Methods of Defining the Femoral Neck Axis for the Measurement of Femoral Antetorsion

Presentation Format: Educational poster presentation.

Purpose or Learning Objective: (1) To describe methods used to define the femoral neck axis for the measurement of femoral antetorsion. (2) To provide examples of how head-neck morphology may impact femoral antetorsion measurement.

Methods or Background: Femoral antetorsion describes the angle of rotation between the femoral neck axis and femoral condyles. It may play an important role in the management of several hip conditions, such as hip dysplasia, femoroacetabular impingement, Perthes disease, and slipped capital femoral epiphyses. We outline the main methods described to define the femoral neck axis using cross-sectional imaging and the potential impact on femoral torsion measurement.

Results or Findings: Methods of assessing the femoral neck axis have been described using axial imaging, either using a single axial slice or superimposed axial slices, in addition to axial oblique reformats/acquisitions.

Single axial slice techniques propose different levels to represent femoral neck orientation. Suggested levels include the axial image where the anterior and posterior cortices appear parallel and an axial image through the femoral neck that includes the superior border of the greater trochanter.

Superimposed axial slice techniques typically define the neck axis as extending from the center of the femoral head on a more superior slice to a reference point on a more inferiorly located second image. Differing levels and reference points have been suggested for the inferior image including the center of the femoral shaft at the base of the femoral neck, the center of the femoral neck at its narrowest point, and a defined site on the greater trochanter.

Axial oblique reformats/acquisitions have also been described, either using single or maximum intensity projection images, with the femoral neck axis defined as the line drawn through the center of the femoral neck paralleling the long axis or a line passing from the center of the femoral head to the center of the femoral neck.

Conclusion: Ambiguity remains regarding the most appropriate technique to define the femoral neck axis when calculating femoral antetorsion with different methods resulting in differing antetorsion values. It is important to be aware of the various techniques described and how these techniques, in addition to head-neck morphology, may impact antetorsion measurement.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
03 June 2021