Objective:To compare the effects of 3 spatial locations of the screw at the injured vertebra on the vertebral height in AO type A thoracolumbar fracture.Methods:A retrospective analysis was performed of the 156 patients with type A thoracolumbar fracture who had been hospitalized at Department of Spine Surgery, The Sixth Hospital of Ningbo from January 2016 to June 2019. They were divided into 3 groups according to the spatial location of the screw at the injured vertebra. In group A of 55 cases, the screws were located in the vertebral body between the longitudinal axis bisector of the vertebral pedicle and the upper endplate; in group B of 52 cases, the screws were located in the vertebral body between the vertical axis bisector of the vertebral pedicle and the horizontal line of the apex of the inferior pedicle notch; in group C of 49 cases, the screws were located in the vertebral body between the horizontal line at the apex of the inferior pedicle notch and the inferior endplate. The anterior, middle and posterior heights of the injured vertebra, Beck index and angulation of the injured vertebra at preoperation, one week postoperation and the last follow-up were compared between the 3 groups and within the same group.Results:There was no significant difference in preoperative general data between the 3 groups, showing comparability ( P>0.05). In all the 3 groups, the anterior and middle heights of the injured vertebra and Beck indexes at one week postoperation and at the last follow-up were significantly larger than those before operation while the angulations of the injured vertebra at one week postoperation and at the last follow-up were significantly smaller than the preoperative values (all P<0.05), but there was no significant difference between one week postoperation and the last follow-up in any of the above indexes ( P>0.05). In all the patients, the posterior height of the injured vertebra at one week postoperation was significantly larger than those before operation and at the last follow-up ( P<0.05), but there was no such a significant difference in comparison between preoperation and the last follow-up ( P>0.05). At the last follow-up, groups A and B had significantly larger anterior and middle heights of the injured vertebra and Beck indexes but significantly smaller angulations of the injured vertebra than group C, but such significant differences did not exist when the above indexes were compared between groups A and B ( P>0.05). Conclusions:In insertion into an injured vertebra, the screw should be parallel and close to the upper endplate, and located in the middle and upper part of the vertebra corresponding to the longitudinal axis of the vertebral pedicle, because this spatial position is conducive to intraoperative reduction, maintaining the postoperative height of the injured vertebra, and decreasing loss of the vertebral height.

Objective:To compare the therapeutic results between axis pedicle screwing assisted by intraoperative 3-D navigation and freehand axis pedicle screwing in the treatment of Hangman fracture.Methods:A retrospective analysis was performed of the 64 patients with Hangman fracture who had received posterior axis pedicle screwing at Department of Spinal Surgery, The Sixth Hospital of Ningbo from May 2014 to December 2019. According to the placement methods of axis pedicle screws, they were divided into a navigation group ( n=34, subjected to axis pedicle screwing assisted by intraoperative 3-D navigation) and a freehand group ( n=30, subjected to freehand axis pedicle screwing). Pedicle screw placement time, operation time, intraoperative bleeding, fluoroscopy time, hospital stay, total hospitalization cost and complications were recorded and compared between the 2 groups. The accuracy of axis pedicle screw placement was evaluated according to the postoperative cervical CT and screw grading criteria proposed by Park et al. At admission, 3 months postoperation, and the last follow-up, neurological function of the patients was evaluated by modified Japanese Orthopedic Association (mJOA) score, neck pain was evaluated by visual analogue scale (VAS), and C2/3 vertebral body angulation and C2 forward displacement were measured. The clinical efficacy was evaluated by Moon grading at the last follow-up. Results:The navigation group and the freehand group were comparable due to insignificant differences between them in the preoperative general data ( P>0.05). The accuracy of screw placement in the navigation group (98.2%, 54/55) was significantly higher than that in the freehand group (85.2%, 46/54) ( P<0.05). The screw placement time, operation time, fluoroscopy time and total hospitalization cost in the navigation group were significantly more than those in the freehand group ( P<0.05). Vertebral artery injury occurred in 3 cases in the freehand group. Screw loosening, screw breakage or rod breakage occurred in none of the patients after operation. There was no significant difference between the 2 groups in the intraoperative bleeding, hospital stay or follow-up time ( P>0.05). In both groups, the VAS score, mJOA score, C2/3 vertebral body angulation and C2 forward displacement were significantly improved at 3 months postoperation and the last follow-up compared with those at admission ( P<0.05), but there was no significant difference between the 2 groups in the contemporary comparisons ( P>0.05). At the last follow-up, Moon grading in the navigation group was significantly better than that in the freehand group ( P<0.05). Conclusion:In the treatment of Hangman fracture, compared with freehand screw placement, axis pedicle screwing assisted by intraoperative 3-D navigation can improve accuracy and safety of screw placement and reduce postoperative complications, leading to better clinical efficacy.