Through the Looking Glass: Specialty Influence on SCS Outcomes

To the Editor: It was with great interest that we read the article by Lad et al. (1) which tested the hypothesis that spinal cord stimulator outcomes, defined as a trial to permanent conversion, can be determined based on specialty demographics of the surgeon. Specifically, specialties traditionally trained in surgical implantation of spinal cord stimulation systems may have a higher trial-to-permanent conversion rate, and, therefore, improve health care economics and better utilize healthcare resources. The magnitude of this effect, deviating from previous work (2), and the possible ramifications for training or policy decisions warrants closer inspection of their methods and data, as it seems the conclusions are flawed and irresponsible. To better describe this assertion of a difference of success among specialties, let us look to the recent randomized controlled trials published in our space: the DRG study (3) and the spinal cord stimulation high frequency 1000 Hz study (4). Each supported a trial to permanent ratio above 80%. Among the authors (and the implanters), 25 of the 26 physicians for the DRG study and 15 of the 15 physicians for the HF10 study were not orthopedic spine or neurosurgeons. This poses an interesting scenario when looking at market scan analysis vs. the innovation introduction to our space. Many of the assumptions within Lad’s work can be only described as a poorly described methodology. Overly simplified, Lad et al. has defined success as a trial to permanent ratio. This statistic is outdated and not representative of the current benchmark for sustainability of the therapy. Further, the physician groups described in the article are not adequate and fail to identify to describe formal neuromodulation training or tenure. With closer inspection, there are questions regarding the analysis that need to be clarified to better understand the authors’ conclusions. First, there are many variables noted in Tables 1 and 2 on the univariate regression analysis that demonstrate statistically significant differences among the patients seen by the different specialties. “Anesthesiology” providers saw older patients, with a higher Medicare/Medicaid mix, and with more difficult to treat pain pathologies such as CRPS. The authors do not include all these significantly different variables in the multiple regression analysis. They do not discuss why they chose to include or exclude the variables they did use, even though they published on the impact of these variables previously (2). Certainly this oversight makes it impossible to make any meaningful conclusions. The inclusion of those significant variables in the analysis would properly control for the differences in the populations and, more importantly, the procedure being done on the dependent variable of trial conversion. Validating this assertion is that explants among the categories defined in this analysis demonstrated a similar explant rate across all specialties, and with aforementioned argument, one could make the argument non-orthopedic or neurosurgeons faired better. As highlighted in the Neuromodulation Appropriateness Consensus Committee on Safety Guidelines for the Reduction of Severe Neurological Injury, published in January of 2017 (5), Petraglia et al. published their investigation of spinal cord injury following percutaneous and surgical paddle leads (6), with no statistical difference amongst lead type (and very likely specialty). A closer analysis of Table 1 suggests the most likely source of the large variation in conversion rate is due to the lead type, with surgical specialists primarily using a combination of paddle and percutaneous implants. For implants, 50–70% of surgical specialist implants were a combination as compared with 4–6% in the other groups. As paddle leads are more traumatic for placement but have been shown to have higher success rates (7), this large variation likely skews the conversion rate rapidly, yet lead type is not included in the multiple variable analysis. Furthermore, the use of combined paddle and percutaneous leads for the implant suggests the majority of surgically placed implants are being done as combination dorsal column stimulation with additional off-label field stimulation, which would greatly complicate any conclusions from this work. Oddly, the authors also noted but chose not to correct for their recently noted volume-effect from this same dataset (8). It has already been suggested that centers of excellence be established to better improve healthcare outcomes and utilization (9). This suggestion was popularized by Malcom Gladwell with his work “Outliers” and the “10,000 hour rule” (10). Further, it is already well described that approximately 20% of the implanting physicians in the United States are performing approximately 80% of the SCS volume. Does a neurosurgical specialist who does a low volume of SCS cases perform better than a PM&R specialist who does a high volume? These highly confounding variables are something the authors could readily have corrected for in their multiple variable analyses, but they did not, and the most recent accepting reviewers must not have asked them to. Overall, we suspect that the Neuromodulation readership would agree that there is a need to increase the utilization of these technologies to those suffering from chronic pain. It is also necessary to identify patient, technology, and provider factors that predict success. We can agree that anesthesiology, internal medicine, neurology, physical medicine and rehabilitation, radiology, orthopedic, and neurosurgical providers have varying amounts of training and