320 - Computer Assisted Trajectory Planning and its Surgical Outcome for Pos...

#320 Computer Assisted Trajectory Planning and its Surgical Outcome for Posterior Atlantoaxial Transarticular Screw Fixation Surgery

Cervical Therapies and Outcomes

Poster Presented by: J. Wang


D.-M. Lai (1)
Y.-H. Wang (1), (2)
Y. Kuo (2)
Y.-S. Chen (2)
J.-L. Wang (2), (3)

(1) National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan, Republic of China
(2) National Taiwan University, Institute of Biomedical Engineering, Taipei, Taiwan, Republic of China
(3) National Taiwan University, Taipei, Taiwan, Republic of China


Objective: To evaluate the feasibility of preoperative computer-assisted trajectory planning for posterior atlantoaxial transarticular screw fixation with surgical outcomes.

Introduction: Cervical C1-C2 instability or dislocation, usually caused by trauma or rheumatoid arthritis, results in nerve compression and assorted disorders. Most of patients can be cured by reduction treatment with the use of neck collar. The patients who suffer from severe symptoms may need surgical treatment. Posterior atlantoaxial fixation with transarticular screw (TAS) is a common treatment for atlantoaxial joint instability due to good stabilization efficacy. However, high complication rates were reported. Complications resulted from screw malposition and neurovascular deficit are catastrophic and fatal. Therefore, constructing patient's individual 3D cervical images and planning TAS trajectory with a computer program prior to surgery are suggested to avoid fetal complications. Ideally, the TAS should penetrate four articular surfaces of C1-C2, and the screw tip should reach anterior surface of C1 arch without crashing the nerve and vertebral artery. The feasibility of preoperative planning of screw trajectory depends on the accuracy of intra-surgical screw pathway. In addition, the change of C1-C2 relative position after surgery remains unclear.

Material and Method: Nineteen patients (average age: 61.1 years; range: 35-71 years) in need of posterior atlantoaxial transarticular fixation based on diagnosis of experienced neurosurgeons were recruited. Prior to surgery, all patients underwent computer tomography (CT) scan for screw trajectory planning. A trajectory planning computer program was self-designed to reconstruct a patient's 3D cervical images with functions of multi-planar section display. The program allowed the evaluation of surface anatomy of cervical spine, which helped surgeons to determine the screw entry point, the horizontal and vertical insertion angle, and the screw size. The patients underwent another CT scan at follow up examination. The following parameters were measured to analyze the deviations between the virtually-planned and intra-surgical screw trajectory: entry point, vertical angle, horizontal angle, and screw length and target point. The pre and post-operative position of C1 and C2 were measured.


(a). Surgical outcome. Overall, 32 transarticular screws were inserted. No massive bleeding and major complications were found.

(b). Deviation of screw trajectory. The vertical angle of intra-surgical screw insertion was significantly larger than that of virtually-planned one (p< 0.05). Other parameters of screw insertion were similar between the virtually-planned and the intra-surgical screw trajectory.

(c). Correlation between parameters. Moderate negative correlation was found between vertical entry point and vertical angle (R=0.567, p=0.01), and moderate positive correlation was found between horizontal entry point and horizontal angle (R=0.378, p=0.039). The increase of intraoperative vertical angle decreased the distance between C1 and C2 along X-axis direction but increased the distance along Y-axis direction.

Conclusion: This study indicates that surgeon can learn the individual stereotactic characteristics of patient's cervical structures during preoperative screw trajectory planning, and thus insert screw more precisely without injuring soft tissue duirng surgery. This study also indicates that higher vertical angle of screw insertion will shorten the distance of C1-C2 after fixation, which may release the pain and the nerve compression resulted from C1-C2 dislocation.