To evaluate mechanical properties of a novel sacral stimulation lead with fin fixation and braid reinforced body with that of a sacral lead with tined fixation.   

To evaluate the leads properties following cyclic stretching mimicking the movement of a lead in a patient.

Five (5) standard tined leads
Five (5) novel finned leads

EQUIPMENT
Instron Test System: ISN 01538 with testing software and accessories

Testing Procedure:
Three tests were conducted:
-	Cyclic Elongation testing: Test samples were engaged in the Instron tester and pulled to defined elongation values of 1,2,3,4,5,10,5,20,30,40,45 mm, respectively. Samples were returned to initial start point between each cycle of elongation. (see Figure 1)
-	Anchor (fixation) Failure testing: Fixation features were constrained in a silicone tube filled with silastic adhesive.  Testing was performed by pulling on the fixation area of each lead and the connector end. 
-	Mechanical Failure testing: Leads were tested for lead body strength from the lead connector end to a point between the fixation feature and the most proximal electrode. Force at mechanical failure was recorded. (See Figure 2)

In cyclic elongation the finned reinforced lead stretched for 20 mm with minimal peak force, after this when the braid reinforcement was engaged the force needed for elongation significantly increased. At an elongation of 20mm the forces within the tined lead were significantly greater.

In the Anchor Failure test a similar force was required for anchor failure (defined as the lead separating from the external silicone tube at the fixation area) for both tined and finned leads.  All finned leads remained mechanically and electrically intact whereas one tined lead failed electrically and mechanically. Following testing, there was less permanent lead length elongation in the finned leads (1.38%) as compared to the tined leads (5.74%).

In the Mechanical Failure test the tined lead failed mechanically at 27.1N average force while the finned leads failed at 46.8N average force.  This represents 73% greater force required to induce mechanical failure in finned leads with reinforced lead bodies as compared to the tined leads.

As compared to the tined lead the stretching quality may reduce force transmitted to the lead tip thus requiring higher forces prior to lead migration in the finned design. The finned sacral lead compensates for force on the lead by temporarily stretching.  

Force required for anchor failure is similar for both leads however permanent lead deformation is more likely in the tined leads. 

The force needed to induce mechanical failure of the tined leads was significantly lower than that of the finned leads.

Finned leads subjected to pull forces initially undergo reversible stretching after which the reinforced braid engages and provides significantly increased axial strength.  In comparison, the tined lead undergoes greater irreversible elongation.  Furthermore, mechanical failure of the tined lead occurs at a significantly lower force than the finned lead.

These qualities may reduce the incidence of lead migration as well as that of lead breakage if removal is required.  These factors may improve sacral neuromodulation efficacy and lower the risk of a retained lead fragment which could be of concern to the patient and physician. In-vivo studies are required to confirm these suggestions. 

Disclosure:
The authors receive compensation for services to COMPANY NAME, Inc., which is developing products related to the research described in this paper.  Opinions and conclusions herein are solely those of the authors themselves. COMPANY NAME makes no claims regarding the opinions expressed herein.