BIOMECHANICAL ANALYSIS OF SHORT-SEGMENT PEDICLE SCREW FIXATION FOR AO TYPE A FRACTURES AT THE THORACOLUMBAR JUNCTION UNDER EXTENSION LOADING
DOI:
https://doi.org/10.15674/0030-59872025326-36Keywords:
Burst fracture, thoracolumbar junction, short-segment transpedicular fixation, intermediate screws, extension loading, finite element method, spinal biomechanicsAbstract
Thoracolumbar junction fractures account for up to 60 % of all spinal injuries, with more than 20 % classified as burst fractures. These injuries are characterized by instability and an increased risk of kyphotic deformity. Short-segment transpedicular fixation, which has been gradually gaining favor as the treatment of choice for burst fractures in this region, undoubtedly reduces invasiveness but can lead to fixation failure if there is no intermediate support in the body of the injured vertebra. Objective. To evaluate the stress-strain state of the thoracolumbar spine with a burst fracture at ThXII under extension loading, considering screw length and the presence of intermediate fixation. Methods. A finite element model of the spine (ThIX–LV) with a burst fracture at ThXII was developed. Four variants of shortsegment transpedicular fixation were analyzed: short or long (bicortical) screws, with or without additional screws in ThXII. A 350 N load was applied to ThIX, and stresses were determined at control points using the von Mises criterion. Results. The highest stresses in the connecting rods were observed with long screws without intermediate fixation (337.2 MPa). Introducing intermediate screws decreased the stress in ThXII from 16.2 to 9.8 MPa. Short screws with ThXII fixation distributed loads more effectively, reducing peak stresses. Long screws led to overload at the entry points (up to 12.8 MPa in LI), while their maximum stress reached 95.1 MPa. Conclusions. Intermediate fixation of the injured vertebra reduces stress in both bone structures and the implant, thereby decreasing the risk of correction loss. The most favorable configuration is a combination of short screws with intermediate fixation. Long screws are advisable in cases of osteoporosis, although they increase local stresses — a factor that must be taken into consideration during surgical planning.
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Copyright (c) 2025 Oleksii Nekhlopochyn, Vadim Verbov, Ievgen Cheshuk, Mykhailo Karpinsky, Olexander Yaresko
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