A method to calculate the femoral neck-stem angle based on 3D coordinate system

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Abstract

BACKGROUND:

Projection angle of femoral neck-stem angle at coronal plane is clinically regarded as reference of femoral neck-stem angle. There has been no precise measurement method for the femoral neck-stem angle in imaging field.

OBJECTIVE:

To explore an accurate calculation method of the femoral neck-stem angle.

DESIGN, TIME AND SETTING:

The study was performed at the Shanxian County Central Hospital of Shandong Province in October 2008.

MATERIALS:

Samples of the femoral neck were provided by Department of Anatomy, Taishan Medical University.

METHODS:

3D coordinate system was established with the center of femoral neck base as coordinate center; the anteversion angle of femur neck was α, femur neck-stem angle was β, and projection angle of femur neck-stem angle on coronal plane was β'. The relationship among anteversion and femoral neck-stem angle and its projection angle on coronal plane was explored to deduce a calculating formula of the femoral neck-stem angle.

MAIN OUTCOME MEASURES:

Anteversion of femur neck, femur neck-stem angle, and projection angle of femur neck-stem angle on coronal plane.

RESULTS:

Femoral neck-stem angle β=90° +arctg[tg(β′-90°)cosα].

CONCLUSION:

This formula is simple and accurate and could serve as clinical reference.

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