Biomechanical Effects of Zero-P Height on Anterior Cervical Discectomy and Fusion: A Finite Element Study

Abstract

Objective: The principle of selecting a Zero-P implant of an appropriate height remains a topic of debate, particularly when similarly sized implants seem to appropriately fit the intervertebral space. Thus, this study compared the biomechanical performance of smaller and larger Zero-P implants within an appropriate height range with that of oversized Zero-P implants for anterior cervical discectomy and fusion (ACDF).

Methods: A three-dimensional finite element (FE) model of the C2–C7 cervical spine was constructed and validated. The implants were categorized as smaller (6 mm), larger (7 mm), and oversized (8 mm) according to the average intervertebral height and implant specifications. Thus, the following four FE models were constructed: the intact cervical spine model (M1), the 6 mm model (M2), the 7 mm model (M3), and the 8 mm (M4) Zero-P implant C5/6 segment ACDF surgical model. Then, a pure moment of 1.0 N·m combined with a follower load of 75 N was applied at C2 to simulate flexion, extension, lateral bending, and axial rotation.

Results: The results indicated that the maximum stress on the vertebral body, intervertebral disc, and facet joints under self-weight increased with increasing Zero-P height. Under six different loading conditions, the maximum stress on the vertebral body in the surgical segment of the M4 model was generally greater than that in the M2 and M3 models. Following an increase in the height of the implant from 6 mm to 8 mm, the maximum stress increased, and the intervertebral disc stress of both segments reached its peak in the M4 model. In the M4 model, the implant experienced the highest stress, whereas the M2 model exhibited the lowest stress on the implant under both self-weight and loading conditions. Furthermore, the stress on the posterior facet joints of the surgical segment increased with increasing Zero-P height. The range of maximum stress on the posterior facet joints for the M3 model was situated between that of the M2 and M4 models.

Conclusion: In summary, after determining the appropriate height range for the implant in accordance with the mean height of the intervertebral space, opting for a larger size appears to be more advantageous. This approach helps maintain the height of the intervertebral space and provides greater stress, promoting a tighter fit between the upper and lower endplates and the Zero-P. This tighter fit is crucial for maintaining spinal stability, enhancing the early bony fusion rate, and potentially leading to better postoperative outcomes.

Keywords

anterior cervical discectomy and fusion / biomechanics / finite element analysis / zero-P

References

[1] G. R. Buttermann, “Anterior Cervical Discectomy and Fusion Outcomes Over 10 Years: A Prospective Study,” Spine (Phila Pa 1976) 43, no. 3 (2018): 207-214.

[2] P. Y. Joo, J. R. Zhu, A. J. Kammien, M. J. Gouzoulis, P. M. Arnold, and J. N. Grauer, “Clinical Outcomes Following One-, Two-, Three-, and Four-Level Anterior Cervical Discectomy and Fusion: A National Database Study,” Spine Journal 22, no. 4 (2022): 542-548.

[3] C. D. Lopez, V. Boddapati, J. M. Lombardi, et al., “Recent Trends in Medicare Utilization and Reimbursement for Anterior Cervical Discectomy and Fusion,” Spine Journal 20, no. 11 (2020): 1737-1743.

[4] E. Chong, M. H. Pelletier, R. J. Mobbs, and W. R. Walsh, “The Design Evolution of Interbody Cages in Anterior Cervical Discectomy and Fusion: A Systematic Review,” BMC Musculoskeletal Disorders 16 (2015): 99.

[5] X. Q. Sheng, Y. Yang, C. Ding, et al., “Uncovertebral Joint Fusion Versus End Plate Space Fusion in Anterior Cervical Spine Surgery: A Prospective Randomized Controlled Trial,” Journal of Bone and Joint Surgery. American Volume 105, no. 15 (2023): 1168-1174.

[6] J. D. Oliver, S. Goncalves, P. Kerezoudis, et al., “Comparison of Outcomes for Anterior Cervical Discectomy and Fusion With and Without Anterior Plate Fixation,” Spine 43, no. 7 (2018): E413-E422.

[7] Y. Zhao, S. Yang, Y. Huo, Z. Li, D. Yang, and W. Ding, “Locking Stand-Alone Cage Versus Anterior Plate Construct in Anterior Cervical Discectomy and Fusion: A Systematic Review and Meta-Analysis Based on Randomized Controlled Trials,” European Spine Journal 29, no. 11 (2020): 2734-2744.

[8] W. Hua, J. Zhi, W. Ke, et al., “Adjacent Segment Biomechanical Changes After One- or Two-Level Anterior Cervical Discectomy and Fusion Using Either a Zero-Profile Device or Cage Plus Plate: A Finite Element Analysis,” Computers in Biology and Medicine 120 (2020): 103760.

[9] C. Huang, H. Abudouaini, B. Wang, et al., “Comparison of Patient-Reported Postoperative Dysphagia in Patients Undergoing One-Level Versus Two-Level Anterior Cervical Discectomy and Fusion With the Zero-P Implant System,” Dysphagia 36, no. 4 (2021): 743-753.

[10] M. Scholz, P. Schleicher, S. Pabst, and F. Kandziora, “A Zero-Profile Anchored Spacer in Multilevel Cervical Anterior Interbody Fusion: Biomechanical Comparison to Established Fixation Techniques,” Spine (Phila Pa 1976) 40, no. 7 (2015): E375-E380.

[11] M. Scholz, P. M. Reyes, P. Schleicher, et al., “A New Stand-Alone Cervical Anterior Interbody Fusion Device: Biomechanical Comparison With Established Anterior Cervical Fixation Devices,” Spine (Phila Pa 1976) 34, no. 2 (2009): 156-160.

[12] K. N. Fountas, E. Z. Kapsalaki, L. G. Nikolakakos, et al., “Anterior Cervical Discectomy and Fusion Associated Complications,” Spine (Phila Pa 1976) 32, no. 21 (2007): 2310-2317.

[13] Z. Sun, Z. Liu, W. Hu, Y. Yang, X. Xiao, and X. Wang, “Zero-Profile Versus Cage and Plate in Anterior Cervical Discectomy and Fusion With a Minimum 2 Years of Follow-Up: A Meta-Analysis,” World Neurosurgery 120 (2018): e551-e561.

[14] T. Zhang, N. Guo, G. Gao, et al., “Comparison of Outcomes Between Zero-p Implant and Anterior Cervical Plate Interbody Fusion Systems for Anterior Cervical Decompression and Fusion: A Systematic Review and Meta-Analysis of Randomized Controlled Trials,” Journal of Orthopaedic Surgery and Research 17, no. 1 (2022): 47.

[15] C. Wu, X. Yang, X. Gao, et al., “The Effects of Cages Implantation on Surgical and Adjacent Segmental Intervertebral Foramina,” Journal of Orthopaedic Surgery and Research 16, no. 1 (2021): 280.

[16] W. Xiong, J. Zhou, C. Sun, et al., “0.5- to 1-Fold Intervertebral Distraction Is a Protective Factor for Adjacent Segment Degeneration in Single-Level Anterior Cervical Discectomy and Fusion,” Spine (Phila Pa 1976) 45, no. 2 (2020): 96-102.

[17] C. H. Cheng, P. Y. Chiu, H. B. Chen, C. C. Niu, and M. Nikkhoo, “The Influence of Over-Distraction on Biomechanical Response of Cervical Spine Post Anterior Interbody Fusion: A Comprehensive Finite Element Study,” Frontiers in Bioengineering and Biotechnology 11 (2023): 1217274.

[18] K. Huang, Q. Wang, X. Rong, et al., “Biomechanical Effects on the Prostheses and Vertebrae of Three-Level Hybrid Surgery: A Finite Element Study,” Orthopaedic Surgery 16 (2024): 2019-2029.

[19] X. Rong, B. Wang, C. Ding, et al., “The Biomechanical Impact of Facet Tropism on the Intervertebral Disc and Facet Joints in the Cervical Spine,” Spine Journal 17, no. 12 (2017): 1926-1931.

[20] T. K. Wu, Y. Meng, H. Liu, et al., “Biomechanical Effects on the Intermediate Segment of Noncontiguous Hybrid Surgery With Cervical Disc Arthroplasty and Anterior Cervical Discectomy and Fusion: A Finite Element Analysis,” Spine Journal 19, no. 7 (2019): 1254-1263.

[21] Y. W. Shen, Y. Yang, H. Liu, et al., “Biomechanical Evaluation of Intervertebral Fusion Process After Anterior Cervical Discectomy and Fusion: A Finite Element Study,” Frontiers in Bioengineering and Biotechnology 10 (2022): 842382.

[22] T. K. Wu, H. Liu, B. Y. Wang, et al., “Incidence of Bone Loss After Prestige-LP Cervical Disc Arthroplasty: A Single-Center Retrospective Study of 396 Cases,” Spine Journal 20, no. 8 (2020): 1219-1228.

[23] G. P. Pal and H. H. Sherk, “The Vertical Stability of the Cervical Spine,” Spine (Phila Pa 1976) 13, no. 5 (1988): 447-449.

[24] D. Shedid and E. C. Benzel, “Cervical Spondylosis Anatomy: Pathophysiology and Biomechanics,” Neurosurgery 60, no. 1 Supp1 1 (2007): S7-S13.

[25] T. N. Degenerative and C. Spondylosis, “Degenerative Cervical Spondylosis,” New England Journal of Medicine 383, no. 2 (2020): 159-168.

[26] T. Yamagata, T. Takami, T. Uda, et al., “Outcomes of Contemporary Use of Rectangular Titanium Stand-Alone Cages in Anterior Cervical Discectomy and Fusion: Cage Subsidence and Cervical Alignment,” Journal of Clinical Neuroscience 19, no. 12 (2012): 1673-1678.

[27] H. Yoshihara, “Indirect Decompression in Spinal Surgery,” Journal of Clinical Neuroscience 44 (2017): 63-68.

[28] Y. Zhang, J. Zhou, X. Guo, Z. Cai, H. Liu, and Y. Xue, “Biomechanical Effect of Different Graft Heights on Adjacent Segment and Graft Segment Following C4/C5 Anterior Cervical Discectomy and Fusion: A Finite Element Analysis,” Medical Science Monitor 25 (2019): 4169-4175.

[29] X. F. Wang, Y. Meng, H. Liu, B. Y. Wang, and Y. Hong, “The Impact of Different Artificial Disc Heights During Total Cervical Disc Replacement: An In Vitro Biomechanical Study,” Journal of Orthopaedic Surgery and Research 16, no. 1 (2021): 12.

[30] M. H. Lawless, E. J. Yoon, J. M. Jasinski, et al., “Impact of Interspace Distraction on Fusion and Clinical Outcomes in Anterior Cervical Discectomy and Fusion: A Longitudinal Cohort Study,” Asian Spine Journal 16, no. 3 (2022): 369-374.

[31] J. S. Lee, D. W. Son, S. H. Lee, et al., “The Effect of Hounsfield Unit Value With Conventional Computed Tomography and Intraoperative Distraction on Postoperative Intervertebral Height Reduction in Patients Following Stand-Alone Anterior Cervical Discectomy and Fusion,” Journal of Korean Neurosurgical Association 65, no. 1 (2022): 96-106.

[32] S. M. Ha, J. H. Kim, S. H. Oh, J. H. Song, H. I. Kim, and D. A. Shin, “Vertebral Distraction During Anterior Cervical Discectomy and Fusion Causes Postoperative Neck Pain,” Journal of Korean Neurosurgical Association 53, no. 5 (2013): 288-292.

[33] Y. Y. Yi, H. Chen, H. W. Xu, S. B. Zhang, and S. J. Wang, “Changes in Intervertebral Distraction: A Possible Factor for Predicting Dysphagia After Anterior Cervical Spinal Surgery,” Journal of Clinical Neuroscience 100 (2022): 82-88.

[34] X. J. Wang, J. B. He, T. K. Wu, et al., “The Influence of Zero-Profile Implant Selection on the Outcomes of Anterior Cervical Discectomy and Fusion,” Orthopaedic Surgery (2024).

[35] E. Truumees, C. K. Demetropoulos, K. H. Yang, and H. N. Herkowitz, “Effects of Disc Height and Distractive Forces on Graft Compression in an Anterior Cervical Discectomy Model,” Spine (Phila Pa 1976) 27, no. 22 (2002): 2441-2445.

[36] J. Wen, J. Xu, L. Li, et al., “Factors Affecting the Nonlinear Force Versus Distraction Height Curves in an In Vitro C5-C6 Anterior Cervical Distraction Model,” Clinical Spine Surgery 30, no. 5 (2017): E510-e4.

[37] H. Igarashi, M. Hoshino, K. Omori, et al., “Factors Influencing Interbody Cage Subsidence Following Anterior Cervical Discectomy and Fusion,” Clinical Spine Surgery 32, no. 7 (2019): 297-302.

[38] D. Z. Yin, X. T. Xin, R. Yang, Y. P. Shi, and H. Y. Shen, “Biomechanical Stability of Lower Cervical Spine Immediately After Discectomy With Grafting,” Orthopaedic Surgery 3, no. 2 (2011): 113-118.

[39] G. P. Pal and R. V. Routal, “A Study of Weight Transmission Through the Cervical and Upper Thoracic Regions of the Vertebral Column in Man,” Journal of Anatomy 148 (1986): 245-261.

[40] W. Ye, Z. Wang, Y. Zhu, and W. Cai, “Analysis of Functional Outcomes and Risk Factors for Facet Joint Distraction During Anterior Cervical Discectomy and Fusion for Cervical Spondylotic Myelopathy,” World Neurosurgery 162 (2022): e301-e308.

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