On the Forefront: Prophylactic laser disk ablation in dogs at Oklahoma State University

Acute or severe intervertebral disk herniations can be catastrophic, and some dogs do not recover after a severe episode. In addition, thoracolumbar disk problems may recur after conservative treatment consisting of rest, corticosteroids, and other anti-inflammatory drugs. And although not definitively documented in the literature, disk extrusion or protrusion recurrence at other thoracolumbar disk spaces after decompressive surgery is also a clinically relevant concern.

For these reasons, laser disk ablation, a procedure for preventing thoracolumbar intervertebral disk herniation in dogs, has been developed and performed in more than 350 dogs at the Oklahoma State University Center for Veterinary Health Sciences. The original research at Oklahoma State University was extrapolated for clinical use in dogs in 1994 from a research project aimed at supporting a similar therapeutic modality in people.

Laser disk ablation is a prophylactic procedure and is not meant to replace decompressive hemilaminectomy or dorsal laminectomy in dogs that are paretic, paralyzed, or that have acute signs of severe thoracolumbar pain. Laser disk ablation is somewhat controversial because not all clinicians agree that prophylactic surgical fenestration of thoracolumbar intervertebral disks may be beneficial.

Figure 1. A 5-year-old dachshund, anesthetized and placed in ventral recumbency about to undergo laser disk ablation. Note the positioning of the seven spinal needles.

INDICATIONS

Dogs with a history of thoracolumbar disk disease that have recovered from either surgical or medical treatment and are virtually neurologically normal are considered candidates for laser disk ablation. If a dog is exhibiting lumbar pain only and a thoracolumbar disk problem is confirmed through imaging techniques (myelography, computed tomography, magnetic resonance imaging) and clinical history, the dog needs to be treated conservatively (confinement) for at least two weeks before disk ablation. No oral or parenteral corticosteroids can be given for a minimum of two weeks before the procedure. Also, most nonsteroidal anti-inflammatory drugs (NSAIDs) should not be administered during this time. These precautions are necessary for two reasons. First, the holmium laser used for disk ablation is a pulsed laser and could push (via a photoacoustic or photomechanical effect) more material into the spinal canal during an acute protrusion or extrusion episode. Second, we need to make certain potential complications from the ablation procedure are not masked by pre-existing signs or the effects of drug therapy.

Figure 2. A close-up of the spinal needles in the dog in Figure 1.

HOW THE PROCEDURE WORKS

After undergoing a presurgical evaluation, the dog is anesthetized and placed in ventral recumbency, and the dorsolateral aspect of the left upper lumbar area extending from the caudal thoracic to the caudal lumbar spinal column is aseptically prepared for percutaneous needle insertion. Seven 20-ga, 2.5- or 3.5-in myelographic or spinal needles (the length of the needles is determined by the dog's size) are placed percutaneously into the center of seven disk spaces between T10 and L4 (Figures 1 & 2). Fluoroscopy is used during needle placement to identify correct positioning (Figure 3). The laser fiber is placed through the needle into the disk space at the level of the nucleus pulposus. A holmium yttrium aluminum garnet (Ho:YAG) laser is then activated, and the disk material is vaporized and coagulated, which diminishes and stabilizes the nucleus of the disk. In theory, the disk is no longer predisposed to herniate.

Figure 3. A lateral radiograph of the spinal needle placement in the dog in Figure 1 obtained during fluoroscopy.

POSTOPERATIVE RECOVERY

Immediate post-ablation problems have been minimal. Dogs are usually kept overnight after the procedure and discharged with instructions to confine them to one floor of the home for two weeks. A few (< 1%) dogs have exhibited lumbar pain for five to seven days, which is presumed to be of muscular origin from needle insertion. Depending on the results of the immediate posttreatment examination, some animals are discharged with a short course (three to five days) of NSAID therapy if they exhibit signs of postoperative discomfort.

For more information

Nine dogs among the more than 350 animals (2.6%) that have undergone the procedure at Oklahoma State University over a 10-year period (1995-2005) have had a recurrence of paraparesis or paralysis within six to 18 months that required surgical intervention (decompressive hemilaminectomy), and all of the dogs recovered uneventfully. Since laser-tissue interaction involving degenerative (calcified) intervertebral disks can't be predicted 100% nor can the precision of needle placement within the disks be guaranteed to achieve total ablation, laser disk ablation is not guaranteed to be effective. Despite the nine recurrences, we think the procedure is beneficial since, conceptually, it potentially reduces the amount of disk material left to herniate.

The information for "On the Forefront" was provided by Kenneth E. Bartels, DVM, MS, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078.