Hemilaminectomy

Intervertebral discs (the cushioning structures between the spinal bones) can be exposed to conditions and mechanical forces that, over time, cause them to bulge or rupture. When a disc ruptures, it can injure the spinal cord in two main ways: compression and concussion. How severe the injury is—and how much nerve cell loss occurs—depends on:

• the type of force involved
• the magnitude of force applied to the spinal cord
• the duration the force has acted

Milder spinal cord injury may cause poor coordination and a “drunken sailor” style gait. More serious injury can lead to loss of the ability to walk or an inability to move the legs voluntarily. The most severe damage can eliminate pain sensation entirely. If pain perception has been absent for a prolonged period, the likelihood of recovery can be very poor.

Most disc ruptures occur in chondrodystrophoid breeds (Dachshund, Pekingese, Beagle, Lhasa Apso, etc.), with Dachshunds representing 45–70% of all cases. In these dogs, signs typically begin between 3 and 6 years of age, although x-rays may show disc calcification as early as 2 years. Nonchondrodystrophoid breeds (such as Labrador Retrievers and German Shepherd Dogs) more often present between 5 and 12 years of age. Ruptures most commonly involve the thoracolumbar region (mid-to-lower back), accounting for 65% of cases, while the cervical (neck) region accounts for up to 18% of presentations.

Disc rupture can produce varying degrees of pain. When neurologic injury develops and progresses, it commonly follows a consistent sequence:

• back or neck pain, sometimes with refusal to walk around the room
• an unsteady, “drunken sailor” gait or hind-end wobbliness; the hind feet often cross during stepping
• complete loss of hind limb motor function; typically, at about the same time, the pet loses normal urination control and cannot fully empty the bladder
• loss of pain perception, indicating severe spinal cord injury with a guarded to poor prognosis

Disc ruptures are typically categorized by broad spinal regions:

• cervical vertebrae 1–5 (C1–C5)
• cervical vertebrae 6 through thoracic vertebrae 2 (C6–T2)
• thoracic vertebrae 3 through lumbar vertebrae 3 (T3–L3)
• lumbar vertebrae 4 through the sacrum (L4–S3)

This regional classification is called neurolocalization and helps an ACVS board-certified surgeon plan the most appropriate diagnostic testing and potential surgical options. Intervertebral disc rupture is generally considered a true surgical emergency, and prognosis depends heavily on how much neurologic function remains at the time of evaluation and treatment.

Figure 1. Lateral myelogram of a Dachshund with a herniated disc.

Primary care veterinarians often recommend initial general health screening and may use one or more imaging methods, such as:

• blood work: complete blood count (CBC), serum chemistry, and urinalysis
• radiographs of the spine and/or chest
• myelogram: a series of x-rays taken after dye is injected around the spinal cord to outline compression (Figure 1)
• CT scan instead of, or following, the myelogram
• MRI in addition to, or instead of, a CT scan
• spinal tap performed at the same time as imaging

The veterinary surgeon determines which tests are most appropriate, and this can vary by case.

Figure 2. Surgical photo of the patient from Figure 1: a portion of bone over the spinal canal has been removed (hemilaminectomy) to expose the spinal cord and remove herniated disc material.

Conservative management—strict cage rest/confinement and pain control—is usually reserved for animals early in their first episode when neurologic deficits are mild. Further discussion with the primary veterinarian may lead to referral to a veterinary surgeon to review all options.

There are multiple surgical procedures and approaches, and the specific choice depends on the surgeon and the disc location. The exact technique selected is determined by the surgeon’s experience and preference. However, surgical decompression by removing bone over the spinal canal is almost always recommended (Figure 2).

Most pets go home 3–7 days after surgery and typically return for recheck and removal of skin sutures or staples (if present). Pain is generally manageable with medications given by the owner.

Postoperative recovery may involve:

• bladder expression 3–4 times per day (if needed)
• physical rehabilitation to restore strength and flexibility
• strict exercise restriction (“bed rest”) for at least 4 weeks
• lifestyle changes such as weight loss, using a body harness instead of a neck lead, and reducing jumping off furniture

Possible postoperative complications include:

• seizures in the first 24 hours after a myelogram
• infection at the incision site
• later herniation of another disc (about 25% recurrence)
• persistent wobbliness or dragging of the hind toes during walking

Prognosis varies substantially with injury severity and location. If pain perception is still present, surgery enables about 90% of dogs to regain limb function, though some may retain mild gait unsteadiness. With strict medical management, about 60–80% may regain function in these pain-positive cases. In contrast, if pain perception is completely absent, surgery results in recovery of limb use in about 50–60%, whereas strict medical management yields recovery in <10%. Overall recovery from intervertebral disc disease can be prolonged, often taking weeks to months, and medical management alone usually requires a much longer recovery period than surgical treatment.

Dogs that cannot use their hind limbs may also have difficulty urinating. If neurologic function improves, independent urination may return. Until then, owners must manually express the bladder multiple times daily so urine can be emptied. These dogs have increased risk of chronic urinary tract infections and urine scald. Also, without motor ability, patients cannot reposition themselves and may develop pressure sores and wounds; keeping them on soft, well-padded bedding can reduce or prevent these injuries. Some patients may experience tingling sensations (paresthesia) that can resolve over time or persist and lead to self-trauma.