Elsevier

World Neurosurgery

Volume 114, June 2018, Pages e199-e208
World Neurosurgery

Original Article
Biomechanical Influences of Transcorporeal Tunnels on C4 Vertebra Under Physical Compressive Load Under Flexion Movement: A Finite Element Analysis

https://doi.org/10.1016/j.wneu.2018.02.140Get rights and content

Highlights

  • We compared the biomechanical performance of cervical vertebra in intact FE model and tunneled models.

  • Compared with the intact model, maximum stress increased with tunnel diameter and endplate excision.

  • Tunnels without endplate excision caused no significant influence to superior endplate if the diameter was limited to 6 mm.

  • According to reported strength of cancellous bone and endplate, oversize would cause high risks of fracture.

Background

Anterior percutaneous endoscopic transcorporeal cervical discectomy is an alternative operation for cervical disc herniation. However, few reports have evaluated the biomechanical influence of tunnels on vertebrae. We compared biomechanical distinctions between intact and tunneled models of vertebrae to analyze the safety of anterior percutaneous endoscopic transcorporeal cervical discectomy based on a C2-T1 finite element (FE) model.

Methods

Groups of C2-T1 FE models were simulated with C4 tunneled by 2 methods (group A: with partial superior endplate excision; group B: without partial superior endplate excision) and various tunnel diameters (6, 8, and 10 mm). All FE models were loaded under a 1-Nm flexion moment.

Results

The area and maximum of stress concentrations were correlated with tunnel diameter. The distribution of stress on C4 superior endplates showed no significant difference between B6 and the intact model (P > 0.05), but significant differences with other tunneled models (P < 0.001). Maximum stress on the lateral wall of tunnels was positively correlated with tunnel diameter and induced high risks of cancellous bone fracture for diameters reaching 10 mm in group B and 8 mm in group A.

Conclusions

Transcorporeal tunnel in C4 vertebrae without endplate excision should be limited with diameter of 6 mm, and a tunnel diameter >10 mm, excision of the endplate >8 mm, and excision of the center side of the endplate should also be avoided.

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.

References (39)

  • K. Wang et al.

    Cervical traction therapy with and without neck support: a finite element analysis

    Musculoskelet Sci Pract

    (2017)
  • Q.H. Zhang et al.

    Finite element analysis of moment-rotation relationships for human cervical spine

    J Biomech

    (2006)
  • A. Mackiewicz et al.

    Comparative studies of cervical spine anterior stabilization systems—Finite element analysis

    Clin Biomech (Bristol, Avon)

    (2016)
  • L. Røhl et al.

    Tensile and compressive properties of cancellous bone

    J Biomech

    (1991)
  • R.B. Cloward

    The anterior approach for removal of ruptured cervical disks

    J Neurosurg

    (1958)
  • G.W. Smith et al.

    The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion

    J Bone Joint Surg Am

    (1958)
  • S. Ruetten et al.

    A new full-endoscopic technique for cervical posterior foraminotomy in the treatment of lateral disc herniations using 6.9-mm endoscopes: prospective 2-year results of 87 patients

    Minim Invasive Neurosurg

    (2007)
  • S. Ruetten et al.

    Full-endoscopic cervical posterior foraminotomy for the operation of lateral disc herniations using 5.9-mm endoscopes: a prospective, randomized, controlled study

    Spine (Phila Pa 1976)

    (2008)
  • Y. Ahn et al.

    Factors predicting excellent outcome of percutaneous cervical discectomy: analysis of 111 consecutive cases

    Neuroradiology

    (2004)
  • 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 Management
      Citation 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.

    View all citing articles on Scopus

    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.

    View full text