1. UHMWPE Superalloy Polyethylene Cemented & Uncemented
Replacement Parts
Hip replacement parts
UHMWPE
Superalloy
Polyethylene
Cemented & Uncemented
Tell the class we are going to be learning about replacement parts today. Ask if anyone can remember some of the replacement parts we have spoken about? Today’s lesson we will be looking at the use of UHMWPE; the use of superalloys in parts; polyethylene coatings; and cemented and uncemented joints.

2. Ultra High Molecular Weight Polyethylene UHMWPE - Properties
Is a long chain of repeating -CH2- units.
Very strong and resistant to abrasion.
Doesn’t deform easily and has strength against fatigue i.e. durable.
Lower density than high-density polyethylene.
Biocompatible and forms a low friction surface on parts.
Tell the class that these are the properties of UHMWPE. Ask the class to copy down the slide.

3. UHMWPE - Uses
Coat metallic surface to give the joint a smooth surface.
If the joints are not coated, friction can occur which can be painful.
Also rubbing of the joint parts can cause metal to flake off and debris accumulates in the joint tissue.
This debris can cause infection and loosening of the joint.
Tell the class the reasons for using UHMWPE, and ask them to copy down the slide.

4. Superalloys
A mixture of metals that combine to form a metal with greater strength than one metal alone.
Titanium alloys are most often used.
Open to page 179, activity and table 6.3.
Tell the class that super alloys are mixtures of metals that make up the stems of hip replacements etc. Ask the class to copy the side down. Hand out text books. Ask the class to open to page 179 and write up the activity on ‘Comparing strengths’. Hand out graph paper. Tell the class to use the table 6.3 to draw up their graphs and title them. When finished, move on to next slide.
Elbow and wrist replacement parts

5. Making the superalloy hip joint
A wax model of the hip joint is coated in ceramic liquid to form a mould.
Tell the class they do not need to copy this down, just for extra information.

6. Making the superalloy hip joint
The ceramic mold is hardened in a kiln.

7. Making the superalloy hip joint
The wax model is removed.
Liquid superalloy is poured into the mold and cooled.

8. Making the superalloy hip joint
When the alloy is cooled, the ceramic mold is destroyed and the body part is revealed.

9. Hip Replacement - Animation
Tell the class that now we are going to watch an animation of a hip replacement. Ask the class to look at how the bone is replaced, the use of polymer coatings and the use of cement.

10. Knee Replacement - Animation
Tell the class that now we will look at a knee replacement. Ask one student to read the information on each of the pages.

11. Cemented joints
The superalloy structure in hip and knee replacements can be ‘glued’ in place.
The metallic femoral stem is cemented into the drilled space in the femur.
Cement can be mixed with an antibiotic to reduce risk of infection.
The cement when exposed with a catalyst reacts and forms a solid bond.
Tell the class that the animation we saw of the hip joint shows the prosthesis being cemented into place. Read through the slide with the class and ask them to copy it down.

12. Uncemented Joints
In uncemented joints the prosthesis has microscopic pores that allow the bone of the femur to grow into and around the artificial stem.
Uncemented joints are believed to have longer duration than cemented ones, especially in younger patients.
Tell the class that although we did not see in the animation, an uncemented joint, because these are more commonly used in young patients. Read through side and ask the class why they think this may be so.

13. Replacement Parts X-ray of a hip replacement
Tell the class that they are now going to look at some images of replacement parts. Tell the class this is an x-ray of a hip replacement. Point out the features.

14. Replacement Parts Artificial knees
Tell the class these are some pictures of the different types of artificial knees. LEFT: fully metal knee joint. RIGHT: has plastic and metal components.

15. Replacement Parts Different types of artificial hips
Tell the class there are now different types of replacement parts. LEFT: common hip. RIGHT: lightweight hip replacement.
Different types of artificial hips

16. Replacement Parts Artificial shoulder joint
Tell the class: LEFT: is a replacement shoulder joint. RIGHT: silicone replacement for a finger joint.
Artificial shoulder joint
Silicone finger replacement

17. Questions
What shape is the human backbone and what does it enable us to do?
Name three parts of the skeleton whose function is protection and name the organ(s) they protect.
How are bones and blood related?
Name one place in the body you might find the following types of joints: sliding, pivot, ball and socket and hinge.
What is the function of cartilage and synovial fluid in the operation of a joint.
What are superalloys? What characteristics must they possess to be used in prosthetics?
Why would the joining ends of a superalloy joint need to be coated in UHMWPE?
Sketch a diagram of how the end of an artificial stem would look if it were going to be implanted without the use of a cement. Why does it have this structure?
Ask the class to answer these question in their books.