Spinal Stabilization
In the human medical device market, today's standard for spinal stabilization is a polyaxial pedicle screw made of titanium, which is highly resistant to corrosion and fatigue, and is MRI compatible. The screw is threaded and the head articulates over 50 degrees; the ability to swivel helps to reduce the stress of securing the implant in the correct plane. Like other spinal screws, polyaxial screws are available in different sizes.
The Problem
Low back pain in dogs is a common clinical problem and can be the result of many different pathologies. Degenerative lumbosacral stenosis (DLSS) is the most common cause of lumbar back pain in mid to large breed dogs. DLSS is characterized by bony and soft tissue changes leading to stenosis of the spinal canal and moderate to severe compression of the cauda equina. The intervertebral disc (IVD) is often degenerated, which results in a shift of the load bearing from the IVD to surrounding bony structures, leading to spinal instability. Low back pain can also be caused by other conditions, such as discospondylitis, trauma (fracture and/or luxation), or neoplasia. The biomechanics, pathogenesis, clinical manifestation, and treatments of lumbar disc herniation are very similar between dogs and humans. ArteMedics has adapted well-known titanium polyaxial pedicle screws from the human market and has customized them for dogs and horses.
Clinical Signs
The clinical signs of DLSS in dogs are well-documented. Clinical examinations generally show symptoms that are related to the compression of the cauda equina. Examples of this include lumbosacral pain, hyperesthesia of the lumbosacral region, difficulty standing from a sitting position, jumping, getting into the car or up on a bed, unilateral or bilateral pelvic limb lameness, and posterior paresis. The most consistent finding during clinical examination in dogs with DLSS is pain evoked by pressure applied over the lumbosacral region (pressing just cranial to the hips directly over the spine). There are specific tests that can be performed to evoke this pain response in the clinic to obtain more information about the patient. An experienced clinician is able to differentiate between pain evoked by hyperextension of the hip joints and pain on hyperextension of the lumbosacral region. Lumbosacral pain can further be examined by individual hyperextension of each pelvic limb and simultaneous lumbosacral pressure to confirm lateralization (left or right) of the lumbosacral pain.
Medical Treatment
The conservative treatment of DLSS consists of the use of nonsteroidal anti-inflammatory drugs (NSAIDs), limited exercise routines, and body weight reduction, the same treatment scheme as osteoarthritis. The use of systemic corticosteroid treatment is somewhat controversial because the analgesic effect provided through their anti-inflammatory actions can be achieved using NSAIDs, which has significantly fewer side effects. Steroids also have many undesirable side-effects.
Surgical Treatment
Surgical treatment of DLSS is indicated in dogs with moderate to severe lumbosacral pain that has been unresponsive to medical treatment and in dogs with neurologic deficits. The aim of the surgery is to decompress the cauda equina and free the entrapped nerve roots. The primary surgical procedure typically comprises dorsal laminectomy, which is extended with additional procedures when further decompression is required: (1) partial discectomy consisting of dorsal fenestration (or dorsal annulectomy) and nuclear pulpectomy (or nucleotomy); (2) foraminotomy; and rarely, (3) facetectomy. Fixation and fusion using polyaxial pedicle screws and rods is a robust method of stabilization, and provides significant improvements over plates or pins and PMMA.
