Training the next generation of orthopaedic surgeons in total knee arthroplasty (TKA) is crucial, but might affect operative time and outcome. We hypothesized that the learning curve of residents in TKA has an impact on (1) operative time, (2) complication rates and (3) early postoperative outcome. In a retrospective analysis of 738 primary TKAs from our institutional joint registry, operative time, complication rates, patient-reported outcome measures (EQ-5D, WOMAC) within the first year and responder rates for positive outcome as defined by the OMERACT-OARSI criteria were compared between trainee and senior surgeons differentiating between conventional and navigated TKA. Mean operative time was 69.5 +/- 18.5 min for trainees compared to 77.3 +/- 25.8min for senior surgeons (95% CI of the difference 1.5-13.9 min, p = 0.02) in conventional TKA and 80.4 +/- 22.1min to 84.1 +/- 27.6min (95% CI of the difference -0.9-8.2 min, p = 0.12) for navigated TKA, respectively. Intraoperative fracture (p >= 0.36), thrombosis (p >= 0.90), neurological deficits (p >= 0.90) and infection rates (p >= 0.28) were comparably low in both groups. Patient-reported outcome measures one year after TKA were similar for trainee and senior surgeons with EQ-5D 0.83 +/- 0.17 to 0.80 +/- 0.21 (p = 0.25) and WOMAC 74.85 +/- 18.60 to 72.77 +/- 20.12(p = 0.44) for conventional TKA and EQ-5D 0.80 +/- 0.20 to 0.82 +/- 0.18 (p = 0.23) and WOMAC 72.71 +/- 18.52 to 75.77 +/- 17.78 (p = 0.07) for navigated TKA, respectively. Similarly, responder rates for positive outcome were comparable between trainees and senior surgeons (90.7% versus 87.0% p = 0.39 for conventional TKA, 88.7% versus 89.4% p = 0.80 for navigated TKA). Supervised TKA is a safe procedure during the learning curve of young orthopaedic surgeons.