| The technology of Occipital Condyle Screw Placement is a new method that fixes the occipital in applying occipital-cervical fusion, and is a remedy when the occipital screws cannot perform fixation, and is an auxiliary way for occipital fixation combined with occipital screws. Due to the discrepancy between Chinese and Europeans in bony anatomy, the risk and feasibility for the technology of Occipital Condyle Screw Placement in Chinese should be further investigated. The process of the vertebral artery in the technology of Occipital Condyle Screw Placement has not been reported so far. In this study, the feasibility and risk for the technology of Occipital Condyle Screw Placement in the Chinese occipital condyle will be evaluated by imaging and applied anatomy analysis.Purpose:1. Evaluate the feasibility for the technology of Occipital Condyle Screw Placement in the Chinese occipital condyle by imaging and applied anatomy analysis.2. Obtain the data about the angle and the long length of placement of screws, and the entrance point by CT imaging, and investigate the method for placement of screws in the technology of Occipital Condyle Screw Placement3. Investigate the risk of the vertebral artery in the technology of Occipital Condyle Screw Placement and how to avoid the risk.4. Investigate the discrepancy of the technology of Occipital Condyle Screw Placement in Chinese.Methods:Twenty fresh occipitocervical specimens were studied. Computerized tomography (CT) scanning and two-dimensional (2D) reconstruction was first performed on these specimens to exclude heads with destroyed occipital condyle. In the specimens with complete occipital condyle, virtual lines with a diameter of 4.0 mm were adopted in CT to simulate the process of inserting screws. Using the longest diameter of the head in sagittal plane as the standard, the position and angle of inserting screws were measured. The data of measurement include the longest diameter of the virtual screws in the sagittal plane, the angle of the virtual screws and the sagittal plane, the angle of the virtual screws and the plane, the distance between the entrance point and the skull base, the distance between the entrance point and the medial margin of the occipital condyle. Virtual screw placement was done on the samples, partially remove the posterior arch of the atlas, determine the entrance point, and determine the entrance angle by the Kirschner tunneling method. According the data of CT measurement, screws with a diameter of 4.0 mm (4-mm screws) were inserted in the fresh specimens, and their position and angle of insertion were determined by CT scanning and 2D reconstruction. After screws placement, the saline was injected to the vertebral artery, and made the posterior arch of the atlas section of the vertebral artery filling, and examine the injury to the vertebral artery.Results:1.20 fresh occipitocervical specimens passed the CT examination (8 men, mean ± SD age:65.4 ±3.2 years; 12 women, mean±SD age:67.2 ±1.9 years).40 complete occipital condyles were chosen.2. According to predicted angle and length by CT imaging, screws were successfully inserted in 36 of the 40 occipital condyles, with a success rate of 90%. Postoperative CT scanning demonstrated that the hypoglossal canal was not damaged, and the screws did not pierce medial wall and lateral wall of the occipital condyle. However,4 crews pierced the medial wall of the occipital condyle. All specimens were performed with partially resection of the posterior arch of the atlas, and the vertebral artery was not damaged, demonstrated by the vertebral artery filling experiment.3. We obtained the following data:the angle of the virtual screws at the sagittal plane (mean ± SD:22.9°± 3.1°(left),21.2°±1.4° (right)), the angle of the virtual screws at the cross section (mean ±SD:8.2°± 0.5± (left),8.0°±1.6° (right)), the plane distance between the entrance point and the medial margin of the occipital condyle (mean ± SD:7.6± 0.8 mm (left),7.4°±0.6°(right)), the vertical distance between the entrance point and the skull base (mean±SD:10.2± 1.6 mm (left),9.9±1.0 mm (right)), and the longest length of the virtual screws insertion (mean±SD: 21.5±1.4 mm (left),21.0±1.7 mm (right)). According the angle of the virtual screws at the sagittal plane and the angle of the virtual screws at the cross section, the angle of screws placement could be determined. According to the plane distance between the entrance point and the medial margin of the occipital condyle, and the vertical distance between the entrance point and the skull base, the entrance point could be determined.4. The longest length of the virtual screws at the sagittal plane of women was shorter than that of men(P< 0.05), whereas other data were not significantly different in sex and both sides (P<0.05).Conclusion:1. There is adequate space in the occipital condyle to accommodate 4-mm screws in Chinese.2. If the screws were inserted accurately, the hypoglossal canal could not be damaged.3. Partial resection of the posterior arch of the atlas and taking away the vertebral artery could leave the vertebral artery undamaged. The Kirschner tunneling method could effectively assist the angel of screw placement.4. To ensure the success rate of screw placement and lower the risk of surgery, CT imaging should be performed to patients to determine the entrance point and the angle of screws placement.5. Measuring the distance between the entrance point and the skull base makes the screws placement simpler and lowers the operation risk. |
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