BACKGROUND: Robotic-assisted TKA was introduced to enhance the precision of bone preparation and component alignment with the goal of improving the clinical results and survivorship of TKA. Although numerous reports suggest that bone preparation and knee component alignment may be improved using robotic assistance, no long-term randomized trials of robotic-assisted TKA have shown whether this results in improved clinical function or survivorship of the TKA. QUESTIONS/PURPOSES: In this randomized trial, we compared robotic-assisted TKA to manual-alignment techniques at long-term follow-up in terms of (1) functional results based on Knee Society, WOMAC, and UCLA Activity scores; (2) numerous radiographic parameters, including component and limb alignment; (3) Kaplan-Meier survivorship; and (4) complications specific to robotic-assistance, including pin-tract infection, peroneal nerve palsy, pin-site fracture, or patellar complications. METHODS: This study was a registered prospective, randomized, controlled trial. From January 2002 to February 2008, one surgeon performed 975 robotic-assisted TKAs in 850 patients and 990 conventional TKAs in 849 patients. Among these patients 1406 patients were eligible for participation in this study based on prespecified inclusion criteria. Of those, 100% (1406) patients agreed to participate and were randomized, with 700 patients (750 knees) receiving robotic-assisted TKA and 706 patients (766 knees) receiving conventional TKA. Of those, 96% (674 patients) in the robotic-assisted TKA group and 95% (674 patients) in the conventional TKA group were available for follow-up at a mean of 13 (± 5) years. In both groups, no patient older than 65 years was randomized because we anticipated long-term follow-up. We evaluated 674 patients (724 knees) in each group for clinical and radiographic outcomes, and we examined Kaplan-Meier survivorship for the endpoint of aseptic loosening or revision. Clinical evaluation was performed using the original Knee Society knee score, the WOMAC score, and the UCLA activity score preoperatively and at latest follow-up visit. We also assessed loosening (defined as change in the position of the components) using plain radiographs, osteolysis using CT scans at the latest follow-up visit, and component, and limb alignment on mechanical axis radiographs.To minimize the chance of type-2 error and increase the power of our study, we assumed the difference in the Knee Society score to be 5 points to match the MCID of the Knee Society with power of 0.99, which revealed that a total of 628 patients would be needed in each group. RESULTS: Clinical parameters at the latest follow-up including the Knee Society knee scores (93 ± 5 points in the robotic-assisted TKA group versus 92 ± 6 points in the conventional TKA group [95% confidence interval 90 to 98]; p = 0.321) and Knee Society knee function scores (83 ± 7 points in the robotic-assisted TKA group versus 85 ± 6 points in the conventional TKA group [95% CI 75 to 88]; p = 0.992), WOMAC scores (18 ± 14 points in the robotic-assisted TKA group versus 19 ± 15 points in the conventional TKA group [95% CI 16 to 22]; p = 0.981), range of knee motion (125 ± 6° in the robotic-assisted TKA group versus 128 ± 7° in the conventional TKA group [95% CI 121 to 135]; p = 0.321), and UCLA patient activity scores (7 points versus 7 points in each group [95% CI 5 to 10]; p = 1.000) were not different between the two groups at a mean of 13 years' follow-up. Radiographic parameters such as the femorotibial angle (mean 2° ± 2° valgus in the robotic-assisted TKA group versus 3° ± 3° valgus in the conventional TKA group [95% CI 1 to 5]; p = 0.897), femoral component position (coronal plane: mean 98° in the robotic-assisted TKA group versus 97° in the conventional TKA group [95% CI 96 to 99]; p = 0.953; sagittal plane: mean 3° in the robotic-assisted TKA group versus 2° in the conventional TKA group [95% CI 1 to 4]; p = 0.612) and tibial component position (coronal plane: mean 90° in the robotic-assisted TKA group versus 89° in the conventional TKA group [95% CI 87 to 92]; p = 0.721; sagittal plane: 87° in the robotic-assisted TKA group versus 86° in the conventional TKA group [95% CI 84 to 89]; p = 0.792), joint line (16 mm in the robotic-assisted TKA group versus 16 mm in the conventional TKA group [95% CI 14 to 18]; p = 0.512), and posterior femoral condylar offset (24 mm in the robotic-assisted TKA group versus 24 mm in the conventional TKA group [95% CI 21 to 27 ]; p = 0.817) also were not different between the two groups (p > 0.05). The aseptic loosening rate was 2% in each group, and this was not different between the two groups. With the endpoint of revision or aseptic loosening of the components, Kaplan-Meier survivorship of the TKA components was 98% in both groups (95% CI 94 to 100) at 15 years (p = 0.972). There were no between-group differences in terms of the frequency with which complications occurred. In each group, 2% of knees (15) had a superficial infection treated with intravenous antibiotics for 2 weeks. No deep infection occurred in these knees. In the conventional TKA group, 0.8% of knees (six) had a motion limitation (< 60°). CONCLUSIONS: At a minimum follow-up of 10 years, we found no differences between robotic-assisted TKA and conventional TKA in terms of functional outcome scores, aseptic loosening, overall survivorship, and complications. Considering the additional time and expense associated with robotic-assisted TKA, we cannot recommend its widespread use. LEVEL OF EVIDENCE: Level I, therapeutic study.