GROUP 2: Martha Ingram, Megan Johnston, Chelsea Samson MENTORS: Dr. Michael Holzman, Dr. William Beck, Dr. Benjamin Poulose AN OPENING IN THE ABDOMEN, AN OPENING IN THE MARKET: HERNIA TENSIOMETERS

Hernias and their repair Background

What is a hernia? Protrusion of the abdominal contents through a hole in the musculature  Affects 5 million Americans every year  Must surgically realign the musculature and create a barrier, or circulatory and digestive complications may result

Repairing Hernias  Minimally-invasive laparoscopic surgery  Open hernia surgery performed for hernias greater than 25cm wide Current solutions……and complications  Tension from the abdominal muscles and fascia pulls sutures apart  Failure in over 40% of patients, despite “tension-free” repair method  Acceptable recurrence rate is 15%

“Making the Case for Hernia Research” Benjamin Poulose et al., 2011 (Vanderbilt Medical Center) Financial Impact of Decreasing Hernia Recurrence

Cost/Benefit Analysis  “Currently, there is a lack of standardization in…hernia repair procedures, with widespread variation in delivery”  Lack of standardization  Increased post-surgical complications  Failures and increased costs  Ventral hernia repairs in 2006:  154,278 inpatient + 193,543 outpatient = 348,000 operations  Inpatient operation = $15,374  Outpatient operation = $3,745 BackgroundResults Total Annual Expenditures on Ventral Hernia Procedures: $3.1 billion

The application of an intra-operative tension-measuring device could increase understanding of and prevent hernia recurrence, significantly decreasing costs.

Device requirements Using Tension Measurements to Determine Recurrence Rates

Data Collection Record tension measurements (in Newtons) for all hernia repair procedures Up to one year post- surgery, monitor if sutures fail Create curve that correlates tension values and probability of repair failure Determine tension at 15% recurrence Tension (N) 100 % 90 % 80 % 70 % 60 % 50 % 40 % 30 % 20 % 10 % 0 % Probability of Recurrence

User Response  Close hernia with sutures  Relaxing incisions  Mesh patch (inelastic polypropylene or Gore-Tex) Tension correlates to ≤15% recurrence probability Tension correlates to >15% recurrence probability

Evolution of the device Designing the Tensiometer

Device Functions and Qualities  Measure tension resisting closure at the central suture line, longitudinal to muscle alignment, after:  dissection of the injury area  separating fascia from muscle  Sterilizable, reusable, strong

Literature Search: Bassini et al., 1988 Disadvantages:  Multiple parts  Invasive  Strain gauge exposed  For use on a limited range of hernia sizes Hernia edges clamped between metal plates Serrations hold tissue in place Lash strain gauges across opening 10 – 25 cm

Design 1: Close and Measure Advantages:  Self-contained  Less invasive  Adapts to hernia sizes Disadvantages:  Not appropriate for small surgical area, thick muscle  Would not withstand large muscle forces FRONT SIDE TOP Static arm Mobile arm Digital display Gear to wind hernia edges together Force Sensor

Design 2: Indentation Testing Advantages:  Point measurements  Non-invasive Disadvantages:  Complex design  Measures transverse, instead of longitudinal, tensions

Tonomoter  “Air puff” glaucoma testing  mmHg pressure applied  Measure deformation with laser  Intraocular pressure can be determined to ±0.5 mmHg  Not very accurate; dependent on thickness of cornea and point of application

Design 3: Modified Surgical Clamp Advantages:  Small  Tool familiar to user  Use on all hernia sizes  Sterilizable and strong Disadvantages:  Surgeon may introduce some variability  Angle of pull  Clamp location  High-frequency noise Strain gauges

Fascia Fiber Directions Transversalis fascia:  Collagen fibers are oriented perpendicular to the muscle fibers  Parallel to the direction of the tensiometer pull  Fibers elongate due to tensile forces and can rupture Surgical Clamp

Proof of Concept Strain gauge in Wheatstone Bridge  Instrumentation Amplifier  [Low Pass Filter  ] Output Voltage Resistance changes when clamp is pulled Voltage changes when clamp is pulled Clamp end Handle end

Design 4: Surgical Table Arm Advantages:  Does not touch tissue  Attaches to any clamp  Use on all hernia sizes  Use a retractor to create sliding height levels Disadvantages:  Hangs over patient  Need to stiffen joints (epoxy) Thompson Retractor Surgical table Turnbuckle Surgical clamp Force scale

Testing on porcine model the week of April 4 th Clamp on one side of hernia; force scale on other Determine tension values and standard deviations