The sacral screw placement depending on morphological and anatomical peculiarities
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Various pathologies of the lumbosacral junction require fusion of the L5/S1 segment. However, pseudarthroses, which often come along with sacral screw loosening, are problematic. The aim of the present investigation was to elaborate the morphological features of the L5/S1 segment to define a so-called “safe zone” for bi- or tricortical screw placement without risking a damage of the iliac vessels.
A total of one hundred computed tomographies of the pelvis were included in this investigation. On axial and sagittal slices, pedicle morphologies, the prevertebral position of the iliac vessels, the spinal canal and the area with the largest bone density were analyzed.
Beginning from the entry point of S1-srews iliac vessels were located at an average angle of 7° convergence, the spinal canal at 38°. Bone density was significantly higher centrally with a mean value of 276 Hounsfield Units compared to the area of the Ala ossis sacri. The largest intraosseous screw length could be achieved at an angle of 25°. The average pedicle width was 20 mm and the pedicle height 13 mm.
A “safe-zone” for bicortical screw placement at S1 with regard to the course of the iliac vessels could be defined between 7° and 38° convergence. Regarding the area offering the largest bone density and the maximal possible screw length, a convergence of 25° is recommended at S1 to reduce the incidence of screw loosening. Screw diameter, as a further influence factor on screw holding, is limited by pedicle height not pedicle width.
KeywordsLumbosacral screw placement Vascular complications Lumbosacral fusion Pseudarthrosis lumbosacral Sacrum Pedicle
CM: Support and advise data collection, manuscript writing. PP: Performed data collection and analysis, manuscript editing. JS: Protocol development, manuscript editing. DG: Data analysis and management, manuscript editing. JB: Data management, manuscript editing. PE: Data analysis and management, manuscript editing. MJS: Project and protocol development, data analysis, manuscript editing.
No funding was achieved.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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