Clinical Evaluation of a New Surgical Augmentation Technique for Transarticular Atlantoaxial Fixation for Treatment of Atlantoaxial Instability

Abstract

The feasibility of a newly developed augmentation of ventral fixation technique for surgical stabilization of atlantoaxial instability was clinically evaluated in a cohort of eleven dogs, and long-term clinical outcomes were retrospectively analyzed. The new technique combines wire/suture fixation through a transverse hole in the axis anchored by two screws placed in the alae atlantis or at the cranial end of plates used to bridge the atlantoaxial joint ventrally. A previous biomechanical study demonstrated good stability of this technique during shear loading, comparable to the stability achieved with other standard techniques. Ten dogs improved clinically after surgery and returned to a normal life within 3-6 months of surgery. One dog developed aphonia, dysphagia, and died of aspiration pneumonia three days after surgery. The augmentation of conventional ventral atlantoaxial fixation with the transverse bony corridor of the proximal axis body may be a valuable way to enhance stabilization of the atlantoaxial joint.

Keywords: atlantoaxial instability; surgical augmentation technique; surgical stabilization; toy breed dog.

Figure 1

Cadaver dissection of the cervical spine of a dog. Lateral approach. The cleidocervical muscle fibers are split, and the omotransversarius muscle is dissected at the level of the alae atlantis (white x). The atlas (a), the axis (b), the joint space between atlas and axis (arrow) and the ventral branch of the C2 nerve (c) are clearly visible after the omotransversarius muscle is dorsally retracted (∗).

Figure 2

Ventrodorsal (A) and laterolateral (B) radiographs of the atlantoaxial region directly after surgical repositioning and transarticular atlantoaxial fixation. A wire fixation was used for augmentation.

Figure 3

Sagittally reconstructed pre-operative CT image of the atlantoaxial region of the same case as in Figure 2, illustrating atlantoaxial instability with severe dorsal dislocation of the axis alongside with a hypoplastic and fragmented dens axis and occipital dysplasia.

Figure 4

Three-dimensional rendered CT images of the atlantoaxial region of the same case as in Figure 2 and Figure 3 directly after surgical repositioning and transarticular atlantoaxial fixation. The augmentation wire was cranially positioned around the heads of the screws, which were fixed in the atlas.

Figure 5

The red dot shows the location for the bone tunnel drilled into the axis, directly caudal to the articular surface. The ventral view shows the position of the wire/suture augmentation (arrow).