The Biomechanics Study Of A Modified Unilateral Open-door Miniscrew-plate Fixation

Since the 1960s, laminectomy have been gradually replaced by laminoplasty. It has been recognized that laminoplasty is the most effective way to treat cervical stenosis and to retain the lamina[1, 2]. Especially the unilateral open-door laminoplasty is widely used because of its advantages[3]. There are many surgical ways to keep the lamina fixed open. Some surgeons fixed the lamina to the paraspinal muscles, some fixed the lamina to the spinous process, or to the lateral mass. For the past few years, the miniscrew-plate fixation have been used more widely. However, the unilateral open-door laminoplasty have a variety of complications[4, 5]. The spring-back phenomenon is the most important and serious complications. This phenomenon is due to inadequate mechanic support and the compression on the lamina.Although the miniscrew-plate fixation provide some mechanic support for the lamina and lateral mass, there are also some defects in it. For example, the support on the hinge side is not enough and the posterior compression can not be distributed effectively. How to protect the lamina from reclosing and to improve the entire stability is a problem needed to be solved. We designed a new modified miniscrw-plate fixation and compare the differences on mechanical effect of the two kinds of fixation. We are trying to seek a standard way to reconstruct the cervical spinal canal both stably and functionally.Objective To evaluate the mechanic effect of a modified miniscrew-plate in the unilateral open-door cervical laminoplasty. Methods 8 cases of adult cadaver cervical spine specimens(C3-C7)were divided into 2 groups randomly. The unilateral open-door cervical laminoplasty was performed in both groups, and then the modified miniscrew-plates and the traditional miniscrew-plates were implanted in each cervical vertebra segment of Group A and Group B respectively. On each cervical vertebra segment, the maximal load and energy of reclose of the open-door were studied with biomechanics methods. The statistics of the two groups were processed with the Statistical Product and Service Solutions software. Results The maximal load were (873.61±154.40) N in Group A and (297.17±133.41) N in Group B; The complete reclose load were (812.98±141.79) N in Group A and (145.77±59.21) N in Group B. The energy was (5.95±0.83) J in Group A and (1.65±0.70) J in Group B. There was significant differences between the two groups (P <0.01).Conclusions Compared with the traditional miniscrew-plates, themodified miniscrew-plates have three main advantages in unilateral open-door cervical laminoplasty:1. The new miniscrew-plate can not only provide mechanic support for the lamina, but also can fix the hinge side. In this way, the spring-back phenomenon and the hinge's collapse can be prevented.2. The new miniscrew-plate can form a new"rigid tube"outside the cervical spinal canal and protect the lamina more effectively. A majority of posterior compression can be distributed effectively and the open-door can be maintained perfectly.3. The new miniscrew-plate is designed by arch-shaped. Compared with the traditional ones, it can provide better stability and also can reconstruct the cervical spinal canal both stably and functionally.