Artificial Total Hip Replacement

Arthur Hernaez

Materials Engineering

Mission College - Spring 2011

Overview• Biomedical Engineering

• The human body

• Understanding Artificial total hip replacement

• Choosing materials and causes of failure

• Conclusion

What is Biomedical engineering? Why learn about it?

Biomedical Engineering

“Biomedical engineering blends traditional engineering techniques with biological sciences and medicine to improve the quality of human health and life” -UConn BME website

Fig 1. Fig 2.

Hip Fracture

• High impact tackles

• Minimal protection of hip joint

• Common fracture location

• Replacement required

Fig 3.

Fig 4.

The Human Body

• Constant body temperature

98.6°F or 37°C

• Bone and muscle anisotropic

Body fluids – corrosive to metals

1 wt% NaCla Other components

• Muscles transfer forces

Fig 5.

The Human Body III

• Biocompatible to foreign objects

Location

chemistry

shape

• Apriori vs. priori testing

Fig 5.

The Human Body II

• Bone and cartilage attatchmennt

• Composite of protein collagen and brittle hydroxyapatite

• Anisotropic composite

These are some typical values:Cortical Cancellous

Stiffness (E, GPa) 17 0.1-2Strength (UTS, MPa) 150 2-20Strength (Yield point, MPa) 100 -Strain to failure (%) 1.5 2.5

Fig 6.

Fig 7.

The Human Body III

perpendicular

parallel

Fig 7.

Hip joint replacement

Fig 8.

Fig 9

Hip Joint replacement II

1.) Ball attached to stem

2.) Femoral Stem

3.) Acetabular cup

4.) Fixing agent

4

3

Callister

Fixing agent• Poly(methyl methacrylate) acrylic

(PMMA)

• Thermoplastic

• Reaction: PMMA powder mixed with

Liquid methyl methacrylate (wik)

+

Callister

Femoral stem

• Yield strength > 500 Mpa

• TS > 650 Mpa

• %EL > 8%

• Corrosion rate < .01 mil per year

• Fatigue Strength:

400 Mpa at 10^7 cycles

• Avg person per year: 10^6

Callister

Ball attached to stem

• Ceramic: polycrystalline aluminum oxide or zirconium oxide

• Good hardness but brittle

• Attached to femoral stem

Acetabular cup

Ultra high molecular weight polyethylene

-Excellent wear and tear resistance

-Low coefficient of friction

-Inert

Hip joint replacement overview

1.) Density

2.) Properties

3.) Reproducibility

4.) Cost

Life span 15-25 years

Callister

Choosing Materials

Callister

Femoral Stem

They all meet

Minimal

requirements

Choosing Materials

Femoral Stem alloys:

316L stainless steel – best corrosive rate

Co-28Cr-6Mo – best Modulus

Ti-6Al-4V – best biocompatibility

Reasons for different materials – people vary

Failure

Failure II

Other causes

Sharp edges

Fatigue strength

Not biocompatible

Conclusion

• Make use of all type of materials and their properties

• Ethical testing for biocompatibility with animals

Citations• Bionic arm• http://www.impactlab.net/2006/12/03/new-bionic-arm-technology-offering-hope-to-amputees/

• http://www.physorg.com/news194246067.html -heart

• http://winmyfantasyleague.com/frank-gore-lost-for-the-season-fantasy-implications/

foorball player

http://www.healthdetails.org/general-information/hip-fracture-diagnosis-treatment-and-protection-methods-147.html

Pg 4 joint

http://www.wisdomwoman.com/nerve/?p=610 –muscles pg 7

http://health.allrefer.com/health/hip-joint-replacement-hip-joint-replacement-series.html pg 6 normal hip joint

http://www.reshealth.org/yourhealth/healthinfo/default.cfm?pageID=P08957 hip joint pg 6

Ball and cup pic pg8-12

http://healthguide.howstuffworks.com/hip-joint-replacement-picture.htm

Callister – materials engineering

http://healthguide.howstuffworks.com/hip-joint-replacement-picture.htm

The overview pg 7

http://www.cposm.com/index.php/orthopaedic-services/hip/ pg7

http://www.orthopaedia.com/download/attachments/23724188/Hip+fractures.jpg?version=1&modificationDate=1290971451000

fracture