PurposeThe purpose of this study was to investigate differences in component alignment between first and second knees in simultaneous bilateral total knee arthroplasty (SBTKA) and unilateral TKA (UTKA).Materials and Methods274 SBTKAs and 198 UTKAs were included in study. Patients were divided into three groups as SBTKA on the right knee (group A), SBTKA on the left knee (group B) and UTKA (group C). Femoral and tibial component alignment was checked in both coronal plane (alpha [α] and beta [β] angles) and sagittal plane (gamma [γ] and delta [δ] angles) radiographs.ResultsThere were no statistically significant differences among groups in the preoperative anatomical varus angle and Kellgren–Lawrence gonarthrosis classification grade (p=0.139 and p=0.329, respectively). In the coronal plane, the alignment of femoral component (α angle) and tibial component (β angle) was similar in all three groups (α angle, 95.01 vs. 95.14 vs. 94.9, p=0.945; β angle, 90.03 vs. 89.67 vs. 89.98, p=0.483). The sagittal plane alignment of femoral component (γ angle) and tibial component (δ angle) did not show significant differences (γ angle, 7.04 vs. 6.98 vs. 7.00, p=0.132; δ angle, 86.56 vs. 87.41 vs. 86.73, p=0.610).ConclusionsThe angular alignment of components was similar between SBTKA and UTKA.