Prosthetics

Question 1

What is a prosthetic

Answer 1

Replacement of a joint

Question 2

Total hip replacement - THR

Answer 2

Stem is inserted into canal and bonded (if it’s a cemented replacement); screws are often used to stabilize the implant. Loosening occurs over time and is the most common failure method (early as 12 mo after replacement)

Question 3

How can you minimize wear in a THR

Answer 3

Use UHMWPE

Question 4

THR Loads

Answer 4

Loads acting on the hip are known; loading is cyclical due to daily activity; torsional loads are more effective in loosening of the device

Question 5

Total Knee Replacement (TKR)

Answer 5

has two components – femoral and tibial component; uses UHMWPE on the articulating surface

Question 6

TKR Loads

Answer 6

loads on TKR are known – flexion is critical; model of the tibial component using loads on an elastic foundation.

Question 7

Flexion

Answer 7

leads to tipping of tibial component in a poorly fixated prosthesis

Question 8

Cementless protheses

Answer 8

A cementless prosthesis has a coating and surface geometry to promote bony ingrowth; stability of the implant is secured by friction and long term stability is secured by bony ingrowth

Question 9

Integration of a cementless prothesis can take

Answer 9

months to years – the bone needs time to grow into and attach onto the prosthetic

Question 10

Press fit on TKR

Answer 10

occurs and the effect on the implant stability is not well known, but is believed to only play a role up to 4 weeks after surgery