An Opening in the Abdomen, An Opening in the Market: Hernia Tensiometers

1. An Opening in the Abdomen,An Opening in the Market:Hernia Tensiometers GROUP 2: Martha Ingram, Megan Johnston, Chelsea Samson MENTORS: Dr. Michael Holzman, Dr. William Beck, Dr. Benjamin Poulose

2. Background Hernias and their repair

3. 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

4. Repairing Hernias Current solutions… …and complications • Minimally-invasive laparoscopic surgery • Open hernia surgery performed for hernias greater than 25cm wide • 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%

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

6. Cost/Benefit Analysis Background Results • “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 • Total Annual Expenditures on Ventral Hernia Procedures: • $3.1 billion

7. 40% recurrence 15% recurrence = $775 million saved The application of an intra-operative tension-measuring device could increase understanding of and prevent hernia recurrence, significantly decreasing costs.

8. Using Tension Measurements to Determine Recurrence Rates Device requirements

9. Data Collection Probability of Recurrence 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 100 % 90 % 80 % 70 % 60 % 50 % 40 % 30 % 20 % 10 % 0 % Tension (N)

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

11. Designing the Tensiometer Evolution of the device

12. 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

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

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

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

16. Tonomoter “Air puff” glaucoma testing 10-20 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

17. 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

18. Fascia Fiber Directions Surgical Clamp 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

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

20. 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 Force scale Surgical clamp

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