Adaptable Retractor for Total Hip Replacement Surgery

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Adaptable Retractor for Total Hip Replacement Surgery Mechanics of Device Cost Benefit Analysis FDA Standards: • Device Classification: Class I • 510(K) – Exempt, GMP – Not exempt [7] Safety Considerations • Material must be biocompatible • No sharp edges or small or loose pieces Sterilization • Autoclave at 273°C for two minutes [8] • 17-4 PH retrains strength up to 315.5°C [6] Safety and Industry Standards Current Surgery Cost • Hip Retractor: $800-$1500 (avg. of $1150) • Surgical Techs: $20/hr * 2 hr surgery time • Three retractors needed in each surgery • Retractors used 50 times a year • Retractor used for 5 years=250 uses/lifetime • Retractor cost per use: $1150/250 uses=$4.60 • Cost/surg.:$4.6*3+2 techs*20/hr*2 hrs=$93.80 Cost with Adaptable Retractor • Hip Retractor: $1400 • 2 retractors,1 surg tech needed in each surgery • Retractor cost per use:$1400/250=$5.60 • Cost/surg.: $5.6*2+1 tech*$20/hr*2 hrs=$51.20 Hospital Savings • $93.80-$51.20=$42.60 savings/surgery • Surgeries with obese patients: 193,000 * 34% =65,620 surgeries/year • Total savings/yr:$42.60*65,620=2.8 mil/year [1]Staff, Mayo Clinic. "Hip Replacement - MayoClinic.com." 2011 [2]"Total Hip Replacement - Your Orthopaedic Connection - AAOS.” [3] Belluck, Pam.” Obesity Rates Hit Plateau in U.S.” NY Times, 2010 [4] NIH, “Hip Replacement,”2010. [5]“Average Wages”. National Bureau of Labor Statistics [6] “Product Data Bulletin: 17-4 PH Stainless Steel.”.2007 [7] FDA,”Product Classification,” 2011. [8] WVR Lead Free Autoclave Instruction Sheets To design a hip retractor that eliminates one retractor during surgery, while increasing the viewing capabilities for the surgeon and that meets the following criteria: 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 • Total hip replacement surgery (THR) surgery involves removing a diseased hip joint and replacing it with an artificial joint [1] • More than 193,000 total THRs are performed each year in the United States [2] • 34% of the U.S. population is obese [3] • Multiple retractors (3-5) are required in obese patients, thus decreasing the amount of work room A retractor is a surgical instrument available in multiple shapes and sizes that functions to: • Hold back adipose tissue • Increase the incision window Surgical Techs needed to hold retractors • Costs $20/hr * 1-2hr/surgery[4,5] References Computer Modeling Protocol • Use PDE Toolbox in MATLAB to analyze pressure exerted by tissue • Obtain force load on the retractor from tissue pressure • Model stress on the retractor using obtained force loads using Finite Element Method Analysis MATLAB Results • 300 Pa of pressure applied to adaptor piece • 1.5 N of force applied to retractor handle Finite Element Method Analysis Previous team designed a single adjustable retractor • Complex and impractical for manufacturing • 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 Final Design Dr. Christie’s Opinion Dimensions of Adaptor Piece • Height: 6 cm • Length: 9 cm • Thickness: 0.3 cm • Top curvature: 4.7 cm • Side curvature: 4.2 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 [6] • High strength maintained up to 600°F [6] Background Purpose & Design Requirements Trey DeLong, Lacey Gorochow, Brian Rappa, Adam Vandergriff, Sandra Wadeer Advisors: Dave Martinez (Zimmer) and Dr. Michael Christie (Southern Joint Replacement Institute) Department of Biomedical Engineering, Vanderbilt University Problem Statement Figure 5. Stress based on the tissue modeling . Figure 1. Surgeon’s work room obstructed by crowding surgical technicians holding retractors in place Figure 3. Assembly of adaptor piece and retractor • “Best one yet” • System is flexible enough to be used in different types of surgeries • Customized retractor set for specific surgeries will save hospitals money • Instead of having 5,000 instruments on hand, move towards customizing instruments and have only five or six ready for use Figure 4. Adaptor piece. Top: Fully Rounded Bottom: Lofted 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 [6] • Displacement not significant in adaptor piece or retractor Figure 2. Incision window of THR. Surgical forceps point to obstructing fat that wraps around retractor. Length of incision:12-16 cm, Width: 7-8 cm, Depth: 4-15 cm