π-shaped Rod Fixation For Unstable Pelvic Fractures: A Biomechanical Evaluation Of Its Dynamic Stabilization

Objective1.To explore the biomechanical effect of normal pelvis in different states in normal loads.2.To explore the dynamic stabilization effect of π-shaped-rod-fixed-pelvis in different states in normal loads. MethodsEight fresh-frozen cadaveric pelvis were prepared, all specimens were cleaned of residual musculature with taken to preserve spinal ligaments.1. Four normal pelvis of eight pelvis were selceted randomly to undergo the biomechanical test in different states. 2. Then, To simulate unstable pelvic fracture, the right sacroiliac complex and ramus of pubis were separated completely in each specimen. The fracture was reduced and fixed with π-shaped rod( πF) or S1 pediculoiliac screw(SF). All specimens were loaded to 500N to comparing stiffness, displacement and straining and the pelvis withπ-shaped rod were loaded in different states: antexion, extension and leftlateral flexion to compare stress shielding.Results1. Different stiffness, displacement and straining in different states of normal pelvis, while the most unstable effect was achieved in extension.2. π -shaped rod can ultilized the normal pelvic load ,which can achieve static stabilization in early stage of fracture. Either stiffness or displacement, π -shaped rod is better in biomechanics than SI pediculoiliac screw3..In different states, it is less stress-shielding in antexion and right lateral flexion than in extension and neutral position (P<0.05), which can stimulate the bone healing, and will not affect intervertebral disc in advanced stage of fracture with π-shaped rod. Conclusionπ-shaped rod can achieved the dynamic stabilization automatically from static stabilization in different stages of bone healing.