Abstract: Objective To apply the method of percutaneous anterior lateral mass fixation for instability of C_1-2 vertebral fracture and determine the outcome of the method by radiology.Methods Thirty-eight cases of C_1-2 instability including 10 cases of Jefferson's fracture, 12 cases of anterior arch fractures of C₁, 7 cases of atlantoaxial dislocation, 5 cases of atlantoaxial subdislocation, and 4 cases of dental old fracture with dislocation were treated with percutaneous anterior lateral mass screws and bone grafting with new designed hole instrumentations. All the patients were followed-up after operation and assessed the screws position by X-ray and CT.Results All casesreached a satisfactory results of fixation without injuring the vertebral artery and spinal cord. Two screws were in poor position. One screwcame loose a year after operation, another screw went into the vertebral artery groove, but no vertebral artery injury. All the other screwswere in good position.Conclusion The operation procedure for instability of C_1-2 has the advantage of simplicity, less trauma and minimized bleeding. The operation procedure is safe with reasonable instrumentations and correct selection of the puncture point, angle and depth.

Key words: atlanto-axial instability, internal fixation, percutaneous