Abstract
The objective of this study is to establish an ankylosing spondylitis (AS) thoracolumbar fracture finite element (FE) model and provide a proper posterior fixation choice from the biomechanical perspective. The ankylosing spondylitis T9-L5 FE model was built and the range of motion (ROM) was compared to previous studies. The L1 transverse fracture was simulated and was separately fixed by five different patterns. The pull force and yielding force of the screws, the von Mises stress of the internal fixation, and the displacement of fracture site were analyzed to evaluate the proper fixation pattern for thoracolumbar fracture of AS. ROM of AS model was obviously restricted comparing to the normal vertebral experimental data. All the fixation patterns can stabilize the fracture. At least four levels of fixation can reduce the von Mises stress of the internal fixation. Four levels fixation has a higher pull force than the six levels fixation. Skipped level fixation did not reduce the stress, pull force and yielding force. The kyphosis correction did not change the biomechanical load. At least 4 levels fixation was needed for AS thoracolumbar fracture. The cemented screws should be chosen in 4 levels fixation to increase the holding of the screws. The skipped fixation has no advantage. The kyphosis correction can be chosen after weighing the pros and cons.
Highlights
Ankylosing spondylitis (AS) is a progressive inflammatory disorder that involves mainly the axial skeleton [1]
The range of motion (ROM) of AS model was decreased comparing to the ROM of the normal spine biomechanical experiments in the corresponding segment (Table 2) [27, 28]
The internal fixation of AS fracture suffered from higher von Mises stress than the internal fixation of normal vertebra fracture under the same fixed levels [22, 23]
Summary
Ankylosing spondylitis (AS) is a progressive inflammatory disorder that involves mainly the axial skeleton [1]. The inflammation makes the ligamentous ossification and zygapophyseal joint fusion [2], which leads to a rigid spine. The inflammation causes osteopenia and osteoporosis of the vertebrae [3]. Both factors increase the risk of vertebral fracture [4]. The fracture of AS always affects all the three columns of the spine [5] and can happen under low energy damage [6]. Though the cervical fracture is the most common site in AS fracture, the thoracolumbar fracture is on its heel and occupies 20%-40% of AS fracture [7]
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