Finite Element Analysis Of Two New Minimally Invasive Internal Fixation For Posterior Pelvic Ring Injuries

ObjectiveTo compare the biomechanical characteristics between s2 alar-iliac(S2AI)screw and sacroiliac joint screw in treating unilateral dislocation of sacroiliac joint.MethodsA healthy 25year-old man was informed consent and performed computed tomography scan,and a contact pelvis model was reconstructed by Mimics、Geomagic Studio、SolidWorks、Abaqus software.Contact pelvis was modified according to previous biomechanical studies.Finite element models of unstable type C sacroiliac joint dislocation were created and fixed by s2 alar-iliac(S2AI)screw and sacroiliac joint screw respectively.The finite element analysis of these three groups were compared.The relative displacement of sacroiliac joint and sacrum and the equivalent stress of screws and bone around screws were recorded and analyzed.ResultsIn the normal pelvic model,the stress was transmitted to the bilateral sacroiliac joint and the iliac arch line to the bilateral acetabulum through the sacral and bilateral sacral wings.The corrected data of displacement data showed that our finite element model had a consistent displacement distribution with the cadaveric bone model.In the TIFI experimental group,the vertical placement was smaller than the horizontal displacement for sacral fracture model,while the horizontal displacement in the sacroiliac joint dislocation model was smaller than that in the vertical placement.The effect of internal fixation and bone around the bone is relatively heavy.The internal fixation stress of vertical placement in sacral fracture and sacroiliac joint dislocation is larger than that of horizontal implantation.The trend of sacroiliac joint displacement and sacrum displacement distribution in the three groups was basically the same.The maximum displacement is arranged from large to small in order:S1>S2AI>S1+S2.The equivalent stress distribution of the internal fixation is mainly concentrated in the sacroiliac joint.The equivalent stress of screws were S1 52.8Mpa,S2AI 62.1Mpa,S1+S2 38.2 Mpa.The equivalent stress of bone around screws were S1 56.8Mpa,S2AI 11.2Mpa,S1+S2 5.8Mpa.ConclusionSingle S1 screw,single S2AI screw and S1 screws combined S2 screws can be used for the treatment of unilateral C type sacroiliac joint dislocation.But the biomechanical stability of single S1 screw shows early weight-bearing is a risk of failure of internal fixation.S2AI screw fixation and S1+S2 screw fixation have similar biomechanical strength,allowing early weight-bearing and contributing to better postoperative rehabilitation.