THA Implant Fixation

Question 1

What are indications for cement fixation of femoral component in THA?

Answer 1

1) Severe osteoporotic bone
2) Irradiated bone
3) Dorr C femur

Question 2

What things optimize cement fixation in THA?

Answer 2

1) Limit porosity (vacuum mix)
2) Stiff femoral stem
3) Cement mantle >2mm
4) Proper stem position
5) Smooth femoral stem

Question 3

How is biologic fixation optimized?

Answer 3

1) pore size 50-300um
2) preferably 50-150um
3) porosity of 40-50%; increased porosity may lead to shearing of metal
4) gaps less than 50um; defined as gap space between bone and prosthesis
5) micromotion less than 150um; increased micromotion may lead to fibrous ingrowth
6) maximal contact with cortical bone

Question 4

What effect does coating have on stress shielding?

Answer 4

Proximal only decreases stress shielding; extensive coating used for revision and produces more proximal stress shielding

Question 5

What are signs of femoral component loosening in THA?

Answer 5

1) thigh pain

2) start up pain

Question 6

Osteopenia has what effect on the strength of the bone-cement interface in comparison to normal bone?

Answer 6

Improved mechanical integrity