Objective: The aim of this study was to describe the application of the rapid prototyping (RP) life-size 3-dimensional model used to improve accuracy of screw insertion in irreducible atlanto-axial dislocation (IAD). Methods: The study included 10 patients with IAD. All patients were assessed using the Japanese Orthopedic Association (JOA) score. Radiographs, MRI and CT were conducted during the preoperative and postoperative procedure. A 3D RP model was created for each patient. The model was used to obtain detailed information of each pedicle and used as an intraoperative reference. Assisted by the model, transoral atlanto-axial reduction plate fixation was performed in each case. Results: The average operation time was 145 (range: 90 to 180) minutes and average blood loss was 120 (range: 60 to 250) ml. JOA scores improved after surgery. All 40 transoral pedicle/lateral mass screws were placed without serious complications or internal fixation failure. Postoperative radiographs and CT scan showed 38 transoral pedicle/lateral mass screws located in the pedicle tracts. Satisfactory reduction was achieved in 95% of screws. Two screws perforated the lateral wall of the C2 pedicles in an extremely narrow pedicle case. No neurologic sequelae or vertebral artery injury were detected. Conclusion: The RP technique is effective and reliable in achieving an accurate and safe screw insertion during IAD surgery, especially in anatomically abnormal cases.
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