| The goals of the spinal fixation are as follows: to assist in correcting or preventing additional changes in spinal alignment, to enhance fusion rates, and to allow early mobolization of the patient without the need for cumbersome external immobilization. Transpedicular screw fixation ,with its superior biomechanical properties, has been very popular in stabilization of thoralumbar segments. In cervical region, because of relatively small size of the cervical pedicle and its adjacent, placement of screws into the C3-C6 pedicle ever being thought to be an unacceptable risk to the vertebral artery, spinal cord, and nerve roots. However, the anatomical studies and clinical applications of this technique in recent years demonstrated the cervical transpedicular fixation still is a safe technique, and having a tendency of wide application. However ,Compared with comprehensive and abundant studies related to transpedicular fixation in thoralumbar region, the intensive study of this technique in cervical region is very limited. To improve the safety and rationality of cervical transpedicular screw fixation, the following studies were designed..Part 1. anatomic study of lower cervical related to transpedicular screw fixation1.measurement of parameters of C3-C7 pedicleObjective. To measure the dimensions of the lower cervical pedicle and to determine the proper length of cervical pedicle screw. Methods. Fifty-four normal human adult cadaver cervical specimens containing C3 to C7 vertebrae were measured using a digital caliper and a goniometer, parameters measured includes pedicle width, pedicle height, pedicle length, and transverse angle. 20 cadaver cervical specimens were scanned by CT scanner both perpendicular and parallel to the pedicle axis. The outer and inner pedicle width and height, cephalocaudad angulation of the pedicles in the sagittal plane, and the distance between the central line of pedicle axis to the middle point of superior vertebrae end plate were measured using automatic digital CT measurements. Then the proportion of cortical and cancellous bone of pedicle was calculated, the rate of risk of screw penetration into intervertebral disc while coaxiallyplacing a 3.5mm pedicle screw was estimated. Additionally, 100 normal human CT scans of cervical segment were measured. Results.The data revealed variability between individuals and segments. The pedicle width is smaller than corresponding height, pedicle size is smallest at C3 level, with subsequent increasing in size down to the C7 level. From C3 to C7, the inner cancelleous diameter of pedicle was small, and the proportion of cortical bone was larger than the cancellous bone in cervical pedicle. The data of pedicle width, height and length measured from dry cadavers specimens was significantly smaller than that measured from normal human CT scans. In the sagittal plane, the pedicles were directed superiorly in the upper spine and inferiorly in the lower cervical spine. If the depth of screw penetration into vertebra is great, the rate of risk of screw penetration into upper intervertebral disc is 90% in C3, 60% in C4, 40% in C5, 30% in C6, and 10% in C7. the distance between the pedicle entrance point and the anterior edge of posterior cranial anular epiphyses is approximately 18-20mm. Conclusions. Lower cervical pedicle can safely accommodate a screw of 3.5mm outside diameter. If a short screw of 18-20mm in length is placed into the cervical pedicle without entering the vertebral cancellous bone, a good bony purchase still should be achieved. This may result in less risk of injury to the adjacent structures.2.localization of cervical pedicle entrance pointObjective. To localize the middle and lower cervical pedicle entrance point. Methods. The entrance point of each pedicle of fifty-four normal human adult cadaver cervical specimens containing C3 to C7 vertebrae was marked on the posterior surface of lateral mass by visulization. The posterior entrance to the cervical pedicle is described using quantitative and descriptive parameters usin... |
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