gms | German Medical Science

Objectives: External fixation is the most commonly recommended treatment concept for surgical stabilization of the pelvic ring in the emergency setting. Application of the Schanz screws is usually performed under image intensifier guidance. The hypothesis of this study was that screw application can be performed without pre- and intraoperative imaging when anatomical landmarks are considered.

Methods: Insertion of the supra-acetabular Schanz screws was performed by two trauma surgery residents. The study sample involved 14 human adult cadavers. The anterior superior iliac spine (ASIS) was palpated. Starting from this landmark, 2 cm were measured in a distal and 2 cm in the medial direction. At this point, the 150 mm Schanz screws were drilled bilaterally into the supra-acetabular corridor with a drill angulation of 20° inferior and 20° lateral orientation. The cadavers were placed in supine position and a combined obturator oblique-outlet view (COOO) was performed bilaterally in each specimen by use of an Arcadis© Orbic 3D C-arm (SIEMES; Solothum, Switzerland). In this view, the supra-acetabular corridor is visualised parallel to its path and appears as a rounded triangle ("teardrop-view"). In addition, six of the specimens underwent a 3D-CT-scan. The X-rays as well as the 3D-scans were evaluated concerning correct screw positioning by a further traumatologist.

Results and conclusion: The sample consisted of eight pelves from female and six pelves from male cadavers. Their mean age at time of death was 81.1 years. Concerning the total collective, the mean height was 165.1 cm (SD: 7.3; median: 165; range: 151-176) and the average weight was 59.4 kg (SD: 6.6; median: 61; range: 48-70). During radiographic evaluation of the COOO-scans (14 specimens) and the 3D-scans (6 specimens), the Schanz screws were placed inside the supra-acetabular corridor in all specimens (14/14).

According to these anatomical data a 2-2-2-20-20 concept was defined, starting with a 2 cm skin incision 2cm distal and 2 cm medial to the ASIS with a drill angulation of 20° inferior and 20° lateral orientation. Using this concept, all Schanz screws could be sufficiently inserted, without intraprocedural x-ray imaging and without cortical perforation, even performed by young and less experienced surgeons. Based on this study, we recommend the 2-2-2-20-20 concept for supraacetabular Schanz screw insertion without additional radiography.