Finite element analysis on biomechanical stability of different depths of Schanz nail in pelvic iliac crest external fixator
Objective To compare the biomechanical stability of Schanz nailing at different depths for pel-vic iliac crest external fixator by finite element(FE)analysis.Methods An adult male volunteer of 44 years old,170 cm in height and 75 kg in weight,was selected.Spiral CT was used to scan the iliac spine to the ischial branch continuously.Based on the CT data,a digital model of the pelvis was established by 3D modeling software.Two dif-ferent implantation depths of the Schanz nail were simulated,i.e.Shallow and Deep.In the Shallow scheme,the Schanz nail was inserted into the pelvic iliac crest by 50 mm,which ensured that all the threads entered the bone;while in the Deep scheme,the iliac crest Schanz nail was inserted into the relatively dense bone(10 mm from the top of the acetabulum)in the same direction.An equal constraint load was applied to the sacroiliac joint and the pu-bic symphysis of the two groups of models by FE analysis,and the same load was given to the Schanz nail 50 mm from the outer boundary of the pelvic iliac crest.Then the stress distribution and deformation were calculated.Re-sults In the two groups of models,under the same load,the maximum stress of the Shallow scheme occurred in the cancellous bone of the pelvic iliac crest,and the maximum stress was 87.151 MPa with the maximum displacement of the Shallow Schanz nail being 0.67139 mm.The maximum stress of the Deep scheme occurred in the pelvic iliac crest cortical bone,and the peak stress was 59.183 MPa,with the maximum displacement of the Deep Schanz nail being 0.41773 mm.Compared with the Shallow scheme,the peak stress of the Deep scheme was reduced by 32.1%and the maximum displacement of the Schanz nail was reduced by 37.8%.Conclusion Between the two Schanz nail placement schemes of Shallow and Deep,the biomechanical stability of the Deep scheme is stronger,the change of displacement is smaller,the stress distribution on the Schanz nail is more uniform,and the stability can be im-proved by 47%.In-depth nail placement can more effectively prevent Schanz nail loosening and failure,which is worth popularizing in the treatment of pelvic fractures with external fixators.
PelvicSchanz nailNailing methodFinite element analysis