## 4 Discussion  
This study aimed to investigate the biomechanical changes for lordotic, straight, and kyphotic cervical sagittal alignment models following cervical laminoplasty. The cervical spine is an important part of the body that supports the head and provides sufficient mobility and protection to the cervical spinal cord, but once neurological symptoms occur, anterior or posterior decompression (laminectomy or laminoplasty) may  
Figure 5: Facet contact forces. (**a**) extension, (**b**) lateral bending, (**c**) axial rotation. Vertical axis is force (N), horizontal axis is each intervertebral level. be required. Laminoplasty is usually reported to increase the stability of the cervical spine. [PERSON] et al. reported that mean mobility decreased from 36\({}^{\circ}\) to 8\({}^{\circ}\) following double door laminoinplasty [18]. Additionally, [PERSON] and [PERSON] reported that the ROM was reduced by 50% for double-door laminoplasty relative to pre-operation measurements [19]. The effect of cervical alignment on surgical intervention is debated. There are few reports on what Cobb angles are acceptable for cervical laminoplasty. [PERSON] reported that patients with straight or lordosis (range, 1-14\({}^{\circ}\)) may also be suitable for laminoplasty [20]. In general, it has been reported that laminoplasty is not effective for patients with C-CPLL and having cervical spine kyphosis along with high cSVA [7; 21; 22]. The clinical review reported the ranges of two sagittal parameters for desired post-operative clinical outcomes: C7 slope, average value 20\({}^{\circ}\), must not be higher than 40\({}^{\circ}\) and cSVA must be less than 40 mm (mean value 20 mm) [23]. In this analysis, for extension, both bending and both rotations, the LM-L model only showed a decrease in ROM compared to other models. The ROM became higher as kyphosis increased. These results agree with reports in the literature that claimed that complications such as increased kyphosis may occur after conducting laminoplasty for cases with kyphosis alignment [6; 7]. The annulus stresses generally increased as the kyphosis increased. The largest differences for the annulus stresses between the intact and laminoplasty models were observed in C3-C4. This could be because the posterior ligaments were stretched as kyphosis increased, and the laminoplasty damaged the posterior ligaments, resulting in increased stress in the annulus. For nucleus stresses, lower stresses were observed for the LM-L model than for the intact model in all motions except for left bending. The facet forces were the highest in the LM-L model, which may be due to the distance between the facet joints in that specific alignment. In this analysis, the spinous processes, lamina, and the artificial bones were also closer in the lordotic alignment, but they never came in contact during any motion. The facet forces in the LM-S model were higher than the intact model in flexion, bending, and rotation motions, especially in C2-C3, possibly due to stabilization by laminoplasty. Conversely, in kyphosis, there was a possibility that the load was further decreased by laminoplasty. The facet force was reduced in all motions, and the function of the facet joint can be weakened. The results of the ROM, annulus stresses, nucleus stresses and facet forces suggested that laminoplasty in cervical kyphosis alignments may result in negative clinical outcomes. Conversely, [PERSON] showed that patients having within 10\({}^{\circ}\) of cervical kyphosis had similar postoperative outcome compared to patients with normative cervical lordotic alignment following posterior decompression with laminoplasty [6]. [PERSON] reported successful neurologic outcomes for patients with up to 13 degrees of kyphosis after cervical laminoplasty [24]. Thus, the debate continues about sagittal alignment and posterior procedures, and it will be necessary to analyze a model with increased kyphosis angle in the future.