Biomechanical study of anterior and posterior pelvic rings using pedicle screw fixation for Tile C1 pelvic fractures: Finite element analysis

Abstract

Objective: The purpose of this study was to analyse the biomechanical characteristics of pedicle screws with different placement methods and diameters in the treatment of Tile C1 pelvic fractures by finite element simulation technology and to compare them with the plate fixation model to verify the effectiveness of pedicle screw fixation.

Methods: A three-dimensional digital model of a normal pelvis was obtained using computed tomography images. A finite element model of a normal pelvis containing major ligaments was built and validated (Model 1). Based on the verified normal pelvis finite element model, a Tile C1 pelvic fracture model was established (Model 2), and then a plate fixation model (Model 3) and a pedicle screw fixation model with different screw placement methods and diameters were established (Models 4-15). For all pelvic fracture fixation models, a vertical load of 500 N was applied on the upper surface of the sacrum to test the displacement and stress distribution of the pelvis in the standing state with both legs.

Results: The finite element simulation results showed the maximum displacement of Model 1 and Models 3-15 to be less than 1 mm. The overall maximum displacement of Models 4-15 was slightly larger than that of Model 3 (the maximum difference was 177.91×10-3 mm), but the maximum displacement of iliac bone and internal fixation in Models 4-15 was smaller than that of Model 3. The overall maximum stress (maximum stress of the ilium) and maximum stress of internal fixation in Models 4-15 were less than those in Model 3. The maximum displacement difference and maximum stress difference at the fracture of the pubic ramus between each fixed model were less than 0.01 mm and 1 MPa, respectively. The greater the diameter and number of pedicle screws were, the smaller the maximum displacement and stress of the pelvic fracture models were.The maximum displacement and stress of the pelvic fracture models of the screws placed on the injured side of the pubic region were smaller than the screws on the healthy side.

Conclusion: Both the anterior and posterior pelvic rings are fixed with a pedicle screw rod system for treatment of Tile C1 pelvic fractures, which can obtain sufficient biomechanical stability and can be used as a suitable alternative to other implants.The greater the diameter and number of pedicle screws were, the greater the pelvic stability was, and the greater was the stability of the screws placed on the injured side of the pubic region than the screws on the healthy side.

Fig 1. Construction of the FE models of normal pelvis and A Tile C1 fractured pelvis.

(A) Anterior view of the FE model of the normal pelvis. (B) Posterior view of the FE model of the normal pelvis. (C) Anterior view of the FE model of the Tile C1 fractured pelvis. (D) Posterior view of the FE model of the Tile C1 fractured pelvis.

Fig 2. FE model of anterior reconstruction plate fixation for the treatment of Tile C1 pelvic fractures.

(A) Anterior view of the FE model fixed by the reconstruction steel plate. (B) Posterior view of the FE model fixed by the reconstruction steel plate.

Fig 3. FE model Tile C1 pelvic fractures fixed with pedicle screws and rods.

(A-B) Two screws in the pubic area. (C-D) One screw in the pubic area on the injured side. (E-F) One screw in the pubic area on the uninjured side. (G-H) No screws were placed in the pubic area on either side.

Fig 4. Displacement and Von Mises stress distribution of the normal pelvis model.

(A) Displacement distribution of the normal pelvis model under a vertical load. (B) Von Mises stress distribution of the normal pelvis model under a vertical load.

Fig 5. Displacement distribution of each component of the pelvis model fixed with steel plate.

(A) Displacement distribution of the pelvis model fixed with steel plate under a vertical load. (B) Displacement distribution of the iliac bone of the pelvic model fixed with a steel plate under a vertical load. (C) Displacement distribution of the steel plate and screw of the pelvic model fixed by a steel plate under a vertical load.

Fig 6. Displacement distribution of pelvic models fixed with pedicle screws under a vertical load.

(A) Model 4. (B) Model 5. (C) Model 6. (D) Model 7. (E) Model 8. (F) Model 9. (G) Model 10. (H) Model 11. (I) Model 12. (J) Model 13. (K) Model 14. (L) Model 15, (M) Comparison of the maximum displacement of the pelvic model with pedicle screws of three diameters and four fixation methods under a vertical load.

Fig 7. Displacement comparison of pedicle screw fixation models with different diameters and fixation methods.

(A) Displacement distribution of the iliac bone of the pelvis model fixed with pedicle screws under a vertical load. (B) Comparison of the maximum displacement of the iliac bone of the pelvic model with pedicle screws of three diameters and four fixation methods under a vertical load. (C) Comparison of the maximum displacement of the pubic ramus fracture of the pelvic model with pedicle screws of three diameters and four fixation methods under a vertical load. (D) Displacement distribution of the pedicle screw rod in the posterior ring of the pelvic model fixed with pedicle screws under a vertical load. (E) Comparison of the maximum displacement of the pedicle screw rod in the posterior ring of the pelvic model with pedicle screws of three diameters and four fixation methods under a vertical load.

Fig 8. Von Mises stress distribution of each component of the pelvis model fixed with steel plate.

(A) Von Mises stress distribution of the pelvis model fixed with a steel plate under a vertical load. (B) Von Mises stress distribution of the iliac bone of the pelvic model fixed with a steel plate under a vertical load.

Fig 9. Von Mises stress distribution of pelvic models fixed with pedicle screws under a vertical load.

(A) Model 4. (B) Model 5. (C) Model 6. (D) Model 7. (E) Model 8. (F) Model 9. (G) Model 10. (H) Model 11. (I) Model 12. (J) Model 13. (K) Model 14. (L) Model 15.

Fig 10. Von Mises stress comparison of pedicle screw fixation models with different diameters and fixation methods.

(A) Von-Mises Stress distribution of the iliac bone of the pelvis model fixed with pedicle screws under a vertical load. (B) Comparison of the maximum Von-Mises Stress of the iliac bone of the pelvic model with pedicle screws of three diameters and four fixation methods under a vertical load. (C) Von-Mises Stress distribution of the pedicle screw rod in the posterior ring of the pelvic model fixed with pedicle screws under a vertical load. (D) Comparison of the maximum Von-Mises Stress of the pedicle screw rod in the posterior ring of the pelvic model with pedicle screws of three diameters and four fixation methods under a vertical load.