1285 patients undergoing either hip or knee arthroplasty were randomized to either the mobile app (n=384) or control (n=451) groups. In this secondary analysis, outcomes of interest included compliance rates, health-related quality of life (HRQOL), Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR), and Hip Injury and Osteoarthritis Outcome Score for Joint Replacement (HOOS JR). Comprehensive Joint Replacement (CJR) submission rules were also applied to compare compliance between the two groups. Mobile app users showed significantly higher compliance in completing Patient-Reported Outcome Measures (PROMs) preoperatively and at every time point postoperatively. The strongest predictors of compliance were the use of the app, younger age, and higher preoperative PROMs scores. Patients over 65 years old using the app also showed higher compliance than younger patients using paper methods.