To investigate the efficacy of atlantoaxial instability or dislocation treated with transaxial pedicle nail combined with pivot plate nail fixation and fusion. Methods Among the 7 cases of atlantoaxial instability or dislocation admitted from February 2003 to February 2009, preoperative cervical sagittal CT suggested that the foramen ovale of the pivot vertebrae was high across in 3 cases; the cervical 2 and 3 septum were incomplete, and the pivot arch was narrow in 4 cases. There were 4 male and 3 female cases, aged 10-61 years old, mean 41 years old. Four cases had symptoms and signs of spinal cord disease or spinal cord injury. Posterior cervical approach via bilateral atlantoaxial side blocks, one side of the pivotal pedicle nail, one side of the pivotal plate nail atlantoaxial fixation was performed in 4 cases; 3 cases of occipitocervical fixation was performed via one side of the pivotal pedicle nail, one side of the pivotal plate nail and the occipital bone, respectively. The autologous iliac bone was taken for bone fusion. Results There were no cases of spinal cord and vertebral artery injury during surgery. Seven cases in this group were followed up for 1 to 3 years, with an average of 13 months, and all of them obtained bony fusion, and there was no case of nail plate breakage. Spinal cord function improved significantly in 3 cases and slightly in 1 case. Conclusion Atlanto-axial fusion or occipitocervical fusion can be performed through pivot plate nailing when atlanto-axial instability or dislocation, preoperative pivot CT suggests abnormal development of the pivot pedicles and screw fixation is not possible, and the technique is easy to perform, with low risk and reliable efficacy. 1. Data and methods (1) General data The group consisted of 7 cases, 4 males and 3 females, aged from 10 to 61 years old, with an average of 41 years old. Preoperative cervical spine sagittal CT suggested that the cardinal vertebral artery foramen was high across 3 cases; cervical 2, 3 septal insufficiency, cardinal spinal arch root narrowing 4 cases. Four cases had symptoms and signs of spinal cord disease or spinal cord injury. Two cases were fixed by posterior approach via one side of pivotal pedicle and one side of pivotal plate atlantoaxial fixation; two cases were fixed by bilateral pivotal plate atlantoaxial fixation; and three cases were fixed by one side of pivotal pedicle and one side of pivotal plate with occipital neck of occipital bone. Autologous iliac bone graft was taken. (2) Surgical methods Cranial traction was performed after general anesthesia in 7 cases in this group, and the weight of traction was 6-8Kg, and the atlantoaxial joint was able to be reset by C-arm fluoroscopy. Posterior approach was performed to reveal the lateral block of the atlas, posterior arch of the atlas, or squamous part of the occipital bone. Four cases were fixed by posterior approach via atlantoaxial side block, pivot pedicle root nail combined with pivot plate nail, and three cases were fixed by pivot pedicle root nail combined with pivot plate nail and occipital bone. Atlantoaxial fusion: Bilateral atlantoaxial lateral block nailing, pivot side pedicle nailing, and the other side transforaminal plate nailing were selected. Atlantoaxial lateral block nailing: The C2 nerve root and venous plexus were pushed downward to reveal the posterior continuation of the atlas below the lateral block, from which the middle part of the atlantoaxial pedicle could be explored. The posterior arch border of the atlantoaxial spine corresponding to the mid-axis of the pedicle is the entry point. A drill was used to make a depression at the entry point, and a hand awl was used to puncture the atlantoaxial side block to a depth of 26 mm, and a screw of 3.5 mm in diameter and 3.0 mm in length was screwed into the atlantoaxial side. The same operation was performed on the contralateral side. Pivotal pedicle implantation: The C2 nerve root and venous sinus are picked up to reveal the top of the pivotal arch isthmus, a puncture point is selected in the center of the subaxial articular process, a small hole is drilled out with a drill, and a screw with a diameter of 3.5 mm and a length of 26 mm is inserted along the medullary cavity of the pivotal arch isthmus, a hand awl is withdrawn, and a screw with a diameter of 3.5 mm and a length of 26 mm is screwed into the pedicle root screw. A nail plate is placed on the side of the pivotal pedicle to pre-curve the fixed plate to a certain degree of curvature, and the atlantoaxial joint is reset by the principle of leverage during the process of tightening the fixation nut by utilizing the pre-curvature of the fixed plate. Pivot plate nailing: At the continuation of the pivot plate and the pivot spinous process, a small hole is ground out with a drill, perpendicular to the spinous process, and drilled through the contralateral cortex via the medullary cavity of the plate, and probed with a small ball probe, and if the bottom of the bony channel is bony, a multiaxial screw with a diameter of 3.5 mm and a length of 24 mm is screwed into it. After adequate repositioning of the atlantoaxial joint was obtained using a pegboard device, the pivot plate was reinforced with pegged fixation rods. The autologous iliac bone was taken for implant fusion. Occipitocervical fusion: The occipital scales were chosen to be nailed, 12 mm in diameter, 3 screws/each side, one side of the pivot vertebra was nailed by the pedicle and the other side was nailed by the transforaminal plate, the pivot vertebra was nailed by the pedicle and the pivot vertebra was nailed by the same as the previous one. The nail plate system was placed on the side of the pivotal pedicle, the fixation plate was pre-bent to a certain curvature, and the atlantoaxial joint was reset by the principle of leverage during the process of tightening the fixation nut by utilizing the pre-bending of the fixation plate, and the atlantoaxial joint was implanted with the autologous iliac bone for the fusion. 2 .Results There were no cases of spinal cord and vertebral artery injury during surgery. The 7 cases in this group were followed up for 1 to 3 years, with an average of 13 months, and all of them obtained osseous fusion, and there was no case of plate fracture. For those with spinal cord symptoms, 3 cases showed significant improvement in spinal cord function and 1 case showed slight improvement. Typical case The patient, female, 46 years old, was admitted to the hospital because of pain in the posterior occipital region and clumsiness of the hands for 5 months. She was diagnosed with atlantoaxial instability, high cervical myelopathy, and dentoacromial nonunion. On May 2, 2005, under general anesthesia, atlantoaxial joint reset atlantoaxial lateral block pivot plate endoprosthetic implant fusion was performed. The implant healed at 3 months postoperatively, and the JOA score was 12 at 13 months. Figures (1-9) are attached. Discussion Atlantoaxial instability or subluxation puts the patient at risk, and it is essential to reconstruct the upper cervical spine to remove the risk of high cervical spinal cord injury. Posterior approaches to reconstructing atlantoaxial stability include wire fixation, plate clamp fixation, the Magerl procedure, and transpedicular screw-rod fixation.The Magerl approach to atlantoaxial instability or dislocation is a landmark change in the treatment of atlantoaxial joint instability or dislocation, with screw fixation through the lateral atlantoaxial tuberosity joints, limiting atlantoaxial translation and lateral flexion, and without access to the spinal cord, which is less of a threat to the spinal cord. However, this method is not suitable for all cases. When the atlantoaxial instability or subluxation is of long duration, a gooseneck deformity of the cervical spine is formed, and this patient is unable to flex his head and neck during the surgery, and Magerl’s procedure is very difficult to accomplish. The pedicle is the strongest bony structure located between the vertebral body and the upper and lower articular processes. Screw fixation in the pedicle provides a reliable mechanical basis for reconstructing the stability of the spine and creates favorable conditions for implant fusion. The rate of vertebral artery injury is 2-8% with transforaminal pinning. The vertebral artery foramen of the pivot vertebrae is located relatively inward, and from the lateral view, the position of the vertebral artery foramen is higher, forming a “high span of the vertebral artery”. The placement of pivotal vertebral pedicle nails in such cases is more likely to lead to vertebral artery injury. In cases of congenital cervical segmentation insufficiency, the pivotal pedicle is very narrow and thin, and pedicle fixation is likely to lead to pedicle fracture. Due to the anatomical variation of the isthmus of the pivot arch, 20% to 27.5% of the pivot arch isthmus width is less than 5 mm, which is unsuitable for pedicle screw fixation.Wright firstly reported a clinical case in which a nail was placed in the pivot plate for atlanto-atlantoaxial joint fixation. The use of pivot plate screws instead of pedicle screws for posterior cervical fusion poses no risk of injury to the vertebral arteries, and can be performed under direct visualization without the need for fluoroscopic monitoring. The nail channel of the pedicle screw is tangential to the spinal cord, and even if the screw breaks through the inner cortex of the vertebral plate into the spinal canal, it is not easy to damage the spinal cord. We observed that in cases of congenital C2 and 3 segmentation insufficiency, the vertebral plates of the pivot vertebrae tended to be thicker, which was more suitable for the placement of pedicle nails. The unique anatomy of the pivot vertebrae, with its spinous processes and vertebral plates being the largest in the cervical spine, offers the possibility of pedicle screw fixation. In a study by Ma Xiangyang et al, the thicknesses of the superior, middle, and inferior margins of the cardinal vertebral plate were 3.02 mm, 5.91 mm, and 5.59 mm, respectively; the heights of the root of the spinous process, the vertebral plate, and the middle part of the inferior articular process of the cardinal vertebrae were 12.40 mm, 12.95 mm, and 14.03 mm, respectively; and the average lengths of the superior and inferior pedicle screws were 25.41 mm and 27.39 mm, respectively: superior screws 26.40 for anterior oblique and 7.60 for inferior oblique suggesting that it is feasible to place two screws of 3.5 mm diameter in the upper and lower sites, left and right crosswise. In a study by Gorek et al, there was no difference in the fixation effect on flexion-extension, lateral flexion, and rotational activities of the atlantoaxial joint between pivotal plate placement and pivotal pedicle placement compared with pivotal pedicle placement.Claybrooks et al[8] reported that there was no statistically significant difference between the 2 nailing methods of pivotal plate and pivotal pedicle placement in controlling flexion-extension and anterior-posterior translation of the atlantoaxial joint, but that the pivotal plate nailing had less of a limiting effect than the pivotal pedicle nailing in limiting the effects of lateral flexion and rotational stresses. Lapsiwala et al [9] reported that pivot plate nailing provided less control of lateral flexion activities compared to pedicle nailing. Whether the difference in biomechanical tests between pivot plate and pedicle implantation is clinically significant remains to be seen in comparative studies of the results of treatment of large numbers of cases. Considerations for cardinal plate nailing: Preoperative X-ray, thin-layer CT scan reconstruction, and MRI evaluation are important in selecting the choice of cardinal plate nailing fixation. Firstly, the principle of pivotal pedicle pinning was selected. For the cases of “high vertebral artery crossing” and congenital C2 and 3 segmentation insufficiency of the pivot vertebrae, preoperative atlantoaxial thin-layer CT examination was performed, and we observed that one of the pivot vertebrae could be nailed with relatively normal pedicle development, and we determined the point of entry and the angle of entry of the nail based on the measurements of the CT films, and we implemented the pivot plate nail fixation as an auxiliary fixation on the other side of the pivot vertebrae, otherwise, we implemented bilateral pivot plate nail fixation. Fixation was performed on the other side of the pivot vertebra as a secondary fixation, otherwise, the pivot vertebra was nailed bilaterally. A combination of nail rod and nail plate fixation was chosen. The plate fixation system is applied on the side of the pivotal pedicle for atlanto-axial joint repositioning, and the nail-rod system is applied on the side of the pivotal plate for fixation. The nails and rods of the nail-rod system can be connected and locked at any relative angle in three-dimensional space; the nail-plate system can only accomplish fixation in two-dimensional space. First, we placed the nail plate on the pivot plate side and pre-bent the plate to a certain curvature, utilizing the pre-bend of the plate to reset the atlantoaxial joint with the principle of leverage during the process of tightening the fixation nut. Then, a fixation rod is attached to the nailed side of the atlantoaxial plate for fixation. Atlantoaxial repositioning and fixation is the foundation, and atlantoaxial fusion is the goal. Posterior atlantoaxial fusion requires roughness on the surface of the spinous process and the vertebral plate to facilitate implant fusion. By fixing the pedicle on the side of the pivot with normal pedicle development, the pivot plate on that side can be fully utilized and more cancellous bone can be implanted to increase the success rate of implant fusion.