Biomechanics

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pedicle screw size


C.-C. Hsu, C.-K. Chao, J.-L. Wang, S.-M. Hou, Y.-T. Tsai, and J. Lin, “Increase of pullout strength of spinal pedicle screws with conical core: biomechanical tests and finite element analyses,” Journal of Orthopaedic Research, vol. 23, no. 4, pp. 788–794, 2005.

M. R. Zindrick, L. L. Wiltse, and E. H. Widell, “A biomechanical study of intrapeduncular screw fixation in the lumbosacral spine,” Clinical Orthopaedics and Related Research, vol. 203, pp. 99–112, 1986.

W. Cho, S. K. Cho, and C. Wu, “The biomechanics of pedicle screw-based instrumentation,” Journal of Bone and Joint Surgery B, vol. 92, no. 8, pp. 1061–1065, 2010.

P. S. D. Patel, D. E. T. Shepherd, and D. W. L. Hukins, “The effect of screw insertion angle and thread type on the pullout strength of bone screws in normal and osteoporotic cancellous bone models,” Medical Engineering and Physics, vol. 32, no. 8, pp. 822–828, 2010.

S. D. Cook, J. Barbera, M. Rubi, S. L. Salkeld, and T. S. Whitecloud III, “Lumbosacral fixation using expandable pedicle screws: an alternative in reoperation and osteoporosis,” Spine Journal, vol. 1, no. 2, pp. 109–114, 2001.

W. Lei and Z. Wu, “Biomechanical evaluation of an expansive pedicle screw in calf vertebrae,” European Spine Journal, vol. 15, no. 3, pp. 321–326, 2006.

J. N. Weinstein, B. L. Rydevik, and W. Rauschning, “Anatomic and technical considerations of pedicle screw fixation,” Clinical Orthopaedics and Related Research, vol. 284, pp. 34–46, 1992.



Pedicle screw fixation strength: pullout versus insertional torque


Level Patients Title Authors Takeaway
V, animal 3 screw types, 54 pedicles Pedicle screw fixation strength: pullout versus insertional torque. Spine J . Sep-Oct 2004;4(5):513-8.

S Inceoglu, L Ferrara, RF McLain

Spine Research Laboratory, The Cleveland Clinic Spine Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA

  • Insertional torques for conical screws were significantly greater than those of cylindrical screws (p<.0001).
  • There was no significant correlation between pullout strength and insertional torque (p>.05).
V, synthetic bone 9 screw types, 54 pedicles Biomechanical comparison of pedicle screw fixation strength in synthetic bones: Effects of screw shape, core/thread profile and cement augmentation. PLoS One. 2020 Feb 21;15(2).

Mu-Yi Liu T,sung-Ting Tsai, Po-Liang Lai, Ming-Kai Hsieh, Lih-Huei Chen, Ching-Lung Tai

Graduate Institute of Biomedical Engineering, Chang Gung University, Taoyuan, Taiwan.

  • In healthy vertebrae, conical and dual-core/dual-thread designs can improve pullout strength
  • In osteoporotic bone, thread profile has little impact on screw fixation strength in pedicle screw with cement augmentation
V, synthetic bone 9 screw types, 54 pedicles

Biomechanical analysis of pedicle screw thread differential design in an osteoporotic cadaver model. Clin Biomech. 2012; 27(3):234–40.

Mehta H, Santos E, Ledonio C, Sembrano J, Ellingson A, Pare P, et al.

Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA.

  • Dual lead osteoporotic-specific pedicle screws demonstrated significantly larger insertion torques
  • Standard pedicle screws and dual lead osteoporotic-specific pedicle screws have similar pullout properties
  • Thin crest dual lead pedicle screws had enhanced purchase in osteoporotic bone.


V, synthetic bone

The Comparison of Pullout Strengths of Various Pedicle Screw Designs on Synthetic Foams and Ovine Vertebrae. Turk Neurosurg . 2015;25(4):532-238.

Onur Yaman, Teyfik Demir, Arslan Kagan Arslan, Mehmet Akif Iyidiker, Tolga Tolunay, Necip Camuscu, Murat Ulutas

Tepecik Education and Training Hospital, Clinic of Neurosurgery, Izmir, Turkey.

  • Transpedicular screws redesigned with modified helical angles exhibit higher pullout strength compared to the classical transpedicular screws



V, synthetic bone

Minimizing pedicle screw pullout risks: A detailed biomechanical analysis of screw design and placement. Clin Spine Surg. 2017 Apr;30(3):E226-E232

Rohan-Jean Bianco, Pierre-Jean Arnoux, Eric Wagnac, Jean-Marc Mac-Thiong, Carl-Éric Aubin

Department of Mechanical Engineering, Polytechnique Montréal Sainte-Justine University Hospital Center, Montreal, QC, Canada

  • Transpedicular screws redesigned with modified helical angles exhibit higher pullout strength compared to the classical transpedicular screws



V, synthetic bone

Minimizing pedicle screw pullout risks: A detailed biomechanical analysis of screw design and placement. Clin Spine Surg. 2017 Apr;30(3):E226-E232

Rohan-Jean Bianco, Pierre-Jean Arnoux, Eric Wagnac, Jean-Marc Mac-Thiong, Carl-Éric Aubin

Department of Mechanical Engineering, Polytechnique Montréal Sainte-Justine University Hospital Center, Montreal, QC, Canada

  • Transpedicular screws redesigned with modified helical angles exhibit higher pullout strength compared to the classical transpedicular screws




Results: The design of experiment analysis revealed significant effects (P<0.01) for all tested principal parameters along with the interactions between diameter and trajectory. Screw diameter had the greatest impact on anchorage performance. The best insertion trajectory to resist pullout involved placing the screw threads closer to the pedicle walls using the straightforward insertion technique, which showed the importance of the cortical layer grip. The simulated cylindrical single-lead thread screws presented better biomechanical anchorage than the conical dual-lead thread screws in axial loading conditions.

Conclusions: The model made it possible to quantitatively measure the effects of both screw design characteristics and surgical choices, enabling to recommend strategies to improve single pedicle screw performance under axial loading.



12.Abshire BB, McLain RF, Valdevit A, Kambic HE. Characteristics of pullout failure in conical and cylindrical pedicle screws after full insertion and back-out. Spine. J 2001; 1(6):408–14. pmid:14588297 View ArticlePubMed/NCBIGoogle Scholar

13.Tsai WC, Chen PQ, Lu TW, Wu SS, Shih KS, Lin SC. Comparison and prediction of pullout strength of conical and cylindrical pedicle screws within synthetic bone. BMC Musculoskelet Disord. 2009; 10:44. pmid:19402917 View ArticlePubMed/NCBIGoogle Scholar

14.Chen LH, Tai CL, Lee DM, Lai PL, Lee YC, Niu CC, et al. Pullout strength of pedicle screws with cement augmentation in severe osteoporosis: A comparative study between cannulated screws with cement injection and solid screws with cement pre-filling. BMC Musculoskelet Disord. 2011; 12:33. 2011. pmid:21284883