Digital study of the ideal position of lag screw internal fixation in the anterior column of the acetabulum

Abstract

To find the ideal position of lag screw internal fixation in the anterior column of acetabulum by digital technology, and measure its related parameters, so as to improve the accuracy of lag screw implantation. The CT scan data of 266 semi-pelvic raw in 133 cases (78 males and 55 females, aged 18-65 years old with an average age of 42 years) were collected between January 2019 and January 2020 to compose three-dimensional models. According to the relationship between the peripheral bone cortex of the anatomical channel and the lag screw, a new standard for the ideal position of lag screw fixation in the anterior column of acetabulum was proposed to simulate the implantation of the screw. After the screw was in the ideal position, the following indicators were measured: the maximum allowable diameter of the virtual screw (the diameter of the cylinder up to the new standard, R), the length (the distance between the center of the nail point on both sides, L); the position of the retrograde nail point (the interval between the nail insertion points and the midpoint of the pubic symphysis and the pubic tubercle, respectively, D1 and D2) and the position of the antegrade nail insertion point (the distance between the nail insertion point and the anterior superior iliac spine, the major ischial notch, and the vertical distance between the nail insertion point and the apex of the posterior upper edge of the acetabulum, respectively, D3, D4, D5); and the direction of the virtual screw at the ideal position (the angle between the screw and the horizontal plane, sagittal plane, and coronal plane, respectively, ∠β, ∠γ, ∠δ) were calculated. The maximum allowable diameter of virtual screws was 5.70-14.10 mm for males, with an average of 9.25 mm; for females, it was 4.40-10.40 mm with an average of 7.29 mm. The antegrade insertion point of the anteroposterior acetabular lag screw was located at 2.0-2.5 cm above the apex of the acetabulum, which was almost the same distance from the anterior superior iliac spine and the ischial notch, about 5 cm; the insertion point of the retrograde implant was located at the pubic bone 2.5-3.0 cm below the nodule. When the acetabular anterior column screw was in the ideal position, there was no significant difference in the comparison of ∠β and ∠γ between the male and the female ( P>0.05), and the differences in the other indicators were significant ( P<0.05). Except for D4 and ∠β showing no significant difference between the left and right sides ( P>0.05), the differences in the other indicators were significant ( P<0.05). In the bony channel of the anterior column of the acetabulum, all males can accommodate screws with a diameter of <5.70 mm, and females can accommodate screws with a diameter of <4.40 mm. The anterograde or retrograde screw insertion points are different for male and female. The use of digital technology to individually measure the appropriate screw parameters can improve the accuracy and stability of the lag screw internal fixation for acetabular anterior column fractures.