Design of Minimal Invasive Screw on Posterior Pelvis Ring and Pelvic Finite Element Analysis

【Abstract】 Objective To design minimal invasive screw on posterior pelvic ring and perform threedimensional finite element analysis based on a pelvis finite element model. Methods We measured the pelvic anatomical data of 20 healthy volunteers and identified potential designs for minimal invasive screw on posterior pelvic ring. A finite element model of pelvis was then established. Threedimensional finite element analyses were performed under static and dynamic mechanical loading, respectively. Results Three screw tracks on ilium (A, B and C) were identified based on a threedimensional reconstruction of pelvis. Nail track B and C had greater length and width, but shorter distance between nailing and soft tissue compared with nail track A. Static loading under an external rotation load of 500 N generated a maximum Mises Von stress of 582.05 Pa and sacral iliac complex of 107.38 Pa. The greatest strain was located at the articular cartilage on the side of the nail, followed by lateral sacral joint cartilage and symphysis pubis. The largest displacement was located at the ilium on the side of the nail, with a gradient decrease to the opposite side. The largest displacement of the anterior superior iliac spine was 0.35 cm on the side of the nail. The dynamic loading identified displacement of the anterior superior iliac spine with 1.5 mm in Z axis, 1.8 mm in X axis and -0.2 mm in Y axis; and displacement of the pubic bone with 0.8 mm in Z axis, 1.0 mm in X axis and 0.03 mm in Y axis. The maximum displacement appeared along the impact direction: Y axis. Relatively large equivalent stress was found in pubis and ischium, anterior superior iliac spine, sacrum, acetabular that are prone to fracture. With increased impact force, the stress of pelvis increased over time. The maximum