Evaluate the long term safety and effectiveness of the X-Stop interspinous process decompression system In the patients who received the X-Stop under the IDE. These patients consist of two cohorts to be evaluated: patients who had moderately impaired physical function prior to X-Stop implantation (as determined by a baseline score \>2.0 in the physical function (PF) domain of the Zurich claudication questionnaire), and patients who had mildly impaired physical function prior to X-Stop surgery(as determined by a baseline score \<=2.0 in the PF domain of the Zurich claudication questionnaire (ZCQ), through the fifth postoperative year. Clinical examination will be performed at each office visit to confirm the absence of neurological complications. X-ray films (AP/lateral views) taken during the fifth postoperative year will, be analyzed to confirm A) maintenance of distraction and B) the absence of radiological evidence of device-related complications. Secondary endpoints will include mean scores from the SF-36, and incidence rates of adverse events, device failures, and secondary surgeries.
