Evaluation of version of acetabular component following total hip replacement on conventional radiograph and computed tomography

Abstract

Background/Purpose: Total hip replacement (THR) is considered as one of the most successful orthopedic procedures. However, improperly placed components can lead to instability and accelerated wear. Acetabular cup inclination can be very well accessed by anteroposterior pelvis X-rays; for acetabular version assessment, computed tomography (CT) scan is the gold standard. CT scan is not readily available at many centers and the surgeon has to rely on X-ray methods for evaluation of acetabular version to audit results and to predict behavior of the surgical intervention. This prospective study was undertaken to compare Woo and Morrey’s and ischiolateral methods of assessment of acetabular version on cross-table lateral radiographs with CT assessment and to assess the validity of radiographic methods with respect to CT scan method. Material and methods: A prospective follow-up study was conducted for 18 months’ duration (October 2016 to March 2018) on 30 adult patients who underwent THR surgery. Cross-table lateral radiograph was obtained at 3 and 6 weeks in the postoperative period. Two observers made each observation at two different points of time. CT scan was performed at 3 weeks. Version as measured by radiographs and CT scan was recorded. Results: The major overlap in the distribution of the values of the Woo and Morrey method suggests that there is no significant difference between the observations. Distribution of the values of the ischiolateral view and the CT scan value distributions have a very small overlap and hence suggest a strong significant difference between the two. Conclusion: In this study, Woo and Morrey’s method and ischiolateral method of assessment of acetabular version were compared with CT assessment. We found that in Woo and Morrey’s method, values were comparable to CT scan values, when put on regression line. However, in situation of change in patient positioning, namely hip stiffness in contralateral hip, measurement of component changed in series of radiography due to differences in pelvis tilt. So, in these circumstances, we can use ischiolateral method which can give consistent measurement. But it will not be in concordance with CT scan values and Woo and Morrey values, as represented in regression line. The high intra-class correlation coefficients for both intra- and inter-observer reliability indicated that the angle measured with these methods is consistent and reproducible for multiple observers. CT, however, be considered as gold standard for measurement owing to control over pelvic rotation and/or tilt/patient positioning.