RESUMO
Objective To design an atlantoaxial lateral mass fusion cage and evaluate its biomechanical stability when it is combined with atlantoaxial vertebral pedicle screw fixation.Methods Forty-six sets of CT 3D reconstruction pieces of the normal atlantoaxial junction were chosen to measure sagittal diameter and transverse diameter of atlantoaxial lateral mass joint,sagittal diameter and transverse diameter of epistropheus lateral mass and space height of atlantoaxial lateral mass joint.An atlantoaxial lateral mass fusion cage was designed on this basis.Six fresh human cadaveric cervical spines (C0-C4) were used as samples to measure 3D motion range of C1,and 2 segments under 1.5 N · m load.3D motion range of samples under the following situations was measured at random:intact state,unstable state (ligament around odontoid process was cut off),fixation with atlantoaxial joint screw+Gallie steel wire,atlantoaxial pedicle screw,atlantoaxial lateral mass joint fusion cage+atlantoaxial vertebral pedicle screw.Results Corresponding width/length of fusion cage is 8/11,9/12,10/13 mm,respectively,and the height is designed to 3.5,4.0,and 4.5 mm,respectively.The motion range of three internal fixation methods is less than that under intact state and unstable state.The difference has statistical significance.The C1+C2+cage fixation produces the least motion range in lateral bending and axial rotation directions and generates the highest motion range in flexion/extension direction.But,the difference has no statistical significance.Conclusion The C1+C2+cage internal fixation technique has similar stability with common atlantoaxial intemal fixation method and can provide extra atlantoaxial fusion spots.Thus,it may be a feasible alternative for atlantoaxial fusion when the posterior arch of the atlas is absent.
RESUMO
Objective To evaluate the outcome of posterior screw-rod fixation system in reduction and internal fixation of atlantoaxial dislocation. Methods A retrospective study was done on 27 patients with atlantoaxial instability including 18 male and 9 female (at age range of 13-51 years, mean 31 years) from January 2007 to May 2009. There were 11 patients with chronic odontoid fractures, five with isolated bone odontoid, seven with transverse ligament rupture of atlas and four with rheumatoid arthritis. Skeletal reduction was performed in all the patients. The anterior atlantodens interval (ADI)ranged from 8 mm to 15 mm, average 11 mm. All the patients underwent an intraoperative reduction by posterior C1 lateral mass and C2 pedicle screws with rod fixation. According to American Spine Injury Association (ASIA) impairment scale, there were eight patients at grade B, 15 at grade C and four at grade D. Results All patients were followed up for 6-24 months (average 13 months), which showed that the neck symptoms were improved, with bony union. The ADI was reduced to 2-4 mm (average 2.8 mm)postoperatively. Postoperative ASIA scale was grade C in four patients, grade D in 12 and grade E in 11.There were no neurologic or vascular complications occurred, or no failure of the internal fixtors, pseudarthrosis or instability. Conclusion Posterior screw-rod fixation system has advantages of simple procedures, few complications and good results and can be used for intraoperative reduction of atlantoaxial dislocation.