3D Imaging Evaluation of Distal Reference Axes for Tibial Rotational Alignment in Medial-Type Knee Osteoarthritis

Background Precise tibial rotational alignment is essential for successful total knee arthroplasty (TKA). While Akagi's line is established proximally, the optimal distal reference axis remains uncertain. Methods We analyzed 120 medial knee osteoarthritis (OA) patients (mean age 71.7 years) using three-dimensional computed tomography. The proximal anteroposterior (AP) axis (Akagi's line) was compared with three distal axes: ankle AP (d-AP1), talar AP (d-AP2), and second metatarsal bone axis (d-AP3). Associations with Kellgren-Lawrence grade and femorotibial angle were assessed. Results Mean deviations from the proximal axis were -17.55 ± 9.49° (d-AP1), -3.36 ± 10.13° (d-AP2), and -0.85 ± 11.18° (d-AP3). d-AP3 showed the closest alignment and was unaffected by OA severity, though with gender-related variation. d-AP1 rotated externally with increasing varus deformity. Conclusion The second metatarsal axis (d-AP3) provides the most reliable distal reference for tibial rotational alignment in TKA, particularly when proximal landmarks are inaccessible during minimally invasive surgery.