A 15-year evaluation of two total knee arthroplasty designs

Aims To compare 15-year patient-reported outcomes measure (PROMs), pain characteristics, implant survivorship, and radiological findings between two total knee arthroplasty (TKA) systems to determine whether modern implant design influenced outcomes. Methods A minimum 15-year follow-up of a randomised controlled trial was undertaken of patients undergoing primary TKA with either the Kinemax or Triathlon implant. We compared 15-year survivorship, mortality, patient-reported outcome measures (PROMs: Oxford Knee Score (OKS), Forgotten Joint Score (FJS), EuroQol five-dimension questionnaire (EQ-5D), and EQ visual analogue scale (VAS)), pain and location, and radiological assessments between groups. Results There were nine revisions during the follow-up period (six aseptic and three septic), and there was no difference between the groups (p = 0.721, log-rank). A total of 108 deaths occurred, corresponding to 50.7% (95% CI 44.1 to 57.3) patient mortality at 15 years, with no difference between groups (p = 0.603, log-rank). Overall, 61 patients completed functional assessment at 15 years (mean age 80 years (SD 8.5); 41 female (67%)). There were no statistical (p ≥ 0.170) or clinically meaningful differences between groups in OKS, FJS, EQ-5D, EQ VAS, or satisfaction. Longitudinal analysis demonstrated no between-group differences in postoperative OKS or EQ-5D. However, both declined significantly over the study period (p < 0.001), but remained clinically meaningfully better than those observed preoperatively. Pain VAS scores were comparable, although anterior knee pain was more frequent in the Kinemax group (OR 3.2, p = 0.037). Radiological assessment showed no loosening. Tibial zone 1 radiolucent lines (OR 12.1, 95% CI 2.6 to 57.6, p < 0.001) and severe patellofemoral osteoarthritis (OR 5.1, 95% CI 1.4 to 18.4, p = 0.010) were more prevalent in the Kinemax group. Conclusion Both implants were associated with comparable PROMs, and despite deterioration with increasing follow-up, they remained superior to preoperative scores. The Kinemax group demonstrated higher rates of anterior knee pain, though this difference did not result in clinically meaningful outcome disparities. Cite this article: Bone Jt Open 2026;7(10):1312–1321.