Recon 2 (THA) Flashcards
Interval for anterior approach, cons
Ant = Smith Pete
Sup: sart (fem) + TFL (SGN)
Deep: rect (fem) + glut med (SGN)
Cons: difficult femoral exposure can undersize and varus stem
Interval for lateral approach
Lateral = Hardinge
Medius + vastus splitting (both SGN)
Interval for ant-lat approach, pro/cons
Ant lat = Watson Jones
Medius + TFL (both SGN)
Pro: lowest dislocation
Cons:
1. Limp because violate the abductors
2. If you split the muscle too high up, hit the gult art/n and deinnervate glut med
What is normal femoral and tab version
Fem: 15 deg AV
Fem NSA 120-135
Tab: 45deg caudal, 15deg ant
What is the difference between femoral implants for cementing vs press fit
Cement: stainless steel or CoCr, stiff and smooth
- If flexible will move within the cement mantle
- Precoated have higher failure rates in cement (fails at the cement/bone interface because cement sticks to the precoat)
Only cement elderly + Dorr C bone
Pressfit: titanium porous coat, flexible to avoid cortex engagement
Tab components:
- Cement vs press fit
- Screws vs no screws
- Position
Always press fit, cement can’t resist the shearing forces (fast failure)
Screws vs none = equiv
Position:
- 40deg aBd (AP)
- 20deg AV (lat)
What is the modern bearing?
Ceramic head on poly tab
What is the 3 step process of preparing poly to make wear resistant?
- Irradiate in inert gas = create free radicals that cross links the poly
- Eliminate free radicals via reheating/melting
Melting = reduces mechanical properties so not ideal
Annealing = heat to a sub melting point to maintain mechanical properties - Sterilize
What is the best way to manufacture poly
Compression molding
Not: ram bar, sheet molding, Ca stearate, gamma irradiation in air
Write out the Young’s modulus for materials (8 total)
Sir Kobe Steels Tricks
Ceramic CoST Could Cement Polly to Cancel her Telephone Carrier
Ceramic (Sir)
Co Cr (Kobe)
Stainless steel (steels)
Titanium (tricks)
Cortical bone
Bone cement
UH ME PE
Cancellous bone
Define creep
Progressive deformation over time
What is a ductile vs brittle material
Ductile = large plastic deformation (chewing gum)
Brittle = NO plastic deformation (glass)
What is stress shielding? What stems are at risk for this?
Distal spot weld, proximal osteopenia
Fully coated, CoCr large stems
- Larger (radius^4) = stiffer
Distal fixation stems stress shield vs proximal fixation stems osteolysis
If you see a distal fixation stem broken in the implant, what happened?
Cantilever bending
Stem is fixed distally, sees a load, stem flexes but is too stiff, breaks at a point between the stem being fixed vs not
Breaks at the proximal junction
What is the difference between ingrowth and ongrowth stems?
Ingrowth = bone grows into a porous structure
Ongrowth = prosthesis surface is rough and the bone grows into the roughening, LESS COMMON
What do you need for good ingrowth
1. Host
2. Material properties
3. Motion?
- ALIVE bone
- Material - rule of 50
50% porosity
50 microns deep pores
<50 microns between gaps - NO motion (motion = fibrous ingrowth)
What is the formula for hydroxyapatite
Ca10 (PO4)6 (OH)2
Osteoconductive
Bone grows onto the HA then must continue to grow into the stem
What is jump distance? How does head diameter change jump distance?
Distance the head must displace before dislocating
Larger head = larger jump distance
Literally just harder to get a big ball out of a big hole
How do these parameters affect soft tissue balance?
Liner offset
Neck length
High off set / lateral offset femur
High off set / 127 neck (normal 132)
Liner offset : leg length + offset
Neck length: “ “
High offset / lateral offset : offset only
High offset / 127 neck : offset, inverse leg length (127 decreases LL)
Difference between linear and volumetric wear
Linear = in 1 direction (smaller heads)
Volumetric = 3D aka poly wear
- Larger heads
- In theory more volumetric wear yields more wear particles (osteolysis), but doesn’t seem to be true for HW CL poly
What is abrasive wear
Difference in material hardness
Poly wears more than the femoral head
What is adhesive wear?
What can you do to protect against adhesive wear?
Bonds between surfaces need to be broken down for movement - the weaker material breaks
Head forms bonds to the poly, break and reform through motion, submicron poly particles
Highly cross linking poly increases adhesive wear
Mechanism of osteolysis
Submicron particles -> marcophage activation -> blasts activate clasts = bone resorption
TNFa
IL1 beta
IL6
2 CI to metal on metal prosthesis
Female child bearing age
Renal failure
Theoretical risk
