Researchers have found the Superion (VertiFlex Spine) interspinous process spacer to be non-inferior to the X-Stop (Medtronic) spacer, while also employing a less invasive surgical approach. The study was published by The Spine Journal.
Vikas V Patel, University of Colorado Hospital, Denver, USA, led the prospective, multicentre, randomised, controlled, investigational device exemption noninferiority trial. The objective of the project was to determine two-year outcomes in patients with intermittent neurogenic claudication, secondary to moderate lumbar spinal stenosis, who were treated with the Superion interspinous process spacer.
Patel et al compared the Superion spacer with the X-Stop spacer, which in 2005 became the first, and to date the only, FDA-approved interspinous spacer for the treatment of neurogenic claudication secondary to lumbar spinal stenosis. The team decided to carry out their study because “High-quality comparative data with these devices are lacking”.
Patients presenting with intermittent neurogenic claudication secondary to moderate lumbar spinal stenosis who failed at least six months of nonsurgical management were randomly allocated to treatment with the Superion spacer or the X-stop (control) spacer and followed for two years.
A total of 391 randomised patients were implanted with Superion (n=190) or control (n=201) spacers at 29 sites in the USA between August 2008 and December 2011. Implants were successfully implanted in 99.5% of patients with Superion and 99% of control patients. The primary composite endpoint of this study was met, “which demonstrated that the Superion spacer was noninferior to the X-Stop spacer”, Patel reports.
Patel and colleagues write, “Leg pain, the predominant patient complaint, decreased in severity by 70% during two years in each group. Most (77%) patients achieved leg pain clinical success (improvement ≥20mm) at two years. Back pain clinical success (improvement ≥20mm) was 68%, with no differences between groups. Oswestry Disability Index clinical success (≥15% point improvement) was achieved in 65% of patients.” The rates of complications and reoperations were similar between groups.
As well as providing “patient outcomes comparable with the X-Stop”, the “significant” differences in the device design and surgical placement techniques of the two spacers means that the Superion device presents a less-invasive alternative to the use of the X-Stop device. Superion’s minimally invasive approach via a cannula requires no surgical dissection of the spinal musculature. The authors “attribute the lower blood loss and shorter hospital stay associated with Superion to these procedural differences”.
The authors also suggest that the Superion device may be biomechanically superior to the X-Stop, due to a “significant number of dislodgements and migrations with the X-Stop device whereas none were observed in the Superion group.” They hypothesise that this may be as a result of the greater anatomic disruption caused by the X-Stop insertion technique, and may even be a result of the X-Stop’s slender-winged device.
Though this study did not compare the two techniques, Patel argues that the data from this, and previous, studies suggest that the midterm efficacy of interspinous spacers is “at least comparable with that of open decompression surgery”. The existing literature shows that leg pain is reduced by 43–69% after laminectomy, compared to 70% in this study. Furthermore, this treatment may be more attractive than open decompression for patients due to its less invasive approach. For example, in the SPORT (Spine Patient Outcomes Research Trial), procedural outcomes included blood loss of more than 300ml, procedure time of more than two hours and hospitalisation of more than three days. In contrast, interspinous spacers results in blood loss of 5–25ml and reductions in procedure and hospital stay time of around 50%.
Patel does make clear that the “long-term durability of interspinous process spacers is unknown and requires further investigation”.