Unit 3 - Knee Joint Replacement Flashcards
What does the ACL do?
Resists posterior subluxation of the femur
What does the PCL do?
Resists anterior subluxation of the femur
What does the LCL do?
Resists adduction of the femur
What does the MCL do?
Resists abduction of the femur
What does the posterior capsule do?
Resists hyperextension
What is the centre of rotation of the knee called?
Instantaneous centre of rotation
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?
- Gravitational forces
- Contracting forces of the muscles
- The balancing loads of the ligaments
What is the vertical component of ground reaction force at the knee during the stance phase of gait?
Just exceeds body weight
What is the fore-aft component of ground reaction force at the knee during the stance phase of gait?
Up to 20% body weight
What is the horizontal component of ground reaction force at the knee during the stance phase of gait?
About 5% body weight
What are the minimum functional requirements of a knee replacement?
- Should extend to 180 degrees
- Should flex to 90 degrees
- Should permit slight axial rotation as the knee extends
What must be dissected off the back of the femur to ensure that the replacement knee can fully extend?
Posterior capsule
If no ligaments are intact what prosthesis is used?
Hinged prosthesis
What 3 important mechanical factors relate to the surface shape of a knee prosthesis?
- Effect of constraint on load transmission and the generation of high shear stresses
- Effect of surface contact on wear of the HDP tibial component
- Effect of the surface contact area on the stresses in the HDP tibial component
What undesirable properties does HDP have?
- Adverse effect of its wear debris on bone tissue which leads to reabsorption
- It’s surface becomes stiffer due to increase in density after sterilisation with gamma radiation
Name 2 ways to minimise the production of wear particles involving surface contact area?
- Sliding distance of the bearing surface should be minimised
- To reduce depth of wear, increase contact area by having a wide bearing
What thickness of HDP tibial components is recommended if there is no metal backing tray?
8mm
What is the tibial backing tray under an HDP tibial component intended to do?
Distribute the high contact stresses under the condyles in order to provide an even loading on the bone beneath it
List 4 design features of a table component that affect the magnitude of the stresses on the underlying bone?
- The thickness of the HDP component
- Whether or not the HDP has a metal backing plate
- Whether the tibial component has a stem
- The stiffness of the material.
Name an advantage and a disadvantage of using a meniscal bear knee prosthesis?
Advantage - lowers contact stresses
Disadvantage - requires removal of more bone, more difficult operation to perform
