CT outperforms radiography for determination of acetabular cup version after THA

Abstract

Precise evaluation of acetabular cup version is necessary for patients with recurrent hip dislocation after THA. We retrospectively studied 42 patients, who underwent THAs, with multiple cross-table lateral radiographs and CT scans to determine whether radiographic or CT measurement of acetabular component version is more accurate. One observer measured cup version on all radiographs. CT scans were interpreted by one observer. Twenty radiographs were measured twice each by two observers to determine intraobserver and interobserver reliability. We implanted cups in four model pelvises using navigation and compared measurements of anteversion made with radiographs and CT scans. Intraclass correlation coefficients (ICC) for anteversion measurements of two observers were 0.9990 and 0.9998, respectively, when comparing measurements of identical radiographs (intraobserver). Paired values for two observers measuring the same radiograph had an ICC of 0.9686 (interobserver) compared with 0.7412 for measurements from serial radiographs of the same component. The ICC comparing radiographic versus CT-based measurements was 0.6981. CT measurements had stronger correlations with navigated values than radiographic measurements. Accuracy of anteversion measurements on cross-table radiographs depends on radiographic technique and patient positioning whereas properly performed CT measurements are independent of patient position.

Fig. 1

A reformatted CT scan shows the angle used to determine acetabular cup version.

Fig. 2

A cross-table lateral radiograph shows measurement of the acetabular cup version.

Fig. 3

An AP radiograph was obtained of a model pelvis after performing navigated placement of the left acetabular cup.

Fig. 4

This cross-table lateral radiograph of a model pelvis after navigated placement of the left acetabular cup shows apparent retroversion of the cup.

Fig. 5A–B

The measured anteversion of the two serial cross-table lateral radiographs of the same patient with well-fixed components and no interval surgeries are (A) 27.6° and (B) 37.6°.