Currently, the anterior ilioinguinal approach is commonly used in treating patients with pelvic and acetabular fractures[18,19]. Internal fixation with a screw-plate system is currently the most frequent method of fixing acetabular fractures, and plate placement on the superior border of the arcuate line is commonly used[7, 20-22].With the ilioinguinal approach, the area of the projection of the acetabulum onto the anterior surface can be exposed through the middle window[1].
The quadrilateral plate is an area similar to a trapezoid. It is bound by the obturator foramen anteriorly, the greater sciatic foramen posteriorly, the pelvic arcuate line superiorly, and the horizontal line joining the obturator foramen and the ischial spine inferiorly[23,24]. Because of the special location of the quadrilateral plate, soft tissue structures are at risk when fixing quadrilateral plate fractures. Bleeding from the corona mortis, direct or indirect injury of obturator vessels and nerves, and direct injury to the urinary bladder by retractors are common complications[25,26]. Quadrilateral plate fractures are mostly encountered in fractures of both columns, accompanied by central dislocations of the hip[7,27]. In addition, T-type fractures, anterior column and posterior hemi-transverse fractures, posterior column and transverse fractures involve this inside wall[27,28]. Open reduction and internal fixation with spring plates, H-shaped, T-shaped, L-shaped and reconstruction plates buttressing the quadrilateral surface, even with cerclage wires are common methods[29-31]. In some other studies, buttress plates have proven helpful in maintaining the quadrilateral surface or medial acetabular wall[21,32]. However, the quadrilateral plate is too thin and is located in the danger zone, so these technologies include indirect or elastic fixation. In some studies, it is considered that the screws have to run parallel to the anterior border of the greater sciatic notch and parallel to the quadrilateral plate[1,18,33]. However, there are some limitations on the insertion point in clinical practice. Moreover, if the quadrilateral plate is too thin, we cannot place the screw in parallel and have to use a certain tilt angle. There is no systematic study in which screws are placed in the danger zone to directly fix the quadrilateral plate. In other words, it is very difficult to place a double cortical screw in the danger zone to fix the quadrilateral plate[7].
The combination of Mimics software and CT data not only saves manpower, materials and financial resources, but can also be repeated and verified by test results with high reliability in guiding practice[34]. At present, this combination is widely used in basic and clinical trial studies[35-37]. This digital anatomical measurement provides a reference for screw placement in pelvic and acetabular fractures. In this study, we confirmed the locations of three insertion points according to the location of the eminelntia iliopectinea and arcuate line. We studied the screw placement penetrating the double cortices via three different angles. As shown in Fig 2, we could operate the drill-bit at safe angles from point A, O and B during the surgery.
In this study, we described that screw placement in the danger zone of the anterior surface of the acetabulum could be used as a common method for the treatment of acetabular fracture. Our results were analysed to find the ranges of effective and safe angles. Given the data obtained from our study, more screws could be applied to increase stability, without penetrating the acetabulum.
As shown in Tables 2 and 4, the MIMIA from insertion points A and B in males was significantly smaller than that in females. Consequently, it can be seen that females required a greater tilt towards the quadrilateral plate surface than males to avoid screw penetration of the joint. The reason for this may be that the thickness of the acetabular medial wall in this region was smaller in females than in males. There were no significant differences in angles between males and females in terms of point O, as shown in Table 3. We speculated that this could be due to the larger femoral head and wider acetabular margin in males, even though the thickness of the medial wall of the acetabulum was smaller in females.
Some related studies have reported screw placement in the danger zone of the acetabulum. Our data differ from those of some previous studies. Benedetti[38] selected the vertical line of the anterior surface of the anterior column as the reference for screw placement. However, this landmark is unreliable for the irregular outline. As the quadrilateral surface is relatively flat, it is very convenient to touch or mark its direction with a Kirschner wire. Therefore, in our study, we considered the quadrilateral surface as a reference to determine the angle of the screw, which could ensure the accuracy of the screw placement. In contrast to the research of Ji et al[14], we performed a study of the anterior and posterior angles of screw placement. As shown in Fig 2, the anterior and posterior inclination screws were long and able to penetrate into bilateral cortices. These screws are more stable than inward tilted screws and can be widely used in clinical practice. Confirmation of the screw insertion sites was decided by the holes on the steel plate in some related digital anatomical studies[34]. In our study, we determined the insertion points through the eminelntia iliopectinea. In the actual operation, 2 or more screws can be placed first to secure the reduction of quadrilateral plate fracture, as shown in Figs 3 and 4. Then, the contoured plate can be inserted to strengthen the fixation.
Mimics software has been widely used in 3D reconstruction for the development of digital orthopaedics technology. Preoperative 3D modelling enables more effective diagnosis and simulates the surgical procedure[39-44]. Our study provides surgeons with accurate data for selecting the correct zones of entry and angles before the implantation of screws. Upper transverse and upper oblique fracture lines are often involved in acetabular fractures based on fracture mapping[45,46], but we can place the screws into the quadrilateral plate and control the angle to ensure double cortices. The obstacle to applying the technique is the complex anatomical structure through the middle window of the ilioinguinal approach. The difficulty of exposure and the risk of neurovascular injury are problems we need to pay attention to and deal with. Perhaps we can further study the intraoperative guide tool to improve the technique.
There are some limitations to this study. Quadrilateral screws can be effectively applied to transverse and oblique fractures around the arcuate line. Nevertheless, they play a limited role in severe comminuted fractures or lower fracture lines. We only studied the fixation of the fracture. However, how to perform fracture reduction was not mentioned. We only researched the common method of screw placement (superior border of the arcuate line). In addition, more patterns of fixation should be considered. We only studied the pelvises of Chinese people, who have different skeletal shapes than the American and European populations. In addition, we did not collect data according to height, weight or body bone density. Moreover, during the actual operation, we had to account for not only the bone but also the soft tissue. These factors may affect the implantation of screws.