ATLANTOXIAL INSTABILITY(제1,2경추 아탈구)

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Figure 1: Increase in the angle between the 1st and 2nd vertebrae, with bending in the canal leading to compression of the spinal cord.  The dens is absent, with a rounded off edge on the cranial aspect where the dens is normally projecting.

Figure 2: Note the angulation between the first and second vertebrae. 
A dens is absent in this dog.

Figure 24-2: X-rays from a one-year-old toy breed dog with congenital atlantoaxial instability. The X-ray on the left (A) is taken with the dogs neck in a normal, neutral position and the X-ray on the right shows how the first and second vertebrae separate abnormally when the dog’s neck is flexed (B). Note the marked increase in the gap between the first and second cervical vertebrae, shown by the distance between the arrowheads.

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Canine-Neurology : 1

Category Canine, 19/04/2011

 History: male Yorkshire terrier, 7 yo. Presented for acute ataxia since 4days progressing to tetraparesis. No improvement with symptomatic treatment with steroïds.

Clinical exam: Dog poorly ambulatory. Decreased proprioception on the 4 legs, deep pain sensation conserved. Lesion type MNC on the 4legs.

A cervical lesion is suspected and cervical radiographs taken.

Do you see abnormalities? Can these abnormalities explain the clinical signs?

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 There is a marked increase in space between the dorsal lamina of C2 and the dorsal neural arch of C1. On the VD view, the dens of the axis is hypoplastic. The facet joints between C1 and C2 are enlarged and uneven. There are step defects visible along both joint margins with a loss of alignment. The intervertebral disc space between C2 and C3 is reduced compared to adjacent spaces.

Assumptions: Atlanto-axial subluxation and suspected herniated disc C2C3.
Both lesions may explain the clinical signs.

A CT scan revealed a cervical atlanto-axial subluxation and hypoplasia of the dens of the axis. A slight disc protrusion has been demonstrated in C2C3.
Hypoplasia of the dens of the axis is due to a congenital malformation and predisposes to an atlanto-axial subluxation. The small breeds and toy breeds are predisposed (chihuahua..). Atlanto-axial subluxation may be present despite the presence of the dens of the axis. In this cases, a traumatic rupture of the ligaments stabilizing the dens is more likely. A fracture of the dens is also possible.
Surgical stabilization of C1 and C2 by nailing was performed.
Here under normal radiographs of another yorkshire. Note the decreased space between C1 and C2 and the well developped dens.

Assumptions: Atlanto-axial subluxation and suspected herniated disc C2C3.
Both lesions may explain the clinical signs.

A CT scan revealed a cervical atlanto-axial subluxation and hypoplasia of the dens of the axis. A slight disc protrusion has been demonstrated in C2C3.
Hypoplasia of the dens of the axis is due to a congenital malformation and predisposes to an atlanto-axial subluxation. The small breeds and toy breeds are predisposed (chihuahua..). Atlanto-axial subluxation may be present despite the presence of the dens of the axis. In this cases, a traumatic rupture of the ligaments stabilizing the dens is more likely. A fracture of the dens is also possible.
Surgical stabilization of C1 and C2 by nailing was performed.

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Congenital atlantoaxial subluxation usually causes problems in immature animals, although signs can develop at any age. It is seen most often in small breeds of dog. Instability or subluxation are usually the result of a malformed or absent dens. The dens is a small, finger-like projection from the front of the second vertebra in the neck (Figure 24-1). A normal dens has strong ligaments that anchor the first and second vertebrae together; these ligaments may be weak or absent if the dens is malformed.

Figure 24-1: 3D reconstruction of CT scans; the dens is indicated by an asterix (*). A: A normal toy breed dog. B: A toy breed dog with atlantoaxial subluxation and a malformed dens, which occupies much of the vertebral canal. X-rays of these same dogs are shown in Figure 24.2.

Neck pain and sometimes weakness or even paralysis in all four legs are the most common clinical signs. Other conditions may coexist with atlantoaxial subluxation, such as hydrocephalus (which is an abnormal accumulation of fluid within the brain) or hepatic encephalopathy and see Schulz et. al., below.

구부린목에서 비정상으로보임.

Figure 24-2: X-rays from a one-year-old toy breed dog with congenital atlantoaxial instability. The X-ray on the left (A) is taken with the dogs neck in a normal, neutral position and the X-ray on the right shows how the first and second vertebrae separate abnormally when the dog’s neck is flexed (B). Note the marked increase in the gap between the first and second cervical vertebrae, shown by the distance between the arrowheads.

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A young pomeranian was referred to us unable to stand. The referring vet had already made the diagnosis of atlantoaxial subluxation from xrays of the head and neck, viewing the neck from the side with the head in various degrees of flexion. As the neck was flexed, their x-rays showed that a gap opened up where it shouldn’t have, at the place shown by the arrows. This indicated instability between the first cervical (neck) vertbra which is called the atlas, and the second one which is called the axis. This instability was stabilised with two small screws.

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Here under normal radiographs of another yorkshire. Note the decreased space between C1 and C2 and the well developped dens.