Intraoperative Imaging in Pelvic Surgery

Pelvic fractures may range from highly severe, life-threatening injuries to less acute clinical entities. There are several sub-entities that are summed up as pelvic injuries. Anatomically, there are fractures of the anterior or posterior pelvic ring. Apart from these, there are fractures of the acetabulum that make up about one fifth of all pelvic injuries. The indication for surgical treatment of pelvic ring injuries depends on the type of injury, involvement of anterior and/or posterior elements of the pelvic ring, demands and the general condition of the patient. In acetabular fractures, indications depend on the dislocation of the fracture and of course also the needs of the patient and his general condition. An intraarticular step-off of more than 2 mm is usually considered as an indication for open reduction and osteosynthesis. Usually in all these injuries, a preoperative CT scan is mandatory to allow precise planning of the operative approach and technique. Intraoperatively, the surgeon should be familiar with the acquisition of the 2D standard views, including 2D imaging of the pelvic ring and the acetabulum. These consist of the anteroposterior view for both pelvic ring and acetabular osteosyntheses. For further assessment of pelvic ring treatments, inlet and outlet views are achievable by angulating the C-arm cranially and caudally. To assess aspects of the anterior and posterior column of the acetabulum, iliac oblique views are used. Here, the C-arm is rotated laterally. As evaluation of 2D views can be limited due to anatomy and superposing structures, intraoperative 3D imaging has become common in the last decade. Special C-arms allow the automatic acquisition of large numbers of projections and create CT-like views of the central volume. Although this method has significantly widened the possibilities of intraoperative imaging, some issues remain. Depending on the amount of implants placed in the imaging field, assessment can be seriously impaired due to artefacts caused by the implants. Intraoperative CT imaging promises enhanced image quality for artefacts and allows a considerably larger field of view. The use of radiation-free navigation facilitates implant placement in minimally invasive procedures like screw placement in the sacroiliacal joint or the acetabulum by visualisation of instruments and implants in a pre- or intraoperative 3D data set.