hip biomechanics

Question 1

how can you judge the adequacy of the cementation?

Answer 1

Barrack classification

A - complete whipeout
B - some radiolucency
C - severe radiolucency but less than 50%
D- gross radiolucency greater than 50%

Question 2

what is the Dorr classification?

Answer 2

ratio of the canal diameter to the inner canal diameter

dorr A - <0.5% - uncemented
dorr B - 0.5-0.75% - uncemented
dorr C - >0.75% - cemented

Question 3

what are the indications for cementation?

Answer 3

bone unable to get an adequate biological fixation
* pagets
* porotic bone - osteoporosis
* irradiated

large canal - Dorr C femur

Question 4

what are the DeLee and Charnley zones?

What are the gruen zones for cement lossening?

Answer 4

Question 5

what are the principles of fixation of composite beam femoral stem?

Answer 5

composite beam cemented stem
* single unit
* 3 point fixation - cement, stem and bone:
* bond ban roughened stem and cement
* bone between cement and bone
* leads to stress shielding
* collar - to promote calcar loading and prevent stress sheilding
* slits - to reduce stress shielding by dissipating stresses

Question 6

how do cemented taper fit stems work?

Answer 6

taper slip cementedstem
- highly polished double tapered - exeter/ CBT
- controlled subsidence due to creep - creating hoop stresses which then push back on the stem holding it in the cement mantle