Effect of medial tibial torsion on the sagittal alignment of lower legs in patients with medial knee osteoarthritis

Purpose: The fibular axis (FA) and anterior tibial cortex (ATC) are good determinants of the sagittal mechanical axis (MA) of lower legs during total knee arthroplasty (TKA).When compared with healthy subjects, a significant medial tibial torsion has been reported in patients with medial knee osteoarthritis; this should affect the alignment of lower legs. The purpose of this study was to clarify the effect of the medial torsion on relationship between sagittal MA and intraoperative references (FA and ATC). Methods: Fifty knees of 50 patients with medial knee osteoarthritis who underwent primary TKA were included in this study. Using preoperative computed tomographic data, the tibial torsion angle was measured in the axial plane. The angle between FA and MA, and the angle between ATC and MA were also measured in the sagittal plane. Results: The tibial torsion angle was 7.9 ± 7.2 (range -11.3 to -24.3). The angle between MA and FA was -1.8 ± 0.8 (range -0.1 to -4.3), and the angle between MA and ATC was 4.6 ± 0.5 (range 3.1 to 5.5). The population variance was significantly larger for the angle between MA and FA than that between MA and ATC (P = 0.0160). There was a significant positive correlation between the tibial torsion angle and the angle between MA and FA (R ² = 0.5111, P < 0.0001). Conclusion: The angle between FA and MA in the sagittal plane increased in patients with large medial tibial torsion.