Mechanical stability of the fracture at the junction of
lumbar vertebral body and pedicle after implantation with different diameters
of pedicle screws

doi:10.3969/j.issn.2095-4344.2656

Abstract

Abstract:

BACKGROUND: Most scholars believe that the fracture of the lumbar spine and pedicle is stable, and transvertebral pedicle screw implantation can improve the stability of fractures. However, the diameter of the transvertebral pedicle screw, mechanical stability and safety of the vertebrae still remain controversial.

OBJECTIVE: To analyze the effect of pedicle screws of different diameters and pedicle cortex on the mechanical stability of the fractured vertebrae and pedicle by three-dimensional finite element method.

METHODS: Based on normal adult L₂-L₃ CT DICOM data, a mimics software was used to establish a model of the fracture at L₂vertebral body and the pedicle. At the same time, a three-dimensional model of L₃ vertebra was created. The L₂-L₃ model was imported into 3-matic in stl format, and a model of pedicle screws with different diameters (diameter of 6.5 and 6.0 mm, and length of 45 mm) was established. The model was imported into ansys after the material attributes were assigned in the mimics software. A vertical load of 500 N was applied to the upper surface of the L₂ vertebral body to simulate the biomechanical performance of a adult with standard body mass after implantation with transvertebral pedicle screw with different diameters under upright condition.

RESULTS AND CONCLUSION: (1) After implantation with 6.0 mm screw, the equivalent load on the lower, upper, inner, and outer walls of the pedicle at the junction of the lumbar vertebra and the pedicle was (1.28±0.62), (0.95±0.18), (0.62±0.37), and (0.36±0.16) MPa, respectively. The difference was significant among groups (F=4.298, P < 0.05). (2) After implantation with 6.5 mm screw, the equivalent load on the lower, upper, inner, and outer walls of the pedicle at the junction of the lumbar vertebra and the pedicle was (1.82±0.76), (1.11±0.18), (0.93±0.38), and (0.43±0.14) MPa, respectively. The difference was significant among groups (F=7.034, P < 0.05). (3) The equivalent load on the lower, upper, inner, and outer walls of the 6.5 mm pedicle screw model was significantly higher than that on the 6.0 mm pedicle screw model (P < 0.05). (4) These results imply that the larger the pedicle screw is, the greater the load on the cortical bone at the junction of the lumbar vertebra and the pedicle is, and the stronger the holding force is. The load on the upper, lower, inner and outer walls of the pedicle is positively related to its cortical thickness. The cortical bone of the inferior wall is thickest, the equivalent load it bears is largest, and the cortical bone of the outer wall is thinnest, and it has the smallest equivalent load. The closer the pedicle screw is to the lower medial wall within the pedicle, the stronger the holding force and the better the stability. The closer it is to the upper and outer side walls, the smaller the gripping force and the worse the stability. However, the placement of nails on the upper and outer walls is safer than the placement of nails on the lower inner wall, and the pros and cons need to be weighed in accordance with the experience of the surgeon during placement.

Key words: joint of lumbar vertebral body and pedicle, pedicle screw, three-dimensional finite element, equivalent load, threshold segmentation, meshing, cortical bone, intervertebral disc

CLC Number:

Zong Zhiguo, Liu Su, Ma Pengpeng, Zhang Xin, Li Wei, Su Feng, Zhang Chunlin, Guo Jianwen, Wen Yi. Mechanical stability of the fracture at the junction of lumbar vertebral body and pedicle after implantation with different diameters of pedicle screws [J]. Chinese Journal of Tissue Engineering Research, 2020, 24(18): 2794-2798.

Figures/Tables 2

References

[1] 李世梁,杜兰翔,崔晓荣,等.个体化伤椎单侧置钉联合植骨术治疗胸腰椎爆裂骨折[J].中国矫形外科杂志,2019,27(14): 1254-1258.
[2] BRUNO AG, BURKHART K, ALLAIRE B, et al. Spinal Loading Patterns From Biomechanical Modeling Explain the High Incidence of Vertebral Fractures in the Thoracolumbar Region.J Bone Miner Res.2017;32(6):1282-1290.
[3] WANG W, PEI B, PEI Y, et al. Biomechanical effects of posterior pedicle fixation techniques on the adjacent segment for the treatment of thoracolumbar burst fractures: a biomechanical analysis.Comput Methods Biomech Biomed Engin.2019;22(13):1083-1092.
[4] MCDONNELL M, SHAH KN, PALLER DJ, et al. Biomechanical Analysis of Pedicle Screw Fixation for Thoracolumbar Burst Fractures.Orthopedics. 2016;39(3): e514-e518.
[5] CHEN HC, LAI YS, CHEN WC, et al. Effect of different radial hole designs on pullout and structural strength of cannulated pedicle screws.Med Eng Phys.2015;37(8):746-751.
[6] KRISHNAN V, VARGHESE V, KUMAR GS. Comparative Analysis of Effect of Density, Insertion Angle and Reinsertion on Pull-Out Strength of Single and Two Pedicle Screw Constructs Using Synthetic Bone Model.Asian Spine J.2016; 10(3):414-421.
[7] OZDEMIR B, KANAT A, ERTURK C, et al.Restoration of Anterior Vertebral Height by Short-Segment Pedicle Screw Fixation with Screwing of Fractured Vertebra for the Treatment of Unstable Thoracolumbar Fractures.World Neurosurg.2017;99:409-417.
[8] XU M, YANG J, LIEBERMAN IH, et al.Lumbar spine finite element model for healthy subjects: development and validation.Comput Methods Biomech Biomed Engin.2017; 20(1):1-15.
[9] LEE CH, LANDHAM PR, EASTELL R, et al. Development and validation of a subject-specific finite element model of the functional spinal unit to predict vertebral strength.Proc Inst Mech Eng H.2017;231(9):821-830.
[10] BISWAS JK, RANA M, MAJUMDER S, et al.Effect of two-level pedicle-screw fixation with different rod materials on lumbar spine: A finite element study.J Orthop Sci. 2018;23(2): 258-265.
[11] SRINIVAS GR, KUMAR MN, DEB A. Adjacent Disc Stress Following Floating Lumbar Spine Fusion: A Finite Element Study.Asian Spine J.2017;11(4):538-547.
[12] ZAHARI SN, LATIF MJA, RAHIM NRA, et al. The Effects of Physiological Biomechanical Loading on Intradiscal Pressure and Annulus Stress in Lumbar Spine: A Finite Element Analysis. J Healthc Eng.2017;2017:9618940.
[13] 文毅,苏峰,刘肃,等.L4-5椎体有限元模型建立及退变椎间盘力学分析[J].中国组织工程研究,2019,23(8):1222-1227.
[14] 闫石,苏峰,张春林,等.椎弓根劈裂对内固定稳定性影响的生物力学研究[J].实用骨科杂志,2014,20(9):821-823.
[15] WINNARD A, NASSER M, DEBUSE D, et al.Systematic review of countermeasures to minimise physiological changes and risk of injury to the lumbopelvic area following long-term microgravity Musculoskelet Sci Pract.2017;27 Suppl 1: S5-S14.
[16] ROZAN M, ROUHOLLAHI V, RASTOGI A, et al.Influence of Physiological Loading on the Lumbar Spine of National Level Athletes in Different Sports.J Hum Kinet.2016;50:115-123.
[17] KOMATSUBARA T, TOKIOKA T, SUGIMOTO Y, et al. Minimally Invasive Cervical Pedicle Screw Fixation by a Posterolateral Approach for Acute Cervical Injury.Clin Spine Surg.2017; 30(10):466-469.
[18] ZHANG Z, MU Z,ZHENG W. Anterior pedicle screw and plate fixation for cervical facet dislocation: case series and technical note.Spine J.2016;16(1):123-129.
[19] UEHARA M, TAKAHASHI J, MUKAIYAMA K, et al.Mid-term results of computer-assisted cervical pedicle screw fixation. ASIAN SPINE J.2014;8(6):759-767.
[20] CHRISTODOULOU E, CHINTHAKUNTA S, REDDY D, et al. Axial pullout strength comparison of different screw designs: fenestrated screw, dual outer diameter screw and standard pedicle screw. Scoliosis. 2015;10:15.
[21] .MAEDA T, HIGASHINO K, MANABE H, et al.Pullout Strength of Pedicle Screws Following Redirection After Lateral or Medial Wall Breach.Spine (Phila Pa 1976). 2018;43(17): E983-E989.
[22] LUTHER E, URAKOV T, VANNI S. Percutaneous Instrumentation of a Complex Lumbar Spine Fracture with Bilateral Pedicle Dissociation: Case Report and Technical Note.J Neurol Surg A Cent Eur Neurosurg. 2018;79(5): 416-423.
[23] BIANCO RJ, ARNOUX PJ, WAGNAC E, et al. Minimizing Pedicle Screw Pullout Risks: A Detailed Biomechanical Analysis of Screw Design and Placement.Clin Spine Surg. 2017;30(3):E226-E32.
[24] 杜心如,赵玲秀,叶启彬.经椎弓根脊柱内固定术的一些进展[J].实用骨科杂志,2000,6(3):167-171.
[25] SPIESSBERGER A, BAUMANN F, HÄUSLER M, et al. A Posterior Oblique Approach to the Lumbar Disk Spaces, Vertebral Bodies, and Lumbar Plexus: A Cadaveric Feasibility Study.Clin Spine Surg. 2018;31(1):E8-E12.