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Reliability Analysis of Knee Prosthesis Aashish B. Bapat 1 , April A. Boldt 1 , Jason J. Deaner 1 , Grainger L. Greene 1 , Danielle M. Shuck 1 Advisors: Robert Tryon 2 , Maggie Curtin 2 and Ganapathi Krishnan 2 , Paul King 1

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Reliability Analysis of Knee Prosthesis

Aashish B. Bapat1, April A. Boldt1, Jason J. Deaner1, Grainger L. Greene1, Danielle M. Shuck1

Advisors: Robert Tryon2, Maggie Curtin2 and Ganapathi Krishnan2, Paul King1

Department of Biomedical Engineering at Vanderbilt University1, VEXTEC Corporation2

Conclusion

Introduction

Methodology

  • VEXTEC Corporation is a technology company based in Nashville, Tennessee founded in 2000.
  • VEXTEC has developed a fleet level reliability management software tool called RCMTM (Reliability Chain Management) and a probabilistic micromechanical fatigue prediction tool VPS-MICRO™
  • Customers include aerospace and automotive companies
  • Technology Features:
  • Technology operates within the OEM design frameworks on a Pentium desktop computer and integrates with FEA codes
  • Application within automobile industry: can simulate 10,000 vehicles for 100,000 miles in a few minutes
  • Project:
  • Analyze the reliability of a knee prosthesis using RCMTM and
  • VPS-MICROTM

An Endolite ESKMKL knee prosthesis was used in this analysis problem.

A system level reliability analysis was performed to identify components with high failure rates.

These components were analyzed using finite elements and VPS-MICROTM to determine the

minimum life and scatter in real-life usage.

The knee components were of Titanium with a Young’s modulus of 14.8E3 ksi.

Failure in trunnion and bolt when used by a 220 lb man for jogging was analyzed.

  • The results validate the application of VEXTEC's tools to analyze the reliability of a knee prosthesis. 
  • The process enables principal component analysis and top down design reliability. Problem areas can then be identified for detailed modeling and improved design. 
  • In addition, fatigue failure localization occurs within specific sub-components, reducing overall redesign costs.
  • According to the results, VEXTEC can add value to the prosthetic engineering methods through the use of their analysis techniques.

Marketing

Value Proposition

  • Virtual physical testing allows quicker design iterations and faster market induction
  • System reliability approach allows for identification of failure causing sub-systems and components
  • Simulates real usage conditions, allows for estimating warranty costs

Customer Analysis

  • Otto Bock: VEXTEC has prior experience and reputation in the automotive industry and a portion Otto Bock’s revenues come from its automotive parts division. This would lead to a common understanding between VEXTEC and Otto Bock. They have been receptive to the technology so far in phone interviews.
  • Ossur: Voluntarily recalled Total Knee models due to faulty pins located in the axis of the knee in 20061. VEXTEC could help in prevention of similar issue. Also have been receptive in phone interviews.

Goals

1. Apply VEXTEC’s tools to a medical device to assess reliability

2. Perform finite element analysis on a prosthetic sub-component

3. Use the VEXTEC physics of failure models to predict the minimum time to failure and the sites of failure of the sub-component

4. Analyze the medical device market and quantify a value proposition and a marketing strategy for VEXTEC

System Level Reliability Analysis

Results

Medical Device Industry

  • Market Capital - $200 billion4
  • 2006 Facts
  • 27 million (10% US population) used assistive medical devices
  • $1.45 billion designated to improve durability
  • About 50% of all medical device recalls are due to design errors that could have been prevented by adequate design controls
  • FDA Quality System Regulation requires risk analysis as a portion of its Design Control requirements2
  • Physical Testing
  • Testing in time consuming, expensive and crudely defined
  • Medical devices undergo several iterations of real stress simulation in labs to understand modes of failure and mean times
  • Making alterations to the design or material is costly as the whole reliability testing process has to often be physically repeated

1000 knee systems simulated over 5 years

Future Directions

  • Technical
  • Perform reliability analysis on other types of prostheses and medical devices, both mechanical and electronics based
  • Collaborate with medical device manufacturer to better understand different phases in physical testing and design
  • Collaborate with VU faculty to approach STTRs
  • Marketing
  • Develop relationship with medical device manufacturers to better understand the needs of the customer
  • Develop VEXTEC brand name through publications and tradeshows in the medical device sector

Bolts and Trunnions in the Strut assembly have high failures in the 5 year period simulated

Prosthetics

  • $500 million prosthetic market - 80% lower limb4
  • Projected growth rate of 3-5%
  • $89 millionprosthetic industry repair cost in 2006
  • Prosthetics: Avg. life 1-3 years; Avg. Warranty: 6 months
  • Industry relies heavily on physical testing and VEXTEC’s technology reduces physical testing needs
  • Minimum biocompatibility issue
  • Reliable and better above the knee prosthesis is being heavily investigated by the Veteran Association after the Iraq war

References

  • “Defective pin leads Iceland Company Ossur to voluntarily recall Total Kneees. Hospital
  • Materials Management. 31.6 (June 2006): 7(1). InfoTrac OneFile. Thomson Gale.
  • 2. Reliable design of medical devices. Richard Fries..Boca Raton : CRC/Taylor & Francis, 2006.
  • 3. http://www.fda.gov/bbs/topics/NEWS/2006/NEW01506.html
  • 4. http://tools.euroland.com/arinhtml/is-ossr/2006/AR_ENG_2006/index.htm

Stress Analysis and Fatigue Failure in Trunnion over 5 years