Adaptable Retractor for Total Hip Replacement Surgery

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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) Cost Benefit Analysis 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 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 Department of Biomedical Engineering Department, Vanderbilt University 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 References 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 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] Final Design Problem Statement Design Requirements 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 [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,MedicalRetractors,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> Trey DeLong, Lacey Gorochow, Brian Rappa, Adam Vandergriff, Sandra Wadeer Advisors: Dave Martinez (Zimmer) and Dr. Michael Christie (Southern Joint Replacement Institure) 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 5. Stress based on the tissue modeling . Figure 1. Surgeon’s work room obstructed by crowding surgical technicians holding retractors in place Figure 3. Adaptor piece. Figure 4. Assembly of adaptor piece and retractor 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 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