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

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.