Elsevier

The Journal of Arthroplasty

Volume 20, Issue 8, December 2005, Pages 1060-1067
The Journal of Arthroplasty

Original Article
The Functional Flexion-Extension Axis of the Knee Corresponds to the Surgical Epicondylar Axis: In Vivo Analysis Using a Biplanar Image-Matching Technique

https://doi.org/10.1016/j.arth.2004.08.005Get rights and content

Abstract

We investigated the concept that the knee has a fixed flexion-extension axis in the posterior femoral condyles and that this functional axis corresponds to the surgical epicondylar axis in vivo. We used a biplanar image-matching technique to perform the in vivo analysis of 9 normal knees to determine the location of the functional flexion-extension axis of the knee using an optimization technique. The functional flexion-extension axis passed through the sulcus of the medial epicondyle and the prominence of the lateral epicondyle. Flexion and extension of the knee could be represented as a rotation around a fixed axis, and this functional axis corresponded to the surgical epicondylar axis during a 0° to 90° flexion. This study assists more understanding of knee kinematics and provides useful information for the design and positioning of the prostheses used in total knee arthroplasty.

Section snippets

Simulation of Knee Motion Using a Biplanar Image-Matching Technique

Nine healthy male Japanese volunteers with an average age of 32 years (range, 25-43 years) were the subjects in this study. Computed tomography (CT) scan images of the left knee of each subject were made at levels ranging from 80 mm proximal to the joint to 80 mm distal to the joint (Hispeed Advantage, GE Medical Systems, Inc, Milwaukee, Wis). These scans were made at 2-mm intervals with a 1-mm-wide source beam so that the functional axis of lower extremity (the femoral head to midankle plafond

Results

The functional flexion-extension axis was identified successfully for all subjects. The radius of the optimal circle was 380 ± 11 mm and percentage error was 0.61% ± 0.23%. The functional flexion-extension axis was found in all cases to pass through the posterior femoral condyles. When the axis was viewed end on, each femoral condyle was found to conform to the perimeter of a circle with a common center on the axis. However, the most posterior aspects of the femoral condyles, which contact the

Discussion

Some analyses of the knee, based on cadavers, have shown that the knee has a fixed flexion-extension axis in the posterior femoral condyles and that this fixed axis coincides with the transepicondylar axis 5., 6., 7., 8., 9.. Elias et al [5] found isometric points on the distal femur, which suggested a fixed flexion-extension axis located in the posterior femoral condyles. Stiehl and Abbott [7], in their anatomical study, showed that the transepicondylar axis parallels the knee

Acknowledgments

We thank Y Yukawa and J Kinoshita, (Kyoto University Hospital, Kyoto, Japan) for their technical assistance and advice in radiographs. We also thank M Taniguchi for his technical assistance and advice in CT scanning.

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