Biomechanical Comparison of Three Internal Fixation Techniques for Stabilizing Posterior Pelvic Ring Disruption: A 3D Finite Element Analysis

Abstract

Objective: To compare the biomechanical stability and compatibility of two iliosacral screws (ISS), a tension band plate (TBP), and a minimally invasive adjustable plate (MIAP) for treating Tile C pelvic fractures.

Methods: Three groups of finite element models of the intact pelvis, including the main ligament and the proximal one-third of both femurs, were developed to simulate vertical sacral fractures and treated with the three abovementioned internal fixation techniques. A 500 N vertical load, a 500 N vertical load plus a 10 Nm moment of forward sagittal direction, and 500 N vertical load plus a 10 Nm moment of right lateral direction were applied to the sacrum to simulate standing status, bending status, and flexion status, respectively. The maximum displacement value, the stress value, and the stress value of the fracture interface were compared among the three internal fixation techniques.

Results: The results showed that all three internal fixation techniques effectively restored the biomechanical transmission of the injured pelvis. The stress on the implants in the TBP model was 167.47% and 53.41% higher than that in the ISS model and the MIAP model, respectively, and the stress shielding phenomenon of the TBP model was more obvious than in the other two models. Meanwhile, the stress between the fracture interfaces in the TBP fixation models was apparently higher than that in the other two models. However, the vertical displacement of the MIAP model was not significantly different from that in the ISS and TBP model; therefore, strong fixation could be obtained in all three models.

Conclusion: Based on our results, we believe that the stability of Tile C pelvic fracture fixed with MIAP was similar to that of fractures fixed with ISS and TBP, but the stress shielding phenomenon and safety of implants in the TBP models were inferior to those in the MIAP and ISS fixation models. Meanwhile, MIAP and ISS fixation were more helpful to the healing processing than was TBP fixation, especially at the fracture interface of the second and third vertebral body levels.

Keywords: Biomechanics; Implant; Pelvic fracture; Pelvic ring.

Figure 1

Stress distribution of the three models under compression states: the stress distribution is transmitted along the iliopectineal line in all three models, and the maximum stress value is less than the yield strength of bone. (A, B) In the ISS model, the maximum stress is located at the upper screw near the processus spinosus of the first sacral vertebra (anterior and posterior views). (C, D) In the TBP model, the maximum stress is located at the first screw near the right sacroiliac joint (anterior and posterior views). (E, F) In the MIAP model, the maximum stress is located at the upper screw near the sacroiliac joint (anterior and posterior). ISS, iliosacral screw; MIAP, minimally invasive adjustable plate; TBP, tension band plate.

Figure 2

The maximum stress values of the implants in three different motion states: under compression, the maximum stress value of the implant in the TBP model is 167.47% and 53.41% higher than that in the ISS model and the MIAP model, respectively; under lateral bending states, the maximum stress value of the implant in the TBP model is 165.01% and 54.61% higher than that in the ISS model and the MIAP model, respectively; under flexion states, the maximum stress values of the implant in the TBP model is 165.14% and 54.61% higher than that in the ISS model and MIAP model, respectively. ISS, iliosacral screw; MIAP, minimally invasive adjustable plate; TBP, tension band plate.

Figure 3

The stress distribution in the implants among the three models in a standing state. (A) In the ISS model, the maximum stress is located at the proximal screw near the spinous process of the first sacral vertebra. (B) In the MIAP model, the maximum stress is located at the proximal screw, which is located in the sacrum. (C) In the TBP model, the maximum stress is located at the first screw in right sacroiliac joint. ISS, iliosacral screw; MIAP, minimally invasive adjustable plate; TBP, tension band plate.

Figure 4

The comparison of the stress shielding among the three finite element models under different statuses. The stress shielding value of the TBP model was higher than that in the ISS and the MIAP models in all motion states. ISS, iliosacral screw; MIAP, minimally invasive adjustable plate; TBP, tension band plate.

Figure 5

Stress at the fracture interface in different motion states: in all three motion states, the maximum stress between the fracture interface of the TBP model was higher than that in the others, especially in the second vertebral fracture interface. (A) Under compression status. (B) Under bending status. (C) Under flexion status.