VEXTEC Reliability Analysis of Above-the-Knee Leg Prosthesis Group 11 Aashish Bapat, April Boldt,...

VEXTECReliability Analysis of Above-the-Knee Leg Prosthesis

Group 11Aashish Bapat, April Boldt, Jason Deaner, Grainger Greene, Dani Shuck

Current Work:

Find component with highest rate of mechanical failure

Determine loads on component Perform transfer functions to model the

failure in other component

Next: Use VEXTEX software to perform statistical analysis

Finite Element Modeling

Forces for transfemoral single-hinge prosthesis of a kneeling subject

Focusing on the knee joint/cap with titanium material

Next step: Create a model with actual prosthesis dimensions

Finite Element Analysis

Use MSC/Patran to create model with constraints and forces for kneeling subject

Perform finite element analysis with MSC/Nastran or ANSYS

Follow with microstructure analysis using VPS-MICRO™ from VEXTEC

“Prosthetic Loading During Kneeling of Persons with Transfemoral Amputation.”

Ultimate Goal

Compare current analysis techniques with results achieved using VEXTEC’s software

Figure out what VEXTEC can add to current analysis methods used by the prosthesis industry

Knee System

Manual Lock 1.2kg/2.64lbs

including shin K1-k2 activity level Choose lock or

stabilizing knee

http://www.blatchford.co.uk/prosthetics/products_ak/eskmkl/eskmkl.html

Manual Lock Tech Information

http://www.blatchford.co.uk/images/market_pdfs/938100%20Iss4%20Endolite%20Pros%20Prod%20Cat.pdf

Manual Lock Parts for Assembly


Foot System

Super SACH 25 cm Integral pyramid 0.36kgs/.79lbs K1-k2 level activity Differs from SACH in

adjustable heel cushion


Orthotist (Dr. Gregory Mencio) & Prosthetist (Dr. Mark Watson)1) What are the most widely used makes/models of above-

the-knee prostheses?• Popular makes: endolite, ossur, ottobock• Models catered to individual lifestyle• Work with interface of socket• Exoskeletal: hard crustacean design• Endoskeletal: inside all laminated foam, internal pylon

2) What basic advantages do the most popular models have over others in their design and or materials used?• Steel vs. carbon fiber• Carbon fiber: lighter, enhanced performance, more

comfortable• Steel: more durable• Endoskeletal: lightweight

Orthotist (Dr. Gregory Mencio) & Prosthetist (Dr. Mark Watson)3) What is the most common source of failure in these

prostheses? Do they differ among models?• Breakage at knee joint: inevitable, life depends on quality

and activity of patient• Loosening at socket: atrophy causes loosening around the

socket• Selection of prosthetic:• Cost: approx $30,000-500,000• Activity: hydraulic versus geriatric patient• Vets from Iraq receive new prostheses about every 2 years• Cheaper models break down quickly, less comfortable, fewer

“bells and whistles”

4) How common are mechanical failures in these prosthesis?• Set screws often toggle and break• Failure at knee linkage

Orthotist (Dr. Gregory Mencio) & Prosthetist (Dr. Mark Watson)

5) What kind of warranties (if any) come with above-the-knee prostheses?

• 0-3 years• Most often 6 months – 1 year• Warrantees = improves life of product

6) Do the prostheses manufacturers offer any technical support in your practice?

• New product education• Insight on amputation and fitting for prostheses

Mark Watson: Orthotist/Prosthetist

7) How much time and money to these manufacturers spend on reliability analysis?

• Endless process for better/more durable models

8) What does their process for reliability analysis involve?• Cheap models break down insurance and prosthetists

pay• Engineers design durable models• Summary: Materials tested, materials combined, models

engineered, models tested, then human testing following FDA approval

Uncertainty

Mark Watson ultimately unsure about reliability testing Will provide contacts at Otto Bock and

Ossur, others Team will contact manufacturers, design

engineers to determine specific processes

Customer Report

Pratt Whitney Testing reduced to half Closed minded medical community ?

Lockheed Martin Warranty/Liability reduction a major

revenue Medical Device trade shows Databases like oracle for testing data

Resources:

Magnissalis, Evangelos Et Al. “Prosthetic Loading During Kneeling of Persons with Transfemoral Amputation.” Journal of Rehabilitation Research and Development 36.3 (1999): 1-15.














VEXTEC Reliability Analysis of Above-the-Knee Leg Prosthesis Group 11 Aashish Bapat, April Boldt,...

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