What is a ventral slot spine surgery?

A ventral slot is a surgery in which a hole centered on an intervertebral disc space is cut upward through the bone of two consecutive vertebral bodies to access the bottom of the spinal canal, enabling the removal of material compressing the spinal cord, such as extruded disc material, a blood clot, a cyst, an abscess, or a mass. 

In this surgery, an incision is made along midline on the front of the neck. Tissues are retracted to either side to expose the affected disc space and the vertebrae in front of and behind it. A rectangular window is carefully cut through the disc and a portion of each adjacent vertebral body. This window is deepened using a specialized drill until the spinal canal is accessed. The material compressing the spinal cord can then be gently removed. After the spinal cord is decompressed, the window is left open, and the tissues of the neck are restored to their normal positions before closing the skin incision. 

What conditions are treated with a ventral slot?

A variety of conditions causing compression of the spinal cord in the neck can be treated with a ventral slot surgery. The most common condition for which a ventral slot is performed is intervertebral disc disease. This disease involves the core of an intervertebral disc extruding into the spinal canal, or the edge of a disc thickening and protruding into the canal. By establishing access to the spinal canal, this procedure enables the removal of compressive disc material. In many cases, a blood clot or abscess that has formed adjacent to the spinal cord can also be removed with a ventral slot. Finally, some tumors growing around the spinal cord can be removed using a ventral slot. 

What symptoms are associated with these conditions?

Signs of compressive spinal cord disease in the neck vary with the severity of the compression. In most cases, pain and muscle spasms are present in the neck. Many patients are hesitant to turn, raise, or lower their head, resulting in a stiff and guarded posture. It is not unusual for them to yelp or whine apparently at random as a result of a slight movement triggering sudden pain. When the compression is lower down in the neck, a limp may be present in one or both of the front legs due to pain radiating down the shoulder and into the forelimb. In the most severe cases of spinal cord compression in the neck, patients may show weakness and incoordination in all four legs, and may even become completely paralyzed from the neck down.

How are conditions requiring a ventral slot diagnosed?

The first step in diagnosing a compressive disease of the spine in the neck is a thorough physical and neurologic exam. During this exam, in addition to evaluating all other body systems, the veterinarian will carefully palpate each vertebra to check for signs of pain, muscle tension, and muscle spasms. The range of motion of the neck in each direction will be assessed. Several different maneuvers will be utilized to assess each limb for the presence of normal responses to changes in balance and body position. Spinal reflexes will also be tested in each limb. If the patient is able to walk, their gait will be observed. If they are paralyzed, their ability to feel pain in the affected limbs will be tested. Finally, anal and bladder tone will be evaluated. 

If the physical exam is consistent with spinal cord compression in the neck, sedated x-rays of the neck vertebrae will be taken. These are used to look for vertebral abnormalities that may be causing the signs, such as a fracture or joint dislocation, an infection of the bone, or a bone tumor. Because the intervertebral discs cannot be seen on standard x-rays, these cannot be used to definitively diagnose intervertebral disc disease, although sometimes changes such as an abnormally narrow disc space and calcified disc material can be suggestive of this condition. 

If the neck x-rays do not reveal a diagnosis, a CT scan or MRI is performed to allow for detailed evaluation of the spinal cord, intervertebral discs, and the surrounding soft tissues. These scans require a patient to be under general anesthesia or heavy sedation, as they must remain very still for the duration of the scan.

What post-operative care is required following a ventral slot?

Following a ventral slot, all patients are hospitalized on IV fluids to maintain hydration and injectable medications for pain and inflammation. They are kept on thick bedding, and if unable to stand up and move around on their own, they are repositioned frequently to prevent pressure sores and lung compression. If bladder control is absent, a urinary catheter or gentle manual pressure is used to empty their bladder on a regular schedule. Patients are bathed as frequently as necessary to keep them clean and prevent skin irritation from developing. Food and water are provided in raised bowls so they do not need to move their neck significantly to eat and drink. Once a patient is eating and drinking on their own and is comfortable on oral medications, they can be sent home. This may take as little as 24 hours, or as much as a week. Disc-related pain is typically significantly improved within 24 hours of surgery, and neurologic deficits often begin to improve within three to five days. Maximal recovery of nerve function can take anywhere from a couple of weeks to several months, and generally relates to the duration of symptoms before surgery. 

At home, patients who are able to walk must be confined to strictly limit their physical activity while they heal. A chest harness must be used instead of a collar to avoid pressure on the neck. Only short, slow leash walks are permitted for the first few weeks after surgery, and they must be prevented from jumping, playing, or stair use. Slick surfaces should also be avoided. Food and water should be provided in bowls that are raised to shoulder-level so they do not need to move their neck very much to eat and drink. 

Patients who are not able to get up and move about on their own, as well as those that do not have complete bladder or bowel control, require more intensive care at home. This includes deep bedding that is kept clean and dry at all times, frequent repositioning to avoid pressure sores, and the use of sling support when taking them outside to use the bathroom. If a patient is not able to empty their bladder on their own, the owner is taught how to catheterize or manually express their bladder. Patients who are incontinent will need to be checked frequently for any urine or feces that might be on their hind end, and cleaned with warm water and a gentle cleanser whenever soiling is present. 

The first follow-up appointment is typically scheduled for two to three weeks after surgery. At this appointment, the progress of healing and restoration of function will be assessed, and the stitches will be removed. Based on the patient’s progress, the veterinarian will determine if an increased level of physical activity can be introduced. For patients who have not yet recovered normal nerve function, a physical rehabilitation program will be implemented to facilitate neurologic recovery. Further recheck appointments are scheduled once a month until maximal neurologic improvement is achieved. 

What are the potential risks and complications of a ventral slot?

Several complications can occur during or following a ventral slot. Because of the close proximity of the spinal cord and spinal nerves to the tissues that must be manipulated during surgery, there is a risk of temporary or permanent damage to these structures. If the large blood vessels located within the spinal canal are disrupted during surgery, significant hemorrhage may result. While this hemorrhage is rarely life-threatening, it often necessitates halting the procedure, closing the surgical site, waking the patient up, and waiting a day or two before attempting a second surgery to finish the procedure. Magnification, specialized instruments, and very careful and precise surgical technique help to minimize these risks. 

In the immediate post-operative period, in addition to the potential for a surgical site infection, patients with significant neurologic deficits are at increased risk of developing pneumonia, urinary tract infections, and skin infections. These risks are minimized by providing intensive nursing care to patients who are immobile and/or incontinent. 

What is the prognosis following a ventral slot?

The prognosis following a ventral slot depends on the disease being treated, the severity and duration of spinal cord compression, and the severity of the neurologic deficits present before surgery. Patients undergoing a ventral slot for intervertebral disc disease who have pain and only minimal neurologic deficits have an excellent prognosis for resolution of pain and return to normal function. Those who have difficulty walking due to weakness and incoordination in their limbs generally have a good prognosis, although some degree of weakness or incoordination may persist, especially in large and giant breed dogs. Patients who are paralyzed due to IVDD in the neck have a more guarded prognosis for functional recovery, and are at an elevated risk for post-operative complications. Those who are paralyzed and have decreased or absent pain sensation in their legs usually have a poor prognosis. 

It is important to keep in mind that an individual who has experienced a disc extrusion is at an elevated risk of having another disc extrusion in the future. Measures that can help reduce the risk of a future disc extrusion include the use of a chest harness rather than a collar to avoid pressure on the neck, the use of ramps and baby gates to discourage jumping and stair use, and the avoidance of vigorous play with other animals.

When a ventral slot is performed to remove a tumor within the spinal canal, the prognosis depends on the condition of the spinal cord and nerve roots, whether the tumor can be completely removed, and what cell type makes up the mass. The prognosis with other causes of spinal cord compression, such as blood clots and abscesses, varies depending on the severity, duration, and underlying cause of the abnormality.

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