Surgery for Lumbar Spinal Stenosis: Sometimes Less is More

Structure: Discs
The disc is the shock absorber for the spine. As the disc undergoes the natural process of degeneration, it begins to desiccate or dry up. The result is loss of structural integrity whereby the disc can no longer support the weight of the spine. As a consequence, the disc bulges much the same way as a tire bulges when it is low on air. The bulging of the front or anterior wall of the spinal canal results in narrowing of the canal.

Structure: Facet Joints
The second structure involved in spinal stenosis is the facet joint. There are actually two facet joints for each level of the spine; one on each side. The facet joints allow motion, mostly during flexion and extension of the spine.

The lining of the facet joint is comprised of the same type of cartilage as hip or knee joints. As such, this lining is susceptible to the same arthritic changes as with other cartilaginous joints. These changes involve erosion and narrowing of the joint space. The inflammatory response leads to growth of bone around the joint. The end result is narrowing of the sides of the spinal canal and the small holes or foramen through which the nerves exit the canal.

Structure: Ligamentum Flavum
The third structure making up the posterior or back wall of the spinal canal is called the ligamentum flavum. It is also called the yellow or elastic ligament. This ligament is a dynamic structure, meaning that it changes its shape depending on the position of the spine. When the spine is flexed as during sitting, the ligament is stretched or narrowed. This opens the spinal canal creating more space for the spinal nerves. When the spine is extended however as when standing, the ligament is shortened and thickened creating less space for the spinal canal. This is why patients with spinal stenosis have symptoms when standing or walking but have almost instant relief from sitting down.

Symptoms
The symptoms of spinal stenosis are very consistent. Simply, standing and walking become intolerable but sitting or driving a car is no problem. A super market can only be navigated by leaning on the shopping cart. A patient with spinal stenosis learns every bench and chair in the mall or doesn’t venture there at all. The symptoms usually involve the legs more than the back and in fact may be misdiagnosed as a problem with the blood vessels in the legs. The legs become painful or cramped after a short period of standing or walking. They may become weak and numb or “feel like wood” due to the impingement of the nerves. Back pain may accompany the leg symptoms due to the facet arthritis or from muscle fatigue resulting from bending forward to keep the spinal canal open. Over time, it becomes more comfortable to sit than stand and life becomes more sedentary. Rarely, a wheel chair becomes the only means of transportation.

Treatment
Early treatment for spinal stenosis includes physical therapy to remain active, and anti-inflammatory medication such as NSAIDs. Injections such as epidural steroid injections can be dramatic in relieving the symptoms. Unfortunately the relief is often short-lived. When non-surgical treatment is no longer successful, it is time to consider surgical decompression.

Surgical Treatment
Historically, the surgical treatment of choice has been the laminectomy. This operation involves removing the structures that comprise the posterior or back of the spine. This includes the spinous processes, the bones that stick out from the back of the spine. The spinous processes are the bumps that one feels when they run their finger up and down the spine. Between the spinous processes runs a ligament that extends from the base of the skull to the bottom of the spine or the sacrum. When leaning forward, this ligament is under significant tension. This allows for a person to lean forward without fatiguing the back muscles. The ligament acts in much the same way as the cable on a crane that runs down the back of the swing arm allowing it to extend out without falling over.

Unfortunately, by removing the spinous processes, the ligament is also removed. This can create instability in the spine resulting in chronic back pain and recurrence of the leg symptoms. Studies on the long-term results of laminectomy often show deteriorating outcomes several years after the surgery. A review of the existing literature in 1991 showed an average success of only 64%.

“Port-Hole” Decompression
In 1992 The New Hampshire Spine Institute developed and tested a surgical procedure for spinal stenosis called the “port-hole” decompression. Instead of performing a laminectomy and removing the spinous process, the spinal canal was decompressed through openings or “port-holes” that left the spinal structures intact.

Laminectomy Decompression

"Port-Hole" Decompression

The long-term results were presented at the North American Spine Society meeting in 1997, receiving the Outstanding Poster award for that year. At four years after surgery 98% of the patients were still satisfied with the results of the operation. Before the surgery only 6% of the patients could stand or walk for more than 15 minutes. At four years from the time of surgery, 96% of the patients could stand or walk for more than 15 minutes. Since that time, hundreds of patients have benefited from this less invasive procedure. The full research article can be found in the journal Spine 2000; 25:865-870.