Joints - Hip Arthroplasty

Question 1

Common reason for joint replacement? (4)

Answer 1

Rheumatoid Arthritis
Gout
Injury/Post-trauma
Osteoarthritis

Question 2

Requirements for a joint implant? (5)

Answer 2

Biocompatible
Wear-resistant
Load bearing
Revise-able
Reliable (insensitive to alignment, size mismatch)

Question 3

What MUST joint implants do?

Answer 3

Restore function

Relieve pain

Question 4

What 3 classes of materials are used

Answer 4

Metals
Ceramics
Polymers

Question 5

What kinds of metals are used?

Answer 5

Alloys

Question 6

Example of metals used?

Answer 6

Titanium alloys (lightest)
Cobalt-Chromium alloys
Stainless steel

Question 7

Example of ceramic materials used?

Answer 7

Alumina
Zirconia
Bioactive glass

Question 8

Good features of Alumina

Answer 8

High Youngs modulus (stiff)
Finished to a high polish (low friction)
Great wear & corrosion resistance

Question 9

Examples of Polymers used?

Answer 9

Ultra-High Molecular Weight Polyethylene (UHMWPE)

Polymethylmethacrylate (PMMA)

Question 10

What is a common use for PMMA ?

Answer 10

Bone cement

Question 11

What is an issue with metal-on-metal implants?

Answer 11

Metallosis - an immune reaction when toxic metal debris shed off the surface and enter bloodstream

Question 12

What is the function of bone cement? (3)

Answer 12

Facilitates fixation between the implant and bone
Allows even transfer of load from the implant to the bone
Shock absorber

Question 13

Indications for bone cement

Answer 13

Osteoporotic bone

Repeatedly Irradiated bone

Question 14

Indication for uncemented implant

Answer 14

Young, healthy individuals

Question 15

Issue with ceramic on ceramic implants

Answer 15

Makes noise
Expensive
Requires expert insertion

Question 16

Advantages of bone cement? (2)

Answer 16

Quick recovery as cement dries quickly

Antibiotics can be added

Question 17

Disadvantages of bone cement? (2)

Answer 17

Cement can break down and lead to debris which can:
Cause inflammation
Embolise to the lungs

Question 18

How do implants fail?

Answer 18

Fracture

Stress shielding

Question 19

What is stress shielding

Answer 19

• Stress shielding refers to the reduction in bone density (osteopenia) as a result of relief of typical stress from the bone by an implant
• Leads to loosening

Question 20

Issues with metal-polyethylene implants (4)

Answer 20

Aseptic loosening
Adhesive wear
Abrasive wear
Fatigue wear

Question 21

Explain aseptic loosening

Answer 21

Loosening of an implant without infection

Question 22

Causes of aseptic loosening

Answer 22

Inadequate initial fixation
Mechanical loss of fixation over time (eg cement breakdown)
Biological loss of fixation (Particulate debris leads to pseudosynovial fluid between implant and bone which causes cytokines to stimulate osteolysis)

Question 23

Explain adhesive wear

Answer 23

Small portions of UHMWPE surface adhere to the opposing metal or ceramic bearing surface
May change the surface topography of the metal component

Question 24

Explain abrasive wear

Answer 24

When 2 surfaces slide across each other the harder scrapes the softer one
causes debris to be released

Question 25

Explain fatigue wear

Answer 25

Repeated loading between 2 surfaces lead to cracks forming

Debris can be released