Abstract: BACKGROUND: Important pathological feature of post-traumatic vertebral osteonecrosis is fissures in the injured vertebra body, bloody fluid and granulation in the fissures. The tissue can form a pseudomembrane. The pseudomembrane formed by necrotic material and granulation tissue can affect the penetration and distribution of the bone cement during vertebroplasty, which can affect the holding power of the bone cement, and increase the risk of bone cement displacement. 
OBJECTIVE: To compare the risk of bone cement displacement in the vertebral body after the treatment of post-traumatic vertebral osteonecrosis with embedded percutaneous kyphoplasty and percutaneous vertebroplasty.   
METHODS: Dicom data of postoperative thoracic CT of a female patient with post-traumatic vertebral osteonecrosis who received embedded percutaneous kyphoplasty treatment were collected. Mimics, Geomagic and Solidwork were utilized to construct three-dimensional embedded percutaneous kyphoplasty treatment models of T9-T11, then build percutaneous vertebroplasty treatment models (anchor point 100%). Embedded percutaneous kyphoplasty models with different size anchors (20%, 40%, 60%, and 80%) were constructed. The finite element analysis software Ansys was used to apply pressures of 150 N in the axial direction and 10 Nm of torque to simulate six movements: flexion, extension, left and right bending, and left and right rotation. The changes in the displacement of the bone cement were observed in the T10 vertebral body of the force model.  
RESULTS AND CONCLUSION: (1) In the six states, the displacement of the bone cement in the T10 vertebral body of the 100% embedded percutaneous kyphoplasty model and the 20% embedded percutaneous kyphoplasty model was smaller than that of the percutaneous vertebroplasty model (P < 0.01). In the states of flexion, extension, right bending and left and right rotation, as the anchor point of the embedded percutaneous kyphoplasty model decreased, the displacement of the bone cement after the force gradually increased (P < 0.001). (2) It is concluded that the risk of bone cement displacement in the vertebral body of embedded percutaneous kyphoplasty treatment is less than that of the percutaneous vertebroplasty treatment in post-traumatic vertebral osteonecrosis. 

Key words: thoracic vertebra fracture, bone cement, post-traumatic vertebral osteonecrosis, percutaneous vertebroplasty, percutaneous kyphoplasty, finite element, osteoporosis, vertebral compression fracture