Biomechanical characteristics of four fixation methods in treatment of pubic symphysis disruption: a finite element analysis

Objective To evaluate the biomechanical characteristics of 4 fixation methods (single reconstruction plate, dual reconstruction plates, single cannulated screw and dual cannulated screws) in the treatment of pubic symphysis disruption. Methods Miniature spiral CT scans were performed on the complete pelvis in 5 healthy volunteers. The primary two-dimensional CT scan data at DICOM format were imported into software Mimics 15.0 for three-dimensional reconstruction of bilateral hips and sacrums. The finite element model of skeletal pelvis was obtained by grid partitioning and assignment using software Abqus 6.13. Models of pubic symphysis disruption were simulated by cutting off the unilateral sacroiliac ligament, sacral spine ligament, sacral tuberosity ligament, pubic ligament and pubic arch. Four implants(single reconstruction plate, dual reconstruction plates, single cannulated screw and dual cannulated screws) were simulated and emplaced onto the models according to standard surgical procedures. Compressive and rotational loads were implemented in all models for finite element analysis. The biomechanical properties were recorded and analyzed, including construct stiffness, micromotion of the pubic symphysis and von Misses stress. Results Under vertical load, the space of pubic symphysis disruption >25 mm. The vertical stiffness and rotational construct stiffness of the pelvis decreased significantly from 442.738±29.946 N/mm and 10.118±1.432 N·m/Deg in the normal group to 14.754±0.876 N/mm and 0.328±0.119 N·m/Deg, respectively. Dual reconstruction plates and dual cannulated screws displayed the best vertical tensile strength; their construct stiffness achieved 117.647±9.193 N/mm and 131.443±4.348 N/mm, respectively. Under anti-rotation load, dual cannulated screws displayed the best performance because they rebuilt 68.6% of the whole structural stiffness. For the local stability of the pubic symphysis, dual reconstruction plates showed a strong local anti-rotation capability and dual cannulated screws a good local anti-tensile capability. The displacement in the dual cannulated screws group was only -0.240±0.119 mm under vertical load while the angular displacement in the dual reconstruction plates group only 0.218°±0.182°. Single reconstruction plate endured the maximum von Misses stress which was obviously concentrated. Conclusion Dual cannulated screws may have biome-chanical advantages for treatment of pubic symphysis disruption. Key words: Pelvis; Finite element analysis; Biomechanical characteristics; Fractures fixation, internal; Comparative study