The Coflex interlaminar device is the latest interspinous implant to come to market, and the results of its FDA IDE trial were published in the August 15 issue of Spine. The non-inferiority study compared two year outcomes between 215 patients treated with Coflex and decompression and 107 patients undergoing decompression and fusion. Patients had either spinal stenosis with significant back pain (defined by an ODI score over 40 or back pain VAS over 50) or stenosis with a grade 1 degenerative spondylolisthesis. At two years, clinical outcomes (SF-36, ODI) were similar, though the Coflex group had significantly more improvement in their Zurich Claudication Questionnaire (ZCQ) scores. The Coflex group also had significantly lower blood loss, operative time, and hospital stay. The re-operation rate for Coflex was higher (10.7% vs. 7.5%), though this difference was not significant. Fourteen percent of the Coflex patients were found to have spinous process fractures, though this did not appear to result in worse clinical outcomes. Coflex was found to be non-inferior to decompression and fusion for one or two level stenosis with significant back pain or low grade degenerative spondylolisthesis.
Like most FDA IDE studies, this was a high quality, Level 1 study that provides valid results. The main criticism that can be levied against this trial is that over 50% of patients who underwent fusion did not have spondylolisthesis or any other evidence-based indication for fusion. While the inclusion criteria did include an ODI score over 40 and back pain VAS over 50, no study has ever demonstrated that stenosis patients who meet these criteria do better with fusion compared to decompression alone. In their classic article, Grob et al. reported no benefit to adding fusion to decompression for stenosis patients without instability.1 While SPORT demonstrated that stenosis and degenerative spondylolisthesis patients with predominant low back pain had less improvement following surgery than those with predominant leg pain, this held true even for the spondylolisthesis patients who underwent fusion.2 Many surgeons would not fuse the majority of patients in this trial (i.e. those without spondylolisthesis), so one could argue that the control group was not appropriate. It seems likely that the advantages in terms of blood loss, operative time, and hospital stay observed in the Coflex group would not be present if the control group underwent decompression alone. Unlike prior studies of interspinous devices, the two year re-operation rate for the Coflex group was relatively low at 10%. While the industry-sponsored IDE trial evaluating the X-Stop reported a re-operation rate of 6% at one year, subsequent studies reported rates of 25-30% at 2 years.3,4 Others have also reported a particularly high failure rate for the X-Stop in degenerative spondylolisthesis patients, and the current study did not report results separately for the spondylolisthesis patients.5 While the current study demonstrated non-inferiority for decompression and Coflex compared to decompression and fusion for spinal stenosis, the more relevant question is whether Coflex offers any advantage versus decompression alone for patients without instability. Hopefully such a study evaluating this will be done in the near future.
Adam Pearson, MD, MS
Associate Web Editor
1. Grob D, Humke T, Dvorak J. Degenerative lumbar spinal stenosis. Decompression with and without arthrodesis. The Journal of bone and joint surgery American volume 1995;77:1036-41.
2. Pearson A, Blood E, Lurie J, et al. Predominant leg pain is associated with better surgical outcomes in degenerative spondylolisthesis and spinal stenosis: results from the Spine Patient Outcomes Research Trial (SPORT). Spine (Phila Pa 1976) 2011;36:219-29.
3. Stromqvist BH, Berg S, Gerdhem P, et al. X-Stop Versus Decompressive Surgery for Lumbar Neurogenic Intermittent Claudication: Randomized Controlled Trial With 2-Year Follow-up. Spine 2013;38:1436-42.
4. Zucherman JF, Hsu KY, Hartjen CA, et al. A prospective randomized multi-center study for the treatment of lumbar spinal stenosis with the X STOP interspinous implant: 1-year results. Eur Spine J 2004;13:22-31.
5. Kim DH, Shanti N, Tantorski ME, et al. Association between degenerative spondylolisthesis and spinous process fracture after interspinous process spacer surgery. The spine journal : official journal of the North American Spine Society 2012;12:466-72.