Relative position of the supra-acetabular bone to the crestal plane: a radiological analysis

Displaced unstable pelvic injuries are life threatening and require rapid reduction and stabilisation, typically achieved with an external fixator. Recently, the benefits of supra-acetabular pins have been proven; however, these are usually inserted under fluoroscopic guidance. In austere environments and in extremis, this facility is limited and fixation using anatomical landmarks is required. Thus, the aim of this study is to determine the relative position of the supra-acetabular bone to the crestal plane and examine its consistency in military-aged European personnel.

A radiological review of 50 randomised pelvic CT scans in European patients aged 18-30 years from a Level 1 trauma centre was performed. The CT scans were analysed using 3D rendering software. The relative position of the supra-acetabular bone to the crestal plane was determined.

The supra-acetabular bone relative to the crestal plane was approximately 28° caudal and 24° medial to the crestal plane. The mean minimum distance from the pin's entry point to the sciatic notch was approximately 73 mm. There were no differences noted between genders or hemipelvic side.

The supra-acetabular bone maintains a consistent relative position to the crestal plane. Thus, with the surgeon's thumb on the anterior superior iliac spine (ASIS) and index finger on the iliac tubercle, defining the crestal plane, a supra-acetabular pin can be inserted into the anterior inferior iliac spine, which lies 3 cm inferior and 2 cm medial to the ASIS, and advanced along the supra-acetabular bone by angling the pin 30° caudal and 25° medial to the crestal plane.