Reliability and Validity of Standing Lateral Radiograph Method for Measuring Acetabular Component Version: A Modified Cross-table Lateral Radiograph Method

Abstract

Objectives: To investigate the effect of the X-ray incidence angle on cup version measurements and the reliability and validity of standing lateral (SL) radiography for measuring cup versions.

Methods: Cup versions under different X-ray incidence angles were investigated by the 3D simulation analysis. Ninety-three patients, who underwent primary total hip arthroplasty (THA) with postoperative SL radiographs and CT scans between April 2020 and December 2021, were retrospectively analyzed. SL radiography was taken under naturally standing position, correcting for the measurement error of pelvic tilt in cross-table lateral (CL) radiography. Cup versions were measured on SL radiographs and CT images by two qualified orthopedic physicians. The intra- and inter-observer reliabilities were assessed by intra-class correlation coefficient. The consistency between radiographic and CT measurements was evaluated using Pearson correlation coefficient.

Results: No significant differences in cup version measurements were observed between groups of different X-ray incidence angles (P = 0.663) in the 3D simulation analysis. All measurements had excellent intra- and inter-observer reliabilities, with an intraclass correlation coefficient of >0.95. Mean cup version measurements from SL radiographs correlated well with those from CT scans (r = 0.853, P < 0.001). The mean difference between radiographic and CT measurements was -0.49° (range -12.62° to 10.37°, SD 3.95°), and the majority of differences were within the 95% limits of agreement.

Conclusion: The cup versions measured with SL radiography were close to the CT measurements. SL radiograph method is reliable and valid for measuring acetabular component version after THA.

Keywords: Acetabular component version; Cross-table lateral radiograph; Hip dislocation; Standing lateral radiograph; Total hip arthroplasty.

Fig. 1

Cup version measurements under different X‐ray incidence angles on the 3D models. Ten groups of X‐ray incidence angles were set from 45° to 90°, at intervals of 5°. Five groups of actual versions were set from 10° to 30°, at intervals of 5°. Different groups of cup versions were measured under different X‐ray incidence angles

Fig. 2

Radiographic method for standing lateral radiography. Patients naturally stood with their feet together and the radiation beam was centered over the greater trochanter, with an X‐ray incidence angle of 90°

Fig. 3

Methods for measurement of cup version on radiographs and computed tomography (CT) scans. (A) Cup version measuring method on a standing lateral (SL) radiograph. Cup version was measured between the vertical line of the body's longitudinal axis and the tangential line. The line tangential to the cup opening face was determined through two intersecting points of the cup's edge fitting circle and the opening face's elliptical arc. (B) Pelvic tilt was adjusted to the value on radiographs before cup version measurement was performed on CT images. Pelvic tilt was defined as the angle between a horizontal line and a line connecting the upper border of the symphysis with the sacral promontory. (C) Cup version measurement on CT images after pelvic tilt adjustment. Cup version was defined as the angle between the line through the most anterior and posterior points of the cup and the horizonal line

Fig. 4

Mean measurements of various actual cup versions under different X‐ray incidence angles in four 3D models. No statistically significant differences in version measurements were observed between different groups of X‐ray incidence angle (ANOVA, F = 0.192, P = 0.663)

Fig. 5

Scatter plot of mean radiographic and computed tomography (CT) measurements with the correlation slope. The correlation coefficient between mean radiographic and CT measurements was r = 0.853 (p < 0.001)

Fig. 6

Bland–Altman graph showing differences between mean radiographic and computed tomography measurements of the cup version. The dashed line represents the mean difference between measurements, and the straight lines represent the 95% limits of agreement (mean ± 1.96 SD)