Bone cement and interface bonding methods Flashcards
Why is the use of screws not practical when securing a femoral stem?
High stress cconc at bone-screw interfaces lead to bone resoprtion and screw loosening
What material is bone cement made from?
Polymethyl methacrylate (PMMA)
What additives are often included in bone cement?
Antibiotics
Radio-opaque material (usually barium sulphate)
How can better keying of cement be achieved?
roughening or coating surface of fem stem with beads or wires to provide large surface area
.What is the main advantage of using cement?
Mating surfaces do not have to be exact fit (cement can fill gaps) - no need to lose bone stock
What are the advantages of cement?
Don’t need exact fit
Allows even stress distribution
What are the disadvantages of cement/
Exothermic reaction Small fragments can cause inflammatory reactions Monomer is more toxic than the polymer Fragments can cause excessive wear Low tensile and shear strength
Why is tensile loading a problem in cement?
Tensile loadin will tend to part cement rom its contact with the bone and stem - reptitive loading can cause loosening
Why is research into new cement materials limited/
Cement is classed as a drug - expesive
Has any cementless stem shown itself to be better than the Charnley cemented ‘low friction’ arthroplasty?
No
What is the main problem with a non-bonded interface in implants?
Will always be relative movement under cyclical loading - lead to release of wear particles which can cause boene resorption
How can the growth of a fibrous layer at the interfaces?
Keep micromotion to a minimum after surgery (accurate fit of prosthesis followed by controlled weight bearing)
What is the disadvantage of using roughening to increase the keying of the cement?
If interlocking is insufficient to withstand the applied stresses and the cement fails the abrasive wear is much greater than it would be with a smooth prosthesis
What is the only option to enable cement to bind to both the prosthesis and the bone and overcome wear debris problem?
Use a cement containing hydroxyapatite
Which hip is made on the principle of making the stem smooth and letting it ink down the canal until it forms an interface fit in the cement mantle?
The Exeter hip
