Islandic horse, male castrated. 6 years of age. Since 4 weeks, the owner noted an abormal gait and stiff neck. Private vet treated him for a muscular problem. Considering the lack of improvement, the horse was referred at the veterinary clinic of the university.
- At the clinical examination the horse was painful in the region of the neck.
- He could not flex the neck to the right and only minimal to the left.
- X-rays of the neck were taken.
Laterolateral view of the occiput an the cervical vertebrae C1 –C2. Radiographic changes
- There is a mild malalignment of the cervical vertebrae at the level of C1-C2.
- The dens of the axis is displaced ventrally.
- The dens of the axis against the ventral atlas provokes a rotation of C1 cranioventrally.
- There is a very small separated mineral opacity ventral to the dens.
- Other bony structures are within normal limits.
Radiographic diagnosis
- Atlantoaxial luxation with corresponding soft tissue damage (tear or rupture of the ligament of the dens of the axis).
- Possible small bony fragments.
- The owner accepted an attempt of close reposition of the luxation.
- Before that and in the same anesthetic session, the horse underwent to CT.
CT Images in a bone window, transverse scan at the level of the dotted line and sagittal sagittal reconstruction at the midline. On the sagittal view, at this level, the dens of the axis should be visible in contact with the articular surface of the ventral arch of the axis.
- In the presented case there is a loss of contact of the dens of the axis from the articular surface of the ventral arch of the atlas and its dislocation ventrally.
- There are multiple, small mineral dense opacities dorsal and ventral to the dens, dorsal to the body of the atlas in the spinal canal. These represent small bony fragments, associated with the articular surfaces or with damaged ligaments or surrounding soft tissues. Mild bone proliferation post trauma also possible.
- In the soft tissue window (not shown) the spinal cord at the level of C1-2 was mild dorsally dislocated.
- The general condition of the horse was deteriorating the following days and the owner elected euthanasia.
3D reconstruction of the atlantoaxial luxation. Laterolateral view, mildly obliqued from ventral left to dorsal right. The dens (arrow) of the axis is visible dislocated as described and surrounded by multiple small bone fragments. The endotracheal tube was removed from the reconstructed images. Comments
- Luxation of the atlantoaxial articulation is described in foals with congenital malformation of the dens.
- Traumatic luxation of this region seems to occur rarely.
- Successful reduction has been reported in horses less than 200Kg of body weight, one case report in a Warmblood of 500Kg of body weight after acute luxation.
- In foals, luxation can be reduced manually.
- An atlantoaxial luxation is characterised and accompanied by a disruption of the longitudinal and paired ligaments at the apex of the dens of the axis.
