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

## TL;DR

This study evaluates different reference axes for tibial rotational alignment in knee osteoarthritis patients to improve total knee arthroplasty outcomes.

## Contribution

The study identifies the second metatarsal axis as the most reliable distal reference for tibial rotational alignment in medial-type knee osteoarthritis.

## Key findings

- The second metatarsal axis (d-AP3) showed the closest alignment to the proximal axis and was unaffected by OA severity.
- The ankle AP axis (d-AP1) rotated externally with increasing varus deformity.
- Gender-related variations were observed in the distal reference axes.

## Abstract

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.