Subluxation Of The Second Cervical Vertebra In Small Dog Breeds

2024 Author: Sebastian Paterson | [email protected]. Last modified: 2023-12-16 13:47

Among congenital anomalies of the spinal column, the most common in small dogs is the malformation of the first two cervical vertebrae. In dwarf breeds such as the Pekingese, Japanese Chin, Toy Terrier, Chihuahua Hua, Yorkshire Terrier and some others, because of this, not only rotational, but also non-physiological angular displacement of the second cervical vertebra relative to the first, that is, subluxation, is possible. As a result, the spinal cord is compressed, leading to very serious consequences.

Among congenital anomalies of the spinal column, the most common in small dogs is the malformation of the first two cervical vertebrae. Anatomically, the first cervical vertebra, atlas, is a ring with wings extending to the sides, planted, as on an axis, on the forward-protruding odontoid process of the second cervical vertebra - the epistrophy. From above, the structure is additionally reinforced with ligaments that attach a special crest of the second cervical vertebra to the occipital bone and the atlas (Fig. 1). This connection allows the animal to make rotational movements of the head (for example, to shake the ears), while the spinal cord passing through these vertebrae is not deformed or compressed.

In dwarf breeds such as the Pekingese, Japanese Chin, Toy Terrier, Chihuahua, Yorkshire Terrier and some others, due to insufficient development of processes and fixing ligaments, not only rotational, but also non-physiological angular displacement of the second cervical vertebra relative to the first, that is subluxation (Fig. 2). As a result, the spinal cord is compressed, leading to very serious consequences.

Puppies born with an anomaly of the first cervical vertebrae show no signs in the first months of life. They develop normally, are active and mobile. Usually, no earlier than 6 months, owners notice a decrease in the dog's mobility. Sometimes the first signs are preceded by an unsuccessful jump, fall or head injury while running. Unfortunately, as a rule, only obvious movement disorders force to see a doctor.

Weakness in the forelimbs is typical. At first, the dog is periodically unable to correctly place its front paws on the pillows and rests on a bent hand. Then he cannot rise on the front limbs above the floor and crawls on his stomach. Movement disorders of the hind limbs appear later and are not so pronounced. External examination does not reveal any neck deformities. Painful phenomena in most cases are absent.

The features described are clearly visible in Toy Terriers and Chihuahua, less pronounced in Chins and at first difficult to distinguish in Pekingese due to the large amount of wool and pedigree deformation of the paws in this breed. Accordingly, dogs of some breeds are referred to a doctor at the initial stage of the disease, and with others they come when the animal cannot walk at all.

Figure: 2 As soon as the outward displacement of the second cervical vertebra is not noticeable, the only possible way to reliably recognize this disease is X-ray examination. Two lateral views are taken. On the first, the head of the animal should be extended along the length of the spine, on the other, the head is bent to the handle of the sternum. In restless animals, short-term sedation should be used, since forcible bending of the neck is dangerous for them.

In healthy animals, flexion of the neck does not lead to a change in the relative position of the atlas and the epistropheus. The process of the second cervical vertebra in any position of the head is located above the arch of the atlas. In the case of subluxation, there is a noticeable separation of the process from the arch and the presence of an angle between the first and second cervical vertebrae. Special X-ray techniques for epistrophy subluxation are usually not required and the risk of their use is unreasonably high.

Since the displacement of the vertebrae, leading to a dysfunction of the spinal cord, is due to anatomical reasons, the treatment of epistrophy subluxation should be surgical. Fixing the head and neck of the animal with a wide collar, prescribing various medications gives only a temporary effect and often only aggravates the situation, since the restoration of the mobility of the sick animal leads to further destabilization of the vertebrae. Sometimes it can be used to prove to pet owners that the problem is not in the paws and the effect of conservative treatment will only be temporary.

There are several ways to stabilize an overly mobile connection between the Atlantean and the Epistropheus. In the foreign literature, methods are described aimed at obtaining a motionless fusion between the lower surfaces of the vertebrae. Probably these methods have their advantages, but the absence of special plates and screws, as well as the high risk of spinal cord injury if they are improperly located on the tiny vertebrae of small dogs, make these methods inapplicable in practice.

In addition to these methods, it is proposed to attach the process of the second cervical vertebra to the arch of the atlas with wire or non-absorbable cords. Moreover, the second approach is considered insufficiently reliable due to the possibility of secondary displacement of the vertebrae.

In recent years, our clinic has been using lavsan cords to fix the vertebrae according to an original technique. To gain access to the problem area of the spine, the skin is cut from the occipital crest to the third cervical vertebra. The muscles in the midline, focusing on a well-defined epistrophic crest, partly sharply, partly bluntly, move apart to the vertebrae. Carefully, the crest of the second cervical vertebra is released from the soft tissues along the entire length. Then, very carefully, the muscles are separated from the arch of the first cervical vertebra. Due to the insufficient development of the first and second cervical vertebrae and their displacement, the gaps between them gap widely, which makes possible damage to the spinal cord at this moment.

Widely spreading the muscles, dissect the dura mater along the anterior and posterior edges of the atlas arch. This moment of the operation is also very dangerous. Since the use of one loop around the Atlanta bow is generally considered not reliable enough, we use two cords that are guided independently of each other. The result is a more reliable system that allows movement between the vertebrae to be within physiological limits, but prevents pressure resumption on the spinal cord.

The threads should be as careful as possible; the angular displacement of the vertebrae, which is inevitable at this moment, should be minimized. Since all manipulations are carried out in the area of the location of vital centers and it is quite possible that breathing is disturbed, intubation and artificial ventilation of the lungs are performed before the operation.

Careful preoperative preparation, maintenance of vital functions during the operation, careful manipulation of the wound, anti-shock measures at the exit from anesthesia allow minimizing the risk of surgical treatment of epistrophy subluxation, but it still remains, and the dog's owners should be warned about this. Since the decision to carry out the operation is finally made by them, the decision must be balanced and deliberate. Pet owners must understand that there is no other way out, and part of the responsibility for the fate of the dog lies with them.

With rare exceptions, the results of surgical treatment are good or excellent. This is facilitated not only by the operation technique, but also by the correct postoperative rehabilitation of the animal. There is a complete restoration of motor ability, we observed relapses only when we used the traditional technique with a wire loop. We consider external neck braces unnecessary.

Thus, timely recognition of this congenital anomaly, which should be facilitated by the neurological alertness of the physician performing the initial examination of dogs of breeds susceptible to this problem, allows for correct treatment and a quick recovery of the affected animal.