Joints flashcards
percent of THA in 2012 that are cementless
93%
How to calculate Dorr
radio of canal diameter 10 cm distal to midportion of lesser trochanter / inner canal diameter at midportion of lesser trochanter
Dorr Type A
Ratio <0.5 (canal is less than half the thickness 10 cm distal to lesser troch than the canal at the troch itself). Cortices seen on both AP and Lateral XR. Uncemented is good.
Dorr Type B
0.5-0.75. Thinning of posterior cortex on lateral XR. Uncumeneted
Dorr Type C
> 0.75, thinning of cortices on both views. Cemented fixation (bad case if you do uncemented.
how does cement act
acts as grout by interlocking fit between surfaces
stovepipe femur is also known as
Dorr C femur. enlarged metaphysis and lack of supporting isthmus.
cementing the cup?
not as good, higher failure rate, cement resists shear poorly
1st generation cement technique
Hand mix, finger packed cement, no canal preparation or cement restrictor
2nd generation cement technique
Cement restrictor, cement gun, femoral canal preparation with brush and dry
3rd generation cement technique
vacuum-mixing to reduce porosity, cement pressurization, femoral canal preparation with pulsatile lavage.
Porosity good or bad for cement
bad, more points of stress if high porosity
Cement mantle thickness
> 2mm to decrease risk of mantle fractures
Mueller type prosthesis difference
French paradox, it aims for a press fit mediolaterally so the cement mantle is <2 mm, but it has shown to have good results as well.
stiff femoral stem for cement
titanium is bad, flexes too much
stem centralizatier for cement
avoid malpositioning
Smooth femoral stem
sharp edges increase stress concetration
Varus or valgus for cement
want to avoid either, especially varus
Barrack and Harris garding system for cement
….do I need to know…
Good indication for cementless THA
younger patient, older patient with good bone stock, revision THA (cemented is not good for revision)
Indications for cemented THA
poor acetabular bone stock, irradiated bone - very rare though
Biologic fixation Pore Size
50-300 microm (preferable 50-150)
biologic fixation porosity
40-50%, if too porous leads to shearing of metal
biologic fixation gaps
<50 um (distance between bone and prosthesis)
micromotion biologic fixation
<150 um (leads to fibrous ingrowth)
grit blasted is what kind of surface
onlay, EXTENSIVELY COATED
onlay vs. inlay
onlay is weaker, which means you need greater surface coating
hydroxyapatite effect on bone
osteoconductive (not osteoinductive)
signs of a wellxed cementless femoral component
spot welds (new endosteal bone that contacts porous surface of implant. No radiolucenet lines around porous portion of femoral stem, proximal stress shielded in extensively coated stems is good, absence of stem subsidence on serial radiographs
signs of well fixed cementless acetabular component
no migration on serial xrays, no progressive radiolucent lines, intact acetabular screws
aseptic loosening cause
poor initial fixation, mechanical loss of fixation over time, particle induced osteolysis
loose acetabular component symptoms
groin/buttock pain
femoral loosening symptoms
thigh pain and startup pain
how to eval for aseptic loosening
sequential xrays adn bone scan
risks for stress shielding
stiff femoral stem is the most important, extensively porous coated stem (in a revision stem scenarior - not an extensively coated ongrowht but an ingrowth extensivelyc oated stem). Large diameter stem. greater preop osteopenia
causes of aseptic loosening
poor initial fixation, loss of fixation over time, particle induced osteolysis
treat stress shielding?
no
unstalbe fmeur fracture intraop treatment
remove prosthesis, stabilize fracture, reinsert new stem that bypasses fracture by two cortical diameters
