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The impact of pedicle screw transitional segment and thread distribution on postoperative rod-screw system failure :
Wen Peng1,2, Weichao Wang3,4, Jie Zhang1
1Department of Orthopaedic Surgery, The First Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, China.
Aims:
This study aimed to evaluate the differences in postoperative internal fixation system failure between two distinct pedicle screw designs, and to examine how variations in the transitional segment and thread distribution of these screws influence the bending mechanical properties of the rod-screw system.
Methods:
A retrospective analysis was performed on 81 cases of thoracolumbar posterior internal fixation surgery from January 2020 to December 2023, focusing on comparing the postoperative fracture and loosening rates associated with the two pedicle screw designs. Finite element analysis was employed to assess the impact of different transitional segment and thread distribution designs of pedicle screws on stress distribution within the rod-screw system under physiological stress conditions in a T10-L2 fracture model. Dynamic and static bending performance tests were conducted on pedicle screws and rod-screw systems featuring various transition segment and thread distribution designs.
Results:
The clinical analysis revealed significant variations in postoperative fracture rates among rod-screw systems with different pedicle screw designs (p < 0.05), while the rates of loosening remained largely consistent postoperatively. Finite element analysis and mechanical testing demonstrated that extending the transitional segment can mitigate the maximum stress across the entire rod-screw system and enhance the uniformity of stress distribution. This modification improves the bending performance of the pedicle screw and its rod-screw system, shifting the failure point from the pedicle screw to the connecting rod. Conversely, variations in thread distribution design exhibited minimal impact on the stress distribution and bending performance of the entire rod-screw system.
Conclusion:
Pedicle screws with optimally extended transitional segments can effectively alleviate local stress concentrations and enhance the bending performance of the screw and its rod-screw system, thereby reducing the risk of postoperative screw fracture.
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