multinomial regression determined the relative contribution of each variable and a classification tree method determined variable combinations contributing to final classification.
Patient age and hip OA severity were the dominant predictors of appropriateness classification in both statistical models. Function-limiting pain made a slight contribution relative to age and hip OA severity while hip motion and the presence of modifiable prognostic factors did not meaningfully contribute to final classification. The regression model explained about 99% of the variance and the classification tree had an accuracy of 87.8%.
Classification for hip arthroplasty appropriateness in the AAOS system is driven almost exclusively by age and OA severity. Function-limiting pain, a major reason patients seek surgery, contributes only slightly to the AAOS appropriateness criteria. The system relies heavily on traditional variables of patient age and radiographic hip OA severity. Future study of actual patient outcomes is needed to further test the validity of the AAOS system.