Localization of the ilioischial line on axial computed tomography images for preoperative planning of total hip arthroplasty

Abstract

Background If the bony region indicating the ilioischial line is established on the preoperative axial computed tomography (CT) image, the distance between the simulated cup and the ilioischial line can be measured on this image so that the surgeon can use these data to define a more accurate preoperative two-dimensional (2D) template of total hip arthroplasty (THA). This study aimed to verify the hypothesis that on the CT axial image, the cortical bone area, indicated by the superimposition of a line (line α) with a perspective projection angle to the ilioischial line on radiography and tangent to the medial acetabular wall, is the cortical bone that represents the ilioischial line on radiography. Methods Study 1: If the two measured distances (distance A’ and distance B) are sufficiently equal, then the hypothesis can be supported. Distance A’ was calculated by multiplying the distance A, between the ilioischial line and the medial margin of the metal cup after THA measured at the level of the hip joint center on the pelvic radiograph, by 0.91 to correct for radiographic magnification. Distance B was defined as the distance between the medial margin of the metal cup and line α on the axial CT image at the level of the hip joint center. These two distances were measured for all 51 hip joints included in the study. Study 2: The difference between distance A and distance A# (distance A on the 2D template) was compared between the group containing 59 primary THAs in which distance B′ was measured (distance B in the simulation) and the control group containing 59 primary THAs. Results Study 1: The average distance for A’ was 4.5 ± 2 mm, and the average distance for B was 4.7 ± 2.1 mm. The difference between distances A and B was 0.2 ± 0.2 mm. Study 2: The mean difference between distance A and distance A# for the measurement and control groups was 1.8 ± 1.3 mm and 3.7 ± 2.4 mm, respectively (P < 0.001). Conclusions The ilioischial line is located in the bony region where line α intersects the medial acetabular wall with a maximum overlap on axial CT images.

Morphological features of the acetabulum with coxa profunda: A retrospective observational study

“…The mean difference between the distances from the ilioischial line to the acetabular oor on radiographs and distances from the acetabular oor to the ischial wall on CT was 0.87 mm, indicating a good approximation. Our results are supported by the ndings of a previous study [17], which showed that the region of the bone on the axial CT image that overlaps the line (line α) tangential to the medial wall of the acetabulum, with a perspective projection angle of 4° tilted to the perpendicular line to the table, represents the ilioischial line on radiography [17].…”

“…Subsequently, we considered that the cortical bone region of the medial wall represents the ilioischial line on radiographs. In contrast, previous studies have suggested that the ilioischial line is located on the medial acetabular wall of the ischium [13,17]. We used the perspective projection angle (4°) of the X-ray beam around the ilioischial line, which was calculated using a trigonometric function in a previous study [17], for the line tangential to the ischial cortex that reveals the ilioischial line on CT images.…”

“…In contrast, previous studies have suggested that the ilioischial line is located on the medial acetabular wall of the ischium [13,17]. We used the perspective projection angle (4°) of the X-ray beam around the ilioischial line, which was calculated using a trigonometric function in a previous study [17], for the line tangential to the ischial cortex that reveals the ilioischial line on CT images. The mean difference between the distances from the ilioischial line to the acetabular oor on radiographs and distances from the acetabular oor to the ischial wall on CT was 0.87 mm, indicating a good approximation.…”

“…The X-ray tube (Radnext32; FUJIFILM, Tokyo, Japan) was positioned parallel to the oor and centered on the pubic symphysis, with a focal lm length of 100 cm. The average distance from the hip joint to the lm was 10.7 cm, corresponding to a magni cation of approximately 110% on the radiographs [17].…”

“…The perspective projection angle of the X-ray beam around the ilioischial line was calculated to be approximately 3.8° in a previous study [17]; therefore, we set the projection angle as 4° to the perpendicular line for simpli cation. The region of the bone that overlaps the line (line α) tangent to the medial wall of the acetabulum with a perspective projection angle of 4° tilted to the perpendicular line to the table on the axial CT image represents the ilioischial line on radiography [17].…”