A Review of Available Interspinous Spacers

In this article, two neurosurgeons bring us up-to-date on the use of four different interspinous spacers for the treatment of back pain from spinal stenosis. Interspinous means the spacers are placed between two spinous processes. Those are the bumps you feel along your back. They are knobs of bone that extend out from the vertebral bodies.

Spinal stenosis is a narrowing of the spinal canal, the opening formed by the vertebral arches. This is where the spinal cord travels from the brain to the base of the spine. Lumbar spinal stenosis is a common problem in older adults (age over 65). Low back pain and/or leg pain/discomfort are the first signs of this problem. Flexion bending forward relieves the pain, so patients adopt a bent posture called the shopping cart sign.

Because symptomatic spinal stenosis can be very disabling, surgeons are looking for ways to help support and stabilize the spine. Keeping the vertebrae from bending backwards (a direction that makes the symptoms worse) is the goal. These interspinous spacers may be helpful when more conservative (nonoperative) care doesn't improve symptoms. They can be used in frail, elderly adults who aren't well enough to have surgery.

Only one spacer on the market has been approved by the Food and Drug Administration. That's the X-Stop. Three others are being studied with the intent to seek FDA approval. They are the Interspinous U (also called Coflex, the DIAM, and the Wallis system. They all work to limit spinal extension.

Color photos or schematic drawings of each system are included. These pictures help show where and how these spacers are used. Again, each one does the same thing: holds the spine in a position of slight flexion to decompress (take pressure off) the spinal cord or spinal nerve roots. The spine can still rotate or bend to the side when the spacer is in place.

The placement varies slightly based on the shape and design of the device. The manufacturer of some of these spacers says they can be used for more than just spinal stenosis. Scoliosis, compression fractures, herniated discs, spinal instability for any reason, and degenerative disc disease are some of the conditions listed.

Each one of these has its own pros and cons. Some are static (they have no give; they keep a constant state of the same amount of distraction no matter what) while others are dynamic (they compress and distract a bit, especially with spinal movement). The X-stop is the only one that can be inserted under local anesthesia. The ligaments around the spine are saved from being cut. The device slips right through a slit made in the ligament.

So, everyone agrees the X-stop is easy to use. But does it work? That's the question! Right now, there isn't enough evidence from high-quality designs to answer that question. Early, short-term results show a positive benefit (pain reduction, improved function) in more than three-fourths of the patients. Safety is a concern but complications such as infection, fracture, increased pain, or implant movement or breakage have been very low so far.

There's no data on larger groups of patients or on the long-term results. The authors of this review commented on the poor quality of some of the research that has been done. They say that the study design was questionable for some of the studies. Research must be done to look at the adjacent levels for possible adjacent vertebra degenerative disease. The authors strongly urge random controlled trials to find out when these devices should be used and with whom.

Dhruve Jeevan and Kaushik Das, MD. Interspinous Process Devices for the Treatment of Lumbar Degenerative Disease. In Current Orthopaedic Practice. May/June 2009. Vol. 20. No. 3. Pp. 232-237.

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