Luna Bell’s examination indicates a neurological problem affecting the C1-C5 spinal cord. She is alert and responsive, has normal cranial nerves, has postural reaction deficits in all four limbs, but has normal spinal reflexes in all four limbs.

Possible causes include a malformation such as atlantoaxial instability, Chiari-Like Malformation (CM) and Syringomyelia (SM), meningitis/myelitis, infection, slipped disk (unlikely based on age), tumor (unlikely based on age) or other less likely cause.

Radiographs of the cervical vertebral column were performed.

There is increased space between the dorsal aspect of C1 and the cranial/dorsal aspect of C2. There is subluxation at C2 relative to C1, with dorsal angulation of the caudal portion. Note that one cannot visualize the spinal cord, or the intervertebral disks. Additionally, there is overlap of structures within the cervical region. Atlantoaxial instability (AAI) and subluxation was diagnosed through the radiographs.

Magnetic resonance imaging (MRI) was performed to further define the abnormalities. Multiple congenital abnormalities can occur concurrently (e.g. synovial cyst associated with AAI, etc). MRI shows these soft tissue abnormalities best and is the only way to diagnose CM and SM.

MRI is superior for evaluating the soft tissues of the brain, spinal cord, meninges and disks. Note the ‘kinking’ of the cranial cervical spinal cord where it is being compressed by the dorsal subluxation of C2 relative to C1.

At Southeast Veterinary Neurology (SEVN), we typically perform computed tomography (CT) scan prior to surgery. While MRI is the ideal way of imaging the spinal cord and brain, CT is excellent for evaluating the bone. The treatment of choice for atlantoaxial instability is surgical stabilization with screws and bone cement. Since AAI is typically diagnosed in small dogs (sometimes less than one kg), pre-operative planning for size and angle of the implants is indicated. Below is a three dimensional (3D) reconstruction of Luna Bell’s cervical vertebral column and caudal skull. CT and MRI are able to be performed under the same anesthetic period at SEVN.

At SEVN, we have the ability to print 3D images of our CTs. Below is a 3D print of Luna Bell’s vertebral column. This can be used to help plan the surgery.

An atlantoaxial stabilization procedure was scheduled. Stabilization is provided by forming an arthrodesis at C1-2. There are several reported ways of providing stabilization. The preferred method at SEVN is with multiple screws placed into C1 and C2 (+/- C3) fused with polymethylmethacrylate. The size and number of implants depends on the size of the patient. Below is a photograph from Luna Bell’s surgery. In the upper left, there is a video screen that shows a low-resolution version of what Dr. Wong is seeing through the operating microscope. On the screen, we are viewing the ventral aspect of the vertebral column. Cranial is toward the left of the screen and the left side of the dog is toward the top of the screen. Three 1.5 mm titanium self-drilling screws have been placed into C1. Three screws have also been placed into C2. There are two in the cranial aspect of C2 and one on midline in the caudal aspect of C2. The articular cartilage at C1-2 is debrided with a #11 scalpel blade and house curette. In larger dogs, a small burr can be used to remove the articular cartilage. The joint is packed with bone graft. Polymethylmethacrylate is then placed over the screws to stabilize the construct.

Post-operatively, another CT scan was performed to ensure proper placement of the screws, excellent coverage of the screws by the bone cement and reduction of the subluxation. Here is a 3D reconstruct of the post-op CT. Notice that the subluxation is reduced and that there is excellent alignment. The screw placement was perfect with excellent bone purchase and angulation.

Post-operatively, Luna Bell was placed into a neck brace to limit her activity and stress on the arthrodesis. She is doing well and is recovering. She is walking well and has not had any evidence of pain.

Sixteen year-old Domestic Shorthair


What do you see?


MRI of Luna Bell’s head and neck


Luna CT

luna screw placement

luna's screw placement


Luna's CT post treatment

Luna post treatment

Luna post treatment