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 ID: 709727
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GROUP 2: Martha Ingram, Megan Johnston, Chelsea SamsonMENTORS: Dr. Michael Holzman, Dr. William Beck, Dr. Benjamin Poulose
An Opening in the Abdomen,
An Opening in the Market:
Hernia
TensiometersSlide2
Hernias and their repairBackgroundSlide3
What is a hernia?Protrusion of the abdominal contents through a hole in the musculatureAffects 5 million Americans every year
Must surgically realign the musculature and create a barrier, or circulatory and digestive complications may resultSlide4
Repairing HerniasMinimally-invasive laparoscopic surgeryOpen 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%Slide5
“Making the Case for Hernia Research”Benjamin Poulose et al., 2011(Vanderbilt Medical Center)
Financial Impact of Decreasing Hernia RecurrenceSlide6
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
Background
Results
Total Annual Expenditures on Ventral
Hernia Procedures:
$
3.1 billionSlide7
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.Slide8
Device requirementsUsing Tension Measurements to Determine Recurrence RatesSlide9
Data CollectionRecord tension measurements (in Newtons) for all hernia repair procedures
Up to one year post-surgery, monitor if sutures failCreate curve that correlates tension values and probability of repair failureDetermine tension at 15% recurrence
Tension (N)
100 %
90 %
80 %
70 %
60 %
50 %
40 %
30 %
20 %
10 %
0 %
Probability of RecurrenceSlide10
User ResponseClose hernia with sutures
Relaxing incisionsMesh patch (inelastic polypropylene or Gore-Tex)
Tension correlates to ≤15% recurrence probability
Tension correlates to >15% recurrence probabilitySlide11
Evolution of the deviceDesigning the TensiometerSlide12
Device Functions and Qualities Measure tension resisting closure at the central suture line, longitudinal to muscle alignment, after:dissection of the injury areaseparating fascia from muscle
Sterilizable, reusable, strongSlide13
Literature Search: Bassini et al., 1988Disadvantages:
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 cmSlide14
Design 1: Close and MeasureAdvantages:
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 SensorSlide15
Design 2: Indentation TestingAdvantages:
Point measurements
Non-invasive
Disadvantages:
Complex design
Measures transverse, instead of longitudinal, tensionsSlide16
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 Slide17
Design 3: Modified Surgical ClampAdvantages:
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 gaugesSlide18
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 ClampSlide19
Proof of ConceptStrain 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 endSlide20
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 scaleSlide21
Future Proof of Concept
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