Treatment of atlantoaxial instability with posterior lateral mass screw technlque

Objective:To evaluate safety and reliability with freehand technique of posterior lateral mass screw implantation in the treatment of atlantoaxial instability.Methods:Seventeen patients with atlantoaxial instability were treated with internal fixation of AXIS(15 cases)and VERTEX(2 cases)system through posterior lateral mass screw implantation.Sixty-eight screws were inserted in the 17 cases.11 male and 6 female were included in this group with the mean age of 43.5 years(range 17-71).One case was cervical tumor and the other 16 cases were odontoid fractures.Among the odontoid fractures,11 cases were Anderson type Ⅱ(4 old and 7 fresh fracture)and 5 case were Anderaon typeⅢ(1 old and 4 fresh fracture).Results:The X-ray and CT image showed the location of screws were good.Screws in 2 cases perforated the external cortex of lateral mass(pedicle),screws in another 3 cases perforated the superior cortex of posterior arch,but no effect to fixation strength.No other screw complication was found in the patients.Conclusion:If the anatiomic structure of C1-2 in X-ray and CT image is well understood,freehand technique of posterior lateral screw implantation for the treatment of atlantoaxial instability is safe and feasible.