Disorders of the patella are among the most prevalent knee injuries. While exercise therapy is widely accepted as an effective treatment strategy, the positive effects of conventional exercise therapy under the guidance of a physiotherapist may be offset by inherent limitations, such as difficulties in scheduling appointments or statutory policies restricting the number of training sessions. Home-based exercise interventions using digital health applications (DHAs) may help address some of these limitations. This study aimed to assess the efficacy of a 12-week exercise intervention using a web-based DHA for improving knee function and reducing pain in patients with disorders of the patella (International Classification of Diseases code M22). The outcomes of the DHA intervention group (IG) were compared to a control group (CG) that received conventional physiotherapy covered by statutory health insurance in Germany (SHI-PT). A total of 259 patients with diagnosed disorders of the patella were included in the trial and randomly allocated to IG DHA (n=136, 52.5%) and CG SHI-PT (n=123, 47.5%). Two primary end points were examined: "knee function" (Knee Injury and Osteoarthritis Outcome Score-Activities of Daily Living [KOOS] subscale, range 0-100 points) and "knee pain" (visual analog scale [VAS], range 0-100 points). Participants were asked to complete 2 surveys: one before the first therapy session (PRE) and one after completing the treatment period of 12 weeks (POST). Training with the DHA resulted in a 4.5-fold greater improvement in "knee function" (PRE-POST differences in KOOS score; IG DHA: 15.7 points, 95% CI 13.7-17.6 vs CG SHI-PT: 3.5 points, 95% CI 1.5-5.5) and a 3.5-fold greater reduction in "knee pain" (PRE-POST differences in VAS pain score; IG DHA: -22.5 points, 95% CI -25.2 to -19.9 vs CG SHI-PT: -6.5 points, 95% CI -8.7 to -4.4) compared to SHI-PT. The improvements in IG DHA exceeded the limits of clinical relevance. The differences between the treatment groups (KOOS score -10.1 points, 95% CI -infinity to -8.0; VAS pain score 14.3 points 95% CI 11.7-infinity) were statistically significant (P<.001) for both end points in favor of IG DHA. No effect was found for age or sex. The reported use of pain medication decreased substantially in IG DHA, and showed almost no change in CG SHI-PT. Our findings indicated that the investigated DHA is superior to SHI-PT for treating disorders of the patella. Therefore, DHA has been approved by the German Federal Institute for Drugs and Medical Devices for treating disorders of the patella in persons of all sexes aged ≥12 years. German Clinical Trials Register (DRKS) DRKS00023454; https://drks.de/search/en/trial/DRKS00023454.