| BackgroundIncidence of fragility fractures of pelvis in the elderly is increasing with the aging population.The iatrogenic injury and high risk of open surgery,and severe osteoporosis in elderly patients,make it a great challenge to treat fragility fractures.A minimally invasive treatment is an ideal alternative to provide solid fixation,and we innovatively propose a new nail placement method,the modified LC-Ⅱ screw,to treat fragility fractures in the elderly pelvis.PurposeTo establish an osteoporotic pelvic model and compare the mechanical stability of modified LC-Ⅱ screw and other conventional internal fixations in FFP type Ⅲa and type Ⅲb injury models by using finite element analysis.Methods1.The CT data of the osteoporotic pelvis of the elderly volunteers are obtained and the 3D model of the pelvis is established and validated using Mimics,Geomagic Studio,Solidworks and ANSYS software.2.The models of modified LC-Ⅱ screw(Group A),conventional LC-Ⅱ screw(Group B)and FFP type Ⅲa are constructed by using Solidworks software.In ANSYS software,a load of 600N is applied to the sacrum in a simulated standing position.After obtaining the stress and displacement distribution,the overall displacement values of the pelvic,the displacement values on both sides of the fracture line and the stress distribution of the two internal fixation methods are compared and analyzed.3.The models of modified LC-Ⅱ screw(Group A),S1 sacroiliac screw(Group B),S1+S2 sacroiliac screws(Group C),the anterior sacroiliac plates(Group D)and FFP type Ⅲb pelvic model are constructed and a load of 600N was applied to the sacrum in a simulated standing position.After obtaining the stress and displacement distribution,the overall displacement values of the pelvic,the displacement values on both sides of the fracture line and the internal fixation stresses of the four internal fixation methods are compared and analyzed.Results:1.In the standing position of the normal pelvic model,the stress starts from the upper surface of the sacral 1 vertebral body,passes through the sacroiliac joint from the sacral wing,conducts to the anterior iliac arch to the acetabulum,and posteriorly to the ischial great notch,and finally reaches the femur.The overall pelvic displacement is symmetrically distributed in the median sacral line,gradually decreasing from top to bottom.2.In the FFP type Ⅲa model in the standing position,the maximum value of overall pelvic displacement:Group B(3.684mm)>Group A(3.604mm).The mean displacement of each node on the proximal iliac bone:Group B(2.594±0.459mm)>Group A(2.351±0.424mm).The mean displacement of the distal iliac bone:Group B(2.508±0.381mm)>Group A(2.318±0.336mm),and the p-value of the mean displacement of the proximal and distal iliac bones is less than 0.05 after statistical analysis.The maximum stress value of internal fixation:Group A is 177.00 MPa,Group B is 229.90 MPa.3.In the FFP type Ⅲb model in the standing position,the maximum value of overall pelvic displacement:Group D(4.211mm)>Group B(4.112mm)>Group A(4.020mm)>Group C(3.929mm).The mean value of displacement of each node of the ilium:Group D(2.988±0.255mm)>Group B(2.717±0.157mm)>Group A(2.695±0.169mm)>Group C(2.546±0.162mm),p-value less than 0.05.The mean value of displacement of each node of sacrum:Group D(3.244±0.578mm)>Group B(3.163±0.576mm)>Group A(3.147±0.556mm)>Group C(2.982±0.555mm),p-value greater than 0.05.The maximum stress value of internal fixation:Group A is 87.75 MPpa,Group B is 99.93 MPpa,Group C is 78.12 MPpa and Group D is 327.13 MPpa.Conclusion:The modified LC-Ⅱ screw is effective in fixing both FFP type Ⅲa fracture and FFP type Ⅲb fracture.The modified LC-Ⅱ screw provides stronger fixation than the conventional LC-Ⅱ screws in fixing FFP Ⅲa fracture.In fixing FFP Ⅲb fracture,the modified LC-Ⅱ screw is more effective than the anterior sacroiliac plates,similar to the sacral 1 sacroiliac screw,and inferior to the S1+S2 sacroiliac screws.The promotes further application of modified LC-Ⅱ screws in clinical practice. |
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