The acetabulum has a complex anatomical structure and is surrounded by some important blood vessels, nerves, and organs. The acetabular fracture surgery is the most complex and challenging surgery in the field of traumatic orthopedics . Hence, patients with acetabular fractures may face many post-surgical complications, including traumatic osteoarthritis, deep vein thrombosis, and heterotopic ossification. [1, 8]. Conducting a good fracture reduction and strong internal fixation can allow postoperative patients to be able to perform functional rehabilitation exercises earlier, thereby reducing the occurrence of related complications and achieving the best clinical effect .
In 2010, the infra-acetabular screw was reported to be able to help close the incomplete “frame” system around the acetabulum, including both acetabular columns, supra-acetabular screws, and the true pelvic rim plate . Meanwhile, researchers indicated the range of application of infra-acetabular screw, including acetabular fractures, that require ilioinguinal approach treatment. The column separation caused by the fracture line passing through the acetabular quadrilateral, as well as obturator foramen, are indications . Specifically, the indication includes anterior column fracture, double-column fracture, T-type fracture, and anterior and posterior hemitransverse fracture. A biomechanical study showed that the locking plate internal fixation system cannot significantly reduce the displacement of high anterior column fractures after fixation. However, no matter what kind of internal fixation was used, adding an infra-acetabular screw can approximately double the strength of the internal fixation . The same fracture pattern was used for another biomechanical study, in which three groups of screws of different materials (titanium, stainless steel, degradable materials) were compared to the general plate. The results indicated that the screw fixation could be applied to non-comminuted acetabular anterior column fractures. The screw fixation had a fixation strength that was equivalent to that of the general plate fixation, which is a promising alternative to steel plate fixation. Moreover, the use of an infra-acetabular screw can significantly increase the strength of fracture fixation, regardless of the implant type . Clinical application has demonstrated that the infra-acetabular screw can achieve good results, including good reduction, fewer complications, and lower risk of postoperative displacement [5, 6].
Despite the fact that the infra-acetabular screw has several advantages, its disadvantages include that it is difficult to place the screw as the screw corridor is relatively narrow and it is an unconventional screw corridor. Some researchers believe that some patients are not suitable for infra-acetabular screws . Therefore, in order to provide references for successful placement of the infra-acetabular screws, many scholars have studied the diameter, length, entry point, spatial position and spatial shape of infra-acetabular corridor (IAC). An anatomical study of 523 pelvises using computer-aided technology showed that 93% of specimens had an IAC with a diameter of lower than 5 mm . A morphological research based on CT scanning demonstrated that the IAC always presents a biconical shape and the narrowest part is located in the fovea of the acetabulum . In addition, development the dysplasia hip does not adversely affect infra-acetabular screw placement. The perfect insertion point of the infra-acetabular screw is highly consistent, and the distance between the entry point and the caudal and medial sides of the ilio-pubic / ilio-pectineal eminence (IPE) center is 10.2 mm and 10.4 mm respectively, which provides a reference for the rapid insertion of infra-acetabular screw through the intrapelvic approach for treatment of related acetabular fractures . The results of these researchers have given surgeons a comprehensive understanding of the anatomical characteristics of the infra-acetabular screw, which can greatly help the rapid and accurate placement of screws during an operation. However, the specimens used by these researchers are from Europe and North America, which means the research results are not applicable to East Asians due to the differences in bone structure between the two races.
In this study, the exit points of the infra-acetabular screw have been located in the ischial tuberosity [5, 7-10]. For Chinese patients that have acetabular fractures, we often cannot successfully insert an infra-acetabular screw. Therefore, we used computer-aided technology to study the structure around the acetabulum and found that when the exit point is located between the ischial tuberosity and the ischial spine, there is also an IAC. This discovery may provide an additional option for IAC. However, at present, there are limited reports on the anatomical characteristics of this new IAC. Therefore, we conducted a purely anatomical study to determine the anatomical differences between the two different IACs. We hypothesized that when the screw exit point is between the ischial spine and ischial tuberosity, the IAC has a larger diameter, which helps increase the range of infra-acetabular screws that can be utilized in East Asian populations represented by Chinese.