Biomechanical comparison of reconstruction plate versus pedicle screw-rod system in fixation of the models of Tile B1 pelvic injury

Abstract

Objective To compare the biomechanical properties of reconstruction plate and pedicle screw-rod system in fixation of the models of Tile B1 pelvic injury.Methods We used 7 cadaveric specimens of normal adult pelvis from 2 males and 5 females with an average death age of 42.1 years.The cadaveric pelvis preserved an intact spine from the fifth lumbar vertebra to 20 centimeters above the proximal ends of both femurs,intact pubic symphysis,bilateral hip joints,bilateral sacroiliac joints,and major pelvic ligaments.After the pelvic specimens were put in an AGS-X biomechanical testing machine at a simulated standing neutral posture,they were subjected to a vertical load of up to 500 N downward from the L5 vertebral body.The displacements of the symphysis pubis were recorded sequentially in the following 4 conditions:1.intact pelvis (the intact group); 2.models of Tile B1 pelvic injury simulating rotatory unstable injury of the pelvis in which the symphysis pubis was cut apart in combination with ruptures of ipsilateral sacrospinous and sacrotuberous ligaments (the injury group); 3.Tile B1 pelvic injury fixated with a reconstruction plate (the plate group).4.Tile B1 pelvic injury fixated with the pedicle screw-rod system (the screw-rod group).Results Under the vertical load of 500 N,the displacements of the symphysis pubis in the intact,injury,plate and screw-rod groups were respectively 0.121 ±0.025 mm,4.512 ±0.391 mm,0.358 ±0.051 mm,and 0.656 ±0.103 mm.There were significant differences between the 4 groups (F =725.707,P =0.000).The displacement increased from the intact group,the plate group,the screw-rod group to the injury group.The differences between any 2 groups were significant (P ＜ 0.05).Conclusions In fixation of the models of Tile B1 pelvic injury,the reconstruction plate and the pedicle screw-rod system can both effectively restore the biomechanical stability of the injured pelvis.However,internal fixation with the reconstruction plate may yield better biomechanical stability than that with the pedicle screw-rod system. Key words: Pelvis; Fracture fixation, internal; Bone plates; Bone nails; Biomechanics