Chapter 44 - Primary Hip Arthroplasty Flashcards
first generation cementing techniques
cement mixed by hand, open bowl, no pressurization, no gun, no canal prep
second gen cementing techniques
pressurizing via cement gun, mixing bowl, restrictor/plug
third general cementing techniques
goal: porosity reduction
pulse lavage, canal prep, pressurization, vacuum mixing
what does vacuum mixing do for cement properties?
minimizes porosity
increases fatigue strength
what are the indications for cementing an acetabular cup?
something wrong with the bone - eg radiation, sometimes osteonecrosis
retained hardware that you cannot get out and get in the way of solid fixation without cement
what does the taper of a stem do for loading characteristics?
taper allows subsidence into a tight fit and optimizes proximal load sharing, optimizes bony ingrowth, and minimizes stress shielding
what do cylindrical stems initially rely upon?
tight diaphyseal fit. see “cylindrical stem” = diaphyseal fit
downsides of a cylindrical stem
high rates of thigh pain, high rates of stress shielding
what pore size is ideal for bony ingrowth in arthroplasty
100-500um
osteolysis cell that predominates
macrophage
with a acetabular cup with multiple holes, where is most of the osteolysis?
retroacetabular
wit
with an acetabular cup without holes, where is the majority of the osteolysis?
proximal femoral osteolysis
what types of corrosion are modular taper necks susceptible to?
fretting and crevice corrosion
how does head size relate to risk of trunnionosis?
larger head size -> increased risk of trunnionosis, 2/2 increased moment arm/torques felt at junction, especially in metal on metal hips
what bearing combination has the lowest wear rates?
ceramic on ceramic (.5-2.5um/yr)
then metal on metal bearings (2.5-5um/year) .1mm/yr for metal on poly
where are metal ions cleared
kidneys
pass thru the placenta, eg fetus is exposed
hemiarthroplasty indications
- displaced femoral neck fracture in the elderly
- osteonecrosis in a young person
- rare - salvage when not enough bone for cup
indications for hip resurfacing
general: advanced hip arthosis with preserved femoral bone stock
- proximal femoral deformity that makes standard THA difficult
indications for hip resurfacing
general: advanced hip arthosis with preserved femoral bone stock
- proximal femoral deformity that makes standard THA difficult
- hx of immunosuppression or rigk of sepsis
- neuromuscular - huge fem heads -> decreased dislocation risk
Contraindications
- women of childbearing age - big head diameters -> increased risk of metallosis -> metal particles pass thru placenta
- femoral bone loss or large femoral neck cysts found in OR
- small acetabuli
Most common complication of hip resurfacing requiring revision?
femoral neck fracture
when do majority of tha dislocations occur
70% occur with in one month of surgery
most common reason for revision THA
- infection
- dislocation
what to use for HO prophylaxis?
indomethacin
700g radiation within 72 hours of surgery
where do PEs originate post op from THA?
popliteal veins or proximal
LMWH vs warfarin for dvt ppx
studies demonstrate decresed symptomatic DVT with LMWH but more bleeding events with LMWH
pathogenesis for osteolysis
particulate wear triggers macrophage activation then osteoclast activation and osteolysis
osteolysis is a MACROPHAGE driven process
what cytokines are involved in osteolysis?
IL-1, IL-6, tnf-a, pge2
what cell type mediates metallosis?
lymphocytes
what is the. mechanism of action of LMWH
activate ANTIthrombin -> inhibit factor Xa
