Using Sourcil vs Bone Margin as Anatomic Landmark on False-Profile Radiographs Yields Different ACEA Values: Letter to the Editor.

Dear Editor:

I read with interest the article by Mozingo et al titled “Effect of Patient Positioning on Measurement of the Anterior Center-Edge Angle on False-Profile Radiographs and Its 3-Dimensional Mapping to the Acetabular Rim.” I believe it is important to recognize that the radiographic landmark used to measure the anterior center-edge angle (ACEA) in their article does not correspond with the original (and also the most commonly referenced) landmark used to determine ACEA in the literature.

In the Methods section, it is stated, “The ACEA was defined as the angle between 2 vectors passing through the femoral head center: (1) a vertical vector and (2) a vector that intersected the anterior aspect of the acetabular bone edge, as described by Crockarell et al and Lequesne and de Seze.” In 1961, Lequesne and de Seze defined anterior coverage measured as center-edge angle on false-profile radiographs by measuring to the most anterior limit of the radiological subchondral condensation, or “sourcil.” Crockarell et al used a modified measurement of ACEA to “the foremost aspect of the acetabulum” in their study published in 2000. Over the years, there has been a drift in resident training as well as in the literature to measure the ACEA to the bony acetabular rim (as done by Crockarell et al) instead of the sourcil. While it may be easier to identify the bony rim, I believe the majority of articles in the literature have used the sourcil/subchondral sclerosis method established by Lequesne to measure the ACEA.

Significant differences have been shown when measuring the lateral center-edge angle to the bony margin of the lateral acetabular rim (Wiberg method ) versus measuring to the sourcil (Ogata method ). Similarly, an ACEA derived by measuring to the sourcil typically yields significantly smaller values than an ACEA measured to the bony rim of the acetabulum, although I am not aware of a published study comparing these 2 methods in the literature.

In Figure 1, I have added a yellow arrow to an image from the Mozingo et al article indicating where the edge of the sourcil lies, which demonstrates how this angle can result in a significantly different ACEA value than an angle derived from measuring to the edge of the bone.

Figure 1.

Anterior center-edge angle (ACEA) measurements on a false-profile radiograph demonstrate that a larger ACEA value will be obtained when the angle is measured from the edge of the bone (red arrow) instead of the edge of the sourcil (yellow arrow). Image adapted from Figure 2A of Mozingo et al.

To my knowledge, it has not been established which landmark provides a more accurate and useful measurement to guide hip preservation surgeries. I think it is therefore important to acknowledge the difference in the 2 methods cited by the authors, and to note that the 3-dimensional localization method used by Mozingo et al to mark the anterior edge of the acetabulum may not correlate with the location of the anterior edge of the sourcil.