• Systematic review and meta-analysis of randomized control trials to assess the clinical outcomes of IPD alone compared to bony decompression.

This study was funded by the National Natural Science Foundation of China and represents a systematic review of the literature and meta-analysis  of interspinous process devices (IPD) alone versus decompression for lumbar spinal stenosis.  The author’s database search found 866 potential articles.  IPD devices included X-stop, Coflex, DIAM, Wallis, and Asperious.  Studies were included if they were a randomized control trial, compared IPDA along with bony decompression, and had to have compete data for quantitative assessment at each time interval. Studies were excluded if they covered biomechanics, abstracts, case reports, or conference presentations.  Using this criteria, four randomized control trials (7 articles) were selected resulting in 200 patients in the IPD alone group and 200 patients in the decompression group.  Based on the pooled data, the authors did present the risk of various types of bias that can affect the conclusions.  The risk of bias associated with blinding of outcome assessment and “other bias”, was unclear based on the author’s judgments.

Outcome measures varied by study and included VAS, Oswestry Disability Index (ODI), Zurich Claudication Questionnaire (ZCQ), SF-36, EuroQol 5-dimensional questionnaire, complications, and reoperation rate.

The data revealed that 120 patients included (IPD alone group) had an X-stop implanted, while 80 underwent distraXion implantation.   All of the studies populations varied based on geographic location (Egypt, Sweden, Norway, Netherlands) making any type of generalizations difficult. Furthermore, no discussion regarding method of decompression (extent or levels) was presented. One randomized trial included instrumented fusion in the decompression group.

The authors of this study concluded that IPD alone had significantly higher re-operation rates and VAS scores of low back pain at follow-up. Two studies showed that IPD had higher healthcare costs and lower improvement of quality of life. No significant differences were seen in VAS (leg pain) score, ZCQ scores, ODI scores, and complication rates between the two groups.

There are many limitations to this analysis as noted by the authors including a relatively small sample size, different devices used, short follow-up duration (2 years), and no subgroup analysis. We do not have any information regarding patient selection including type and degree of stenosis and whether there was pre-op instability present.

In the opinion of Spineopedia, due to the many weakness described above along with unknowns of patient selection, there is limited usefulness of this study in drawing any conclusions regarding the use of interspinous process devices. Additional investigations by Phan et al (J Spine Surg 2016) and Nunley et al (Biomed Research Intl  2016) have also been published on this same topic and also have limited utility due to varying devices used, surgical techniques, and patient selection methods. There does appear to be a role for the use of interspinous process devices for a select group of patients with isolated lumbar spinal stenosis, but studies with appropriate sample sizes, comparison groups, and limited potential for bias, is currently lacking.