Anatomic, Biomechanical And Clinical Study Of The Posterior Pedicle Screw Fixation On Atlas

ObjectivesThere are numerous posterior fixation technique for atlantoaxial instability, posterior transarticular screws in combination with posterior Gallie wiring fixation produced a three-point fixation at the atlantoaxial segment and offered a best biomechanical stability, provided the highest fusion rates. However, the transarticular screw technique is technically demanding and requires considerable experience. There are numerous reports of screws penetrating the vertebral artery, sometimes with fatal consequences. Recently, Cl and C2 individual pedicle screws with rods fixation technique was introduced as a salvage procedure or as an alternative technique for patients who were excluded as a candidate for Cl-2 transarticular screw fixation; and it is superior to other posterior fixation technique. However, few anatomic studies concerning this technique are available, especially lacking of a simple and reliable method to determine the drill point of Cl pedicle screw. This study aimed to set up a new simple and reliable technique for Cl pedicle screw placement, and evaluated the present technique from anatomy, biomechanics and clinics. Including:1. To evaluate the feasibility of the pedicle screw placement on atlas by anatomic measurements on dry specimens of the first cervical vertebra.2. To set up a new technique to determine the drill point of Cl pedicle screw, and describe the main parameters of the technique.3. To establish a safe and simple exposure technique for the operation.-6-4. To assess the feasibility and the reliability of the present technique of Cl pedicle screw placement with the measuring of cervical cadaver specimens.5. To adjust and reform the Cl pedicle screw placement technique, and the same time to offer experiences and lessons for clinical application by imitating the Cl pedicle screw fixation on the cervical cadaver specimens.6. To evaluate the biomechanical fixation intensity of Cl pedicle screw through the experiment on screw pull-out strength with different lengths, to provide the proofs for clinical surgeons to choose unicortical or bicortical screw fixation.7. To provide academic data for clinic application of the C1-C2 pedicle screw plate fixation technique by comparing the three-dimension stability with other posterior atlantoaxial fixation technique.8. Clinic using, evaluating, testing and verifying the reliability of the present Cl screw placement technique on the patients.Materials and Methods1. Fifty paired first and second cervical vertebrae for anatomic measurements were obtained from the Department of Anatomy, and the following parameters were measured or evaluated, including the: (D the width and the height of Cl pedicle and that of Cl lateral mass; (2) setting the entry point of the Cl pedicle screw; (3) measured the anatomic parameters related to the screw entry point, and set up the primary technique of Cl pedicle screw placement; (D evaluated the anatomic relation between Cl pedicle and C2 lateral mass, established a new technique of Cl pedicle screw fixation with the C2 lateral mass as an anatomic landmark.2. Using two fresh human cervical cadaver specimens, the artery perfusion with red latex, vein perfusion with blue latex, the exposure procedure of the upper cervical posterior operation was imitated, the anatomic relation between axis and atlas, and the anatomic relation among?7 -the muscle, nerve and blood vessel around the posterior region of C1-C2 joint were observed.3. Twenty human cadaver specimens were used to insert pedicle screws on atlas, via the posterior arch or the 'pedicle' of Cl into the lateral mass. Without additional dissection of the lateral joint of C1-C2, the screw entry point was at the posterior surface of C1 posterior arch, in line with the center of C2 lateral mass, and at least 3 mm below the superior rim of the Cl lamina. The direction of the screw trajectory was determined to be 10?in a medial direction, and 5?in a cephalad direction. After Cl pedicle screw placeme...