Biomechanical evaluation of adjacent segment degeneration after one- or two-level anterior cervical discectomy and fusion versus cervical disc arthroplasty: A finite element analysis

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Highlights

  • A finite element cervical model consisting of C2-C7 vertebrae was developed to compare the segmental range of motion (ROM) and intradiscal pressure after one or two-level anterior cervical discectomy and fusion (ACDF) and cervical disc arthroplasty (CDA).

  • In both one- and two-level model of ACDF, the ROM of the fused segments were sacrificed, the ROM and intradiscal pressure at the adjacent segments were increased. However, in both one- and two-level model of CDA, the ROM of the surgery segments were preserved, avoiding the increase of the ROM and intradiscal pressure at the adjacent segments.

  • Abnormal ROM and intradiscal pressure at the adjacent segments may contribute to the higher risk of adjacent segment degeneration after ACDF compared with CDA.

Abstract

Background and objective

To compare the biomechanical changes of adjacent segment degeneration (ASD) after one- or two-level anterior cervical discectomy and fusion (ACDF) versus cervical disc arthroplasty (CDA).

Methods

A three-dimensional finite element (FE) model of intact C2-C7 segments was constructed and validated. In the one-level surgery model, the cage with plate implant or Prestige LP cervical disc prosthesis were integrated at C5-C6 segment into the FE model; while in the two-level surgery model, the prostheses were integrated at both C4-C5 and C5-C6 segments into the FE model. A pure moment of 1.0 Nm combined with a follower load of 73.6 N were imposed on C2 to investigate the flexion-extension, lateral bending, and axial rotation of different segments in the FE model. The segmental range of motion (ROM) and intradiscal pressure of the surgery models were investigated and compared with the intact model.

Results

In the one-level model of ACDF, the ROM at C5-C6 was decreased, the ROM and intradiscal pressure at C4-C5 and C6-C7 segments were increased. In the two-level model of ACDF, the ROM at C4-C5 and C5-C6 were decreased, the ROM and intradiscal pressure at C3-C4 and C6-C7 were increased. However, in both one- and two-level models of CDA, the ROM of surgery segments were preserved, avoiding the increase of the ROM and intradiscal pressure at the adjacent segments.

Conclusions

Abnormal ROM and intradiscal pressure at the adjacent segments may contribute to the higher risk of ASD after ACDF compared with CDA.

Introduction

Anterior cervical discectomy and fusion (ACDF) and cervical disc arthroplasty (CDA) are common surgical treatments for patients with cervical myelopathy, radiculopathy, or myeloradiculopathy [1], [2], [3], [4]. Despite ACDF was considered as the “gold standard”, symptomatic adjacent segment degeneration (ASD) may develop after fusion surgery [1], [2], [3], [4]. Compared with the standard ACDF, the primary goal of CDA is to preserve the range of motion (ROM) at the surgery segment, avoiding or mitigating ASD [1], [2], [3], [5]. Many previous studies have shown that ASD is more likely to occur after cervical fusion compared with CDA during long-term follow-up [1], [2], [3]. Abnormal segmental ROM and intradiscal pressure may be the main causes of ASD [2], [3], [6], [7]. Different internal fixation devices were of different biomechanical design and kinematic properties [8], [9], [10], [11]. Even though the incidence rate of ASD has been investigated and compared in many clinical studies and biomechanical studies, the biomechanics changes of adjacent segments after one- and two-level standard ACDF and CDA were still uncertain [3], [4], [12], [13].

The finite element (FE) analysis has been widely used to investigate the spinal biomechanics, and to predict the biomechanical response after different spine surgeries [8], [9], [10], [11]. In the present study, a FE model consisting of C2-C7 vertebrae was developed. We aimed to compare the segmental ROM and intradiscal pressure after one- or two-level ACDF and CDA using FE analysis.

Section snippets

Development of intact cervical model

The three-dimensional FE model of C2-C7 vertebrae was developed according to the computed tomography (CT) images of a healthy volunteer (male, 22 years old, 175 cm, 65 kg) without history of cervical disc disease. Written informed consent was obtained from the volunteer. The CT images of the subject were obtained with an interval of 0.625 mm (Dual Source CT; Siemens, Munich, Germany). The intact model consists of six vertebrae (C2-C7), five intervertebral discs and associated ligaments. The

Validation of the intact cervical model

The present intact cervical model of C2-C7 vertebrae was compared with previous biomechanical models to assess the validity. The predicted segmental ROM of the flexion-extension, lateral bending, and axial rotation of the intact cervical model were well in agreement with previous experiments studies (Table 3, Fig. 4) [10], [15].

One-level ACDF and CDA

The segmental ROM of one-level ACDF and CDA models were listed in Table 4. The ROM at C5-C6 of the one-level ACDF model was significantly decreased, while the ROM at

Discussion

Whether ASD is caused by natural degeneration or aggravated by cervical surgery is still unknown [3], [6], [17], [18]. ASD was statistically less frequent after CDA than ACDF in most of the clinical trials [18]. The C5-C6 segment behaves as the most flexible segment [19], [20]. As a result, one-level surgery models were constructed at C5-C6, and two-level surgery models were constructed at both C4-C5 and C5-C6. Most FE studies based on one- or two-level cervical surgery have explored the

Conclusions

According the FE analysis, abnormal ROM and intradiscal pressure at the adjacent segments may contribute to the higher risk of ASD after one- or two-level ACDF. However, no significant difference of the ROM and intradiscal pressure can be observed at the adjacent segments after one- or two-level CDA.

Declaration of Competing Interest

The authors declare that they have no conflict of interest.

Acknowledgements

This work was supported by the National Key Research and Development Program of China (2018YFB1105700), the National Natural Science Foundation of China (Grant nos. 81904020 and 81772401), the Natural Science Foundation of Hubei Province (2019CFB305), and the Fundamental Research Funds for the Central Universities (2019kfyXMBZ063).

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    These authors contributed equally to this work.

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