Ventral stabilization of C1-C2 with additional fixation of C3 using screws and polymethylmethacrylate in a toy breed dog with atlantoaxial instability.

Atlantoaxial instability (AAI) predominantly affects toy and miniature breed dogs, causing spinal cord compression and variable neurological deficits. This study aims to report a case of ventral stabilization of C1-C2 with additional fixation of C3 using screws and polymethylmethacrylate (PMMA) in a 5-month-old, 0.8 kg female Yorkshire Terrier with AAI. The patient presented with non-ambulatory tetraparesis after mild cervical trauma. Neurological examination revealed signs consistent with C1-C5 myelopathy and cervical pain. Radiographs and computed tomography of the cervical spine indicated dorsal displacement of C2 and severe spinal cord compression, confirming the diagnosis. After failure of conservative treatment, ventral stabilization was performed using 8 locked screws distributed between C1 and C3, combined with PMMA. Progressive clinical improvement was observed, with return to ambulation within 7 days and excellent neurological recovery at 165 days, with no complications during 12 months of follow-up. The stabilization technique using multiple screws and PMMA proved effective and safe in this case, enabling excellent neurological recovery even in the presence of severe neurological deficits. The inclusion of C3 in the stabilization process may have provided greater biomechanical resistance and reduced the risk of implant-related complications, representing a potentially relevant surgical approach in very small-sized patients.