Atlantoaxial instability (subluxation) in dogs. Dorsal stabilization for atlantoaxial instability in toy dog breeds Atlanto axial instability

Atlantoaxial instability or atlantoaxial dislocation in dogs causes a symptom complex of disorders that is characterized by the appearance of neurological problems.

The dog may be forced to hold its head up, weakness of the pelvic and thoracic limbs appears, loss of coordination and a sharp decrease in appetite. The severity of the disorder directly depends on the degree of instability and the underlying causes.

Atlantoaxial instability in dogs can be acute or chronic.

What's happening?

The normal anatomical relationship between the first (C1) and second cervical vertebra (C2) is disrupted, resulting in their displacement relative to each other and compression of the spinal cord structures (Fig. 1a, b).

The main causes that can cause instability of C1-C2 are the following: hypoplasia, aplasia of the odontoid process, malformations, articular fracture, rupture of the dorsal ligament, or a combination of these.

A true traumatic factor is rare and occurs mainly in large dogs.

Who is sick?

This disease mainly affects dwarf dog breeds, such as Yorkies, Spitz, and Toy terriers. The hereditary factor is determined.

Diagnosis of atlantoaxial instability

When examining these patients, the specialist must be very careful in manipulating the head so as not to cause possible secondary damage. The main and accessible diagnostic method is x-ray examination.

A lateral X-ray shows a ventral displacement of C1 relative to C2. A displacement of 2-4 mm indicates the presence of pathology (photo 1).

To assess the condition of the odontoid process, a direct projection with forced rotation of the head is performed.

Often, in patients aged 4 months or older with atlanto-axial instability, a wide open “fontanel” remains, evidence of increased intracranial pressure. Here it will be valuable to conduct an ultrasound examination of the brain (photo 2) and an assessment of the cerebrospinal fluid to exclude related problems. Inflammatory processes in the form of meningoencephalitis can be associated problems.

Treatment of atlanoaxial instability

There are conservative and surgical methods for treating atlantoaxial instability.

First of all, it is necessary to make a neck corset to limit the rotation of the head and neck. Anti-inflammatory drugs are also used.

The goal of conservative therapy is to provide temporary anatomical stability to enable the formation of scar-connective tissue in the area of the vertebral joints.

The surgical method will be the main one, since it has a higher percentage of favorable outcomes and good results immediately after surgery.

The main goal of surgical treatment is to fix the vertebrae in an anatomically correct position using various methods and designs.

There is a method of dorsal and ventral stabilization.

Each method has its own advantages and disadvantages.

With dorsal stabilization, it is difficult to design a fixation structure that will accommodate displacement load forces (Figure 3). However, even with minor postoperative displacement, these patients may feel well.

Today, the ventral stabilization method is considered the most effective (photo 4). Complete fixation of the articular surfaces of the atlanto-axial joint is carried out using knitting needles, screws, etc. depending on the size of the dog.

Forecast

If conservative treatment is not successful within 50-80 days, then it is necessary to focus on surgical correction.

If, after starting conservative treatment, neurological signs do not go away or worsen, then surgical treatment is urgently needed.

Surgical treatment of atlantoaxial instability in dogs under 7 months of age and weighing up to 1.5 kg should be performed by an experienced surgeon, since the bone tissue is not yet “mature”, and complications of structural failure can be fatal. If a relapse of the disease occurs in the early postoperative period, the prognosis will be cautious.

Atlanto-axial instability is a pathological condition associated with an unstable connection of the first (atlas) and second (axis or epistrophy) cervical vertebrae. This is primarily due to the underdevelopment of the ligamentous apparatus of the epistrophic tooth (second cervical vertebra). As a result, the tooth is more unstable. This becomes especially important when the head moves up and down. The fact is that this tooth is located in the spinal canal and is located in close proximity to the spinal cord (Figure 1). Therefore, with every movement in the neck there is a risk of damage to the latter. As a result of atlantoaxial instability, spinal compression (squeezing) occurs, which causes deterioration of blood circulation in the area of the pathological focus and, as a consequence, dysfunction of the nerve conduction of the spinal cord. In a simplified way, this can be imagined as a watering hose (spinal cord) on which a stone (epistropheus tooth) was placed. The larger the stone, the stronger the pressure on the hose, the worse the water (nerve impulses) flows through the hose.

As a rule, this disease is observed in decorative dwarf dogs.

Clinical signs

Atlantoaxial instability is a congenital pathology. However, this does not mean that clinical signs develop from the first days of life. In the vast majority of cases, the manifestation of the disease occurs in the first year. Less commonly, the disease manifests itself at a later date. And most often, owners simply do not notice clinical manifestations unless they are global in nature.

Mostly, Chihuahuas, toy terriers, and Yorkshire terriers suffer from this disease. It is also found in King Charles Spaniels, Miniature Pinschers, Papillons, Pomeranians and many other representatives of toy breeds.

As a result of atlantoaxial instability, a number of neurological signs can be observed:

The first thing you should pay attention to is pain in the neck, which can manifest itself as shortening and thickening of the neck, tension in this area, stiffness of movement not only of the head and neck, but also of the dog as a whole (especially the forelimbs). Sometimes pain is detected only when lifting or touching the neck.
Often such dogs walk with their heads down, as if they have done something wrong (the “Guilty Dog” pose).
In more severe cases, there is a lack of coordination of movements of the limbs, which can manifest itself as a prancing gait of the front legs (dysmetria), or more severe disorders (unsteadiness, falling to one side, incorrect positioning of the limbs, as if the dog was drunk).
Owners often note instability of the head, which is expressed by rolling (wobbly) of the head from left to right, like a puppet.
In extreme situations, paralysis of all four legs is possible.

If you find any of the listed signs in your pet, immediately contact our clinic for consultation, urgent diagnosis and assistance. Sometimes a delay of more than 12 hours from the moment the first symptoms appear leads to the development of irreversible processes that are detrimental to the animal.

Diagnostics

When patients with suspected atlanto-axial instability appear at the AVERS veterinary clinic, the severity of the disease is assessed. Next, during an examination by a neurologist, the ability to move and reflexes are checked, which is very important for making an accurate diagnosis. In particular, the following are assessed:

Mental status (patient's level of consciousness)
Reflexes of the cranial nerves to exclude brain pathologies (for example, craniocervical malformation). Because the symptoms of these diseases are often similar.
Posturing reflexes (postural reflexes, proprioception)
Own reflexes of the spinal cord (lower motor neuron reflexes), such as the withdrawal reflex of the thoracic and pelvic limbs, the knee reflex, the anal reflex.

It is also worth excluding banal weakness, which may be associated with diseases of other organ systems. For example, with a viral infection, failure or severe weakness of the pelvic limbs is often recorded.

Additional research methods in our clinic are often used:

X-ray of the cervical spine in lateral projection. Including the use of stress films, when the patient's head is pressed tightly to the chest (Figure 2), which is often more indicative of the problem described.
If the situation does not require emergency treatment, an MRI (magnetic resonance imaging) or CT (computed tomography) scan may be needed to confirm the diagnosis. These studies also make it possible to exclude concomitant pathologies of the brain, cervical spine and spinal cord, which can radically change treatment tactics.
If the situation is urgent, and there is no MRI or CT scan at hand, then myelography (a series of radiographs with the introduction of a contrast agent into the spinal canal) can be performed to confirm the diagnosis and exclude concomitant pathologies of the cervical spine.

Pathologies associated with atlantoaxial instability

It is not uncommon that, along with atlantoaxial instability, other pathologies of the nervous system and surrounding tissues are recorded. They can be divided into 2 groups:

Diseases that are a consequence of the underlying problem
Diseases that develop independently of atlantoaxial instability.

The first group includes problems such as hydrocephalus and syringomyelia. These are diseases in which stagnation of cerebrospinal fluid (cerebrospinal fluid) occurs in the natural cavities of the brain and spinal cord, respectively. The fact is that the compression caused by the instability we are talking about partially or completely blocks the flow of cerebrospinal fluid along the cerebrospinal fluid pathways, just as platinum blocks the flow of a river. Which in turn leads to the accumulation of cerebrospinal fluid in the cerebral ventricles and the spinal canal. If hydrocephalus or syringomyelia are detected during diagnosis, the prognosis of the disease worsens sharply.

Diseases of the second group include craniocervical malformation, degenerative diseases of the intervertebral discs (“herniated intervertebral discs”) of the first and second types, otitis media, meningoencephalitis. In all of these diseases, the symptoms are very similar to the manifestations of atlanto-axial instability. It should also be noted that all of the above problems are characteristic of the same dwarf dog breeds.

Therefore, it is very important to conduct a full diagnosis of such patients. Since the identification of one or another concomitant pathology can lead to fundamental changes in the treatment tactics of such a patient. Conversely, the lack of information about an additional problem not only leads to a lack of treatment results, but can also be fatal for your pet.

Treatment

To develop treatment tactics for atlantoaxial instability, it is first necessary to assess the severity of clinical symptoms. If necessary, your pet will be provided with emergency neurological care, which includes decongestant therapy and elimination of the consequences caused by the disease. Such therapy often provides time for a full diagnosis of the patient, since quite often this disease requires the use of emergency therapeutic and diagnostic measures. However, this is not a full-fledged treatment, but only temporary support for the patient.

Treatment of atlantoaxial instability is carried out only by surgery. There are several ways to fix this problem. But the essence of all operations comes down to stabilizing the first two cervical vertebrae in an anatomically correct position. Without going into details, all methods can be divided into two types:

Dorsal stabilization (stabilization from the upper side of the spine)
Ventral stabilization (lower side)

Dorsal stabilization (Figure 3) is simpler in terms of execution, but is an older and, often, more dangerous method. The danger lies in the fairly frequent relapses (renewal) of the disease and the risk of damage to the cerebellum with concomitant pathologies (for example, craniocervical malformation), which often go hand in hand with atlantoaxial instability. The essence of the method is the fixed connection of the epistrophic ridge with the arch of the atlas using cerclage (medical) wire.

The second, more progressive method is ventral stabilization (Figure 4). There are several varieties of this method of treatment. But they all boil down to fixing the bodies of the first two vertebrae with screws in a stationary state. This method is more reliable, but requires more training for the surgeon, since it is more technically complex. In our clinic, we usually use this method for treating atlantoaxial instability.

Cost of diagnosis and treatment of atlanto-axial instability at the AVERS veterinary clinic

The AVERS veterinary clinic treats neurological patients, including those with atlantoaxial instability. This is a rather complex pathology that requires a comprehensive diagnostic and treatment approach, which includes:

Examination by a neurologist
Laboratory and instrumental research
Surgery.

It's worth seeing a neurologist ) .

In a planned situation, 2-3 x-rays will be taken: a standard x-ray of the cervical spine in the lateral projection and a stress x-ray in the same projection; an x-ray of this area in the frontal projection may also be required. The cost of one x-ray is ) .

If the situation is urgent, then in such cases we perform myelography of the cervical spine. This is a specialized neurological study, which consists of a series of x-rays of the spine with the preliminary introduction of a contrast agent into it. Naturally, such manipulation is performed under general anesthesia (anesthesia). The cost of this study is ) + cost of anesthesia () + cost of consumables.

As a rule, such an examination algorithm is sufficient to make a final diagnosis and exclude pathologies associated with atlantoaxial instability.

If the diagnosis is confirmed, then in the vast majority of cases the patient will undergo surgery to stabilize the atlantoaxial joint, the cost of which is () + cost of anesthesia ) + cost of drugs and consumables.

Despite the significant budget for all activities related to the diagnosis and treatment of this pathology, the prices of our clinic are average in Moscow for veterinary institutions that have the appropriate specialists and equipment.

For more complete cost information, call our clinic.

Neurosurgeon-traumatologist at VK "AVERS"

Candidate of Biological Sciences

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

Among congenital anomalies of the spinal column, the most common in small dogs is the abnormal formation of the first two cervical vertebrae. Anatomically, the first cervical vertebra, the atlas, is a ring with wings extending to the sides, mounted, as if on an axis, on the protruding odontoid process of the second cervical vertebra - the epistrophea. From above, the structure is additionally strengthened by ligaments that attach a special crest of the second cervical vertebra to the occipital bone and atlas (Fig. 1). This connection allows the animal to make rotational movements with its head (for example, shaking its 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 the processes and fixing ligaments, not only rotational, but also non-physiological angular displacement of the second cervical vertebra relative to the first is possible, that is subluxation (Fig. 2). As a result, compression of the spinal cord occurs, leading to very serious consequences.

Puppies born with an anomaly of the first cervical vertebrae do not show any 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 appearance of the first signs is preceded by an unsuccessful jump, a fall, or a head injury while running. Unfortunately, as a rule, only obvious movement disorders make you see a doctor.

A typical sign is weakness of the forelimbs. At first, the dog periodically cannot place its front paws correctly on the pillows and relies on a bent hand. Then he cannot rise on his forelimbs above the floor and crawls on his stomach. Motor disorders of the hind limbs appear later and are not as pronounced. No neck deformities are detected during external examination. In most cases there are no pain symptoms.

The described signs are clearly visible in toy terriers and Chihuahuas, less pronounced in chins and at first difficult to distinguish in Pekingese due to the large amount of hair and breed-specific deformation of the paws of this breed. Accordingly, some dogs of some breeds go to the doctor in the initial stage of the disease, while others come when the animal cannot walk at all.

Rice. 2 Since the displacement of the second cervical vertebra is not externally noticeable, the only possible way to reliably recognize this disease is an x-ray examination. Two photographs are taken in lateral projection. In the first, the animal’s head should be extended along the length of the spine; in the other, the head is bent towards the handle of the sternum. In restless animals, short-term sedation should be used, since forceful flexion of the neck poses a danger to them.

In healthy animals, flexion of the neck does not lead to a change in the relative position of the atlas and epistrophe. The process of the second cervical vertebra is located above the arch of the atlas in any position of the head. In the case of subluxation, there is a noticeable departure of the process from the arch and the presence of an angle between the first and second cervical vertebrae. Special radiological 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 dysfunction of the spinal cord, is due to anatomical reasons, the treatment of epistrophic subluxation must be surgical. Fixing the animal's head and neck with a wide collar and prescribing various medications gives only a temporary effect and often only aggravates the situation, since restoring the mobility of a sick animal leads to further destabilization of the vertebrae. Sometimes it can be used to prove to animal 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 the excessively mobile connection of the atlas and epistrophe. Foreign literature describes methods aimed at obtaining a fixed fusion between the lower surfaces of the vertebrae. These methods probably have their advantages, but the lack of special plates and screws, as well as the high risk of damage to the spinal cord if they are incorrectly positioned 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 not reliable enough due to the possibility of secondary displacement of the vertebrae.

Over the past years, our clinic has been using vertebral fixation with Mylar cords using an original method. To gain access to the problem area of the spine, the skin is incised from the occipital crest to the third cervical vertebra. The muscles along the midline, focusing on the well-defined crest of the epistrophy, partly sharply, partly bluntly, move apart to the vertebrae. The crest of the second cervical vertebra is carefully removed from soft tissue throughout its 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 spaces between them gape widely, which makes possible damage to the spinal cord at this moment.

By spreading the muscles wide, the dura mater is dissected along the anterior and posterior edges of the arch of the atlas. This moment of the operation is also very dangerous. Since the use of one loop around the arch of the atlas is, in general opinion, not reliable enough, we use two cords, passed independently of each other. The result is a more reliable system that allows movement between the vertebrae within physiological limits, but prevents the resumption of pressure on the spinal cord.

The insertion of the threads should be as careful as possible; the angular displacement of the vertebrae, inevitable at this moment, should be minimized. Since all manipulations are performed in the area where vital centers are located and breathing problems are quite possible, intubation and artificial ventilation of the lungs are performed before the operation begins.

Careful preoperative preparation, maintaining vital functions during surgery, careful manipulation of the wound, and anti-shock measures upon recovery from anesthesia make it possible to reduce the risk of surgical treatment of epistrophic subluxation to a minimum, but it still remains, and dog owners should be warned about this. Since they ultimately make the decision to carry out the operation, the decision must be balanced and deliberate. Animal 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 surgical technique, but also by properly performed 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 fixators unnecessary.

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

Atlantoaxial instability typically occurs in small breed dogs and begins clinically in young animals, although it can occur at any age. This condition can be inherited or result from injury. With atlantoaxial instability, subluxation, or displacement, of the second cervical vertebra (epistrophy) relative to the first (atlas) occurs, followed by compression of the spinal cord, which leads to severe neurological symptoms: tetraparesis, paralysis, and proprioceptive deficit. The disease may be accompanied by hydroencephaly and syringohydromyelia. Among the main causes of atlantoaxial instability are the following:

Abnormal shape of the odontoid process or its absence
Underdevelopment of the odontoid ligaments
Post-traumatic rupture of the atlantoaxial ligaments
Fracture of the odontoid process due to trauma (strong flexion of the neck)

Anatomically, there are no intervertebral discs between the occipital bone, atlas and epistropheus, and these vertebrae form a flexible segment of the cervical spine, providing good mobility of the neck. The interaction between the first and second cervical vertebrae is carried out due to the articular surfaces, ligaments and the odontoid process of the epistrophe, which enters the fossa of the atlas tooth. The odontoid process, in turn, is fixed by the longitudinal and alar ligaments, as well as the transverse ligament of the atlas. The epistrophic crest is attached to the dorsal arch of the atlas by the dorsal atlantoaxial ligament.

Rice. 1 - ligamentous apparatus of the atlanto-axial joint.

Rice. 2 - congenital absence of the odontoid process, predisposing to rupture of the dorsal atlantoaxial ligament and leading to the displacement of the epistrophy dorsally, and the atlas - ventrally.

Rice. 3 - fracture of the odontoid process and rupture of the transverse atlas ligament, rupture of the dorsal atlanto-axial ligament (can occur independently of each other).

Normally, the odontoid process is fixed by strong ligaments that reliably articulate the first two vertebrae. These ligaments can be weak or underdeveloped and can be damaged by the slightest impact on the cervical spine. If the odontoid process has an abnormal shape, then the ligaments, as a rule, are torn, and the epistrophy is displaced relative to the atlas. The odontoid process may be completely absent - in this case, the vertebrae are not fixed in any way, which also leads to subluxation of the atlanto-axial joint and compression of the spinal cord. Although atlantoaxial instability is a congenital disorder found in small breeds, ligament rupture and subsequent vertebral displacement can occur as a result of trauma in any animal.

Clinically, the disease manifests itself as pain in the cervical spine, as well as partial or complete loss of sensitivity, paresis and paralysis. Proprioceptive deficits, resulting from an excessive increase in the amount of cerebrospinal fluid in the cranial cavity (hydroencephaly), are characterized by impaired motor skills and coordination of movement. Congenital atlantoaxial instability is often combined with syringohydromyelia (formation of cysts and cavities in the central canal of the spinal cord).

Some dogs with congenital AO instability also have portosystemic shunts: this may be due to the inheritance of genes that influence the development of these two diseases. Thus, if one of them is detected, it is advisable to conduct diagnostic studies aimed at identifying (or excluding) the other.

The disease is diagnosed based on X-ray examination. A radiograph of an animal with AO instability shows a sharp increase in the space between the epistrophic crest and the dorsal arch of the atlas, which indicates a rupture of the dorsal atlantoaxial ligament. With a fracture of the odontoid process and its abnormal shape, the lower contour of the epistrophy is displaced dorsally and does not coincide with the lower contour of the atlas (the dorsal AO ligament may be intact, and the separation of the atlas from the epistrophy may not be observed).

Rice. 4 - radiographs: normal spine (A), AO instability (B). White arrows indicate an increase in the distance between the epistrophic crest and the dorsal arch of the atlas

The images are taken in a lateral projection, with the head bent at the cervical spine, which should be done extremely carefully, since excessive force directed at the damaged segment of the spine can cause damage to the spinal cord. Direct and axial views can also be useful in assessing the shape of the odontoid process. Myelography is contraindicated because it can cause unnecessary compression of the spinal cord and cause seizures.

Computed tomography provides more detailed diagnostic information than x-ray examination. However, the presence or absence of syringohydromyelia can be concluded only from the results of MRI. These diagnostic methods are associated with anesthetic risk, since the animal must be under general anesthesia at the time of the study.

Rice. 5 - computed tomograms: A - normal, B - AO instability. An asterisk indicates an abnormal odontoid process; the displacement of the lower contour of the epistrophe is indicated by a white arrow.

Treatment is mainly surgical, aimed at fixing the vertebrae with wire cerclages or bone cement. If the odontoid process has an abnormal shape, its resection is performed. If there are cysts in the central canal of the spinal cord, they are drained.

Conservative treatment is also possible, when the animal is placed in a cage and the cervical region is immobilized with a bandage. But it is ineffective and is mainly used as a temporary measure for animals that have contraindications for surgery, for example, with deep paresis and an individual who is too young. This treatment aims to stabilize the animal before surgery and allows young animals to reach a relatively safe age for surgery.

According to D.P. Beaver and others, the prognosis for dogs with congenital AO instability is in most cases favorable if the animal survives the operation and tolerates the postoperative period well. Operative mortality reaches about 10% of cases, and about 5% of animals require reoperation.

With atlantoaxial instability, the normal anatomical relationship between the first (C1) and second cervical vertebrae (C2) is disrupted, resulting in their displacement relative to each other and compression of the spinal cord structures.

Atlas instability in dogs can be acute or chronic.

The acute form is usually an injury with a separation of the ligamentous apparatus. A true traumatic factor is rare and occurs mainly in large dogs.
The chronic form of instability of the atlanto-axial joint is the most complex variant of the disease, where it is aggravated by dysplastic manifestations of the osteoarticular apparatus. This form of the disease poses a problem from the point of view of surgical treatment using traditional techniques.

The main reasons that can cause instability of C1-C2:

hypoplasia,
aplasia of the odontoid process,
malformations,
articular fracture,
dorsal ligament rupture
combination of reasons.

Symptoms of atlantoaxial instability

Dislocation of the atlas in dogs causes a complex of disorders, which is characterized by the appearance of neurological problems.

the dog may be forced to hold its head up,
weakness of the pelvic and thoracic limbs appears,
lack of coordination
a sharp decrease in appetite.

The severity of the disorder directly depends on the degree of instability and the underlying causes.

Breed predisposition

This disease mainly affects dwarf dog breeds, such as Yorkies, Spitz, and Toy terriers. The hereditary factor is determined.

Atlantoaxial instability in Yorkies

Diagnosis of atlantoaxial instability

A lateral X-ray shows a ventral displacement of C1 relative to C2. A displacement of 2-4 mm indicates the presence of pathology.

To assess the condition of the odontoid process, a direct projection with forced rotation of the head is performed.

Often, in patients over the age of four months with atlantoaxial instability, a wide open “fontanel” remains - evidence of increased intracranial pressure. Here, performing and evaluating the cerebrospinal fluid to rule out associated problems will be valuable. Inflammatory processes can cause such problems, and meningoencephalitis appears in dogs.

Atlanto axial instability in dogs treatment

There are conservative and surgical methods for treating atlantoaxial instability.

Conservative treatment

First of all, it is necessary to make a neck corset to limit the rotation of the head and neck. Anti-inflammatory drugs are also used.

The goal of conservative therapy is to provide temporary anatomical stability to enable the formation of scar-connective tissue in the area of the vertebral joints.

Surgery

The surgical method will be the main one. It has a higher percentage of favorable outcomes and good results immediately after surgery. The main goal is to fix the vertebrae in an anatomically correct position using various methods and structures.

There is a method of dorsal and ventral stabilization. Each method has its own advantages and disadvantages.

At dorsal stabilization It is difficult to make a fixation structure that will respond to displacement load forces. However, even with minor postoperative displacement, these patients may feel well.

Method ventral stabilization considered the most effective. The articular surfaces of the atlanto-axial joint are completely fixed with knitting needles, screws, etc., depending on the size of the dog.

Prognosis for recovery

If conservative treatment is not successful within 50-80 days, then it is necessary to focus on surgical correction.

If, after starting conservative treatment, neurological signs do not go away or worsen, then surgical treatment is urgently needed.

– congenital pathology of the spinal column in dwarf dog breeds, which is characterized by displacement of the first cervical vertebra (atlas) relative to the second (epistrophy).

This disease mainly affects dwarf dog breeds, such as Yorkshire Terrier, Chihuahua, Miniature Poodle, Toy Terrier, Pomeranian, and Pekingese. The hereditary factor is determined.

Fig 1. X-ray of a Yorkshire Terrier. The arrow indicates an increase in the distance between the atlas and the odontoid process of the axial vertebra.

The atlantoaxial joint provides rotation of the skull. In this case, the first cervical vertebra rotates around the odontoid process of the second cervical vertebra. There is no intervertebral disc between the first and second cervical vertebrae, so the interaction between these vertebrae is carried out mainly due to the ligamentous apparatus.

Atlantoaxial instability develops in dogs in which the odontoid process is absent or underdeveloped, as well as when it is fractured and when the ligamentous apparatus is ruptured. Underdevelopment occurs in approximately 46% of cases, ligamentous rupture occurs in approximately 24%. These anomalies are congenital, but injuries to this area can force the appearance of clinical symptoms of the disease.

Clinical signs of atlanto-axial instability

Often, in patients aged 4 months or older with atlanto-axial instability, a wide open “fontanel” remains - evidence of increased intracranial pressure. Here it will be valuable to conduct an ultrasound examination of the brain and evaluate the cerebrospinal fluid to exclude related problems. Associated problems may be inflammatory processes in the form of meningoencephalitis.

The main clinical signs include:

acute pain symptom, which is manifested by a loud squeal of the animal when turning or raising its head;
ventroflexion – forced position of the head and neck no higher than the level of the withers;
proprioceptive deficit of the thoracic limbs;
tetraparesis/tetraplegia.

Symptoms of atlanto-axial instability

Also noted symptoms brain damage, which may be a consequence of impaired circulation of cerebrospinal fluid and the development or progression of hydrocephalus, which is sometimes accompanied by syringomyelia.

Another potential explanation for forebrain symptoms in dogs with atlantoaxial instability is hepatic encephalopathy secondary to portosystemic shunts. This pathology is noted in two of six dogs operated on for atlantoaxial instability.

Compression of the basilar artery by the odontoid process can cause symptoms such as disorientation, behavioral changes, and vestibular deficits.

Differential diagnosis:

Tumors of the PS and spinal cord;
Herniated intervertebral discs;
Discospondylitis;
Spinal fractures;
Intervertebral disc herniation type Hansen 1;
Hypoglycemia is a common pathological condition in Yorkshire terrier puppies and other miniature dogs.

Diagnosis

The diagnosis of “atlantoaxial instability” is established based on the results of an X-ray examination of the cervical spine in the lateral projection. In some cases, it may be necessary to bend the animal's neck slightly to see the off-axis deviation.

Myelography is not necessary for diagnosis. In addition, the introduction of a contrast agent into the cerebellomedullary cistern can cause death. If after a survey X-ray there are still doubts about the correctness of the diagnosis, it is recommended to perform a contrast spondylography of the cervical spine through a lumbar puncture.

Using CT or MRI of the cervical spine, the disease is differentiated from a disc herniation, discospondylitis, tumor of the spine and spinal cord, and also receives more complete information about spinal cord edema, myelomalacia or syringomyelia.

Treatment of atrlanto-axial instability in dogs

There are conservative and surgical methods for treating atlantoaxial instability.

First of all, it is necessary to make a neck corset to limit the rotation of the head and neck. Anti-inflammatory drugs are also used.

The goal of conservative therapy is to provide temporary anatomical stability to enable the formation of scar-connective tissue in the area of the vertebral joints.

The surgical method will be the main one, since it has a higher percentage of favorable outcomes and good results immediately after surgery.

The main goal of surgical treatment is to fix the vertebrae in an anatomically correct position using various methods and structures. There is a method of dorsal and ventral stabilization.

In the clinic, to make a diagnosis of atlantoaxial instability, a medical history is taken, radiography of the cervical spine, and contrast spondylography of the cervical spine.

Portugeis A. A., veterinary clinic "Exvet", Odessa.

List of abbreviations: C1–C2 – atlantoaxial joint; AAN – atlantoaxial instability; C1 – atlas (first cervical vertebra); C2 – epistrophy (second cervical vertebra); NSAIDs – non-steroidal anti-inflammatory drugs; GCS – glucocorticosteroids.

AAN in dogs was first described in 1967. This pathology mainly occurs in young dogs of dwarf breeds (Chihuahua, Yorkie, Toy Terrier, Spitz), but can also occur in larger breeds and even in cats 1. The usual age interval for the onset of this disease is from 4 months to 2 years. This pathology is most often the result of a congenital malformation of the C1, C2 vertebrae and the ligaments connecting them.
In the ontogeny of the epistropheus, there are seven centers of ossification, while its tooth consists of two such centers. The cranial center arises in the atlas, and the caudal center in the epistrophe. The fusion of ossification centers occurs at 4 months of age. The main causes of AAN are dysplasia, hypoplasia or aplasia of the epistrophic tooth (32%), as well as underdevelopment of the internal ligaments C1–C2 (mainly the transverse ligament of the atlas) (Fig. 1) 2. Trauma can also be the cause of this pathology.

Clinical signs

The main clinical sign of AAN, neck pain of varying intensity, occurs in 55–73% of cases (Cerda-Gonzalez & Dewey, 2010; Parent, 2010). The pain can be either periodic, mild, manifested during periods of any specific movements, or high intensity, accompanied by obvious vocalization, lowering of the head, and careful and minimal body movements. Neurological deficits can also vary in severity, from mild ataxia of movement, which can manifest as weakness in the fore and hind limbs, to moderate and, in rare cases, severe tetraparesis. In exceptional cases, a pre-comatose and comatose state may occur (Fig. 3). Asymmetric symptoms of spinal cord damage may occur (displacement of the epistrophy can occur not only in the dorsoventral, but also in the lateral direction). The development of symptoms can be either acute or chronically progressive. In dwarf breeds of dogs with defects in the development of the C1–C2 joint, acute symptoms of the disease can arise from minor injuries (jumping from a sofa, sudden jumping out of the owner’s hands, etc.). Most owners of representatives of mini-breeds with this pathology go to the clinic before the age of one and a half years. pets

Visual diagnostics

AAN should be suspected in all toy dog breeds with pain, cervical stiffness, and ataxia even after 2 years of age. Differential diagnoses in these patients may include Chiari-like malformation, atlantooccipital overlap, dorsal compression of C1–C2 (Dewey's cavity), syringomyelia, arachnoid cyst, trauma, intervertebral hernia (unlikely before 1.5 years 3)
Plain lateral radiographs may show the presence of C1–C2 instability (Figure 4). Sometimes it is necessary to gently bend the patient's head during an x-ray. The sensitivity of the radiographic method is 56% (Plessas & Volk, 2014). You should not neglect this simple and accessible study, especially if already at the initial examination there is an assumption about the presence of AAN; in addition, this will help to avoid accidental deterioration of the patient’s condition as a result of careless handling in the future. Sedation before Rg-imaging should be carried out with great caution. Relaxation of the neck muscles may worsen compression of the spinal cord, however, if this is necessary, it is better to use more accurate diagnostic methods, such as CT or MRI. CT has a high sensitivity for detecting various bone pathologies. Also, this method is good at identifying changes in the location of bone structures/implants (atlanto-occipital overlap, AAN, malformation and incomplete ossification of the vertebrae). The sensitivity of the method is 94%. (Rylander & Robles, 2007; Cerda-Gonzalez & Dewey, 2010; Parry, Upjohn et al., 2010) (Figure 5).
Preference is given to the MRI method, which is the gold standard for studying the nervous system (Fig. 6). It can show not only the location of compression, but also secondary changes in neural tissue (Westworth & Sturges, 2010; Middleton, Hillmann et al., 2012).

Treatment

The goal of treatment for AAN is to stabilize the C1–C2 vertebrae. There are conservative and surgical treatment. The latter is preferred. There was a direct relationship between the speed and completeness of restoration of neurological functions and the speed of contacting the clinic with the development of AAN 4.

Conservative treatment is acceptable in cases of very young patients (up to 4 months) when the owner refuses surgery, and this treatment option can also be considered in cases of mild and intermittent pain symptoms. Conservative treatment is aimed at strictly limiting head mobility (application of a corset, which should start from the middle of the head and end in the caudal third of the thoracic region) for 1.5–2 months" (Fig. 7). NSAIDs/steroids are also necessary.
The point of this method is that within 1.5–2 months, scar tissue develops in the unstable C1–C2 joint, which can further support this connection and prevent compression of the spinal cord. In a study of 19 dogs (observation period - 12 months), this method showed 62% positive results. Dogs that did not respond to therapy died or were euthanized. Thus, the mortality rate was 38% 5. Possible complications when using this technique: corneal ulcer, bedsores at the points of contact of the corset with the skin, wet dermatitis under the corset (poor ventilation, food getting behind the corset), otitis externa, aspiration pneumonia (associated with difficulty swallowing in a position of permanent fixation of the head and neck, and weakness of the larynx and pharynx may also be present). In a study by Havig and Cornell, the complication rate was 44% (Havig, Cornell et al., 2005). The disadvantage of this technique is the high relapse rate.
Surgical treatment is indicated for relapse after conservative treatment and for moderate to severe symptoms of the disease.
There are two types of C1–C2 fixation: dorsal and ventral methods.
The dorsal method consists of dorsal access to C1–C2 and reduction and fixation using an orthopedic wire/polypropylene suture over the C1 arch and the C2 ridge (Fig. 8). After this, the same corset is applied as for conservative treatment for 1–1.5 months. The method was described in 1967 by Dr. Geary (Geary, Oliver et al., 1967).

The advantage of this technique is the relative simplicity of its implementation, however, the implants are often much denser than the arch of the atlas bone, resulting in numerous relapses. Also, due to the specific position of the patient on the surgical table (sternal position with a bolster under the ventral part of the neck and flexion of the head), iatrogenic compression of the spinal cord is created, which can significantly aggravate the patient’s vital functions until his death. This technique does not eliminate the rotational movements and shear forces that continue to operate at the C1–C2 junction 8. Complications associated with migration/fracture of implants or bone when using the dorsal technique are 35–57% 6, 7. The success rate of the method ranges between 29 and 75%. The mortality rate may average 25%. (Beaver, Ellison et al., 2000).
The ventral method has two modifications. The first technique is the installation of transarticular implants (wires/screws) with or without cement (it is better to use cement with an antibiotic). The method was described by Drs Sorjonen and Shires (Sorjonen & Shires, 1981). Positive results were recorded in 71% of cases (44–90%) (Beaver, Ellison et al., 2000) (Fig. 9).
The second technique is the placement of multiple implants (wires/screws) in C1–C2, including transarticular placement and placement of bone cement (Schulz, Waldron et al., 1997). Positive results were achieved on average in 87–90% of patients (Fig. 10). At the same time, mortality was up to 10% of cases (Aikawa, Shibata et al., 2014).

A mandatory element of any of the ventral techniques is the removal of cartilage from the articular surfaces of C1–C2 and the transfer of cancellous bone to create arthrodesis at this level. Cartilage is removed with a scalpel, curette or bur. When using a bur, care must be taken not to remove too much bone. Cancellous bone is most often harvested from the proximal humerus because this area can easily be included in the surgical site. Dental acrylic can be used as cement, but you need to be sure that the operation is highly sterile (Fig. 11).

The stages of ventral stabilization of C1–C2 using the multiple fixation technique are shown in Fig. 13-17.

Advantages of the method: high stability and functional fixation, complete neutralization of all forces acting in the C1–C2 joint, no additional fixation of the cervical spine with a corset (except for patients of medium and large breeds). The probability of a positive outcome is 60–92% 9. The success rate is related to the surgeon’s experience in performing this operation.
Disadvantages of the method: the surgical technique is much more complicated compared to the dorsal method, there is a possibility of damage to the spinal cord if implants are placed incorrectly, the most common postoperative complications are laryngeal paralysis (damage to the recurrent laryngeal nerve during access), swallowing disorders (may occur due to too much amount of cement), aspiration pneumonia, infection. The rate of postoperative complications can be about 30% 9.

Conclusion

The method of choice for the treatment of pathology such as AAN today is anterior fixation using multiple implants and bone cement. With a certain level of training in the technical performance of this operation, very good statistical indicators can be achieved. It provides a large margin of safety C1–C2. Thanks to arthrodesis, the load on the implants will last a short time (2–4 months). There is no need for additional actions (corset). Due to a certain positioning of the patient, good reposition of C1–C2 is achieved, which is not always possible to achieve when using the dorsal method.

Literature:

Shelton S. B., Bellah, Chrisman C. et al.: Hypoplasia of the odontoid process and secondary atlantoaxial luxation in a siamese cat. Prog Vet Neurol, 2(3):209–211, 1991.
Watson A. G., de Lahunta A.: Atlantoaxial subluxation and absence of transverse ligament of the atlas in a dog. J Am Vet Med Assoc, 195(2):235–237, 1989.
Veterinary surgery: small animal / Karen M. Tobias, Spencer A. Johnston.
Beaver D. P., Ellison G. W., Lewis D. D. et al.: Risk factors affecting the outcome of surgery for atlantoaxial subluxation in dogs: 46 cases (1978–1998). J Am Vet Med Assoc, 216(7):1104–1109, 2000.
Havig et al.: Evaluation of non-surgical treatment of atlantoaxial subluxation in dogs: 19 cases (1992–2001) in JAVMA, Vol. 227, No. 2, July 15, 2005.
McCarthy R. J., Lewis D. D., Hosgood G.: Atlantoaxial subluxation in dogs. Compend Contin Educ Pract Vet, 17:215, 1995.
Thomas W. B., Sorjonen D. C., Simpson S. T.: Surgical management of atlantoaxial subluxation in 23 dogs. Vet Surg, 20: 409, 1991.
Van Ee R. T., Pechman R., van Ee R. M.: Failure of the atlantoaxial tension band in two dogs. J Am Anim Hosp Assos, 25(6): 707–712, 1989.
Lorenz, Michael D. Handbook of veterinary neurology / Michael D. Lorenz, Joan R. Coates, Marc Kent. – 5th ed.

Clinic of Experimental Therapy of the Russian Oncological Research Center named after. N.N. Blokhin RAMS

Yagnikov S.A., Lukoyanova M.L., Kornyushenkov E.A., Kuleshova Y.A., Pronina E.V., Krivova Yu.V., Sedov S.V.

Introduction

Atlantoaxial instability is a congenital pathology of the spinal column in dwarf dog breeds, which is characterized by displacement of the first cervical vertebra (atlas) relative to the second (epistrophy) (Fig. 1).

Fig.1. Radiographs of the cervical spine in the lateral projection (a). Atlantoaxial instability (increased distance between the dorsal arch of the atlas and the spinous process of the epistrophy, displacement of the odontoid process of the epistrophy into the spinal canal, displacement between the articular fossae of the atlas and the cranial articular processes of the epistrophy.

The atlantoaxial joint provides rotation of the skull. In this case, vertebra C I rotates around the odontoid process C II. There is no intervertebral disc between C I and C II, so the interaction between these vertebrae is carried out mainly due to the ligamentous apparatus 1,2.

This pathology is most common in young dogs of toy breeds (Yorkshire terriers, Chihuahuas and toy poodles). However, the age range for manifestation of the disease may vary. Cases of the disease have been reported in cats and large breeds of dogs, such as Rottweiler, Doberman Pinscher, Basset Hound and German Shepherd.

Atlantoaxial instability develops in dogs with the absence or underdevelopment of the odontoid process or with its fracture, as well as in dogs with rupture of the ligamentous apparatus at the level C I - C II. The absence of the odontoid process and/or its underdevelopment occurs in 46% of cases, and rupture of the ligamentous apparatus occurs in 24% of cases. These anomalies of the spinal column are congenital, but injury to this area can precipitate the onset of clinical symptoms of the disease 1,2.

The main clinical symptoms of the disease are: 1) acute pain, which manifests itself when turning or raising the head in the form of a loud “squeal”; 2) ventroflexion - forced position of the head and neck no higher than the level of the withers, 3) proprioreceptive deficit of the thoracic limbs, 4) tetraparesis/tetraplegia. Symptoms of brain damage may also be noticed, which may be a consequence of impaired circulation of cerebrospinal fluid and the development or progression of hydrocephalus (Fig. 2). Hydrocephalus may also be accompanied by syringohydromyelia.

Fig.2. CT scan of the brain of a dog with atlantoaxial instability. Segmental cut. Enlargement of the right lateral cerebral ventricle ().

Another potential explanation for forebrain symptoms in dogs with atlantoaxial instability is hepatic encephalopathy secondary to portosystemic shunts. This is another favorite condition in small breed dogs, occurring in two out of six dogs operated on for atlantoaxial instability.

Compression of the basilar artery by the odontoid process can cause symptoms such as disorientation, behavioral changes, and vestibular deficits.

To make a diagnosis of atlantoaxial instability, it is necessary to conduct an X-ray examination of the cervical spine in a lateral projection (Fig. 1). In some cases, slight flexion of the neck may be required to see the deviation from the axis, but in no case should it be severe 1,2,3,4.

Myelography is not necessary for diagnosis. In addition, injection of a contrast agent into the cerebellomedullary cistern can be fatal. If, after a survey X-ray, there are still doubts about the correctness of the diagnosis, a contrast spondylography of the cervical spine can be performed through a lumbar puncture.

Computed tomography or magnetic resonance imaging of the cervical spine will differentiate the disease from disc herniation, discospondylitis, tumors of the spinal column and spinal cord, and will also provide more complete information regarding spinal cord edema, myelomalacia, or syringohydromyelia (Fig. 5).

Priority in the treatment of this pathology is given to the surgical method of treatment. Although there is data in the literature about successful conservative treatment of atlantoaxial instability. Conservative treatment includes immobilization of the head and neck with a brace and analgesics. A number of authors note that after 3.5 months, animals with atlantoaxial instability could walk without motor deficits of the limbs 3 . However, in 30-60% of animals, after removing the corset, a relapse of the disease was noted. The technique of applying a corset requires a certain skill from the doctor, and the main requirement is stable immobilization, without squeezing soft tissues by the corset design. If the neck is stretched too much, the animal may aspiration of food into the respiratory tract, since the act of swallowing is unnatural for a dog in this position.

However, this treatment may be an excellent alternative for dogs that have contraindications to general anesthesia 3 . For traumatic fractures C I - C II, conservative management of the patient gives much better results than surgical treatment.
But most authors consider congenital atlantoaxial subluxation to be a direct indication for surgery 1,4,5,6. There are two main ways to stabilize C I - C II through dorsal and ventral approaches.

Dorsal stabilization consists of drawing a wire suture around the dorsal arch of the atlas (C I), repositioning the vertebrae C I - C II, followed by their fixation with a wire loop to the spinous process of the epistrophy (C II) (Fig. 6.0 and 6.1) 4. However, with this technique, the frequency of complications is quite high in the form of rupture or fracture of the fixing implant, cutting through the arch of the atlas with a wire suture, which leads to relapse of instability and requires repeated surgical intervention in 25-63% of cases, and mortality with this surgical intervention technique was noted in 8-63% of cases. 38% of cases (Fig. 7) 1.4,5. With a successful outcome of the operation, residual pain symptoms persist in 6-11% of cases, and residual ataxia in 44-83% 1.4,5.

Using these treatment techniques, we encountered the above complications, or more precisely, a fracture of the fixing wire loop and cutting through the arch of the atlas with a wire suture, which led to relapse of instability and neurological symptoms (Fig. 7).

Literature data and our own negative experience forced us to reconsider the technique of dorsal stabilization for atlantoaxial instability.

Materials and methods: The work was performed on 4 dogs of toy breeds aged from 9 months to 3 years. Two dogs were Yorkshire terriers, one was a toy terrier and one was a miniature poodle. The animals came to the clinic with complaints of acute pain, ventroflexion, tetraparesis and ataxia. In three animals, the disease history was 7-20 days. One dog has an unknown medical history. Based on the radiographic examination of the cervical spine in the lateral projection, spondylolisthesis C I relative to C II was revealed on radiographs in all animals (Fig. 1). Owners are recommended to undergo surgical treatment.

Operation stages. Obtaining a bone autograft from the iliac wing. Skeletonization by removing soft tissue fragments from the surface of the autograft. A dorsal approach was made to the arch of the atlas and the spinous process of the epistrophy, and the dura mater was opened cranial and caudal to the dorsal arch of the atlas. A bone autograft from the iliac wing was placed from the dorsal surface onto the dorsal arch of the atlas and fixed with three wire cerclages made of wire with a diameter of 0.6 mm at three levels (Fig. 8). Three holes were formed in the spinous process of the epistrophy at different levels in height and length using a Kirschner wire with a diameter of 1 mm. The cranial surface of the spinous process of the epistrophy was skeletonized from soft tissues. C I was reduced relative to C II, achieving a good comparison, and the vertebrae were fixed with three wire sutures (Fig. 9). The space between the arch of the atlas and the spinous process of the epistrophy was filled with collapan granules. The soft tissues were sutured in layers with interrupted sutures using 5-0 prolene. Immobilization of the head and cervical spine in relation to each other and the chest was ensured using a plastic turbocast corset for 30 days (Fig. 10)

If there were positive dynamics, the animals were sent home. Control radiography was performed on the 30th day after surgery. If there was no vertebral displacement or fracture of the wire sutures visible on the radiograph, the corset was removed. After removing the corset, owners were advised to limit their dogs' movement for one month.

Treatment results

On days 3-9 after surgery, the animals’ ability to walk improved or was restored, and the animals moved more and more actively. In two dogs with an acute pain symptom at the time of initial admission (whining when moving the head and neck), no pain was noted in the postoperative period.
Animals could eat on their own.

At the time of removal of the corset, the bone callus was not detected on radiographs. The contours of the callus along the dorsal surface of the vertebrae were visualized on days 45-60 (Fig. 11).

Evaluation three months after surgery showed that persistent relief of the pain symptom was noted in all four dogs, partial ataxia persisted in one animal.

X-ray examination showed that in all observations the position of the vertebrae did not change after reposition. And a bone callus has formed along the dorsal surface of the dorsal arch of the atlas and the spinous process of the epistropheus.

The owners of three animals did not observe any symptoms characteristic of atlantoaxial instability 5 or more months after surgery (Fig. 12). Ataxia persists in one animal. However, restoration of the ability to move and relief of acute pain symptoms, according to the owners, significantly improved the patient’s quality of life.

Discussion

The method we tested for stabilizing the spinal column at levels C I - C II allowed us to obtain a lasting improvement in animals with atlantoaxial instability.

The chosen surgical technique is not accidental. It is based on a theoretical rationale, the main goal of which was bony fusion between the dorsal arch of C I and the spinous process of C II.

The choice of surgical approach (ventral or dorsal) and, accordingly, the surgical technique (ventral stabilization or dorsal stabilization) had the following rationale.
We gave priority to the dorsal method of stabilization after analyzing the distribution of forces acting on the ventral and dorsal surfaces of the cervical vertebrae C I - C II. Between the dorsal arch of the atlas and the spinous process of the epistrophy, tensile forces act along the dorsal surface of the spinal column. And along the ventral surface at the junction of these two vertebrae (the articular fossae of the atlas and the cranial articular processes of the epistrophy) there are compression forces (Fig. 13).

This distribution of distraction and compression forces is determined by the laws of physics. The head, as a part of the body, has gravitational forces. When holding the head along the ventral surface of the spinal column, compression forces predominate, and along the dorsal surface, distraction forces predominate. And these forces exist almost always at any moment of movement or rest of the animal (Fig. 13.1).

With dorsal fixation of the vertebrae, we can neutralize the tensile forces that exist physiologically between C I - C II. These forces can be neutralized by creating compression using a wire clamp between the dorsal arch of the atlas and the spinous process of the epistrophy. Compression along the ventral surface of the vertebrae, between the articular fossae of the atlas and the cranial articular processes of the epistrophy exists physiologically. By neutralizing tensile forces along the dorsal surface of the vertebrae, creating compression using the dorsal fixator, we create compression between C I - C II along the ventral and dorsal surface, which increases the stability of fixation (Fig. 13.2).

With ventral fixation of the spinal column, the tensile forces existing between the dorsal arch of the atlas and the spinous process of the epistrophy are preserved, which leads to a cranial-caudal displacement of the dorsal arch of the atlas relative to the spinous process of the epistrophy. Kirschner wires or screws passed through the articular processes of these two vertebrae will experience flexion and shear forces, which can lead to their premature migration or fracture, and, accordingly, to recurrence of instability between C I - C II (Fig. 13.3).

Therefore, from a biomechanical point of view, dorsal fixation C I - C II has priority.

The choice of implant for fixation of C I - C II during dorsal stabilization determines the anatomical structure of the vertebrae. And today, wire is the only material that can be used to fix the vertebrae at this level. However, the use of a wire suture as an implant fixing the vertebrae was marred by relapses of instability due to destruction of the atlas arch by the wire and fracture of the wire suture.

To stop these complications, we needed to solve several problems. The first is to prevent destruction of the dorsal arch of the atlas. It is for this purpose that we implanted a cancellous autograft of the iliac wing onto the arch of the atlas. It is spongy bone that is capable of revascularization and restructuring in a short period of time, and it is spongy autograft that has the maximum potential for osteoinduction, osteoconduction and osteogenesis. We also needed cancellous bone to stimulate the fusion of C I - C II.

To fix the autograft to the arch of the atlas, we used three wire sutures with wire with a diameter of 0.4-0.6 mm. This made it possible to reduce the pressure of the wire sutures on the bone at the site of their contact, and the fixation of the wire sutures to the arch of the atlas and the autograft made it possible to neutralize the effect of “sawing” and the effect of “displacement” of the wire sutures to the center of the arch. This is a very important point. Since the central part of the arch of the atlas in young animals is represented by cartilaginous tissue, and it is this place of the arch that has the greatest tendency to destruction.

Why three wire seams and not four or five? There are certain rules for fixing bone fragments and fragments, formulated by ASIF JSC. It is fixation with three implants that provides the most stable fixation in comparison with one or two implants. And the use of four and five implants does not significantly increase the strength of fixation of fragments and splinters. Therefore, three wire seams are the “gold standard”.

I would like to once again dwell on the theory that we based our method: reposition of the vertebrae, stable fixation, fusion of the vertebrae.

After reposition, the vertebrae are held in place with wire sutures for 20 days after surgery. But with active movements of the animal, this structure breaks down. Yes, we placed three wire sutures, but this does not guarantee us that the fusion of our patient’s vertebrae will occur before metal fatigue during active head movements causes a fracture of the wire sutures. After all, any implant can withstand a certain number of cyclic movements.

To reduce the load on the wire sutures, it is necessary to eliminate head movements, and this requires additional immobilization of the spinal column. To ensure immobility in the cervical spine, it is necessary that the corset extends as a single block to the head, cervical spine and chest of the patient.

We have created conditions for the fusion of C I - C II. The formation of callus between C I - C II can be stimulated using spongy autologous bone. We implanted cancellous bone on the arch of the atlas, reduced the vertebrae, and achieved good alignment between the vertebrae. However, there are gaps that it is advisable to fill with spongy autologous bone in order to increase the area of fusion of the vertebrae. But in dwarf dog breeds, it is impossible to collect spongy autologous bone from tubular bones, as is done in other breeds of dogs and even cats. The only way out is to use the spinous processes of the first thoracic vertebrae or ceramic implants. Unfortunately, the latter have only osteoconductive properties.

The condition of the animal on the 5th day and one and a half months after the operation.

The condition of the animal before surgery, on the first day after surgery, on the 15th day after surgery and on the 30th day after surgery.

Conclusion

Dorsal stabilization of the cervical spine in dogs with atlantoaxial instability should include the following steps: repositioning of the vertebrae, autologous bone grafting of the dorsal arch of the atlas, fixation of the vertebrae with wire cerclages and immobilization in a brace, which will allow for bone fusion along the dorsal surface of the vertebrae. This method will avoid the most common complications during dorsal stabilization of C I - C II in dogs with atlantoaxial instability.

Literature review:

Beaver D.P., Ellison G.W., Lewis D.D., Goring R.L., Kubilis P.S., Barchard C. Risk factors affecting the outcome of surgery for atlantoaxial subluxation in dogs: 46 cases (1978-1998). Journal of the American Veterinary Medical Association, 2000, 216, 1104-1109.
Gibson K.L., Ihle S.L., Hogan P.M. Severe spinal cord compression caused by a dorsally angulated dens. Progress in Veterinary Neurology, 1995, 6, 55-57.
Hawthorne J.C., Cornell K.K., Blevins W.E., Waters D.J. Non-surgical treatment of atlantoaxial instability: a retrospective study. Veterinary Surgery, 1998, 27, 526.
Jeffery N.D., Dorsal cross pinning of the atlantoaxial joint: new surgical technique for atlantoaxial subluxation. Journal of Small Animal Practice, 1996, 37, 26-29.
Knipe M.F., Stuges B.K., Vernau K.M., Berry W.L., Dickinson P.J., Anor S., LeCouteur R.A. Atlantoaxial instability in 17 dogs. Journal of Veterinary Internal Medicine, 2002, 16, 368.
Sanders S.G., Bagley R.S., Silver G.M. Complications associated with ventral screws, pins and polymethylmethacrylate for the treatment of the atlantoaxial instability in 8 dogs. Journal of Veterinary Internal Medicine, 2000, 14, 339.