Kinematic alignment in total knee replacement successfully restores the native knee phenotype in the short term.

Purpose: The goal of kinematic alignment (KA) in total knee arthroplasty (TKA) is to bring back the natural knee phenotypes. This study compared postoperative functional phenotypes in KA-TKAs against native phenotypes of healthy young Iranians, addressing the need for population-specific alignment targets. Methods: The study analysed 300 KA-TKAs and 150 native phenotypes of healthy young Iranians. Full-limb radiographs were used to measure alignment parameters and classify phenotypes. Patient-reported outcomes were collected to assess functional recovery. The research focused on phenotype restoration, gender differences and ethnic variations in constitutional alignment. Results: KA-TKA successfully restored constitutional knee phenotypes in 91.7% of patients. The top five phenotypes showed similar proportions in both TKA (52.7%) and control (54.2%) groups. Females demonstrated higher phenotype restoration rates, particularly for valgus-dominant phenotypes. The Forgotten Joint Scores at 3 months showed a significant improvement of 18% when comparing phenotype-matched patients to outliers. KA-TKA cases that failed to match the control phenotype distribution amounted to 8.3%, and these cases showed significant preoperative deformities as well as high body mass index. The research demonstrated important differences in ethnic populations since 53.7% of Iranians showed constitutional varus compared to 28.3% of Swiss individuals. Conclusion: The study demonstrates that KA-TKA successfully restores native knee phenotypes to most Iranian patients. The alignment targets require customization for population-specific standards together with attention to gender-specific variations. Level of Evidence: Level III.