Publication: Novel technique for s1 pedicle screw fixation- safe zone & morphology in the Malaysian population
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Date
2022
Authors
Shunmugam, Pradeep
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Abstract
Introduction Lumbosacral instrumentation is used in fixation of fractures, tumours, scolilosis and degenerative instability. It is important to understand the anatomy and morphology of the sacrum especially S1 pedicle which is commonly performed and is associated with neurologic, vascular and visceral complications. The aim of this study is to study and compare morphology of the S1 pedicle of the Malaysian population to other populations and propose a new entry point for S1 pedicle screw fixation. Methodology This cross sectional study examined CT scan images of 100 patients (78 males and 22 females) done in Hospital University Sains Malaysia due to various indications. The desired level of axial cut of CT scan image over L5/S1 articular facet was selected from a point in the sagittal view using Multi Planar Reconstruction in the PAC system. The new entry point over the L5/S1 articular facet was used to measure the following parameters : 1) Optimum angle for screw insertion, 2) Screw length at 0 degree trajectory, 3) Maximum screw length at optimum angle Results The mean length of screw at 0 degree trajectory is 2.63cm ± 0.36 in males and 2.40cm ± 0.25 in females. The mean optimum angle for screw insertion was 21.09 ± 3.20 in males and 20.90 ± 2.90 in females. Maximum screw length at optimum angle was 4.03cm ± 0.68 in males and 3.92cm ± 0.63 in females with the range of screw length from 2.9cm to 5.92cm in males and 3.16cm to 5.41cm in females respectively. Conclusion There is difference in morphology of sacrum in the Malaysian population as compared to other population. Our proposed entry point is safe to use in S1 pedicle screw fixation with a maximum screw length of 4.5cm and 20 degrees insertion angled medially to the sacral promontory. However, the biomechanical stability and strength should be evaluated with cadaveric studies.
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Keywords
S1 pedicle screw fixation , safe zone