Comparison of femoral sagittal axis between navigated total knee arthroplasty and conventional total knee arthroplasty in patients with knee osteoarthritis.

To compare femoral sagittal axis between navigated total knee arthroplasty (TKA) and conventional TKA. A total of 136 cases were assigned to group 1 (navigated TKA) and 77 cases were assigned to group 2 (conventional TKA). Specifically, this study targeted patients with degenerative osteoarthritis. Only patients with primary TKA were analyzed. Hip knee ankle angle and lateral femoral bowing were measured using preoperative scanogram. Anterior femoral bowing was measured using preoperative femoral lateral X rays. The presence of anterior femoral notching and the insertion angle of the femoral implant with respect to the anatomical sagittal plane of the distal femur were checked using postoperative lateral knee X rays. Student t-test was used to compare the difference in the position of the sagittal plane of the femoral implant between the navigated TKA group and the conventional TKA group. When comparing the 2 groups, the sagittal axis of the femoral implant was more extended than the anatomical sagittal plane axis of the distal femur in group 1 than in group 2 (P = .01). There was a significant negative correlation between the value of anterior femoral bowing and the degree of flexion to the sagittal plane of the femoral implant in group 1 (correlation coefficient: -0.40, P = .01). The occurrence of anterior femoral notching was significantly higher in group 1 than in group 2. During navigated TKA, imageless navigation does not consider the anatomical variation of the femoral shaft. Therefore, surgeons should take into consideration that when performing navigated TKA, a femoral implant could be inserted more extended for the anatomical sagittal axis of the distal femur than for the conventional TKA. Also, surgeon should know that the degree of extension insertion of the femoral implant increases as femoral anterior bowing increases.