Unit 3 - Knee Joint Replacement

Question 1

What does the ACL do?

Answer 1

Resists posterior subluxation of the femur

Question 2

What does the PCL do?

Answer 2

Resists anterior subluxation of the femur

Question 3

What does the LCL do?

Answer 3

Resists adduction of the femur

Question 4

What does the MCL do?

Answer 4

Resists abduction of the femur

Question 5

What does the posterior capsule do?

Answer 5

Resists hyperextension

Question 6

What is the centre of rotation of the knee called?

Answer 6

Instantaneous centre of rotation

Question 7

The magnitudes of the compressive joint forces at the contacting femoral/tibial surface are much higher than body weight due to the combined effects of what 3 things?

Answer 7

1. Gravitational forces
2. Contracting forces of the muscles
3. The balancing loads of the ligaments

Question 8

What is the vertical component of ground reaction force at the knee during the stance phase of gait?

Answer 8

Just exceeds body weight

Question 9

What is the fore-aft component of ground reaction force at the knee during the stance phase of gait?

Answer 9

Up to 20% body weight

Question 10

What is the horizontal component of ground reaction force at the knee during the stance phase of gait?

Answer 10

About 5% body weight

Question 11

What are the minimum functional requirements of a knee replacement?

Answer 11

1. Should extend to 180 degrees
2. Should flex to 90 degrees
3. Should permit slight axial rotation as the knee extends

Question 12

What must be dissected off the back of the femur to ensure that the replacement knee can fully extend?

Answer 12

Posterior capsule

Question 13

If no ligaments are intact what prosthesis is used?

Answer 13

Hinged prosthesis

Question 14

What 3 important mechanical factors relate to the surface shape of a knee prosthesis?

Answer 14

1. Effect of constraint on load transmission and the generation of high shear stresses
2. Effect of surface contact on wear of the HDP tibial component
3. Effect of the surface contact area on the stresses in the HDP tibial component

Question 15

What undesirable properties does HDP have?

Answer 15

1. Adverse effect of its wear debris on bone tissue which leads to reabsorption
2. It’s surface becomes stiffer due to increase in density after sterilisation with gamma radiation

Question 16

Name 2 ways to minimise the production of wear particles involving surface contact area?

Answer 16

1. Sliding distance of the bearing surface should be minimised
2. To reduce depth of wear, increase contact area by having a wide bearing

Question 17

What thickness of HDP tibial components is recommended if there is no metal backing tray?

Answer 17

8mm

Question 18

What is the tibial backing tray under an HDP tibial component intended to do?

Answer 18

Distribute the high contact stresses under the condyles in order to provide an even loading on the bone beneath it

Question 19

List 4 design features of a table component that affect the magnitude of the stresses on the underlying bone?

Answer 19

1. The thickness of the HDP component
2. Whether or not the HDP has a metal backing plate
3. Whether the tibial component has a stem
4. The stiffness of the material.

Question 20

Name an advantage and a disadvantage of using a meniscal bear knee prosthesis?

Answer 20

Advantage - lowers contact stresses

Disadvantage - requires removal of more bone, more difficult operation to perform