Sacroiliac fixation in pediatric patients: stability analysis by the finite element method

This study aimed to evaluate, using the finite element method (FEM), the biomechanical stability of a 3.5 mm cannulated screw for sacroiliac fixation of pelvic fractures in children aged ≤ 5 years.

A computerized pediatric pelvic model was constructed from a CT scan of a 5-year-old patient. A Torode and Zieg Type IV fracture was simulated and fixed with a 3.5 mm cannulated screw positioned in the oblique S1 corridor. A bipedal support load condition was applied. For FEM analysis, two fixations were tested: one with a 3.5 mm screw (test) and another with a 7.0 mm screw (control). Visual and quantitative assessments of bone fragment displacement, total pelvic displacement, and maximum von Mises stress in the screws were performed.

Both constructs showed minimal fracture displacement and equivalent stability. The maximum von Mises stress in the 3.5 mm screw was 738 MPa, exceeding the steel alloy limits for plastic deformation and tensile strength, producing a small region of increased surface stress.

In a FEM-based model, sacroiliac fixation with a 3.5 mm cannulated screw in the oblique S1 safety corridor provided stable fixation of pediatric pelvic fractures up to 5 years of age. Nevertheless, the stress observed could lead to screw failure. Therefore, strict postoperative load restriction is recommended.