The Ambiguity of Names and Landmarks in Radiographs of the Pediatric Pelvis: Variations and a Historical Perspective

Abstract

For over a century, the plain radiograph has been used to measure and predict the development of pediatric hip conditions. Classic measurements, such as the acetabular index, the center-edge angle, and the migration percentage, have stood the test of time and remain the default tools for any pediatric orthopaedic surgeons. However, in contemporary research, the terminology regarding these measurements has become markedly inconsistent. A substantial number of synonyms, acronyms, and similar, but not identical, terms are used to label measurements. This is perhaps unsurprising, considering decades of use and numerous suggested modifications. The results of treatment cannot be reliably compared if the measured parameters are not identical, and scientific analysis of disease requires consistent terminology. In this review, we aim both to provide historical definitions and identification of radiographic landmarks commonly used in three parameters of interest on pediatric AP radiographs and to examine the variability of landmarks and definitions in contemporary research.

Figure 1

Chart showing the contemporary nomenclature used to describe the AI, Sharp' angle, and Tönnis angle. The different boxes present the various synonyms encountered in articles published over the past 10 years and the original articles presenting the method. AA = acetabular index angle, AI = acetabular index, ARA = acetabular roof arc angle, HTE = horizontal toit externe, SAA = Sharp acetabular angle, TA = angle of Tönnis.

Figure 2

Diagram showing the pelvis of an approximately 4-year-old child. Hilgenreiner' and Perkin lines are illustrated, as well as MP and the AI. On the right side (Dx), the reference measurements are given for MP, with A/B × 100 giving the value described by Reimers. Contrarily, Heyman focused on the part covered by the acetabulum ([B-A]/B). On the left side, the black X line uses the classic reference points for the AI while the red Y line uses the lateral end of the sourcil. The difference between the classic AI_B (black) and AI_S (red) in a hip with a dysplastic sourcil is clearly visualized. AI = acetabular index, MP = migration percentage.

Figure 3

Diagram showing an adult pelvis. In this adult pelvis, the horizontal line is drawn from the base of the teardrops, although other reference points have been described. On the right side (Dx), Sharp angle is measured from the teardrop to the bony edge with the black line X (AA-c) and in the modified manner to the edge of the sourcil with the green Y line (AA-m). On the left hip, Tönnis angle is visualized using the red Z line. The horizontal line is parallel to Hilgenreiner' line while the second line extends from the medial to the lateral aspects of the sourcil.

Figure 4

Chart showing the contemporary nomenclature used to describe the acetabular coverage of the femoral head with the MP serving as a reference. The different boxes present the synonyms encountered in articles published over the past 10 years and the original articles presenting the method. AHI = acetabulum-head index, MI = migration index, MP = migration percentage.

Figure 5

Chart showing the contemporary nomenclature used to describe the CEA and similar measurements. The different boxes present the synonyms encountered in articles published over the past 10 years and the original articles presenting the method. CEA = center-edge angle, LCEA = lateral center-edge angle, LCE = lateral center-edge angle, VCA = vertical centre antérieure, VCE = vertical centre externe.

Figure 6

Diagram showing an adult pelvis. In this adult pelvis, the horizontal line is drawn from the base of the teardrops, although other reference points have been described. On the right hip (Dx), the traditional CEA, as modified by Massie, is illustrated with the black X line. In the modified version (sometimes referred to as Ogata' angle), the edge of the sourcil is used instead as shown by the red Y line. CEA = center-edge angle.