Permanent trials for spinal cord stimulation.

Introduction: Prior to the permanent implant of a spinal cord stimulator, patients typically undergo a screening trial using a percutaneously placed lead to ensure adequate response. However, due to several factors, patients may not be candidates for this screening trial and therefore instead undergo a "permanent trial" where either a percutaneous lead or paddle lead is placed using a tunneled extension for the trial, with the intent of conversion to a permanent system. If these patients proceed with an implant, the epidural space is not re-accessed and only an impulse generator (IPG) is needed. Although this technique is commonly employed, there is a paucity of literature describing outcomes with the "permanent trial" methodology. We present here our clinical experience with this technique.

Methods: Participants who underwent permanent trials at a single institution between 2014 and 2020 were identified. Charts were reviewed to collect demographic information, numerical rating score (NRS) data, length of follow-up, revisions, complications, and removals.

Results: A total of 27 patients who underwent permanent trial placement were identified from a database of 762 patients who underwent SCS placement (3.54%). The permanent placement group included 7 paddle trials, 14 percutaneous trials, and 6 dorsal root ganglion (DRG) trials. The reasons for pursuing a permanent trial included previously aborted percutaneous trial (n = 8), inability to hold anticoagulation for a prolonged period (n = 4), previous thoracic spine surgery or presence of thoracic stenosis on MRI (n = 4), and significant medical comorbidities precluding typical percutaneous trial lead placement at a surgery center (n = 3). 24/27 (88.8%) proceeded to permanent implant, and 16/24 (66.7%) were considered responders (greater than 50% reduction in pain) after 3 months. Over an average follow-up of 28.7 months, complications included 1 peri-operative intracranial hemorrhage delaying IPG placement, 2 lead fractures, 1 lead migration, and 1 CSF leak. Three patients required revision surgery for lead migration, lead fracture, and CSF leak, respectively. One patient had his system explanted 25.9 months after initial placement due to increased pain from stimulation.

Conclusion: This study aims to characterize our experience with permanent trials for SCS. Here we demonstrate a higher rate of trial-to-implant conversion than previously documented for traditional percutaneous trials. We show similar rates of revisions and complications, elucidating the important role of permanent SCS trials in high-risk patients.