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

Abstract

Background: The anterior center-edge angle (ACEA) is used to quantify anterior coverage of the femoral head by the acetabulum. However, its measurement has not been evaluated in a manner consistent with routine use, and the precise 3-dimensional (3D) anatomic location where it measures coverage is not known. Purpose: To determine the effect of patient positioning on ACEA measurement reliability, magnitude, and 3D location. Study Design: Descriptive laboratory study. Methods: Included were 18 adults; 7 participants had cam morphology and femoroacetabular impingement syndrome, and 11 participants had no radiographic evidence of hip abnormalities and no history of hip pain or injuries. Ultimately, 3D femur and pelvis models were generated from computed tomography images. Radiographs were generated with the models in different degrees of pelvic rotation, tilt, and obliquity relative to the standard false-profile view. The ACEA was measured by 2 raters by selecting the location of the bone edge on each radiograph. Selections were projected onto the pelvis model and expressed as a clockface location on the acetabular rim. The clockface was mirrored on left hips to allow a direct comparison of locations between hips. Interrater and intrarater reliability were quantified via the intraclass correlation coefficient (ICC). The effect of position on ACEA measurements and clockface locations was determined via linear regression. Results: Intrarater and interrater reliability were excellent (ICC ≥0.97 for all). For every degree increase in rotation, tilt, and obliquity, the ACEA changed by +0.53°, +0.93°, and –0.04°, respectively. The mean clockface location (hour:minute:second) in the false-profile view was 2:09:32 ± 0:12:00 and changed by +0:02:08, –0:00:35, and –0:00:05 for every degree increase in rotation, tilt, and obliquity, respectively. Conclusion: ACEA measurements were reliable even with differences in patient positioning. Rotation and tilt were associated with notable changes in ACEA measurements. ACEA bone edge measurements mapped to the anterosuperior acetabular rim, typically in proximity to the anterior inferior iliac spine. Mapped location was most sensitive to rotation. Clinical Relevance: Pelvic rotation and tilt affected ACEA measurements, which could alter the clinical classification and treatment of borderline abnormalities. Rotation in particular must be well controlled during patient imaging to preserve measurement reliability and accuracy and to describe coverage from the intended 3D rim location.

Using Sourcil vs Bone Margin as Anatomic Landmark on False-Profile Radiographs Yields Different ACEA Values: Response

“…Lequesne and de Seze 3 first described the ACEA using the sourcil as the anterior reference point, and Crockarell et al 1 later described the ACEA using the acetabular bone edge. In our study, 4 we utilized the acetabular bone edge for all ACEA measurements.…”

“…It is possible that the 3-dimensional (3D) anatomic correlate of the bone-edge and sourcil ACEA also differ based on the selected 2D landmark; however, addressing this question was outside the scope of our study. 4 …”

“…It is possible that the 3-dimensional (3D) anatomic correlate of the bone-edge and sourcil ACEA also differ based on the selected 2D landmark; however, addressing this question was outside the scope of our study. 4 Dr Needell rightly acknowledged that a gold standard has not been established for the ACEA anterior reference point, and it is unknown which measurement is more useful in the context of hip preservation surgical planning. We believe that both sourcil and bone-edge ACEA measurements provide valuable information in characterizing the anterior acetabular rim bony morphology.…”

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

“…I read with interest the article by Mozingo et al 3 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.” 3 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.” 2 Crockarell et al 1 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.…”