Biomechanical stability evaluation of isolated straddle fracture using finite element analysis

Area of Science:

• Orthopedic biomechanics
• Trauma surgery
• Finite element analysis

Background:

• Straddle fractures (bilateral pubic rami fractures) are often deemed stable if the posterior pelvic ring is intact.
• Concerns exist regarding the true biomechanical stability of isolated straddle fractures due to potential displacement or delayed union.

Purpose of the Study:

• To quantitatively assess the biomechanical stability of isolated straddle fractures with an intact posterior pelvic ring.
• To compare the stability of isolated straddle fractures versus posterior pelvic ring injuries using finite element analysis.

Main Methods:

• Development of two 3D pelvic models derived from CT scans: Model A (isolated straddle fracture, intact posterior ring) and Model B (posterior pelvic ring fracture).
• Application of axial (600 N), bending (600 N), and torsional (10 Nm) loads to evaluate displacement and von-Mises stress.
• Comparison of calculated stresses against the ultimate tensile strength (UTS) of cortical bone.

Main Results:

• Model A demonstrated physiological displacement (< 2.03 mm) and stress (< 100.6 MPa) under axial and bending/torsional loads, remaining below the UTS (110 MPa).
• Model B exhibited severe instability with displacement > 50 mm and stress exceeding UTS under axial load.
• An intact posterior pelvic ring was found to provide significant biomechanical stability.

Conclusions:

• Isolated straddle fractures with an intact posterior pelvic ring possess sufficient biomechanical stability for conservative management.
• Posterior pelvic ring integrity is critical for pelvic load transfer and overall stability.
• This study provides quantitative evidence to refine treatment principles for pelvic ring injuries.