Virtual mapping of 260 three-dimensional hemipelvises to analyse gender-specific differences in minimally invasive retrograde lag screw placement in the posterior acetabular column using the anterior pelvic and midsagittal plane as reference.
BACKGROUND
Due to complex pelvic geometry, percutaneous screw placement in the posterior acetabular column can pose a major challenge even for experienced surgeons.


METHODS
The present study examined the preformed bone stock of the posterior acetabular column in 260 hemipelvises. Retrograde posterior column screws were virtually implanted using iPlan CMF (BrainLAB AG, Feldkirchen, Germany); maximal implant length, maximal implant diameter and angles between the screw trajectories and the reference planes anterior pelvic plane as well as the midsagittal plane were assessed for gender-specific differences.


RESULTS
The virtual analysis of the preformed bone stock column showed two constrictions of crucial clinical importance. These were located 49.6 ± 3.4 (41.0-60.2) mm (inferior margin of acetabulum) and 77.0 ± 5.6 (66.5-95.3) mm (centre of acetabulum) from the entry point of the implant in men and respectively 43.7 ± 2.3 (38.3-49.3) mm as well as 71.2 ± 3.5 (63.5-79.99) mm in women (men vs. women: p < 0.001). The entry point of the retrograde posterior column screw was located dorsal from the transition of the lower margin of the ischial tuberosity to ramus inferior pointing to the medial margin of the ischial tuberosity. In female patients, the entry point was located significantly closer to the medial margin of the ischial tuberosity. However, 7.3 mm screws can generally be used in men and women. The angle between the screw trajectory and the anterior pelvic plane in sagittal section was 14.0 ± 4.9 (2.5-28.6) °, the angle between the screw trajectory and the midsagittal plane in axial section was 31.1 ± 12.8 (1.5-77.9) ° and the angle between the screw trajectory and the midsagittal plane in coronal section was 8.4 ± 3.8 (1.5-20.0) °. For all angles, significant gender-specific differences were found (p < 0.001).


CONCLUSIONS
Therefore, the anterior pelvic plane as well as the midsagittal plane can facilitate intraoperative orientation for retrograde posterior column screw placement considering gender-specific differences in preformed bone corridor, implant length as well as angles formed between screw trajectory and these reference planes.
BG Trauma Centre, Eberhard Karls University of Tuebingen, Schnarrenbergstraße 95, 72076, Tuebingen, Germany. gochs@bgu-tuebingen.de.
Bjoern Gunnar
BG
Ochs
BG Trauma Centre, Eberhard Karls University of Tuebingen, Schnarrenbergstraße 95, 72076, Tuebingen, Germany. chrgonser@aol.com.
Fabian Maria
FM
Stuby
BG Trauma Centre, Eberhard Karls University of Tuebingen, Schnarrenbergstraße 95, 72076, Tuebingen, Germany. cgonser@bgu-tuebingen.de.
Ulrich
U
Stoeckle
BG Trauma Centre, Eberhard Karls University of Tuebingen, Schnarrenbergstraße 95, 72076, Tuebingen, Germany. christoph.gonser@med.uni-tuebingen.de.
Christoph Emanuel
CE
Gonser
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019060:Minimally Invasive Surgical Procedures / Q000379:methods*; D010384:Pelvic Bones / Q000000981:diagnostic imaging* / Q000601:surgery*; D012727:Sex Characteristics; D014057:Tomography, X-Ray Computed / Q000379:methods; D014584:User-Computer Interface; D055815:Young Adult