# Biomechanical Analysis of Posterior Ligaments of Cervical Spine and Laminoplasty
## 4 Discussion
In cadaver research, there are few papers on cervical laminoplasty. [PERSON] reported that 3D kinematics changes after double-door cervical laminoplasty, with and without the spacer, were studied in a human cadaveric model and the use of hydroxyapatite spacer well contributes to maintaining the total stiffness of cervical spine [41]. [PERSON] reported that open-door laminoplasty leaves the spine in a significantly more stable condition than laminectomy compared with biomechanical stability during flexion and extension [42]. [PERSON] analyzed five human cadaveric specimens with laminoplasty at C5-C6, laminoplasty at C3-C6, and laminectomy. Laminoplasty was closer to intact than laminectomy, and there was no significant difference in laminoplasty, but laminoplasty at C3-C6 was associated with greater motion in lateral bending and axial rotation [43]. However, they did not report on the role of LF in laminoplasty/laminectomy. To study the effect of preserving/resecting LF in laminoplasty, the FE model of cervical spine was developed and validated. The model was considered validated as ROM, intervertebral nucleus stress, and facet force were all within the range of the experimental results of the in vitro data. Some differences for average data of cadaver about ROM, intervertebral nucleus stress, and facet loads, and our results were considered acceptable due to the higher mean age and possible deformed cervical spine in the cadaver. It will be necessary to compare the FE model analysis with the experiments of any individual in the future. In this laminoplasty-pre and laminoplasty-res analysis, the ROM of C2-C7 was decreased except for flexion. [PERSON] et al. reported that mean mobility decreased from 36 to 8\({}^{\circ}\) following double-door laminoplasty [44]. [PERSON] and [PERSON] reported that the range of motion was reduced by 46% for open-door laminoplasty and 50% for double-doorlaminoplasty relative to pre-operation [45]. Thus, these suggest that the laminoplasty affects stability, and the results of this study were in agreement with the literature. On the other hand, the increased mobility in flexion suggests that posterior ligament may be one of the causes of post-operative kyphosis. The intervertebral nucleus stress and facet force stress were higher at C4-C5 and were elevated in laminoplasty-pre and laminoplasty-res than the intact model. There are no papers that have experimentally verified the stress on the disc and facet of laminoplasty. However, the clinical and radiological analysis of the ROM of the cervical vertebrae indicate that when the stability of the caudal vertebrae increases, the mobility and instability of the cranial side (C3-C4, C4-C5) also increases [46; 47]. In the present analysis, the bottom of C7 was fixed, and due to the increased stability of laminoplasty, the load of the cervical vertebrae was considered to be concentrated in the cranial side (C3-C4, C4-C5). There are several limitations to our study. It does not include the trapezius or other muscles. Spine alignment was lordotic only. This model simulates an immediate postoperative scenario and does not consider conditions such as fusion and non-fusion of the lamina, and does not fully simulate the long-term condition of laminoplasty. The LF covered the interlaminar space. In the present model, it is impossible to conclude the mechanical characteristics of the partial or total resection of LF for laminoplasty [48]. Although there are several methods of laminoplasty [49], this paper only analyzes double-door laminoplasty. This study does not consider the change in material property that may be altered by osteoporosis or osteoarthritis. Despite these limitations, this study provides valuable insights on the effect of preserving/resecting the LF during laminoplasty.