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Updated: Aug 19, 2026
An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model
Published on: May 31, 2017
Biomechanical advantages of double-trajectory screws technique combined with multiple-rod constructs in lumbar
Hu Lyu1,2,3, Qiyang Wang1,2,3, Hongbang Liu1,2,3
1Department of Orthopedics, The First People's Hospital of Yunnan Province, The Affiliated Hospital of Kunming University of Science and Technology, Kunming, China.
Introduction:
Although multi-rods constructs (Multi-RCs) have been demonstrated to reduce the risk of rod fracture (RF) following pedicle subtraction osteotomy (PSO), they offer limited improvement in terms of screw-related complications. The double-trajectory technique (combining traditional trajectory (TT) and cortical bone trajectory (CBT) screws) has been demonstrated to enhance screw fixation. Consequently, the employment of the double-trajectory technique in conjunction with Multi-RCs has the capacity to augment the fixation strength of both rods and screws. Thus, the study aimed to evaluate the biomechanical performance of a novel configuration combining double-trajectory screws with multi-rod in lumbar PSO.
Methods:
A validated L1-5 nonlinear FE model was modified to simulate a 25° PSO at L3. Three configurations were analyzed under both normal and osteoporotic conditions: (a) 2R-TT (one rod with TT screws on each side); (b) 4R-TT (one rod with TT screws on each side, supplemented by a lateral satellite rod); and (c) 4R-TT/CBT (one rod with TT screws and one rod with CBT screws on each side). Loads of 400 N and 7.5 Nm in various directions were applied, with L5 fixed. Outcomes measured included range of motion (ROM) and maximum von Mises stress on rods and screws.
Results:
The 4R-TT/CBT configuration had the smallest ROM in all directions, with reductions of 17.3%-26.4% compared to 2R-TT and 10.9%-16.8% compared to 4R-TT. It also showed the lowest von Mises stress on rods, particularly in flexion, where reductions ranged from 20.5% to 21.4% compared to 2R-TT and 20.9%-21.4% compared to 4R-TT. Considering the maximum von Mises stress on the screws, it exhibited the lowest and demonstrated a substantial reduction of 8.9%-22.8% and 19.5%-29.8% compared to the 2R-TT and 4R-TT configurations, respectively.
Conclusion:
The 4R-TT/CBT configuration provided superior biomechanical performance in lumbar PSO, enhancing construct stiffness, and substantially reducing stresses on rods and screws compared to the 2R-TT and 4R-TT configurations. However, this was a FE study with inherent simplifications. Therefore, the findings should be further confirmed by cadaveric or clinical studies in the future.
