3D printed navigation template assists pedicle lag-screw placement for atypical Hangman’s fracture

Abstract

Objectives To evaluate the 3D printed navigation template used to assist axis pedicle lag-screw placement in the treatment of atypical Hangman’s fracture (AHF). Methods From May 2015 to January 2017, 12 patients with AHF were treated at Department of Orthopedics, The Fourth People’s Hospital of Zigong.In their operation, the axis pedicle lag-screw placement was assisted by a 3D printed navigation template.They were 8 men and 4 women, aged from 27 to 53 years (average, 45.6 years).There were 7 cases of type Ⅰ, 4 cases type Ⅱ and one case of type ⅡA according to the Levine-Edwards classifi-cation.There were 2 cases of grade D and 12 cases of grade E according to the assessment of America Spinal Injury Association (ASIA).Their preoperative and postoperative neck pain was evaluated by visual analogue scale (VAS); their preoperative and postoperative ranges of cervical motion were recorded and compared.To evaluate the postoperative safety of screws, the insertion point, position within the pedicle, axial angle and sagittal angle of the screws and maximum fracture displacement were compared between actual operation and simulative operation. Results A total of 12 guide plates were designed and printed; a total of 24 lag-screws were placed.All patients underwent surgery uneventfully.They were followed up for 12 to 20 months, with an average of 14.7 months.Two patients with ASIA grade D recovered to ASIA grade E at the last follow-up.All patients showed a significant improvement in neck pain.Their VAS score at 5 days after surgery (5.86±2.02) was significantly lower than their preoperative score (8.29±1.88) (P 0.05).Their postoperative X-ray and CT images showed that the dislocation was all corrected.The last follow-up showed no obvious vertebral in-stability, screw breakage or loosening.Postoperative CT showed that the 24 screws had been located com-pletely in the pedicle (grade 0), indicating that the screw placement was 100% accurate.The postoperative deviation at insertion point (0.70±0.78 mm), deviation within the pedicle (1.3±0.82 mm), axial angle (8.26°±0.88°) and sagittal angle (22.62°±0.86°) of the screws showed no significant differences from the preoperative simulative data (P>0.05).There was a significant difference in the maximum fracture dis-placement between the preoperative data (3.94±0.38 mm) and the postoperative data (2.21±0.39 mm) (P<0.05). Conclusion The 3D printed navigation template can be used to better assist axis pedicle lag-screw placement in the treatment of AHF, because it ensures safe screw placement, leading to good re-duction and fixation and precise match with the preoperative plan. Key words: Axis; Fracture; Fractures fixation, internal; Bone screw; 3D printing tech-nology