Joint replacement

Question 1

Materials for the Charnley hip prosthesis

Answer 1

ball/head: ceramic/alumina
acetabular cup: UHMWPE
bone cement: PMMA

Question 2

Main reason to get a hip prosthesis

Answer 2

Osteoarthritis

- destruction of the cartilage - results in severe pain, loss of motion

Question 3

Wolff’s law

Answer 3

bone responds to changes in load transfer with remodelling

Question 4

Mechanisms that contribute to aseptic loosening

Answer 4

• stress shielding results in bone resorption aka osteolysis
• wear debris: particles or corrosion
• underlying disease
• natural ageing
• fluid/mechanical pressure
• micromotion

Question 5

what is stress shielding?

Answer 5

caused by high young’s modulus of metal prostheses
prosthesis carries the load and reduces the stress on the bone and this results in bone resorption
fixation is lost or a fracture fails to heal fully

Question 6

3 Mechanisms of wear debris generation

Answer 6

• abrasive wear
  harder material plough grooves into softer material
• adhesive wear
  softer material smeared onto harder surface
• fatigue wear
  formation of cracks propagate to form particles

Question 7

biological reaction to wear debris

Answer 7

• wear debris stimulate pro-inflammatory response
• cytokine mediated recruitment of inflammatory cells
• indigestible wear particles perpetuate cellular activation = chronic inflammation
• chemokine/cytokine mediated bone resorption

Question 8

What is the birmingham hip?

Answer 8

two-part system

1) cobalt chrome alloy cap is placed over the resurfaced femoral ball
2) a cobalt chrome alloy cup fits into the acetabulum