Technological advances and digital solutions have been proposed to overcome barriers to sustainable rehabilitation programs in patients with musculoskeletal disorders. However, to date, standardized telemonitoring systems able to precisely assess physical performance and functioning are still lacking. To validate a new mobile telemonitoring system, named System for Tracking and Evaluating Performance (Step-App ), to evaluate physical performance in patients undergone knee and hip total arthroplasty. Prospective cohort study. A consecutive series of older adults with knee and hip total arthroplasty participated in a comprehensive rehabilitation program. The Step-App , a mobile telemonitoring system, was used to remotely monitor the effects of rehabilitation, and the outcomes were assessed before (T0) and after the rehabilitation treatment (T1). The primary outcomes were the 6-Minute Walk Test (6MWT), the 10-Meter Walk Test (10MWT), and the 30-Second Sit-To-Stand Test (30SST). Out of 42 patients assessed, 25 older patients were included in the present study. The correlation analysis between the Step-App measurements and the traditional in-person assessments demonstrated a strong positive correlation for the 6MWT (T0: r =0.9981, P<0.0001; T1: r =0.9981, P<0.0001), 10MWT (T0: r =0.9423, P<0.0001; T1: r =0.8634, P<0.0001), and 30SST (T0: r =1, P<0.0001; T1: r =1, P<0.0001). The agreement analysis, using Bland-Altman plots, showed a good agreement between the Step-App measurements and the in-person assessments. Therefore, we might conclude that Step-App could be considered as a validated mobile telemonitoring system for remote assessment that might have a role in telemonitoring personalized rehabilitation programs for knee and hip replacement patients. Our findings might guide clinicians in remote monitoring of physical performance in patients with musculoskeletal conditions, providing new insight into tailored telerehabilitation programs.