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Lower Spine News

New Problem Discovered with X-Stop Devices

Neurosurgeons from Italy are the first to report a new complication with X-stop devices used in the lumbar spine. What are X-stops? And what's the new problem?

X-stops are spacers placed between two vertebrae to hold them apart. They are used to manage various degenerative conditions of the lumbar spine such as spinal stenosis (narrowing of the spinal canal) and disc degeneration. The surgeon implants the X-stop between the spinous processes -- not between the main bodies of the vertebrae. The device is called an X-stop because it stops the movement of spinal extension at that level. The spinous process is the bony projection off the vertebra that you feel as you run your hand down along your spine.

The new problem is a fracture of the spinous process with dislocation of the X-stop distractor. Three cases have been reported in patients who had two X-stops placed between L3-L4 and L4-L5. The surgeons named this new type of fracture the sandwich phenomenon because the broken spinous process (L4) was sandwiched between two X-stop distractors.

The spinous process at L4 between the two implanted X-stops fractured without warning and without apparent cause. Fractures without injury or outside force are called atraumatic (without trauma).

Although X-stop is a fairly new treatment technique, two-level implants of this type have been used in many patients around the world without problems. The atraumatic fractures described in this report affected three men of different ages. It is considered a rare postoperative complication. In all three cases, the initial response after surgery was complete pain relief. But after a few months, the patients' back and leg pain came back.

That's when the diagnosis of spinous process fracture was made. X-rays and CT scans showed that with a fracture of this type at the base of the spinous process (where it attaches to the main body of the vertebra), the X-stop was pushed away from the spine (dislocated). Surgery was done in all three cases to remove the X-stops and fuse the spine.

What causes a spontaneous fracture like this? That presents an unsolved puzzle. There could be some anatomic difference in these three men contributing to the fractures. But what exactly that difference is remains a mystery. There was no sign of osteoporosis (decreased bone density leading to brittle bones) that could account for the fracture. The double-level procedure was the most likely key feature.

The authors of this report suggest a possible piston effect on the spinous process. Having an X-stop above and another one below the process applied pressure to the bone with every spinal movement until the spinous process finally snapped. They concluded that despite this rare sandwich phenomenon, X-stop implants are still safe and effective.

Future cases of fatigue fracture in double-level X-stop devices from the sandwich phenomenon will be investigated carefully to find out why this happens. Anatomy, biomechanics, device size, and spinal mobility will be studied as possible contributing factors.

Placement of the devices too far forward or too far back in relation to the spinous process may be another possible cause. And there's some speculation that each patient has one or more risk factors unique to him or her. No recommendations are being made to avoid double-level surgeries until further information has been gathered and data analyzed.

In summary, by distracting the spinous processes of two vertebrae, the X-stop takes pressure off the spinal nerve roots and reduces back and leg pain. But in rare cases, there can be complications with spinous process fractures when double-level X-stops are used. Patients should be warned about this. Any recurrence of pain and neurologic symptoms should be reported to the surgeon right away for evaluation.


Giuseppe M. V. Barbagallo, MD, et al. The Sandwich Phenomenon: A Rare Complication in Adjacent, Double-Level X-Stop Surgery. In Spine. February 1, 2010. Vol. 35. No. 3. Pp. E96-E100.

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