Technological Innovation in Spinal Cord Stimulation: Development of a Novel Mechanical Anchoring System
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NANS 2010 SwiftLock Poster

Published on: Mar 3, 2016

Transcripts - NANS 2010 SwiftLock Poster

  • 1. INTRODUCTION Technological Innovation in Spinal Cord Stimulation: Development of a Novel Mechanical Anchoring System Stephanie Washburn, PhD; Jazzmyne Buckels, MSc; Sudeep Dutta St. Jude Medical Neuromodulation Division, Plano, TX COMPETITIVE COMPARISON FOR HOLDING FORCE DESIGN VERIFICATION TESTS & RESULTS This work was supported by St. Jude Medical Neuromodulation Division. NANS 2010 Lead migrations and lead fractures remain two of the most common causes of revisions of spinal cord stimulation (SCS) systems (Monroe and Washburn, 2009). These complications arise from insufficient anchor retention and poor anchoring technique. Improved anchoring solutions can help to reduce these complications. A newly developed anchor has been designed to remove the technique dependent issues and frustrations associated with anchoring. The Swift-Lock™ anchor (St. Jude Medical Neuromodulation Division, Plano, TX) eliminates the need for sutures or medical adhesive when anchoring to the lead and reduces anchoring time, thereby enhancing procedural efficiency. It is also designed to reinforce the lead where it exits the vertebral column, reducing lead fatigue and subsequent lead fracture as well as potentially reducing lead migration. The Swift-Lock anchor is made of silicone and has a PEEK off-set locking feature designed to enhance holding strength and prevent migrations. It features radiopaque silicone on either end for easy identification under fluoroscopy and an extended distal strain relief to minimize lead breakage. Sliding Force Test The sliding force test measures the amount of force required to slide the anchor over the lead. This test is performed by pulling the lead through the anchor situated in the Swift- Lock anchor insert using an Instron machine at a rate of 3 in/min, while recording the maximum load it takes to slide the lead through the anchor (Figure 1, n=7). ACCEPTANCE CRITERIA: Sliding force for installing the anchor along the lead body shall be less than 0.2 LBF. RESULTS: Frictional force due to sliding was 0.097 ± 0.021 LBF. Instron machine at 3 in/min and recording the maximum load it took to move the anchor on the lead body by 2 mm (Figure 3, n = 10). ACCEPTANCE CRITERIA: Lead shall not slip through the anchor more than 2 mm after being subjected to a predetermined minimum load . RESULTS: All Swift-Lock anchors passed the criteria and met all the functional requirements of the lead. Lead Distal Tip Movement Lead distal tip movement test during anchoring measures the amount of movement at the lead’s distal tip during anchoring (n=8). ACCPETANCE CRITERIA: Anchor engagement shall not move the distal tip of the lead more than the following: Axial or longitudinal movement: +/- 3 mm; side or lateral movement: +/- 1 mm. RESULTS: All Swift-Lock anchors passed the lead distal movement test during anchor installation. Flex Test The flex test bends the lead bodies in a back and forth motion at a set radius. Upon securing the anchor to the lead, the lead- anchor assembly is secured to the Lead Flex tester using a specially designed holder that facilitates bending of the leads at a set radius of 6mm +/- 0.1mm bend radius. The anchor strain relief is flexed to a minimum of 47,000 flex cycles at +/- 90 degrees without electrical or mechanical damages (Figure 2, n=10). ACCEPTANCE CRITERIA: Lead anchor assembly shall pass the test without any mechanical damage or change of electrical integrity. Several types of anchors from different companies (BSX: Boston Scientific; MDT: Medtronic; SJM: St. Jude Medical) were tested for holding force capabilities. Anchors were separated into three categories: 1) Conventional silicone anchor Short by BSX (n=4) Medium by BSX (n=5) Butterfly by SJM (n=7) Long by SJM (n=7) 2) Enhanced conventional silicone anchor Cinch by SJM (n=10) Titan by MDT (n=8) 3) Mechanical locking anchor Twist-Lock by MDT (n=3) Swift-Lock by SJM (n=10) Test Method All silicone anchors were sutured to the SJM lead body using 2-0 silk suture with a surgeon’s knot. Mechanical locking anchors were locked normally. All anchors were subsequently soaked in saline at 37°C for a minimum of 3 days and then pulled on an Instron machine at 1 in/min while recording the maximum load it takes to move the anchor on the lead body by 2 mm (Figure 4). NOTE: This test does NOT represent in-vivo conditions, but was used for mechanical performance comparisons. RESULTS: In the data presented the average holding force has been normalized to the overall average holding force for conventional silicone anchors (set to 100%). Significance (p<0.05) between groups denoted by asterisk. The results of the verification tests indicate that the Swift-Lock anchor provides anchoring strength and integrity. In addition, benchmark testing for competitive comparison of holding force show that the mechanically locking Swift-Lock anchor provides superior holding force on the lead. CONCLUSION Figure 1: Sliding force test. (A) Instron testing machine (B) Sliding force test fixture A   B   Figure 2: Flex test (A) Flex testing machine (B) Anchor distal strain relief flexed at 90 degrees A   B   Figure 3: Holding Force test (A) Instron testing machine (B) Dacron sheet (C) Temperature controlled anchor retention chamber B   C   A   C   Figure 4: Holding Force test for Competitive Comparison (A) Test fixture (B) Titan anchor sutured to SJM lead body A   B   RESULTS: All the samples tested met the criterion of no electrical or mechanical damage after 50,000 flex cycles (exceeded min. 47,000 flex cycles requirement). Holding Force Test The holding force test measures the amount of force required to pull the lead through the anchor. Before insertion of the lead into the anchor, lubricant was applied to the lead to simulate the lubricity of the lead when exposed to human fat. Once situated, the anchor was locked and sutured to a dual Dacron sheet using two surgeon’s knots to simulate attachment to the fascia. All anchor/lead/Dacron sheet assemblies were subsequently soaked in saline at 37°C for 72 hrs, and then inserted into a temperature controlled (37°C) anchor retention force tester to simulate in-vivo conditions (Figure 3). A tensile test of the lead was then performed using an

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