RESEARCH POSTER PRESENTATION DESIGN © 2011

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Adaptable Retractor for Total Hip Replacement Surgery

• More than 193,000 total hip replacements (THR) are performed each year in the United States [1]

• 34% of adults are obese and in THR surgery [2]• Multiple retractors ( 3-5) are required in obese

patients, thus increasing the time of surgery • A retractor is a surgical instrument available in

multiple shapes and sized that functions to:• Hold back adipose tissue• Increase the incision window [3]

• Total hip replacement surgery involves removing a diseased hip joint and replacing it with an artificial joint [4]

• Surgical Techs($20.00/hr*2-4hr/surgery*200k surgeries/year)

Background

• Able and strong enough to retract adipose tissue

• Fit multiple patient sizes and provide a clear view of the surgical site

• Must be cost efficient • Simple manufacturing• Inexpensive material

• Ready for use in surgery• Easily attached• Easily sterilized

Purpose

• Computer Modeling Protocol• Use PDE Toolbox in MATLAB to analyze

pressure exerted by tissue on • Obtain force load on the retractor from

tissue pressure • Model stress on the retractor using found

force loads using Finite Element Model analysis

• MATLAB Results• 300 Pa of pressure applied to adaptor

piece• 1.5 N of force applied to retractor handle

Finite Element Model Analysis

Mechanics of Device Safety and Industry Standards

• FDA Standards:• Device Type: Retractor • Classification: Class I

• 510(K) – Exempt• GMP – Not exempt

• Safety Considerations• Material must be biocompatible• No sharp edges• No small or loose pieces

Cost Benefit Analysis

•Market Environment• Retractor Prices:$100.00-$250.00 (250

surgeries lifetime)[7]• Surgeries w/obese

patients:193,000*34%=65,620/year(US)[2]

•Surgery without Adaptor• Surgical techs: $20/hr[6]• Surgical time:2-4hrs[2]

•Savings(Hospital and Industry wide)• Per surgery: $40/$1.00=$40.00• For 50 surgeries/year*.34

*$40.00=$680.00/yr• Total Industry: 65,620*$40.00=$2.62mil

References[1]"Total Hip Replacement - Your Orthopaedic Connection - AAOS." AAOS - Your Orthopaedic Connection. 2011. <http://orthoinfo.aaos.org/topic.cfm?topic=a00377>.[2]Belluck, Pam. Obesity Rates Hit Plateau in U.S., Data Suggest. (2010). The New York Times. 2011. <http://www.nytimes.com/2010/01/14/health/14obese.html?_r=1>.[3]Conditions, Digonostic. "Surgical Retractors,Medical Retractors,Hand Held Retractor,Surgical Retractor Manufacturers." Surgical Instruments,Surgical Medical Instruments,Surgical Instruments Manufacturers,Medical Instruments Manufacturer. 2011. http://www.surgicalsindia.com/surgical-retractors.html.[4]Staff, Mayo Clinic. "Hip Replacement - MayoClinic.com." Mayo Clinic. Web. 12 Apr. 2011. <http://www.mayoclinic.com/health/hip-replacement/MY00235>.[5] “Product Data Bulletin: 17-4 PH Stainless Steel.” AK Steel Corporation.2007[6]“Average Wages”. National Bureau of Labor Statistics <http://www.bls.gov/bls/blswage.htm>[7]“Product Catalog” Zimmer,Inc. <http://investor.zimmer.com/salestables.cfm?id=60>

• Previous team designed a single adjustable retractor

• Complex and impractical for manufacturing

• Plastic prototype could not be used in surgery

• Mechanism causing problem:• Physical properties of adipose tissue

allow it to wrap around narrow retractors which decreases the range of view of the surgeon

• Consequences of problem:• Poor surgical field of vision increases cost

for additional materials and personnel

Department of Biomedical Engineering Department, Vanderbilt University

Trey DeLong, Lacey Gorochow, Brian Rappa, Adam Vandergriff, Sandra WadeerAdvisors: Dave Martinez (Zimmer) and Dr. Michael Christie (Southern Joint Replacement Institure)

Problem Statement

Final Design

• Dimensions of Adaptor Piece• Height: 6 cm • Length: 9 cm • Thickness: 0.3 cm • Top curvature: 4.6 cm • Side curvature: 4.1 cm

• Design of Adaptor Piece• Increasing curvature along top to retract

and envelop fat and skin tissue• Dimensions based on incision size of

overweight patient• Curvature based on angle of retraction• Sliding mechanism for simple

attachment• Clip holds it in place

• Material• 17-4 Precipitation Hardening Stainless

Steel• Corrosion resistant, easily sterilized [5]• High strength maintained up to 600°F

[5]

Figure 6. Maximum Von Misses stress is 20.93 MPa.

Figure 7. Maximum displacement is 1.226 mm .

• Both retractor and adaptor assigned to stainless steel material properties

• Assembly constrained at bottom surface of retractor

• Maximum stress of retractor retractor significantly less than ultimate tensile strength of 17-4 PH stainless steel: 1000-1340 MPa [5]

• Displacement not significant in adaptor piece

Figure 3. Adaptor piece. Figure 4. Assembly of adaptor piece and retractor

Design Requirements

To design a hip retractor that eliminates the use of multiple retractors during surgery of patients of varying sizes, while increasing the viewing capabilities for the surgeon.

Figure 1. Surgeon’s work room obstructed by crowding surgical technicians holding retractors in place

Figure 2. Incision window of THR. Surgical forceps point to obstructing fat that wraps around retractor. Length of incision:12-15 cm, Width: 7-8 cm, Depth: 4-15 cm

Figure 5. Stress based on the tissue modeling .