Original ArticleBiomechanical Influences of Transcorporeal Tunnels on C4 Vertebra Under Physical Compressive Load Under Flexion Movement: A Finite Element Analysis
Introduction
Cervical disc herniation could cause cervical radiculopathy or myelopathy, which presents as arm pain, numbness, motor function decline, or claudication. Surgical treatment is necessary if conservative treatments are not successful. The standard procedure for cervical disc herniation is anterior cervical decompression and fusion,1, 2 which was first reported in the 1950s. However, anterior cervical decompression and fusion has many disadvantages, such as inducing loss of motion due to intervertebral fusion, approach-related morbidity, graft-related complications, and adjacent segment diseases. To avoid loss of motion by fusion, endoscopic techniques are a feasible way to remove the herniated disc, yet preserving cervical mobility. For example, posterior percutaneous endoscopic cervical foraminotomy3, 4 is used to treat lateral disc herniation or stenosis of the foramen, and anterior percutaneous endoscopic cervical discectomy with a transdiscal approach5 is used to treat central cervical disc herniation.
For anterior percutaneous endoscopic transdiscal cervical discectomy, Wen-Ching Tzaan6 performed a long-term follow-up study and compared the mean decrease in vertical height between postoperative and preoperative magnetic resonance imaging scans, which was 1.1 mm and was statistically significant (P < 0.001). To avoid complications and the acceleration of disc degeneration by anterior percutaneous endoscopic cervical discectomy, anterior percutaneous endoscopic transcorporeal cervical discectomy (APETCD)7 was developed by our research group to treat herniated and even migrated cervical discs without affecting the intervertebral disc area. In some cases, APETCD allows partial endplate excision or enlargement of the tunnel in the vertebra to provide a better vision under the endoscope. As only the feasibility but not the limitations of APETCD are known, the stress concentration induced on the vertebrae and endplate by transcorporeal tunnel and excision of endplate remained to be elucidated. No biomechanical study has been performed to analyze this type of operation, and therefore, this research was performed to evaluate the biomechanical influence of APETCD on cervical vertebrae.
At present, as no finite element (FE) analysis of the APETCD procedure has been performed, we conducted this FE study to analyze the biomechanical differences of superior endplate and vertebra body between the intact cervical model and simulated tunneled models under normal flexion loads. Based on the biomechanical predictions, we could measure the safety of APETCD and conclude some restrictions on this surgical operation.
Section snippets
FE Modeling and Validation
Computed tomography (CT) images were taken at 0.5-mm intervals from the C2 to T1 vertebrae of a 19-year-old healthy male volunteer in a supine position. He had no history of neck pain or other spinal disorders that required treatment. His cervical lordosis value (32.1, Jackson method) was in the normal range for men (21 ± 14), as documented by Gore et al.8 Ethical approval was given by the Institutional Ethics Board of The Second Affiliated Hospital of Chongqing Medical University. The cervical
FEM Validation
As shown in Figure 5, the predicted ROM of the intact FEM was compared against the results reported in the literature28, 29, 30, 31, 32 and was found to be in good agreement. The following studies and simulations were made based on this intact C2-T1 FEM.
Distribution of von Mises Stress
Figure 6 shows cloud charts of the C4 vertebrae in all models. The concentration of von Mises stress appeared on the removal edges of the superior endplates in group A and on the lateral walls of tunnels in both groups. The maximum stress and
Discussion
An FEM of the multilevel cervical spine was used to assess ROM changes. However, in the present study, the C2-T1 cervical FEM was developed to simulate the anatomic situation of load bearing in the C4 vertebra. We used a hybrid loading condition, which is a well-known condition that has been widely used in recent spinal biomechanical research studies,24, 29, 34 by applying a bending moment of 1 Nm along the flexion direction with a compressive follower load of 50 N and firm fixation of the
Conclusion
The APETCD approach without partial endplate excision induces a stress distribution on the C4 vertebra with no statistical difference if the tunnel diameter was limited to 6 mm. However, a tunnel diameter >10 mm, excision of the endplate >8 mm, and excision of the center side of the endplate should be avoided for the risk of fracture.
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Cited by (16)
The key hole augmentation with demineralized bone matrix in anterior cervical trans-corporeal discectomy – Preliminary result of a novel technique
2020, Interdisciplinary Neurosurgery: Advanced Techniques and Case ManagementCitation Excerpt :Several authors have speculated that these could be reasons of iatrogenic instability or remnant symptom after the surgery [7,9,10,20]. Recently published biomechanical studies reported that a keyhole diameter of <6 mm during ACTD causes no significant biomechanical differences between the intact model and keyhole tunneled model [6,7]. However, there was no study on how to prevent vertebral height loss after ACTD and the benefit of keyhole augmentation in maintaining the body height after surgery.
Conflict of interest statement: This work was supported by the National Natural Science Foundation of China, grant 81672230, the Chongqing Municipal Public Health Bureau, Chongqing People's Municipal Government, grants 2016ZDXM007, 2017ZDXM031, and the Chongqing Science and Technology Commission, grant cstc2013jcyjA10090.