The Design And The Biomechanical Study Of Transoralpharyngeal Atlantoaxial Reduction Plate System

Atlanto-axial dislocation by reason of a variety of disorders is common in the clinic. But it is difficult to manage the dislocation if the dislocation is irreducible and is with spinal cord compression. This study aimed to introduce and evaluate a new kind of transoralpharyngeal atlantoaxial reduction plate (TARP) system. The purposes of this thesis are:1. To introduce TARP system including the plate and its operating instruments so as to supply the clinical surgeons with a brand-new method to treat the irreducible atlanto-axial kyphosis.2. To evaluate the biomechanical stability of TARP by means of studying three-dimension range of motion (ROM) so as to supply the surgeons with the basis for later clinical application.3. To evaluate the biomechanical fixation intensity of TARP through the experiment on C1-C3 screws pull-out strength.Materials and Methods1. TARP and all the screws were made from titanium-aluminum- vanadium alloy (TieALtV) and operating instruments were made from medical stainless steel. The design scheme was completed by Dr. Yin Qing-shui, et al. The company was responsible for the manufacture of the plate and the operating instruments.2. Six atlantoaxial spine specimens were designed to compare TARP with four clinical anteroposterior atlantoaxial arthrodesis. Each specimen served as its own control and was tested in the following sequence: (l)Control (intact); (2)Injured (after resecting anterior arch of atlas, odontoid process, transverse ligament, alar ligaments and apical ligament of dens); (3)Anterior transoralpharyngeal atlantoaxial reduction plate(TARP); (4)Brooks; (5)Magerl+Brooks; (6)Magerl; (7)Anterior transarticular screw fixation through C2 vertebral body(ATS). The atlantoaxial motion segment was testedby a non-destructive flexibility method using a nonconstrained testing apparatus (MTS-858 , USA). The pure moment was applied to 2.0Nm. The ROM of Cl-2 motion segment was measured. With the flexion-extension, lateral bending and axial rotation ROMs of these seven groups compared each other, the stability of C1-C2 using various internal fixators was analyzed.3. Six fresh C1-C3 spine specimens (totally 12 cases including both sides) were designed to compare screw pull-out strength (tested by sensor) of C1 and C2 with controlled C3. They were divided into three groups: (1) Atlas; (2)Axis; (3)Controlled C3. Test speed was 1mm/min with maximum pull strength being 1000N and maximum displacement being 5mm. Screw head was caught by special clamp. After load had been applied, test would be terminated once the screw was mostly pulled out. The practically inserting depth (screw path length) was measured by electrical caliper whose precision was 0.01mm. Pull-out strength and screw failure length could be worked out by the software directly. Subsequently, pull-out strength, path length and failure length of C1-C3 screws were analyzed.C1 screw was inserted into the lateral mass and C2~~C3 screws were anchored into the vertebraes. Entrance of atlas screw was located at the center of anterior surface of Cl lateral mass and the screw was inserted in the posterolateral direction along the long axis of Cl lateral mass. Entrance of C2 screw was located at the point 3~4mm lateral to the center of the anterior surface of the vertebrae and the screw was inserted in the posteromedial direction vertical to the vertebrae surface. The entrance and the direction of C3 screw were the same as those of C2. In all these procedures, 3.5mm cortical screws were inserted unicortically. The inserting depth of C1 screw was estimated by most part of the length of long axis of C1 lateral mass in front of the vertebral artery groove. The practical depth was decided by measuring the path length depth. C2 and C3 screws were limited not to penetrate through the back cortex of the vertebraes.Results1. The design of TARP system was as follows:(l)Plate: Butterfly profile, arc transect and 2mm thick. There were two slotlike holes for atlas on the s...