Evaluation of early implant failure in Japanese patients undergoing unrestricted kinematic alignment total knee arthroplasty

Total knee arthroplasty (TKA) traditionally involves mechanical alignment with a target range of ±3°. However, unrestricted kinematic alignment (urKA) has emerged as a viable alternative, potentially maintaining a favorable implant survival rate without the constraints of neutral alignment. Japanese people have more pronounced tibial varus than other populations. This study evaluated early implant failures in Japanese patients with osteoarthritis who underwent urKA-TKA. In this study, 557 knees of 460 patients who underwent urKA-TKA between June 2019 and September 2021 were retrospectively analyzed. Surgeries were conducted by four surgeons using standardized urKA techniques, ensuring consistent ligament balancing and component positioning. The primary outcome was the rate of revision for aseptic loosening over at least 2 years, with secondary outcomes focusing on post-operative alignment. The follow-up rate was 95%, with a mean of 3.0 years. The implant survival rate was 100% considering implant revision as the endpoint, and 99% when re-operation was included. Post-operative alignment revealed that 60.3% of tibial components and 39.3% of limbs had varus alignment exceeding 3°; however, this did not compromise implant survival during the follow-up period. The follow-up of at least 2 years for urKA-TKA in a Japanese cohort demonstrated no early implant failures with no significant effect on outcomes from deviations in varus alignment. These results support the use of urKA-TKA and underscore the need for long-term studies to further substantiate these findings in the Japanese population. • Total knee arthroplasty (TKA) traditionally involves mechanical neutral alignment. • Unrestricted kinematic alignment (urKA) has emerged as a potential viable alternative. • Study of Japanese patients with osteoarthritis undergoing urKA-TKA. • No early implant failures were found. • The study supports the use of urKA-TKA.