Erosion of the spinous process: a potential cause of interspinous process spacer failure.

Interspinous process spacers have recently become available for treatment of symptomatic lumbar spinal stenosis. To date, there have been few data regarding the causes of failure. The authors present 2 cases in which there was erosion of the spinous processes adjacent to the interspinous process spacers. In 1 patient, the recurrence of symptoms was likely related to the erosive changes. Such abnormal changes allow settling of the posterior spinal elements and probably results from continued motion at the treated levels.