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Updated: Jun 1, 2026

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy
Published on: July 2, 2021
Kinematic analysis of the flexion axis for correct femoral component placement
Georg Matziolis1, Sascha Pfiel, Georgi Wassilew
1Department of Orthopaedic, Center for Musculoskeletal Surgery, Charité-University Medicine Berlin, Charitéplatz 1, 10117 Berlin, Germany. Georg.Matziolis@Charite.de
Purpose:
This study evaluates a new method for intraoperative determination of femoral component rotation by a navigation system (flexion axis, FA) driven by joint stability over the range of motion.
Methods:
Seventy-five patients were treated with a navigated total knee replacement. Intraoperatively, the posterior condylar axis (PCA), the Whiteside's line (WL), and the surgical epicondylar axis (EA) were palpated, the flexion gap (FG) was determined, and the FA was calculated. The anatomical landmarks, lines, and angles were determined based on a postoperative computed tomography in all knees. The femoral rotation was intraoperatively determined by the surgeon based on the knowledge of the EA, the PCA, and the FG but not the FA.
Results:
The deviation of the palpated EA was 3.5° [0°-13.8°], of the PCA externally rotated by 3° was 2.2° [0°-9.6°], of the WL was 3.8° [0.1°-10.0°], of the FG was 2.5° [0.2°-8.8°], and of the FA was 2.5° [0°-10.0°].
Conclusions:
The FA is a new functionally acquired axis for the determination of optimal femoral component alignment. Whether the FA leads to clinically superior results must be clarified by subsequent studies.
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