# A Novel Potential Landmark for Intraoperative Estimation of Femoral Stem Anteversion: An Analysis of Computed Tomography Measurements

## TL;DR

This study identifies a new anatomical landmark to help surgeons estimate femoral stem anteversion more accurately during hip replacement surgeries.

## Contribution

The study introduces the anterior lesser trochanter line as a reliable anatomical landmark for intraoperative estimation of femoral stem anteversion.

## Key findings

- The anterior lesser trochanter line (ALTL) showed consistent correlations with femoral anteversion angles.
- Inter- and intra-observer reliability measurements exceeded 0.81, indicating high reproducibility.
- Angle 1 positively correlated with femoral anteversion (FA), suggesting ALTL's potential as a surgical landmark.

## Abstract

Background/Objectives: Femoral anteversion (FA) is the angle between the femoral neck axis (FNA) and the posterior condylar axis (PCA). Surgeons generally estimate intraoperative femoral stem anteversion visually relative to the PCA, but this method can be challenging even for experienced surgeons. This study aimed to find an anatomical proximal landmark within a CT coordinate system for intraoperative estimation of femoral stem anteversion. Methods: Seventy patients were included. The anterior lesser trochanter line (ALTL) was defined as the line passing through two tangent points: one between the rounded part of the lesser trochanter and the medial edge of the anterior lesser trochanter cortex, and the other between the anterior cortex of the femur and the lateral edge of the anterior lesser trochanter cortex at the level of the lesser trochanter tip. The following angles were measured and analyzed: Angle 1 (angle between the FNA and the ALTL), Angle 2 (angle between the ALTL and the PCA), and Angle 3 (angle between the FNA and the PCA [FA]). Results: In all measurements, the inter-observer and intra-observer intraclass correlation coefficients exceeded 0.81. Angle 1 negatively correlated with Angle 2 (r = −0.79, p < 0.01), whereas Angle 1 positively correlated with Angle 3 (r = 0.70, p < 0.01). Conclusions: We found a consistent relationship between the ALTL and FA, and the ALTL may serve as a proximal landmark for intraoperative estimation of femoral stem anteversion during anterior or anterolateral approaches.