Atlantoaxial “pedicle” fixation technique for C1-2 instability Cai Xiaojun, He Bin, Han Jianhua, Li Daijun (Department of Spine Surgery, Zunyi Hospital, The Third Affiliated Hospital of Zunyi Medical College, Zunyi, Guizhou 563002, China) Abstract: Objective: To treat C1-2 instability with pedicle screw fixation technique and to explore safe and reliable atlantoaxial pedicle nailing methods. Methods Atlantoaxial “pedicle” screw fixation was performed in 14 cases of C1-2 instability. In the atlantoaxial spine, the “posterior node of the vertebral artery sulcus” was used as the reference mark, and the inner and upper and lower edges of the atlantoaxial pedicle were used as the nail placement selection points and nail insertion directions, while in the atlantoaxial spine, the inner and outer edges of the isthmus were used as the boundary, and the posterior extension of the central axis of the isthmus corresponding to the projection point of the inferior articular eminence of the cardinal spine was used as the nail entry point. Results: 26 nails were placed in the atlantoaxial spine, and one case of posterior arch fracture occurred; 28 nails were placed in the pivot spine, and one case of screw loosening occurred. The rest of the implanted screws were in good position. Conclusion The atlantoaxial “posterior vertebral artery sulcus node”, the inner and upper and lower edges of the vertebral arch and the inner and outer edges of the isthmus and central axis of the cardinal spine were used as reference marks for the safe and reliable nail placement method. Cai Xiaojun, Department of Orthopedics, Zunyi First People’s Hospital Keywords: atlantoaxial instability; pedicle; internal fixation In recent years, due to the in-depth study of the applied anatomy of the upper cervical spine, the technique of transatlantoaxial lateral block or pedicle screw fixation has been gradually applied in clinical practice. The technique was used to treat 14 cases of atlantoaxial instability from May 2004 to August 2008, with good results, which are summarized as follows: 1 Data and methods 1.1 Clinical data 14 cases in this group. Male 10 cases, female 4 cases; age 9 to 58 years old, average 32.5 years old. The shortest duration of the disease was 2 hours and the longest was 6 years. There were 2 cases of fresh odontoid fracture (type II) with atlantoaxial joint dislocation, 6 cases of old odontoid fracture with atlantoaxial joint dislocation, 1 case of simple traumatic atlantoaxial joint dislocation, 1 case of congenital absence of the odontoid process and 3 cases of discontinuity, and 1 case of atlanto-occipital fusion and dislocation. All of the cases in this group had symptoms of occipital and cervical pain, neck stiffness, and restricted movement; nine cases were accompanied by high cervical spinal cord compression. All cases were diagnosed by cervical spine X-ray, CT, MRI and other examinations. 1.2 Operation method Operation points: prone position, the forehead was placed in a horseshoe brace (Mayfeild head frame) in front of the operating table with continuous cranial traction (the direction of traction force was maintained at 20° to the level of the trunk) and braking. A median posterior cervical occipital incision, approximately 6-8 cm in length, is made to expose the posterior arch of the atlantoaxial spine and the spinous processes, plates, and inferior articular processes of the cardinal spine. Atlantoaxial nail placement: the posterior atlantoaxial node is stripped subperiosteal to the junction of the posterior atlantoaxial arch and the vertebral artery sulcus, where there is a bony migration marker, the “posterior vertebral artery sulcus node”, and the nail entry point is approximately 2 mm outward from the “node”. At the same time, the inner, upper and lower edges of the atlantoaxial “pedicle” are probed with a nerve stripper to further determine the central axis of the atlantoaxial “pedicle” accurately. Pivot nail placement: The C2 nerve root and blood vessels are gently picked up with the pointed nerve stripper, and the pivot isthmus is stripped and exposed under the periosteum, and the medial and lateral edges of the pivot isthmus (the inner wall of the transverse foramen) are explored, and the central axis of the pivot isthmus is carefully sensed with the nerve stripper, and the point where the posterior extension of the central axis of the pivot isthmus penetrates the inferior synovial cortical bone is the pivot pedicle screw entry point. After nail placement, the atlantoaxial repositioned fixation plate is pre-bent and shaped according to the required curvature, and the locking nut is screwed in and tightened. The posterior atlantoaxial arch, pivot spine, and lamina were decorticated, and autogenous cancellous bone graft was taken from the posterior superior iliac spine. 2 Results: 26 nails were placed in the atlantoaxial “pedicle” and 28 nails in the cardinal spine, i.e., 1 case of occipitocervical (cardinal) fixation and 13 cases of atlantoaxial fixation, and no spinal cord, nerve roots, vertebral artery, etc. were injured during surgery. In the atlantoaxial spine, there was one case in which the posterior arch of one side was cut off from the displaced part of the vertebral artery sulcus, but it did not affect the screw implantation, atlantoaxial repositioning and fixation; in the pivotal spine, there was one case in which one of the implanted screws was loosened during surgery, and the skull was repositioned by traction and fixed with Halo-vest for 3 months until the bone healed. 2 cases occurred in which the pivotal arch screws were bent in the bone channel after atlantoaxial repositioning, but the fixation did not fail. 14 cases of surgery The time of surgery was 2.5~4.5h, average 3.1h; the bleeding volume was 100~500ml, average 280 ml. The follow-up period was 2~46 months, average 18 months, 12 cases had bone graft fusion; symptoms such as neck pain and stiffness disappeared, and those with nerve compression symptoms were relieved and disappeared to different degrees. 3.1 Points and experience of surgery The technique of transatlantoaxial pedicle screw fixation has been reported by domestic and foreign scholars [1-4]. According to our experience in actual operation, the atlantoaxial “pedicle” screw was placed with the “posterior node of the vertebral artery sulcus” (i.e., the junction of the posterior atlantoaxial arch and vertebral artery sulcus) as the general reference mark for the stripping area and nail entry point selection. The nerve stripper is used to dissect under the periosteum and carefully explore the inner and upper and lower edges of the atlantoaxial “pedicle”, and to accurately determine the central axis of the “pedicle” and the nail entry point is the key to this operation. The central axis of the isthmus is the direction of nailing, and the point of penetration slightly above the midpoint of the inferior articular eminence of the pivot vertebra is the nail entry point, and the travel of the open hand cone in the central axis of the isthmus is truly perceived under direct vision. In such a familiar anatomy, nail placement should be easy to perform. By following the principle of individualized nail placement, damage to adjacent vital tissues can be avoided. No serious complications such as spinal cord, nerve root, or vascular injuries occurred in this group. There were some mistakes and lessons learned during the early use of this technique. ① Atlantoaxial posterior arch cut fracture. In one case, the posterior arch of the atlantoaxial side was cut and broken during nail placement. The reason for this was that the posterior atlantoaxial tuberosity was mechanically selected 20 mm outward as the nail entry point and was cut and broken during tapping with a 3.0 mm wire. Although this error did not affect the atlanto-lateral block screw placement and its robustness after screw placement, there was a risk of injury to the spinal cord if the nail entry point was too far inward. Lesson: Operate according to the true intraoperative anatomic landmarks. ②The instability of the “sitting nail” of the pivot affects the effect of repositioning and fixation. We have a case of instability after the pivotal arch nail implant, the case of nail placement in the angle of inclination is too small, down, the effective travel of the screw in the nail channel is too short, the atlantoaxial repositioning and fixation of the atlantoaxial spine due to the principle of leverage screw in the nail channel tension cut, resulting in the pivotal arch screw instability, reset failure. Lesson: The access to the pivot nail tract must be within the central axis of the isthmus, which is both safe and strong and reduces damage to the vertebral artery. In the event of fixation screw loosening, assist Halo-vest fixation until the bone heals. (iii) Bending of the pivot pedicle screw. Two cases occurred in this group, which are related to the atlantoaxial joint dislocation preoperative traction or intraoperative large-weight traction reset still did not achieve complete anatomical reset. In this case, the atlantoaxial joint is still in a state of strong elastic repositioning (i.e., strong external force is required to reposition the atlantoaxial joint dislocation or to maintain the required repositioning requirements) when it is forcibly lifted and repositioned and fixed with the help of an internal fixation device, thus easily leading to atlantoaxial screw extraction or bending of the pivot screw. This also increases the stress on the fixation nail, which can lead to fracture of the nail [5]. Complete repositioning of the dislocated atlantoaxial joint prior to fixation, when possible, may prevent this complication. References (omitted)