Short transpedicular fixation of burst fractures in the thoracolumbar junction during forward bending: a finite element biomechanical study

Background. Injuries to the thoracolumbar junction (T11-L2) account for approximately 46.5 % of all spinal fractures. Burst fractures most frequently occur at the transition from thoracic kyphosis to lumbar lordosis, which is influenced by the distinct morphological and biomechanical features of this region. In surgical practice, there is a trend toward minimally invasive techniques, including short transpedicular fixation, yet in cases of unstable burst fractures, this approach often carries a high risk of hardware failure. Objective: to evaluate the stress-strain state of thoracolumbar spine models with a burst fracture of the T12 vertebral body during forward bending under different variants of short transpedicular fixation (short or long screws, with or without additional fixation of T12). Materials and methods. A previously developed finite element 3D model of the thoracolumbar spine with a burst fracture of the T12 vertebral body was used. Four variants of transpedicular fixation of the two vertebrae adjacent to the injury were modeled: with short and long screws passing through the anterior vertebral wall, as well as an additional pair of short screws inserted into T12 or without them. A forward-bending movement was simulated, while the lower surface of the L5 disc was fixed. Von Mises stress was evaluated at several control points. Results. Without additional T12 fixation, using long screws (as opposed to short one) lowered the peak stresses in the T12 body, adjacent vertebrae, and instrumentation. Although the highest stress levels on the screws and support beams remained significant, they were noticeably reduced with long screws. Using intermediate screws considerably decreased stress in the bony elements, which is important for preventing screw loosening and migration. Combining long screws with additional T12 fixation proved to be most effective in minimizing stress in both bony structures and the instrumentation. Conclusions. Short transpedicular fixation with additional T12 fixation substantially lowers stress levels in the vertebrae but can lead to excessive loading on hardware components. The most favorable option for stress distribution in both the bony structures and the instrumentation is the combination of long screws and additional T12 fixation.