Non-equivalent Results from Different Anteversion Measurements Methods for the Evaluation of the Acetabular Cup Orientation in Total Hip Arthroplasty

Abstract

Objective: To determine the comparability among 10 radiographic anteversion methods for acetabular cup orientation in total hip arthroplasty (THA) found in the literature and the "gold" standard of assessing the anteversion with CT.

Methods: This is a retrospective study that blindly compares 10 different conventional radiographic anteversion measurements with the "gold" standard, the measurement of anteversion on the transverse plane of the 3-D images made with CT. The patient archiving and communications system (PACS) was systematically searched for subjects that had undergone a CT angiogram of the abdomen and lower extremities, including the pelvis, had at least one THA in situ and had undergone anterior-posterior (AP) and cross-lateral pelvic radiography between January 2013 and August 2016 in the Diakonessenhuis Hospital Utrecht/Zeist, a non-academic institution. CT scans of patients (n = 16) were systematically collected. Three observers independently measured cup anteversion from radiographs, using a total of 10 different methods, and measured the "gold" standard on CT images. The outcomes of the 10 radiographic anteversion were compared in terms of linear correlation with the "gold" standard on CT images.

Results: The correlations of the radiographic measured anteversions with the "gold" standard measured on CT images were 0.528 for the method of Liaw, 0.556 for Wan, 0.562 for the cross-lateral method, 0.586 for Hassan, 0.594 for Dorr, 0.602 for Lewinnek, 0.624 for Widmer, 0.671 for the lateral CT, 0.747 for Ackland, and 0.771 for the method of Riten Pradham.

Conclusion: Anteversion measurement methods represent different projectional angles of the acetabular cup in different planes around different axes. Therefore, they differ from the "gold" standard and are not interchangeable, as is shown by this study. We consider the anatomical anteversion in the transverse plane rotating around the longitudinal axis as the "gold" standard and recommend avoiding using the term anteversion for other projectional angles in different planes.

Keywords: Acetabular cup; Anteversion; Orientation; Total hip arthroplasty.

Figure 1

(A) Different spatial anteversion angles, defined by Murray, rotating around different axes11, 15. The colored planes show the three anatomical planes. The yellow angels describe the definitions in relation to the three anatomical planes: AA, anatomical anteversion in the transverse plane; OA, operative anteversion in the sagittal plane; RA, radiographic anteversion in a projectional plane. (B) Anatomical planes: green is coronal plane, red is sagittal plane, and blue is transverse plane. X is the transverse axis, Y is the longitudinal axis, and Z is the sagittal axis.

Figure 2

Category 1 methods. Definitions and algorithms of the included anteversion (AV) measurements methods with CT. The angle is measured by the opening of the cup in relation to the axis of the respective plane. (A) Transverse‐CT anteversion. (B) Sagittal‐CT anteversion.

Figure 3

Category 2 method. Definition and algorithm of the included anteversion measurements on a cross‐lateral radiograph16. The angle is measured by the opening of the cup in relation to the axis of the respective plane. AV, anteversion; β, angle.

Figure 4

Category 3 methods. Definitions and algorithms of the included anteversion (AV) measurements methods with anterior–posterior radiographs. The respective distances are measured and filled in the respective formulas: (A) Lewinnek et al. 1, (B) Widmer et al. 7, (C) Riten Pradham17, (D) Ackland et al. 18, (E) Dorr et al. 19, (F) Wan et al. 20, (G) Liaw et al. 21, and (H) Hassan et al. 3 . β = angle.

Figure 5

Results per patients for the different anteversion measurement methods on the x‐axis versus the “gold” standard on the y‐axis.