Knee Replacement 2 Flashcards
What is the problem with copying the asymmetry of the natural knees?
doubles the size of the required inventory of components and matching instruments
What do posterior stabilised designs provide?
prevent posterior femoral subluxation
cause the femur to roll back as it flexes
What is the gold standard knee prosthesis?
total condylar prosthesis
Why should PMMA bone cement provide good anchorage in knee prostheses?
if all is done correctly, then it should be in compression at all times during joint range of motion
What happens if the ligaments are not balanced?
in lateral loading one side lifts off causing tensile stresses on the remaining area and between the tibial tray and underlying bone
How can additional rotatory control be acquired?
use of projections built into the underside of the tibial components
Why is there hesitancy in using cementless prostheses?
the cemented ones perform so well
What additional fixation is needed for cementless prostheses?
screw fixation/stem
femoral component needs just press fit
What is the function of the patella?
increases the lever arm of the quadriceps - without it 30% more force is required
Why might the anterior part of the femoral component be grooved?
accommodate the patella and encourage patellar tracking
What is the replacement patellar bearing surface made from?
HDP
Which wear more - conforming or non-conforming shapes?
non-conforming
In metal backed patella, what happens to wear rate?
increased
HDP is insufficiently thick to distribute loads and therefore higher contact stresses
Why in rheumatoid arthritis, are all joint surfaces replaced?
the whole joint is involved
What are meniscal bearings made from?
HDP
