DESIGN OF KNEE PROSTHESIS

Ashish Sharma

Common Causes of Knee Pain and Loss of

Knee Function

ARTHRITIS

• Osteoarthritis (wear and tear)

• Rheumatoid arthritis

Post-traumatic arthritis caused by:

• Fractures

• Ligament injuries

• Meniscus tears

Knee Prosthesis comprised of

• Femoral- replaces arthritic

portion of thigh bone

• Tibial- replaces arthritic portion

of shin bone

• Tibial insert- replaces cartilage

and acts as shock absorber

• Patella- replaces knee cap

Types of Knee Prosthesis

• Fixed Knee Prosthesis : The more traditional fixed

bearing implant which can only flex and extend

• Mobile-Bearing Prosthesis: More advanced the rotating

platform knee implants move almost like a normal knee

joint. They allow the knee to twist and turn (rotation) as

well as flex and extend. The Rotating Platform Knee is

designed to bend and rotate, move back and forth, flex

and extend, helping to accommodate more normal

movement.

Design Input

Distal Portion of FemurKNEE REPLACEMENT SYSTEM by

Amplitude

Design Dimensions

Features

• PEGS

• PATELLAR FLANGE

• GROOVES ON CONDYLES

• INTERNAL SUPPORT

METHOD

Sketch Rectangle (Right Plane) Anterior plane

Box cut

SWEEP CUT

• Trajectory Cut sweep dialog box Section

Removal of extra material

Top View of Extrude-Cut Posterior Biew

Patellar flange

New Right Datum Plane Sketch Extrude

Intercondular notch

• Sketch Top view Extrude cut Final cut

PEGS

Sketch(Right plane) Revolve Final Peg

Longitudnal ridges on the condular posterior surface

• Sketch from the front view Final ridges

Longitudnal Ridges in Pegs

Sketch Axis Pattern Final Ridge

Ridges increase the holding power with bone cement

CUT TOOL

Family table

Rounds

• Features

1. Variable radii

2. Stress prone edges moved before Sweep cut

Component operation

Tool Cut/ Bone Cuts

Finite Element Analysis (FEA)

• Test I : Yield tensile strength test

• Test II: Fatigue strength test

• Loads were applied on lateral condyle to checkout the

strenght in extreme situation

Material Used

• Co-Cr-Mo

• Material properties

Properties Values

Tensile strength 855 MPa

Yield Strength 650 MPa

Fatigue Strength 510 MPa

Young’s Modulus 230 GPa

Density 8.3 g/Cm^3

Constraints

• One end is fixed- Displacement constraint

• Other end force given on lateral condyle- Force constraint

Results

• Max Stress without rounds

• Max Stress without round

conclusion

On rounding the internal edges there is a reduction in stress and

it is uniformly distributed

Final Assembly

REFRENCES

http://www.amplitude-ortho.com

http://orthoinfo.aaos.org/topic.cfm?topic=a00389

http://www.ofc-oregon.com

http://www.endotec.com

THANK YOU