Riddle DL, et al. - Given that, at the end of 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), researchers identified the contribution of predictor variables in the system to final classification, rated as “appropriate,” “may be appropriate,” or “rarely appropriate” for hip arthroplasty. According to findings, appropriate classification for hip arthroplasty in the AAOS system is driven by age and severity of OA almost exclusively. Function-limiting pain, a major reason patients seek surgery, only contributes slightly to the criteria for AAOS appropriateness. The system strongly relies on the traditional variables of patient age and severity of radiographic hip OA. In order to further test the validity of the AAOS system, future study of actual patient outcomes is required.