Biomechanical State of the Operated Thoracolumbar Junction in Lateroflexion

Abstract

Summary. The zone of the thoracolumbar junction is the most susceptible to traumatic injuries due to anatomical and physiological features. Accordingly, the stabilization of this section of the spine requires high reliability.
 Objective: to study the stress-strain state of the model of the thoracolumbar spine after resection of Th12-L1 vertebrae with different types of transpedicular fixation under lateroflexion.
 Materials and Methods. Mathematical finite element model of a fragment of the human thoracolumbar spine (Тh9-L5) was developed. We modeled the result of decompressive-stabilizing surgery with total removal of Th12-L1 vertebrae including installation of vertebral body replacing implant and fixation with a transpedicular system using 4 pairs of screws. Lateroflexion was modeled by applying a load of 350 N.
 Results. When evaluating the model without crosslinks and using monocortical pedicle screws, it was found that the maximum loading values in Th10, Th11, L2, and L3 vertebral bodies were 3.4, 2.0, 3.5, and 8.6 MPa, respectively; loading on pedicle screws installed in the indicated vertebrae was 48.4, 48.3, 23.3 and 43.5 MPa. When using bicortical screws without crosslinks in the vertebral bodies, the values were 3.1, 2.5, 3.8, 9.6 MPa and 49.9, 51.9, 25.8, 44.8 MPa, respectively; when using a combination of short screws and crosslinks in the vertebral bodies, the values were 3.2, 2.0, 2.6, 7.5 MPa and 47.6, 47.5, 22.6, 41.2 MPa, respectively; when using crosslinks and bicortical screws, the values were 3.0, 2.2, 2.7, 8.8 MPa and 48.3, 49.6, 24.3, 42.5 MPa, respectively.
 Conclusions. In lateroflexion, monocortical pedicle screws cause lower critical loading rates compared to long screws at all control points of the model. Crosslinks help to reduce stress levels. The use of monocortical pedicle screws in combination with transverse ties seems to be the most biomechanically effective in lateroflexion.

Some aspects of biomechanics of the operated thoracolumbar junction following two-level corpectomy

“…The distal surface of the L5 disc in the model was rigidly fixed. For effective investigation of changes in the stress-strain state of the models, depending on the method of transpedicular fixation, the following control points were selected for recording stress magnitudes: Vertebral body of Th9 (1), Vertebral body of Th10 (2), Vertebral body of Th11 (3), Vertebral body of L2 (4), Vertebral body of L3 (5), Vertebral body of L4 ( 6), Vertebral body of L5 (7), Lower endplate of the vertebral body of Th11 (8), Upper endplate of the vertebral body of L2 (9), Entry zone of the transpedicular screw into the arch of Th10 (10), Entry zone into the arch of Th11 (11), Entry zone into the arch of L2 (12), Entry zone into the arch of L3 (13), Screw in the body of Th10 (14), Screw in the body of Th11 (15), Screw in the body of L2 (16), Screw in the body of L3 (17), Transverse ties between Th10 and Th11 (18), Transverse ties between L2 and L3 (19), Vertebral replacement support (20).…”

“…12,13 This article is extracted from a broader study dedicated to the biomechanics of the operated thoracolumbar junction. [14][15][16] It posits that the surgical approach to spinal trauma, particularly at the TLJ, must be rigorously determined by the extent and nature of the osteoligamentous alterations incurred through injury. 17 The study analyses a model for massive structural damage, necessitating vertebral resection and subsequent stabilization to restore spinal alignment and functionality.…”