The ventral slot technique is a procedure that allows the surgeon to reach and decompress the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

and associated

nerve root A nerve root (Latin: ''radix nervi'') is the initial segment of a nerve leaving the central nervous system. Nerve roots can be classified as: *Cranial nerve roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving ...

s from a ventral route in veterinary medicine. There are also alternative ways to open the

spinal canal The spinal canal (or vertebral canal or spinal cavity) is the canal that contains the spinal cord within the vertebral column. The spinal canal is formed by the vertebrae through which the spinal cord passes. It is a process of the dorsal body ca ...

from dorsal by performing a hemilaminectomy, but this often gives only limited access. Even when the main pathological changes evolve from the

midline In typography, the mean line is the imaginary line at the top of the x-height. upright 2.0, alt=A diagram showing the line terms used in typography Round glyphs will tend to break ( overshoot) the mean line slightly in many typefaces A typ ...

, it is necessary to choose a ventral approach. The ventral slot is commonly performed by splitting the ventral soft tissues of the neck, pushing the

great vessels Great vessels are the large vessels that bring blood to and from the heart. These are: *Superior vena cava *Inferior vena cava *Pulmonary arteries * Pulmonary veins *Aorta Transposition of the great vessels is a group of congenital heart defec ...

laterally and entering the disc space, securing

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

and

trachea The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...

which are located in the midline. Then taking out the medial part of the disc, leaving the lateral part intact and cutting away a small part of the adjacent vertebrae to extend the gap in a vertical manner. By this way a vertical slot including the upper and lower bone plates next to the disc is created. This makes possible to decompress the spinal cord from the midline and if necessary to both sides including the leaving nerve roots if also compressed. If necessary a spacer can be placed in the disc space to prevent the operated segment from collapse or secondary

kyphosis Kyphosis is an abnormally excessive convex curvature of the spine as it occurs in the thoracic and sacral regions. Abnormal inward concave ''lordotic'' curving of the cervical and lumbar regions of the spine is called lordosis. It can result fr ...

. Possible serious complications can be complete or incomplete tetraplegia,

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...

or unnoticed injury of the esophagus.

History

General data about the discovery and development of the original procedure belong to the British physician

Charles Bell Sir Charles Bell (12 November 177428 April 1842) was a Scotland, Scottish surgeon, anatomist, physiologist, neurologist, artist, and philosophical theologian. He is noted for discovering the difference between sensory nerves and motor nerves in ...

who was the first to describe the extent of soft tissue from the ventral into the spinal canal. “It was not until the 1940s that the condition was recognized as a prolapse of the nucleus pulposus.” And it took till 1881 until the first vet, Janson realized a disc extrusion as a classical condition in a dog as the main pathology. The more detailed descriptions and more precise

radiological imaging Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to rev ...

of the pathologic changes in a

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

did not develop until the 1950s. “Hoerlein, Olsson, Hansen, Funquist, and many others contributed significantly to the literature in the 1950s and 1960s, forming the foundations of our current medical and surgical therapies for IVD protrusion” and extrusion. Especial belonging to the surgical technique important advancements in human surgery were made by Robert Robinson, Ralph Cloward and Robert Baily. These basic contributions were taken over to veterinary medicine.

Uses

In veterinary medicine, this is a common procedure to “treat centrally located intervertebral

disc herniation Spinal disc herniation is an injury to the cushioning and connective tissue between vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or sensation in different parts of the body, and physical ...

”. Veterinary surgeons use the ventral slot technique when the animal shows symptoms of pain and or sensorimotor deficits belonging either to compression of the spinal cord or a single nerve root. Alternatively, if only a single nerve root is affected it is also possible to release the compressed nerve root via a hemilaminectomy.

Technique and Risks

This surgery is performed on dogs and

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s and a meticulous preparation is needed to prevent any damage on the region of the involved part of the neck and

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

. The ventral slot procedure is divided into eight main steps. Because the surgeon isn't allowed not to mobilize or shift the spinal cord - otherwise the affected animal is paralyzed afterwards - for any midline pathology an approach from the ventral direction is mandatory. A vertical skin incision is made from the ventral side in the

, the ventral musculature is split in the midline, vascular structures are retracted laterally,

, and

are mobilized across the midline to the opposite side. Attention is paid on any deep nerve structures as the

recurrent laryngeal nerve The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve (cranial nerve X) that supplies all the intrinsic muscles of the larynx, with the exception of the cricothyroid muscles. There are two recurrent laryngeal nerves, right and le ...

. The goal is to expose the affected disc and the ventral surface of the adjacent two vertebral bodies. During these steps it is important not to break through the lateral border of the disk space, otherwise the

vertebral artery The vertebral arteries are major arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry o ...

could be damaged. By entering the disk space and taking out its material a slot is created, following the natural orientation of the disc space itself. This can be expanded into adjacent vertebral bodies by staying in the midline. The extent of the slot should not exceed half of the vertebral body - cranial or caudal, but at the same time is providing more surgical room. Through this slot, disc material can be taken out easily until the disc ligament is reached. By removing this ligament the spinal canal finally is opened. By this step and by taking away bone spurs simultaneously the myelon is decompressed. By now working in a laterally orientation the “foraminotomy” starts. During this part the “

osteophyte Osteophytes are exostoses (bony projections) that form along joint margins. They should not be confused with enthesophytes, which are bony projections that form at the attachment of a tendon or ligament. Osteophytes are not always distinguished f ...

” is removed in “a 180-degree fashion” and the nerve root is free visible. “The foramen is probed with a nerve hook to ensure that the nerve is free”. To decompress a longer part of the cervical canal a corpectomy is performed from one disc to another, just by the same ventral approach. Because every surgery comes along with some kind of risk, possible complications are an injury of the structures on the way to the disc space (like nerves, trachea and esophagus or vessels), resulting in intraoperative blood loss, apoplexy, postoperative paresis or tetraparesis or pneumonia.

Implanted material and effects

To avoid collapse across the opened disc space several implants are available. Implanted material can consists of “a cervical disc prosthesis”, a fixed spacer out of metal (

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

) or synthetic material (

PEEK Polyether ether ketone (PEEK) is a colourless organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. The polymer was first developed in November 1978, later being introduced to the market by Vic ...

). Veterinary medicine is using similar materials as human medicine. Referring to this it is common to insert a cage or allograf. In some cases, the surgeon is using a ventral plate and screws to keep the vertebral bodies together with the implant in position. The main goal of using of a prosthesis is to obtain physiological motion between the two affected vertebral bodies. However, in most cases of myelopathy a secure fusion is attempted. So the compressed myelin will recover after decompression and by time the initial paralysis or sensorimotor deficits will resolve step by step.

Recovery

In general, the animal needs up to 6 weeks for recovery with a normal and positive path of development past surgery if everything goes as planned. During the recovery, statistics have shown that in some cases

urinary catheter In urinary catheterization a latex, polyurethane, or silicone tube known as a urinary catheter is inserted into the bladder through the urethra to allow urine to drain from the bladder for collection. It may also be used to inject liquids used ...

is needed besides a continuous pain medication. In any doubt of infection especially pneumonia antibiotic therapy should be started early. Based on actual data dogs receiving

physiotherapy Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patient ...

which serves the strengthening of the

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s and stimulating the spinal cord functions show a more quickly and better recovery than dogs without such a therapy.

Aftercare and adverse effects

There is a risk of early

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

or damage to the operated vertebrae if the animal moves too quick and uncontrolled. Adverse effects like postoperative paresis or tetraparesis or pneumonia appear in some cases. Depending on the width or lateral extension of the slot some dogs may suffer from

subluxation A subluxation is an incomplete or partial dislocation of a joint or organ. According to the World Health Organization (WHO), a subluxation is a "significant structural displacement", and is therefore always visible on static imaging studies, suc ...

of included vertebrae. One can control the early postoperative course by making sure that the animal stays calm and gets controlled, short walks to prevent the overuse of the fixed and still fusing vertebral segment. To ensure a good recovery and good long-term results “serial neurologic evaluation in the postsurgical patient” are recommended according to the data.

Prognosis

It is hard to foresee the actual outcome on

spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. Symptoms may include loss of muscle function, sensation, or autonomic function in the parts of the body served by the spinal cor ...

even with early surgery due to many important facts like animal breed, age, and size. Statistics have shown that dogs ”with cervical spinal trauma have been reported to have a good prognosis (recovery rate of 82%) if the animal does not suffer from pulmonary complications.” In terms of today's statistical basis surgeons are not able to give a secure prognosis about the outcome of the animal.

References

{{Reflist Veterinary procedures