OBJECTIVETo study the clinical problems about posterior atlanto-axial internal-fixation and fusion for atlanto-axial instability or dislocation.

METHODSSurgical treatments of 138 cases with atlanto-axial instability or dislocation were reviewed. There were 62 cases of odentoid malformation, 54 cases of odentoid fracture or rupture of transverse ligament, 22 cases of subluxation and rotation. All cases were treated using Gallie's technique. Six cases were also fixed with transarticular screws, and protected with Philadelphia collar. Other patients were fixed with plaster paris brackets. The followed-up period was 1 to 12 years with an average of 3 year and 5 months.

RESULTSAccording to Sumi's criteria, excellent 70 cases (50.7%), good 40 cases (29.0%), fair 15 cases (10.9%), poor 13 cases (9.4%). 9 cases with bone graft postponed fusion were cured by enhance external-fixation. 2 cases with nonunion were treated with revision surgery. Complication of cord injury happened in 1 case.

CONCLUSIONGallie's fusion technique is an effective method to manage the atlanto-axial instability or dislocation. Skull distraction before operation and reliable external-fixation post operative are important assistant measures. Key points for successful operation are careful wiring or cable traversing, decortication of posterior arc of C1, and maintaining the physiological height between C1 and C2 posterior arc. Indications and objectives should be conformed before revision surgery for failure cases.