The objective of surgical intervention is to reconstruct the stability of atlantoaxial articulation. The surgical methods can be divided into anterior and posterior approach. However, the anterior approach is seldomly used due to the difficulty of exposure and high frequency of complications. The posterior approach, including wiring, apofix clamp, C1-2 pedicle or transarticular screws is the preferred method to be selected in the clinic. Each type of technique has a unique set of risks and benefits.
Although posterior wiring techniques, such as Gallie and Brooks technique, are still used currently, they are considered as less stable compared to C1-2 pedicle or transticular screws based on a biomechanical point of view[21–23]. In addition, it has a potential risk of neurological deficit when the sublaminar wires are passed under the C1 arch. In order to avoid the neurologic risk caused by the sublaminar wires, some professors designed apofix laminar clamp, which uses laminar hook to fix the C1-2 posterior structure, however, it does not improve biomechanical stability as a simple one-point fixation.
In 1986, Magerl and Seemann initially described posterior atlantoaxial transarticular screw fixation technique for stabilization of C1 and C2 (Magerl’s technique). It has been considered to be one of the most rigid atlantoaxial posterior stabilization techniques multidirectionally, and was reported to achieve good clinical outcomes[8, 25, 26]. However, from a biomechanical viewpoint, it is merely a two-point fixation and cannot provide the good stability in 3-D motion of the atlantoaxial articulation, especially in extension and flexion. To achieve more stabilization, Guo et al reported using Magerl’s technique combined with bilateral laminar clamps internal fixation for treatment of atlantoaxial dislocation in 36 cases, and attained effective anatomic reduction and satisfactory clinical outcomes, with no intraoperative complications. Bone fusion was obtained in all cases 6 months after surgery, and no failure of internal fixation was observed during the 7-years follow up period. It revealed that Magerl’s technique combined with bilateral laminar clamps internal fixation could provide reliable biomechanical stability, as well as carry a higher bony fusion rate and reduce the risk of iatrogenic injury of vertebral artery and spinal cord.
Based on the technique mentioned above, we modified the former technique as Magerl’s technique combined with single laminar clamp internal fixation, composed of bilateral atlantoaxial transarticular screws and middle laminar clamp fixation, to create a 3-point fixation which could result in stronger stabilization theoretically. In our study, we used this modified technique in management of atlantoaxial dislocation in 21 cases. all the patients showed satisfactory bone union and anatomic reduction, with the atlas⁃dens interval (ADI) corrected from preoperative 6.25 ± 0.74 mm to postoperative 2.17 ± 2.50 mm and final follow-up 2.61 ± 3.08 mm. The space available for the cord (SAC) at C1-2 segment also significantly increased from 10.42 mm to 16.91 mm, similar to the data reported by Guo. In addition, the clinical function also improved significantly with the JOA recovery rate of 81.2% at the final follow up period. In addition, there was no instrument complications occurred during the follow up. Therefore, we thought that this technique further simplified the operative manipulation by merely using one atlantoaxial laminar clamp to establish an ideal 3-point fixation and reduced the risk of spinal cord injury associated with operation, which meet the need of clinics.
Many of the posterior surgery-associated complications were graft-related problems[27–29]. In the report published by Bahadur et al, patients with atlantoxial dislocation underwent Magerl’s technique combined with laminar bone graft and Brooks technique. The outcome suggested that failure of bone fusion still existed despite of sufficient stabilization, which may be related to insufficient preparation of bone graft bed or unsuitable placement of bone graft. In our experience, in order to increase the fusion rate, the cortical bone of the lower part of the C1 posterior arch and the upper edge of the C2 laminar and spinal process should be removed using the high speed bur, to prepare for the bone graft bed. In addition, the bone block harvested from the iliac bone should be trimmed to butterfly shape, which could keep it riding on the C2 spinal process steady. What is more, the lower single laminar clamp should be exactly inserted through the C2 spinous bifurcation, which makes it more stable. The compressor should be used to tighten the two laminar clamps that were connected with a sleeve in the middle line, which could keep the bone graft compact.
It’s worth noting that Magerl’s technique combined with single laminar clamp internal fixation is only appropriate for management of reducible atlantoaxial dislocation. Thus, anatomic reduction of atlantoaxial dislocation should be confirmed before the surgery, In our experience, preoperative skull traction is essential for reducing atlantoaxial dislocation as much as possible. In addition, Mayfield head holder is helpful for maintaining C1-2 reduction, which should be confirmed with C-arm fluoroscopy or radiography preoperatively. It should be mentioned that, in the cases combined with vertebral artery deformity, such as vertebral artery high-riding or tortuosity, transarticular screws insertion will increase the risk of vertebral artery injury. Paramore et al reviewed the CT scans of 94 cases with atlantoaxial dislocation, and found that the incidence of high-riding vertebral artery was 18%. In this study, three-dimensional CT scan and MRA was performed for the patients to exclude the vertebral artery deformities before operation. In addition, this Magerl’s technique combined with single laminar clamp internal fixation is also not appropriate for treatment of the patients with C1 posterior arch dysplasia or absence.
Although satisfactory clinical outcomes were obtained in this study, the current study has some limitations. This was a small-sized retrospective study and the number of patients was restricted due to the low incidence of atlantoaxial dislocation. Another limitation is that this study was just a preliminary report about an early technical experience. A multicenter prospective controlled study of atlantoaxial dislocation should be considered in the future.