Atlantoaxial instability/subluxation (AAS/AAS) is a state of hypermobility caused by loss of ligamentous support (especially associated with aplasia, hypoplasia, and dorsal deviation of the dens) of the joint between the atlas and axis. It is most commonly seen in toy breed dogs under 1 year of age due to congenital and developmental reasons. It is seen in dogs of all breeds and ages with traumatic instability. It can cause neck pain, severe neurological dysfunction such as tetraplegia and death due to sudden respiratory arrest. Treatment of AAI/AAS can be conservative and surgical. Conservative treatment is preferred in patients with mild clinical manifestations.Our case is a 3-year-old, 2.5 kg Toy Poodle breed dog, referred to Istanbul University Cerrahpaşa Training and Practice Animal Hospital Surgery Clinic. It had been reported that the dog suddenly stop breathing after jumping from the owners lap, and its breathing was restored with CPR in the nearest clinic. In the clinical examination; tetraplegia, severe neck pain and respiratory distress were detected. After first intervention of the patient, cervical region had been evaluated with LL radiography, Magnetic Resonance Imaging (MRI) and Computed Tomography. Focal hyperintensity had been observed on T2-weighted sequences at this level with slight dorsal angulation of dens. It was considered as posttraumatic edema. For pre-surgical planning, a model output was created by generating 3D-CT reconstruction images of the atlantoaxial region. Standard ventral transarticular stabilization technique was applied to the patient with a threaded Steinman pin after determining the entry points ,diameters, angles and advancement depths on this model. Postoperatively, the position of the pins was checked with CT. On the 4th day after the operation, it was observed that the neck pain disappeared and patient started to move voluntarily, and on the 6th day it started walking. The biggest complication of atlantoaxial instability surgery is, cardiovascular arrest due to medulla oblongata or spinal cord injury because of incorrect implant placement. We think that surgical planning on the 3D model obtained from the CT images of the patient reduces the risk.