A novel internal fixation system for sacral fractures: a finite element biomechanical study

Sacroiliac joint screw (SIJS) fixation is widely regarded as the gold standard for treating unstable posterior pelvic ring injuries. However, the technique presents notable challenges, including a high risk of neurovascular injury and a steep learning curve. This study aimed to introduce a novel Posterior Internal Fixation (P-INFIX) system and evaluate its biomechanical performance in the treatment of Denis zone I sacral fractures using finite element analysis.

A three-dimensional pelvic model-cortical bone, cancellous bone, and cartilage-was reconstructed from computed tomography data of a healthy volunteer. A Denis zone I sacral fracture was simulated and stabilized using either the P-INFIX system (bilateral pedicle screws connected by a transverse Kirschner wire) or the standard SIJS. Finite element analysis was conducted under simulated sitting, supine, and lateral decubitus conditions to assess fracture fragment displacement and implant stress distribution.

The P-INFIX system provided fracture stability comparable to SIJS under most testing conditions. Although SIJS demonstrated a slight statistical advantage in limiting lateral fragment displacement (For example, Z2 in the sitting position: 0.13 mm vs. 0.18 mm, P = 0.001), all measured displacements were far below the clinically significant threshold (<1.3 mm). In terms of implant performance, the peak stress in P-INFIX (sitting: 141 MPa; supine: 320 MPa) was higher than that in SIJS; however, it remained well within the safe range below the yield strength of titanium alloy (1,050 MPa).

The novel P-INFIX system demonstrated biomechanical stability comparable to the gold standard SIJS in managing Denis zone I sacral fractures. Given its potential to reduce surgical risks and simplify the procedure through a "safe channel" lateral to the posterior superior iliac spine, P-INFIX represents a promising and more accessible alternative fixation technique.