Percutaneous atlantoaxial anterior transarticular screw fixation combined with mini-open posterior C1/2 wire fusion for patients with a high-riding vertebral artery

Anterior Transarticular Crossing Screw Fixation for Atlantoaxial Joint Instability: A Biomechanical Study

OBJECTIVE

To evaluate the biomechanical stability of anterior transarticular crossing screw (ATCS) and compare it with anterior transarticular screw (ATS) which may provide basic evidence for clinical application.

METHODS

Eight human fresh cadaveric specimens (occiput-C4) were tested with 5 conditions including the intact status, the injury status (type II odontoid fracture), the injury+ATS fixation status (traditional bilateral ATS fixation); the injury+unilateral ATCS fixation status; and the injury+bilateral ATCS fixation status. Specimens were applied to a pure moment of 1.5 Nm in flexion-extension, lateral bending, and axial rotation, respectively. The range of motions (ROMs) and the neutral zones (NZs) of C1 to C2 segment were calculated and compared between 5 status.

RESULTS

ATS and ATCS fixations significantly reduced the motions in all directions when compared with the intact and injury statues (p < 0.05). In flexion-extension, the ROMs of ATS, unilateral ATCS, and bilateral ATCS were 4.7° ± 2.5°, 4.1° ± 1.9°, and 3.2° ± 1.2°, respectively. Bilateral ATCS resulted in a significant decrease in ROM in flexion-extension when compared with ATS and unilateral ATCS (p = 0.035 and p = 0.023). In lateral bending and axial rotation, there was no significant difference in ROM between the 3 fixations (p > 0.05). Three fixations resulted in similar NZs in all directions (p > 0.05).

CONCLUSION

ATCS is a biomechanically effective alternative or supplemental method for atlantoaxial instability.

Minimally invasive robotic cervicothoracic fusion: a case report and review of literature

Minimally invasive surgery (MIS) of the posterior cervical spine with robotic assistance has recently emerged to treat degenerative disc disease. Robotic arms and 3D neuronavigation with preoperatively planned placement are used to achieve real-time intraoperative guidance, reducing screw malposition through increased accuracy and stability. This results in decreased blood loss, postoperative pain, and quicker recovery time compared to other techniques. We aim to demonstrate a novel technical approach to posterior cervical spine fusion using robotic assistance and discuss its advantages. In a patient with right hand weakness and a right paracentral disc herniation of the cervicothoracic spine, we performed a MIS percutaneous and robotically assisted posterior spinal fusion at C7-T2, with complete C7-T1 and T1-2 right-sided facetectomies and also a T1-T2 discectomy. Preoperative software planning and a robotic platform attachment configuration was used. There was immediate postoperative improvement in upper extremity strength and the patient was discharged without complications. Postoperative imaging confirmed accurate hardware placement, and follow-up at both 3- and 4-month confirmed improved upper extremity strength with sensation intact throughout. MIS robotic posterior cervicothoracic fusion can effectively be used to improve patient outcomes. Further implementation of robotic assistance during cervical fusion in larger studies is needed to further evaluate its effectiveness.

[Minimally invasive techniques for traumatic injuries of the cervical spine]

Nowadays, although minimally invasive procedures are the standard for the treatment of thoracolumbar spinal injuries, these techniques are not yet established for the cervical spine. This is due to anatomical and technical reasons and also due to the fact that the classical anterior decompression and fusion procedure already fulfils the criteria of minimally invasiveness and is suitable for the vast majority of injuries. The existing literature consists mainly of case reports and small comparative cohort studies, the results of which are presented. There is a minimally invasive variant for nearly all open procedures, mainly in the upper cervical spine but also in the lower cervical spine. The further development of these promising techniques is still pending.

Design a novel integrated screw for minimally invasive atlantoaxial anterior transarticular screw fixation: a finite element analysis

PURPOSE

To design a new type of screw for minimally invasive atlantoaxial anterior transarticular screw (AATS) fixation with a diameter that is significantly thicker than that of traditional screws, threaded structures at both ends, and a porous metal structure in the middle. The use of a porous metal structure can effectively promote bone fusion and compensate for the disadvantages of traditional AATSs in terms of insufficient fixation strength and difficulty of bone fusion. The biomechanical stability of this screw was verified through finite element analysis. This instrument may provide a new surgical option for the treatment of atlantoaxial disorders.

METHODS

According to the surgical procedure, the new type of AATS was placed in a three-dimensional atlantoaxial model to determine the setting of relevant parameters such as the diameter, length, and thread to porous metal ratio of the structure. According to the results of measurement, the feasibility and safety of the new AATS were verified, and a representative finite element model of the upper cervical vertebrae was chosen to establish, and the validity of the model was verified. Then, finite element-based biomechanical analysis was performed using three models, i.e., atlantoaxial posterior pedicle screw fixation, traditional atlantoaxial AATS fixation, and atlantoaxial AATS fixation with the new type of screw, and the biomechanical effectiveness of the novel AATS was verified.

RESULTS

By measuring the atlantoaxial parameters, the atlantoaxial CT data of the representative 30-year-old normal adult male were selected to create a personalized 3D printing AATS screw. In this case, the design parameters of the new screw were determined as follows: diameter, 6 mm; length of the head thread structure, 10 mm; length of the middle porous metal structure, 8 mm (a middle porous structure containing an annular cylinder ); length of the tail thread structure, 8 mm; and total length, 26 mm. Applying the same load conditions to the atlantoaxial complex along different directions in the established finite element models of the three types of atlantoaxial fusion modes, the immediate stability of the new AATS is similar with Atlantoaxial posterior pedicle screw fixation.They are both superior to traditional atlantoaxial anterior screw fixation.The maximum local stress on the screw head in the atlantoaxial anterior surgery was less than those of traditional atlantoaxial anterior surgery.

CONCLUSIONS

By measuring relevant atlantoaxial data, we found that screws with a larger diameter can be used in AATS surgery, and the new AATS can make full use of the atlantoaxial lateral mass space and increase the stability of fixation. The finite element analysis and verification revealed that the biomechanical stability of the new AATS was superior to the AATS used in traditional atlantoaxial AATS fixation. The porous metal structure of the new AATS may promote fusion between atlantoaxial joints and allow more effective bone fusion in the minimally invasive anterior approach surgery.