Anatomic Study And Accuracy Of Cervical Pedicle Screw Placement Using Cervical Pedicle Screw Guide Technique

Summary of Background Data. Contemporary cervical spinal reconstruction surgery can employ a wide variety of surgical implants to impart immediate segmental stability. Cervical anterior reconstruction plate systems, posterior cervical wiring techniques and cervical posterior later mass plate were used widely in cervical spinal surgery. Cervical lateral mass plate system is a commonly used technique in cervical posterior segmental stability reconstruction, but when the cervical spine have osteoporosis or need multiple segmental stability, the lateral mass plate system might failure. Single application of cervical anterior plate can not afford enough biomechanical stability for cervical spine three-column injury.Cervical pedicle screw internal fixation was a new technique , the application of which was no more than 15 years. In 1991, Panjabi, a Japanese scholar, firstly reported a three-dimensional anatomic study of human cervical pedicle, and proved that the human cervical pedicle can support pedicle screw. In 1994, Kotani et al compared biomechanical ability of all kinds of cervical stabilization systems, including cervical pedicle screw fixation system, they found that the biomechanical ability of cervical pedicle screw fixation system was same with the biomechanical ability of cervical anterior plate associated with posterior wiring. Jones et al. reporteda biomechanical study compared cervical pedicle screw and lateral mass screw, they found that the pullout resistance of cervical pedicle screw was 677N and pullout resistance of lateral mass screw was 355N, and concluded that the biomechanical ability of pedicle screw was better than that of lateral mass screw. The result of these studies demonstrate that compared with cervical anterior plate system and posterior lateral mass plate system, cervical pedicle screw fixation system is the best chose in biomechanical ability. The first clinical applications of cervical pedicle screw fixation technique were completed by Japanese scholar Abumi and Swiss scholar Jeanneret. In 1994, they respectively reported cervical pedicle screw fixation technique was used to treat lower cervical spinal injury, and achieved good results. Thereafter they expanded indications for cervical pedicle screw fixation to lesions orther than spinal trauma. Their clinical results showed that the cervical pedicle screw fixation procedure is one of the potential procedures for posterior reconstruction of the cervical spine in various kinds of disorders. This technique was particularly valuable for simultaneous posterior decompression and reconstruction in the cervical spine. In addition, they reported effectiveness of the cervical pedicle screw as an anchor for craniocervical fixation. The greater pullout strength of pedicle screws enhances the capability for reduction of transitional deformity, for correction of cervical kyphosis and for reduction of flexion deformity at the craniocervical junction.Excellent biomechanical ability and good clinical results demonstrate that cervical pedicle screw fixation should be applied widely. But the smaller size of cervical pedicles, variability in pedicle morhpometry and sophisticated anatomic relationship with adjacent vital neurovascular structure demand careful assessment of the angle and placement of pedicle screws. Incorrect insertion of pedicle screws can cause damage to adjacent vital structures such as the spinal cord, nerve roots, and vertebral arteries. There are five insertion techniques for cervical pedicle screw placement, they are standard technique, laminoforaminotomy technique, computer-assisted surgical guidance technique, Abumi technique and funnel technique. In standard technique is the way that the point of insertion is located by externalmorphometry and the direction of insertion is judged by preoperative CT and introperative fluoroscopy; laminoforaminotomy technique is same as standard technique after a laminoforaminotomy is performed to provide supplemental visual and tactile cues regarding the orientation of the pedicle's medial wall; computer-assisted surgical guidance technique is the way in which the insertion is guided by computer system; Abumi technique is the way in which a burr is used to remove the dorsal cortex of the lateral mass and enough cancellous bone to visualize the cancellous bone at the entrance to the pedicle, then insert the pedicle screw guided by operative fluoroscopy; funnel technique is the way in which every pedicle is built as a funnel, then insert pedicle screws. Cadaveric study show that 12.5% to 53% screws were placed in the pedicle by standard technique; 45% to 75% screws were placed in the pedicle by laminoforaminotomy technique; 76% to 82% screws were placed in the pedicle by computer-assisted surgical guidance technique; 88% screws were placed in the pedicle by Abumi technique and 83.2% screws were placed in the pedicle by funnel technique. The successful pedicle screw placement ratios of five techniques are improved one by one, but the possibility of critical breach and injuries of important neurovascular structure could not be avoided absolutely. The five insertion technique have its own disadvantage respectively, such as radiation injury, sophisticated manipulation, bone structure destruction, biomechanical ability decrease and expensive facilities. All kinds of disadvantages make the technique of cervical pedicle screw placement very complicated, and restrict wide application of cervical pedicle screw fixation.According to previously anatomic studies, the author invite the cervical pedicle screw guide for improvement of cervical pedicle placement and decrease of danger of the surgery. The cervical pedicle screw guide is composed of two parts, the anterior part is guide and the posterior part is handle. There are 6 kinds of guide according to its angle. The angles are 35° ,40° ,45° ,50° ,55° and 60° respectively. All kinds of guide can connect with handle by screw. The principle of cervical pedicle screw guide is the probe of guide can precisely locate the middle point of medial wall of pedicle,ensure the narrow probe could pass through the pedicle marrow, and could not perforate the pedicle bone wall.Objectives. This study was taken to (Dreview the history of the development of cervical pedicle screw fixation and summarize the studies in morphologic observation, biomechanics, clinical application, indications and complications of cervical pedicle screw fixation; (2) introduce the train of thought of cervical pedicle screw guide invitation, operational procedure and principle of cervical pedicle screw guide technique; (3) measurement the distance from lateral border of cervical spinal cord to medial wall of pedicle, locate the point of the holes on the laminae, research the safety of this technique by cadaveric study; (4) research the accuracy and indications of this technique.Methods. (1) Twenty antiseptic cervical cadavers(C3~C7) for dissection to observe the relations of cervical spinal cord to the cervical pedicle medial wall and the medial border of lateral mass. After removal whole posterior bony elements entirely including the spinous processes, laminas, lateral masses, the isthmus of the pedicles, and the dural sac, the cervical spinal cord and the medial walls of pedicles were exposed. Direct measurements included the width of spinal cord , the width of canal (interval distance between two pedicle medial walls), and interval distance of the medial borders of lateral masses. (2)The 50 pedicles (C3-C7) of fresh human cadaveric cervical spine were instruments with pedicle screws with cervical pedicle screw guide technique. The preoperative CT scans were taken to assess the width of pedicles and inclination .The entrance point of screw was determined by standard technique (WANG Dong-lai technique). After lamina bony hole was made, the probe of guide explore the medial wall of pedicle, and located the middle point of he medial wall of pedicle. Probe the pedicle in the direction determined by the guide and insert common 3.5 mm screws. Postoperative oblique roentgenograms were taken. Dissect the adjacent tissues and expose the pedicles to assess the accuracy of screw placement.Results. (1) The mean width of each cervical segment is 23 nun to 25 mm, themean width of cervical spinal cord is 13 mm to 14 mm? the mean distance from spinal cord to medial wall of pedicle is 5 mm. There are no significant statistical difference between width of canal and internal distance between medial borders of lateral masses (P>0.05). There are significant statistical difference between width of canal and width of spinal cord (PO.05). There are significant statistical difference between internal distance between medial borders of lateral masses and width of spinal cord (PO.05). (2) The location of lamina bony hole is 2 mm medial form medial border of lateral mass and on the horizontal line which passes through the entrance point determined by standard technique. (3) Postoperative oblique roentgenograms show that every pedicle screw in a good position. (4) The dural sacs of 5 adaveric cervical spine was intact after operation. (5) The 50 pedicle screws (100%) were all in pedicles.Conclusion. (1) Application of the cervical pedicle screw guide technique will not injury the spinal cord. (2) The accuracy of the cervical pedicle screw guide technique is 100%. (3) The operational procedure of cervical pedicle screw guide technique is simple, safe, responsible, and economic. It can make cervical pedicle screw fixation be used widely. (4) The result of clinical application of cervical pedicle screw guide technique remain unclear.