J Korean Orthop Assoc.  2011 Dec;46(6):484-491.

Distal Femoral Rotational Alignment Based on Mechanical Axis of the Femur: A 3-Dimensional Computed Tomographic Scan in Vivo Assessment

• Kim KK
• Lee WS
• Heo YM
• Yi JW
• Lee JB
• Chae DS

Abstract

PURPOSE
To measure and to analyze the relationships among the rotational axes of the distal femoral region by means of 3-dimensional (3D) computed tomographic (CT) images taken perpendicularly to the mechanical axis and a 3D rendering program.
MATERIALS AND METHODS
Fifty cases involving the lower extremity were included in this study, which used 3D computed tomographic angiograms. CT images of the perpendicular cross-sections to the mechanical axis of the femur were obtained by processing 3D recombinant images using Aquaris NET(R). The following anatomical angles were obtained from axial imaging using the 3D reconstructed bone model: transepicondylar axis, surgical transepicondylar axis, anteroposterior axis, and real posterior condylar axis.
RESULTS
In the tomographic images, the angles to the real posterior condylar axis formed by the anatomical femoral transepicondylar axis, the anatomical femoral transepicondylar axis, and the anteroposterior axis were 6.34+/-1.23degrees, 2.43+/-1.56degrees, and 96.52+/-1.77degrees, respectively. The angles to the anatomical femoral transepicondylar axis formed by the anteroposterior axis and the surgical femoral transepicondylar axis were 90.19+/-1.61degrees and 3.91+/-0.90degrees, respectively. In the recombinant 3D femur model, the angles to the real posterior condylar axis formed by the anatomical femoral transepicondylar axis and the anteroposterior axis were 6.29+/-1.86degrees, and 93.33+/-3.76degrees, respectively. And, the angle for anteroposterior axis from anatomical transepicondylar axis was 87.04+/-4.11degrees.
CONCLUSION
The method of measuring the rotational axes of the distal femur using the CT image taken perpendicularly to the mechanical axis is considered reproducible. In particular, the measurement method using the anatomical transepicondylar axis is more accurate than that using the anteroposterior axis.

Keyword

total knee arthroplasty; anatomical transepicondylar axis; surgical transepicondylar axis; Whiteside's line; posterior condylar axis

MeSH Terms

Axis, Cervical Vertebra
Femur
Lower Extremity

Figure

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  Figure 1 (A) The position of femoral head center (FHC) was determined by placing a circle onto the circumference of the femoral head on a set of axial and coronal section views, showing the largest bone contour of the femoral head. (B) The FHC locations were determined as the center of the circle that matched the largest bone contours.

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

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  Figure 3 Construct of the reference axes on axial computed tomographic scan of the distal femoral condyle is shown.

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  Figure 4 Real posterior condylar axis was drawn. As the most lateral posterior condyle and the most medial posterior condyle did not exist on the same plane, 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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  Figure 5 (A) Construct of the reference axes on 3-dimensional (3D) computed tomographic bone model of the distal femoral condyle is shown. 3D bone model was rotated until the center of femoral head was synchronized with the center of intercondylar notch. From caudocranial view, medial point of surgical transepicondylar axis was not detected because of hoarse-shoe shaped notch. (B) In obliquely rotated view, medial point of surgical transepicondylar axis is seen.

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