# C1 Facetectomy and Ventral Fixation of Occipitoatlantoaxial Complex for Concurrent Congenital Atlanto-Occipital Dislocation and Atlantoaxial Instability in a Toy Poodle

## TL;DR

A Toy Poodle with rare spinal disorders was successfully treated using a novel surgical approach, leading to significant recovery.

## Contribution

This is the first report of a ventral surgical approach for concurrent congenital atlanto-occipital dislocation and atlantoaxial instability in dogs.

## Key findings

- The dog showed recovery of ambulation and gradual gait improvement after surgery.
- Postoperative imaging confirmed successful spinal cord decompression.
- The dog maintained a normal gait with no pain over a 21-month follow-up period.

## Abstract

This case report details the treatment of a dog diagnosed with concurrent congenital atlanto-occipital dislocation and atlantoaxial instability, a rare condition in dogs. The surgical approach, which had not been previously reported for such cases, involved ventral facetectomy and stabilization using screws, wire, and polymethyl methacrylate from the occipital bone to C2. This novel procedure provided valuable insights into the management of complex cranio-cervical junction disorders in veterinary neurosurgery.

An 8-month-old, 3.4 kg, castrated male Toy Poodle was referred for progressive tetraparesis and respiratory disorder without a history of trauma. Repeated computed tomography (CT) and magnetic resonance imaging (MRI) with different positions of the neck revealed concurrent atlanto-occipital dislocation (AOD) and atlantoaxial instability (AAI) with spinal cord compression. This case was unique due to its congenital nature and the absence of trauma. The surgical treatment involved precise removal of the C1 vertebra’s ventral articular facet, which was compressing on the spinal cord, attributed to its fixed and malaligned position within the atlantooccipital joint. Following facetectomy, the stabilization of the occipital bone to the C2 vertebra was achieved by screws, wire, and polymethyl methacrylate. Two days after surgery, the dog recovered ambulation and showed gradual improvement in gait, despite mild residual ataxia. Postoperative CT and radiographs showed successful decompression of the spinal cord. The screw loosening was confirmed at 114 days, which was managed successfully by extracting the affected screws. Through the 21-month monitoring period, the dog showed a normal gait with a wide-based stance of the pelvic limbs when standing and experienced no pain. This case represents the first report of concurrent congenital AOD and AAI treated with a ventral surgical approach, contributing new insights to the understanding and management of such complex cranio-cervical junction disorders in veterinary neurosurgery.