Finite Element Analysis on Iliosacral Screw Fixation for Sacral Stress Fracture: A Comparison between Three Systems

Background: Sacral stress fracture is a rare but severe fracture that can be fixed by screw insertion. However, location and number of screws have been remained controversial. The goal of the present paper is to examine the efficiency of three fixation systems (1S-sup, 1S-inf and 2S) which vary in number and insertion location. Materials and Methods: A 3D precious model of sacrum based on CT images, fractured from zone 2, was undergone to L5-S1 joint forces after the screws inserted in three fixation systems. Finite element method was used for the present research to evaluate stress distribution within the models and find the interfragmentary motion at the sacral fracture line. Results: Stress is concentrated in vicinity to the fracture gap on the screws. Maximum stress was determined for 1S-inf system, considerably greater than two other systems. Although 1S-sup and 2S systems received similar maximum stress values, the relative displacement between the fragments was more limited in 2S system. Conclusion: Screw fixation can be an efficient technique to fix the sacral fracture. By considering one screw to be inserted, superior location to the first foramina is more effective. Two-screw fixation system (2S) noticeably reduced the relative displacement between the fragments and prepared proper situation for fracture healing.