OBJECTIVETo investigate the skill and evaluate the accuracy for application of guide combined with probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement.

METHODSSubaxial cervical pedicle screw was inserted in 11 patients by the guide combined with probing the internal wall of pedicle screw trajectory from January 2014 to October 2016, including 7 males and 4 females with an average age of 48.1 years(ranged 32 to 63 years). There were 4 cases with cervical spondylotic myelopathy, 4 with fracture and dislocation of cervical vertebrae, 1 with cervical cord injury without fracture and dislocation, and 2 with atlantoaxialfracture and dislocation. The target pedicle's diameter, optimal entry point, sagittal angle and cross-sectional angle were measured by CT before operation. During operation, the pedicle screw inserted angle was controlled by a guide with a self-designed protractor and probed the internal wall of pedicle screw trajectory as medial safety margin of insertion screw. The accuracy of cervical pedicle screw was evaluated by CT with classification of four grades and assessed whether there was injury of spine cord or vertebral artery postoperatively.

RESULTSSeventy-one cervical pedicle screws were placed among 11 patients, and no one had been found with clinical manifestations of injury of spine cord (or nerve root) or vertebral artery after operation. According to postoperative CT scan for evaluating the grade of screw position, 52 screws were in grade 0, 13 in grade 1, 4 in grade 2, 2 in grade 3, and 91% (65/71) located in good position. In total, 6 screws were incorreted in placement, and 4 cases of them broke medial wall and 2 cases broke lateral wall.

CONCLUSIONSThe method of probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement is safe and reliable, but the studying curve is long. Probing the internal wall of pedicle screw trajectory and controlling the insertion angle by guide with a protractor are key points of this technology.