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
Introduction
Anterior cervical discectomy and fusion (ACDF) is a well-established surgical treatment and “gold standard” for patients with symptomatic cervical degenerative disc disease [1]. Adjacent segment degeneration (ASD) after ACDF has been recognized as an important problem for surgeons [2,3]. Abnormal segmental range of motion (ROM) and intradiscal pressure may be the main causes of ASD [4,5]. Even though cage plus plate is usually applied in ACDF, risk of postoperative complications, such as dysphagia, tracheoesophageal lesions and adjacent level ossification development, has been reported [[6], [7], [8], [9]]. In recent years, zero-profile devices have been developed to reduce the complications of ACDF using traditional cage plus plate [[8], [9], [10]]. Various internal fixation devices have varying biomechanical designs and kinematic properties. The zero-profile devices can avoid the possible irritation against the adjacent segment caused by the plate, which is regarded as a predisposing factor of ASD [11,12]. Even though the incidence rate of ASD after ACDF has been investigated in some clinical studies, the biomechanical differences of adjacent segments after ACDF using either a zero-profile device or cage plus plate remain uncertain [[11], [12], [13], [14]].
Finite element (FE) analyses have been widely used in investigations of spinal biomechanics to predict the biomechanical response after different spine surgeries. In the present study, we constructed an FE cervical spine model consisting of C2–C7 to compare the ROM and intradiscal pressure after one- or two-level ACDF using either a zero-profile device or cage plus plate via FE analysis.
Section snippets
Development of FE intact cervical spine model
A three-dimensional FE intact cervical spine model of C2–C7 was developed and validated in our previous study [15]. The FE model was constructed according to computed tomography (CT) images of a healthy volunteer (male, age 22 years; height, 175 cm; weight, 65 kg) without a history of cervical disc disease. Written informed consent was obtained from the volunteer. The CT images of the subject were obtained at intervals of 0.625 mm (Dual Source CT; Siemens, Munich, Germany). The intact cervical
Validation of the FE intact cervical spine model
The present FE intact cervical spine model was compared with two previous biomechanical studies (one human cadaveric specimens study and one FE model) to assess its validity [17,19]. The predicted segmental ROM of the flexion-extension, lateral bending, and axial rotation of the intact cervical spine model were in good agreement with those of previous experiments studies (Fig. 4).
Analyses of the differences of ROM after one- and two-level ACDF using either zero-profile devices or cage plus plate
The segmental ROM of the FE models of one- or two-level ACDF using either zero-profile devices or cage plus plate
Discussion
Even though ACDF has commonly been used to treat cervical spine spondylosis resulting in radiculopathy or myelopathy, ASD remains an important problem that should not be ignored [2,3]. It is still uncertain whether ASD is caused by natural degeneration or aggravated by cervical surgery [5]. The zero-profile device is fixed to the adjacent vertebrae with only one screw, while the cage plus plate is fixed to adjacent vertebrae with two screws and plate. The anterior plate is connected to adjacent
Conclusions
Regardless of whether zero-profile devices or cage plus plate was used in ACDF, decreased ROM was observed at the fused segments, and increased ROM and intradiscal pressure were observed at the adjacent segments of the fused segments. Moreover, loss of ROM at the fused segments was greater in cage plus plate models than in zero-profile device models. The difference of ROM at the fused segments may be caused by the lower stability of the zero-profile devices compared with cage plus plate.
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), National Natural Science Foundation of China (Grant no. 81904020 and 81772401), 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.