Four hundred one patients undergoing primary knee arthroplasty were randomized to receive either standard in-person physiotherapy (n=241) or a smartphone-based care platform using the mymobility app with an Apple Watch (n=160). The primary outcome of interest was the Knee Injury and Osteoarthritis Outcome Score for joint replacement (KOOS JR) at one year. Secondary outcomes included the number of physiotherapy visits, emergency department visits, patient-reported satisfaction, and healthcare utilization. Outcomes were assessed at 6 months and 1 year postoperatively. Overall, the study found that the smartphone-based platform led to significantly fewer physiotherapy visits and emergency department visits compared to the control group. However, KOOS JR improvements were similar between groups (p=0.32 at 1 year). These findings suggest that a smartphone-based care platform may be a cost-effective alternative to in-person rehabilitation following knee arthroplasty.