Investigation of thoracolumbar T12-L1 burst fracture mechanism using finite element method.

A finite element model of the T12-L1 motion segment was subjected to dynamic vertical impact to investigate vertebral burst fracture mechanism at the thoracolumbar junction. A rigid ball was directed vertically towards a rigid plate fixed on top of the T12 vertebral body to simulate the axial impact. The results show that upon impact, the T12 vertebra exhibited a vibratory motion. At its maximum compression, the endplates bulged towards their vertebral bodies. The central parts of the endplates adjacent to the nucleus experienced the highest effective stress, and localized stress concentration developed correspondingly within the central parts of the cancellous bone adjacent to the endplates. This appears to confirm the hypothesis that nucleus material is forced to enter the vertebral body, pressurizing it further and squeezing the fat and marrow contents out of the cancellous bone. When the nucleus material enters the vertebral body faster than fat and marrow being expulsed, the vertebral body could burst through the anterior and posterior cortical shell. Upon sudden posterior cortex fracture, the transient fragment encroachment could be further into the spinal canal than the final observed locations, as the fragments are retropulsed to the vertebral body during the bursting process.