J Korean Hip Soc.  2011 Mar;23(1):47-53. 10.5371/jkhs.2011.23.1.47.

Femoral Neck Anteversion Measured Using a 3D CT Scan Perpendicular to the Mechanical Axis of the Femur

• Kim KK
• Roh JY
• Kim SB
• Lee WS
• Won YY
• Chae DS

• KMID: 2190775
• DOI: http://doi.org/10.5371/jkhs.2011.23.1.47

Abstract

PURPOSE
We wanted to measure the femoral neck anteversion (FNA) angles using a 3D CT scan that perpendicularly cut the mechanical axis of the femur and to assess the accuracy and reproducibility of different measuring methods.
MATERIALS AND METHODS
We obtained 95 cases of 3D CT images of the cross-section perpendicular to the mechanical axis of the femur. The methods used to measure the FNA angles included a method using the CT image of the area where the femoral neck is confluent to the greater trochanter (method 1), a method using the CT image taken from the neck base immediately prior to the beginning of the area of the lesser trochanter (method 2) and a method by which measurements are made after putting 3D bone models on a horizontal plane in virtual space (method 3). The reference axes of the distal femur we used were the anatomical transepicondylar axis, the surgical transepicondylar axis and the real posterior condylar axis.
RESULTS
The FNA angles measured by method 1 were 4.79+/-6.41degrees to the anatomical transepicondylar axis (ATEA), 6.09+/-6.58degrees to the surgical transepicondylar axis (STEA) and 7.96+/-6.81degrees to the real posterior condylar axis (rPCA). The FNA angles measured by method 2 were 16.01+/-8.31degrees to the ATEA, 19.52+/-8.38degrees to the STEA and 21.79+/-8.52degrees to the rPCA. The FNA angles measured by method 3 were 20.15+/-12.89degrees to the rPCA.
CONCLUSION
The measurement of the FNA angle using a 3D CT scan perpendicular to the mechanical axis is reproducible. The measurement method on the neck base level is more reliable than the one on the proximal neck confluence, and more similar to the measurement method by classic definition.

Keyword

Femur; Anteversion angle; Mechanical axis; Computed tomography

MeSH Terms

Axis, Cervical Vertebra
Femur
Femur Neck
Neck

Figure

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  Fig. 1 The position of femoral head center was determined by placing a circle onto the circumference of the femoral head on a set of (A) axial and (B) coronal section views, showing the largest bone contour of the femoral head.

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  Fig. 2 The intercondylar notch center was defined as the middle of the line connecting the narrowest anterior-to-posterior borders on an axial section.

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  Fig. 3 (A) Femoral neck axis of method 1 was drawn femoral neck center using of CT image on proximal-most neck confluence slice level and superimposed femoral head center. (B) Femoral neck axis of method 2 was drawn using the center of the base of the femoral neck and superimposed femoral head center.

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  Fig. 4 Posterior condylar line is the tangent of the posterior femoral condyles, the Anatomical Trans Epicondylar Axis (TEA) connects the medial to the lateral epicondyle, the Surgical TEA connects the Medial sulcus to the lateral epicondyle.

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  Fig. 5 Real posterior condylar axis was drawn. (A, B) As the most lateral posterior condyle and the most medial posterior condyle did not exist on same plane, (C) real posterior condylar axis was drawn on the most medial posterior condylar plane by superimposing the most lateral posterior condyle to the medial plane. MAPC: medial apex of posterior condyle, LAPC: lateral apex of posterior condyle.

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  Fig. 6 Femoral neck axis of method 3 was measured on 3D bone model. On the top table position, the 3D bone model aligned to the mechanical axis. femoral neck axis was defined by the line drawn using femoral head center and the center of the middle of the line connecting the narrowest anterosuperior and posteroinferior border of the neck.

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