Purpose <p>The aim of this study was to assess the long-term clinical outcome, quality of life (QoL), and complications associated with low-contact-stress (LCS) mobile-bearing total knee arthroplasty (TKA) with a minimum follow-up of 20 years.</p> Methods <p>This is a retrospective cohort study based on a previous report that initially included 108 patients with 138 prostheses. For a minimum follow-up of 20 years, reevaluation was conducted on the remaining cohort of 15 patients, as 80 had deceased, 11 were lost to follow-up and 2 were excluded due to revision surgery. Patients were assessed for quality of life (QoL), clinical outcomes, and complications. Patient reported outcome measures were obtained via questionnaires, and range of motion (ROM) was clinically evaluated. Descriptive and explorative data analysis was performed.</p> Results <p>During the follow-up period, there were fifteen revision surgeries, however the prostheses had an overall survival of 22 years. Twenty years postoperatively, active range of motion (ROM) remained comparable to 10 years, with no significant differences between females (98.46° ± 27.72° vs. 96° ± 16.7°; <i>p</i> = 0.105) or males (90° ± 14.14° vs. 95° ± 17.3°). WOMAC scores at 20 years (83.77 ± 11.01) were comparable to 10 years (81.46 ± 17.88). Knee Society Score (KSS) pain scores showed no significant changes either (females: 69 ± 20.9, males: 76 ± 24.4) and 20 years (73.81 ± 25.86; <i>p</i> = 0.398). Function scores declined significantly over time, from 80.38 ± 19.20 to 51.54 ± 31.65 in females and from 79 ± 24 to 37.5 ± 53.03 in males (<i>p &lt; 0.05</i>), which is in line with the patients age and natural decline.</p> Conclusion <p>The findings of this 20-year follow-up suggest that the LCS TKA can provide durable outcomes and sustained quality of life benefits in surviving patients. The observed decline in function may reflect age-related changes rather than implant performance.</p>