Background: Screw penetration of the hip joint is a serious complication during plate-screw internal fixation of acetabular anterior column or anterior wall fractures through an anterior approach. The purpose of the cadaveric study is to determine safe paths for screw placement on the anterior column of the acetabulum.
Methods: A total of 46 hemipelvises (24 male, 22 female) were utilized in this study. These hemipelvises were sectioned, and formed cross-sections anterior endpoint (AEP), anterior quarter point (AQP), midpoint (MP), posterior quarter point (PQP) and posterior endpoint (PEP), respectively. Positions at distances of 0.5-, 1.0-, and 1.5-cm lateral to the pelvic brim on cross-section AQP, MP and PQP were marked, respectively. The nearest distance from entry points of the anterior column to the hip joint, the average medial angulation of cortical screws at 0.5-, 1.0-, and 1.5-cm entry points on cross-section AQP, MP and PQP were measured.
Results: The nearest distance from 0.5-, 1.0-, and 1.5-cm entry points to the hip joint is 15.6 +/- 1.5, 13.1 +/- 1.2, and 11.2 +/- 1.4 mm, respectively. The maximum medial angulation to provide safe cortical screw placement at 0.5-, 1.0-, and 1.5-cm entry points is 8.2 +/- 2.2 degrees, 14.9 +/- 3.4 degrees, and 26.1 +/- 4.5 degrees, respectively.
Conclusions: During the operation of plate-screw fixation of the anterior column on the acetabulum, there are three ways to avoid screw penetration of the hip joint. The first one is to use the long screw. Its entry point is placed as close to pelvic brim as possible, and the entry direction is parallel to the quadrilateral surface. The second one is to use the short screws whose lengths are 14, 12 and 10 mm and locate them in the region between the pelvis brim and 0.5-cm entry point, between 0.5- and 1.0-cm entry point, between 1.0- and 1.5-cm entry point, respectively, regardless of the direction of the screw placement. The third one is to take quadrilateral surface as a reference plane, and adjust the medial angulation of the screw placement according to different target locations, i.e., in the coronal plane ranges from 0 degrees to 10 degrees in the region between pelvis brim and 0.5-cm entry point, 10 degrees-20 degrees in the region between 0.5- and 1.0-cm entry point, and 20 degrees-30 degrees in the region between 1.0- and 1.5-cm entry point.