Assessing component orientation of total hip arthroplasty using the low-dose bi-planar radiographs

Abstract

Background: Three-dimensional computed tomography (3D CT) reconstruction is the reference standard for measuring component orientation. However, functional cup orientation in standing position is preferable compared with supine position. The low-dose bi-planar radiographs can be used to analyze standing cup component orientation. We aimed to assess the validity and reliability of the component orientation using the low-dose bi-planar radiographs compared with the 3D CT reconstruction, and explore the differences between the functional cup orientation in standing radiographs and supine CT scans.

Methods: A retrospective study, including 44 patients (50 hips) with total hip arthroplasty (THA), was conducted. CT scans were taken 1 week after surgery and the low-dose bi-planar radiographs were taken in the follow-up 6 weeks later. Component orientation measurement was performed using the anterior pelvic plane and the radiographic coronal plane as reference, respectively.

Results: The study showed no significant difference in cup anteversion (p = 0.160), cup inclination (p = 0.486), and stem anteversion (p = 0.219) measured by the low-dose bi-planar radiographs and 3D reconstruction. The differences calculated by the Bland-Altman analysis ranged from - 0.4° to 0.6° for the three measured angles. However, the mean absolute error was 4.76 ± 1.07° for functional anteversion (p = 0.035) and 4.02 ± 1.08° for functional inclination (p = 0.030) measured by the bi-planar radiographs and supine CT scans.

Conclusions: The low-dose bi-planar radiographs are the same reliable and accurate as 3D CT reconstruction to assess post-THA patients' component orientation, while providing more valuable functional component orientation than supine CT scans.

Keywords: Functional component orientation; The low-dose bi-planar radiographs; Three-dimensional computed tomography.

Fig. 1

A-D The reconstruction process is a software-guided step-by-step procedure. A Identifying the sacral plate, the sacroiliac joints, the acetabula, the pubis and the anterosuperior iliac spines. B Adjustment of the 3D ellipse on the border of the acetabular cup. C Identifying the key landmarks on the femur, the position of the trochlear notch and condyles, and adjustment of the prosthetic head. D Adjustment for the position of the prosthetic neck’s landmarks and identifying the inferior extremity of the stem

Fig. 2

The 3D modeling and radiology parameters of the hip are completed by the sterEOS software

Fig. 3

A-D The pelvis and femur are 3D reconstructed. A Identification of the acetabular axis by the edge of the cup. B Identification of the sacral crest. C Identification of the bilateral anterior superior iliac spine (ASIS) and pubic tubercles, and the midline of bilateral ASIS. D Definition of the stem anteversion as the angle formed by the axis of the femoral neck and the posterior tangential line of femoral condyles

Fig. 4

The APP and the sagittal plane are defined as bony landmarks. The APP is defined as bilateral ASIS and pubic tubercles. The sagittal plane is defined as the midline of bilateral ASIS and sacral crest

Fig. 5

A-C The measured results of bi-planar radiographs and 3D CT reconstruction are examined by Bland-Altman analysis. (A) Cup anteversion with the APP as the reference plane; (B) Cup inclination with the APP as the reference plane; (C) Stem anteversion