Application of reverse axis pedicle screws in the transoral anterior reduction to treat atlas-axis dislocation

Objective To investigate the clinical value of reverse axis pedicle screws in the transoral anterior reduction to treat atlas-axis dislocation.Methods From March 2009 to October 2011,25 patients with atlas-axis dislocation were treated in our department.They were 11 men and 14 women,17 to 65 years of age(mean,39 years).There were 17 traumatic atlas-axis dislocations and 8 atlantoaxial dislocations associated with ossification dens.They underwent transoral release,reduction and instrumentation with transoral atlantoaxial reduction plate (TARP).The atlas was fixated with lateral mass screws and the axis with reverse pedicle screws.After operation,all patients got CT scanning to evaluate screw path,outside tilt angle,downside angle and length of pedicle screw.The Japanese Orthopaedic Association (JOA) scoring system was used for evaluation of spinal function improvement.The atlantodens intervals (ADI) were measured pre-and post-operation to evaluate improvement of dislocation.Results Altogether 50 reverse axis pedicle screws were implanted in the 25 patients.The mean operation time ranged from 125 to 155 minutes and the mean blood loss was 94 mL.CT scan showed 47 screws were in a good trajectory in the axis pedicle.One screw violated into the spinal canal without nerve symptoms due to a too small outside tilt,and 2 screws violated into the vertebral artery foramen which gave rise to occlusion of the cerebellum in one patient who died in the end.The outside tilt angles averaged 20°,the downside angles 15° and the screw lengths 28 mm.The JOA scores increased significantly from 8.9 ± 1.7 pre-operation to 15.7 ± 1.1 (P ＜ 0.05) 3 months after operation.The ADI improved significantly from 8.7 ± 1.5 mm pre-operation to 0.8 ± 0.9 mm post-operation (t =2.937,P ＜ 0.05).Conclusions It is feasible to implant a reverse axis pedicle screw via the transoral approach,but this new technique has a potential risk that should be guarded against so that it should be used carefully in qualified hospitals. Key words: Atlas;  Axis;  Joint instability;  Bone nail