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Long Term Results of Safety and Efficacy Using a Percutaneously Placed Interspinous Distraction Device to Treat Moderate Lumbar Spinal Stenosis. 2014

Category Interventional Purpose To assess the long term safety and efficacy of a novel percutaneously implanted interspinous spacer, placed by an interventional physician, in patients with moderate symptomatic lumbar spinal stenosis. Materials & Methods 14 patients were enrolled from 1 site into a multi-center randomized and controlled study to evaluate the safety and efficacy of the Superion® interspinous spacer. The Superion® is an interspinous spacer that is designed to treat spinal stenosis by distracting the spinous processes, ostensibly widening the spinal canal diameter as well as increasing the area of the foramen and the lateral recess. To place the study device fluoroscopic guidance is used to place an obturator in the interspinous space, via a small incision. A 10mm cannula is then placed over a series of obturators. Utilizing a variety of tools the interspinous space is prepared. An interspinous spacer is then placed between the 2 segmental spinous processes and the expanding lobes of the device are deployed, distracting the interspinous space and fixing the device to the segment. Enrollment criteria for the study consisted of moderate radiological and symptomatic spinal stenosis involving no more than 2 contiguous segments, excluding L5/S1. Spinal stenosis could consist of foraminal, central and/or lateral recess stenosis. In the opinion of the investigator leg pain had to be the prominent complaint. Leg pain had to be relieved with sitting and bending forward to be considered for study enrollment. 6 patients were later dis-enrolled when additional study related diagnostic procedures revealed that not all study criteria would be met. 3 patients were randomized to the predicate device, the X-stop®. 1 patient was randomized to and received the Superion® device after being enrolled by and operated on by a neurosurgical investigator. 4 patients were randomized to and received the Superion® device after being enrolled by and operated on by a neurointerventional investigator (GR). All patients met the enrollment criteria of the Investigating Superion In Spinal Stenosis (ISISS) study, an FDA approved phase 3 IDE study. All study procedures and follow up were performed according to the ISISS protocol. Oswestry Disability Index (ODI) and Zurich Claudication Questionnaires (ZCQ) were filled out at the baseline and each post-operative visit. Visual Analog Scales (VAS) were marked on a 100mm line, according to pain level for leg and back pain. Study questionnaires and VAS scales were scored by study personnel. Successful study outcome was determined to be a 30% improvement in ODI, 30% improvement in pain scores and 0.5 improvement in ZCQ score. Results 4 patients enrolled into the study were enrolled by and treated by the interventional investigator as the primary surgeon. 1 patient received 2 contiguous implants and 3 patients received a single implant. L1/2 was implanted in 1 patient, L2/3 in 1 patient, L3/4 in 1 patient and L4/5 in 2 patients. In 1 patient, 2 contiguous implants were planned but only 1 level was implanted due to anatomical difficulties. There were no immediate complications. However, 1 patient later developed a spinous process fracture following a rear end collision. This patient was later found to be osteopenic. 1 patient developed symptomatic stenosis at an adjacent level, after initially presenting as a good result, and underwent an additional decompressive procedure at that level. 2 patients completed the 36 month study follow up. 2 patients had followed up until the 24 month study mark. The average baseline ODI was 33. At follow up the average ODI was 28, representing a 16% improvement. The average baseline VAS back score was 42, reducing to 32 at follow up. This was a 24% improvement. The average VAS leg pain score was 42 at baseline, reducing to 31 at follow up. This represented a 26% improvement. The baseline ZCQ physical function score at baseline was 3.5. This reduced to 2.2 at follow up, a difference of 1.3 or 37%. Conclusion Symptomatic lumbar spinal stenosis is a difficult entity to treat, often failing conventional treatment and requiring surgical decompression. As most forms of spinal stenosis are due to a degenerative process, the disease itself is dynamic. Furthermore, it is likely that the underlying degenerative process may manifest itself later as a static radiculopathy or as axial back pain, affecting either the targeted study levels or adjacent levels. The effect of such disease progression is that the initial results of any intervention may be ultimately masked by the advancement of the degenerative process. In this interventional series of 4 patients treated with the Superion® device as part of a national multi-center trial we did not meet successful long term outcome criteria for ODI scores. We approached success for VAS leg and back pain scores. Interestingly, the average ZCQ physical function score far exceeded our goals. This may represent the relative ability of the ZCQ scale to ferret out progression or improvement based on spinal stenosis vs. other progressive and degenerative conditions. The use of a percutaneously placed interspinous distraction device may be effective for the amelioration of symptoms of spinal stenosis and seems safe. However, the underlying degenerative process may erode gains made in pain perception or disability faster than that seen in patients undergoing open surgery. As with most implants, pre-operative evaluation of bone density may prevent later insufficiency related complications. References None