NANS 2010 SwiftLock Poster
Published on: Mar 3, 2016
Transcripts - NANS 2010 SwiftLock Poster
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
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
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
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)
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
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
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.
Sliding force test.
(A) Instron testing machine
(B) Sliding force test fixture
Figure 2: Flex test
(A) Flex testing machine
(B) Anchor distal strain relief
flexed at 90 degrees
Figure 3: Holding Force test
(A) Instron testing machine
(B) Dacron sheet
(C) Temperature controlled anchor
Figure 4: Holding Force test for Competitive
(A) Test fixture
(B) Titan anchor sutured to SJM lead body
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