The Study On The Mechanism Of Pelvic Vascular Injury Under Lateral Impact

PurposeThe aim of the study was to(i)analyze the mechanism of vascular injury when pelvis was laterally impacted,(ii)study the strain and stress on pelvis on the moment,(iii)investigate the kinematic features of pelvic displacement caused by lateral impact,(iv)identify the relationship between peak and final deformation of pelvis.MethodsA total of 3 human cadaver pelves were seated uprightly on a slide test table,explored to horizontal lateral impact by a 22.1 kg impactor at speed of 5.2,4.0 and 4.8 m/s.Kinematic data of pelvic osseous interesting points(POIP)were measured by a motion capture system.Trajectories of POIP,duration of impact and deflection of the pelvis were calculated as well as rotational movement of the pelvis was evaluated.After impact,autopsy and CT scan were made to validate the motion capture data.Pelvic finite element model was constructed based on a pelvic CT scan.Boundary conditions and loads were defined according to previous real impact trials.Then the simulation of lateral impact to the pelvis was carried out.After calculation,the distribution of strain,stress and displacement on the pelvis were revealed.Based on the anatomical measurement and CT data,the steric configuration of the internal iliac artery was specified.Applying fluid-structure interaction,the finite element model of the internal iliac artery with blood was established.Afterwards,the cosimulation brought out the strain,stress and displacement on the vessels.ResultsThe procedure of pelvic compression under lateral impact could be divided into an acceleration injury phase and a deceleration injury phase.The latter was the main stage that caused fracture and deformation.During impact,the peak compression of the pelvis was 1.3-2.2 times of final appearance.Internal iliac artery presented bruise.In finite element simulation of lateral impact to the pelvis,deceleration injury created more significant destruction than acceleration injury,principally caused damage to pelvic girdle and vessels.The steric configuration of the pelvis was the primary factor that delimitated the distribution of strain,stress and displacement on the pelvis during impact.The sacroiliac joint,the origin of arcuate line,the sacral alar slope,the greater sciatic notch,the lateral lamella of iliac ala,the superior pubic ramus and the inferior pubic ramus were the concentration areas of strain and stress.The enormous strain and shear force presented at the junction of the pelvic floor and bone,that was 1-3 magnitude higher than other regions of pelvis,might be the crucial cause of the vascular rupture.The finite element analysis of internal iliac artery discovered,the geometrical configuration of internal iliac artery branches and blood flow determined the internal iliac artery bore more stress and strain than the external iliac artery.Comparing with the latter,the speed and pressure of blood in the former were higher,the turbulence is stronger.Thus induced intima degeneration and vessel histopathology more frequently occurred in the internal iliac artery.The three vulnerable branches were superior gluteal artery,lateral sacral artery and iliolumbar artery.Conclusion 1.The strain and stress distribution of the bony pelvis,the shear and stretching movement between the pelvic floor and bone,the vascular steric configuration and blood flow,all these together lead to the fragility of superior gluteal artery when the pelvis is impacted laterally.2.Because of the rebound effect,the pelvic fracture displacement on medical images after lateral impact is much less than what happened at the moment of the accident.The final displacement can be less than half of the peak displacement.3.When treating patients with pelvic fracture,clinicians shall not judge the severity of patient and predict the loss of blood solely based on the fracture displacement showed in medical images.During operation,hemostasis exploration shall not be simply confined to the fracture site.4.Managers and researchers in the field of labour protection and automobile safety should pay more attention to the protection of pelvic deceleration injury.