1. Semi-rigid internal fixation system (Figure 1-2): The semi-rigid fixation system is
made of titanium alloy for surgical implants, which has been used in clinic. It is composed of semi-rigid connecting rod, posterior opening "U" pedicle screw. The semi-rigid connecting rod includes titanium alloy rod, cable, disc spring, pin, etc. Titanium cable and disc spring provide a certain degree of activity and elasticity, so as to achieve the purpose of semi-rigid fixation. (Patent No.: ZL 2009 2 0175651.9). The buckling range of the connecting rod is 0-10 °, and the rotation range is 0-5 °. Model and specification of semi-rigid connecting rod includes 6mm × 90mm and 6mm × 120mm.
2. Rigid internal fixation system:
Including pedicle screws and rigid connecting rods, the diameter of connecting rod is 6mm, made of medical titanium alloy. Provided by Beijing Fule Technology Development Co., Ltd.
3. Test equipment:
1) MTS 858 material testing system (MTS, USA).
2) Spinal 3D motion analysis system:
The digital motion capture system is composed of six digital motion capture lenses around the site (Model EAGLE4, made by Motion Analysis Company, with pixel value of 4 million, maximum acquisition frequency of 2000 frames per second, theoretical accuracy of 0.02mm, rotation angle measurement of 0.02 degree). The data are directly input into the computer, and the software automatically analyzes and calculates the angle change of three-dimensional spine movement.
4. Test specimen:
Six fresh cadaveric thoracolumbar specimens (T12-L3, 28-43 years old, average 31.7 years old, from the Department of anatomy, Southern Medical University, CHINA) were selected. Which exclude spinal trauma, variation, tumor and hyperosteogeny. The specimens were wrapped with multi-layer film and stored in
- 20 ° freezer. Referring to the literature, we successfully made a burst fracture model of L2 vertebral body by means of compression after pre injury. After the L2 vertebral body was pre drilled, the adjacent vertebral body and intervertebral disc were embedded in high-strength gypsum, and the specimen vertebral body was impacted by the free drop hammer method (15kg, 1.1m high). As a result, the L2 vertebral body fracture, the bone block entering the vertebral canal, the small joint relaxation, the upper and lower endplates of all specimens were fractured, which belonged to Denis A type fracture. All specimens were successfully modeled at one time (Fig. 2).
Each specimen was tested in four consecutive states: complete state, fracture state, rigid fixation system and semi-rigid internal fixation system. Two hours before the test, the frozen specimens were taken out, thawed naturally and completely at 25 ℃ room temperature, then covered with wet saline gauze to keep the specimens moist. Drill the Kirschner wire into the L1 and L3 vertebrae and install the marked points. The specimen was fixed on a three-dimensional spinal motion testing machine with a loading moment of 8N.m. Load from 1 N.m to 8 N.m step by step, the loading rate is 0.2mm/sec, three times of loading in all directions, the first two times to eliminate the influence of creep. At the third time, test the angle displacement of specimen forward bending, backward extension, left bending, right bending, left turning and right turning, and take this as the reference data. Then the above specimens were made into thoracolumbar burst fracture model (L2). Six three-dimensional motion indexes of spine were measured. For each model, the end plate fracture block was fixed through the bilateral pedicle drilling. The holes of the arch root of the vertebra were enlarged with series guide cones of different diameters (Diameters up to 7mm). The depth of the guide cones should reach to the anterior column of the vertebra. The guide cones were inserted into the bone grafting funnel, and the bone particles were filled and implanted into the vertebra. The guide cones were used to compact the holes (Fig. 3).
Six three-dimensional motion indexes of spine were measured after transpedicular bone grafting. Pedicle screws were implanted in L1 and L3 bilateral pedicle, and six three-dimensional motion indexes of spine were measured by using semi-rigid connecting rod (Figure 4). Six three-dimensional motion indexes of spine were tested.
7、 Statistical analysis
SPSS16.0 software is used for statistics and analysis. Random block analysis of variance was used to compare ROM and NZ in different states. The significance level was 0.05.