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
Pseudotumor
- Metals that cause this
- Histo changes
- Immune cells involved
- Workup
CoCr
Direct tissue necrosis = aseptic lymphocytic vasculitis
T4 HST rxn = T & B cells
Workup:
1. Aspiration - manual cell count bc dead cell burden messes up automatic count
2. MARS MRI
3. Serum ion levels - anything >2ppb = elevated
4 known RF for pseudotumor
F
Smaller components (aka women)
<40
Hip dysplasia (think eccentric wear)
3 complications associated with MOM revisions
Dislocation - soft tissue damage
Infection - necrotic tissue
Lack of ingrowth - dead bone
How to differentiate between MOM vs trunnion pseudotumor
Just have to look at the XRs
Both cause pseudotumor and elevator serum ion levels
Define corrosion
1. Fretting
2. Crevice
3. Galvanic
Corrosion = how a metal reacts w/ environment and gradually breaks down
Fretting = small cyclic motion disrupts the protective oxide layer -> metal exposed to O2
- Any modular junction
Crevice = pits form -> accelerate corrosion -> increased wear
- Metal on poly hip w/ metal ions >1ppb
- Revise to ceramic head w/ titanium sleeve and poly (remove CoCr)
Galvanic = battery corrosion 2 different metals (CoCr)
What bearing surface has the lowest wear couple
Ceramic on ceramic
Cons: squeaking, fracture risk
Where does the sciatic n come closest to the tab?
What is the most common injury
Level of the ischium
Compression -> peroneal division bc peripheral fibers
- Retractor vs hematoma
50% resolve
HO
- Which approach is a RF
- Prophylaxis
Direct lateral (Hardinge)
Prophylaxis
1. 24pre op 700G
OR 48hr post op 700G
2. Indomethacin - 1-6wks post op, dosing variable
What is the Brooker classification
HO - takes up to a year to fully mature/declare
B1 = bone islands in the soft tissues
B2/3 = bone islands grow together
B4 = ankylosis
When to revise for iliopsoas tendonitis
> 8mm prominent cup overhang
If no overhang, IP tenotomy
Treat poly wear (see eccentric head position and osteolysis)
Well fixed/positioned implants - head/liner exchange
- Use as big head as possible to increase stability
Lytic defect - revision
What is start up pain a sign of?
Aseptic loosening
Groin = cup
Thigh = stem
XR signs for aseptic loosening for a cemented vs cementless stem
Cementless: subsidence, distal pedestal
Cemented: lucent lines, stem migration, cement mantle fracture
Describe 4 levels of Paprosky femoral bone loss and how to revise
T1 = normal (metaphyseal but not structural) - use anything
T2 = metaphy bone loss - cementless diaphyseal stem
T3 = metaph + diaph bone loss - cementless res mod
T4 = structural diaph bone loss - APC, metaprosthesis
What is the most common revision cementless stem
Tapered fluted modular stem (titanium)
I.e. res mod
Revision tab principles :
- How much rim must be intact for press fit
- What is your first choice revision tab
- What do you use for pelvic discont
2/3 rim intact to use press fit
1st choice = large, cementless cup w/ screws
Pelvic discon = cup/cage, plate, custom triflange
What is the safe zone for screws?
Post sup > post inf
Ant sup = ext iliac A/V = bleed out and die
Ant inf = ob N/A/V - more from retractor placement
What are the aspiration threshold for acute vs chronic PJI
All must be off abx for 2wks
Acute <6wks = WBC > 10K, PMN > 90%
Treat if <1mo = I&D, comp change bc no biofilm
Chronic = WBC > 3K, PMN > 80%
Treat 2 stage revision
When can alpha defensin be false positive?
Metallosis/corrosion
When is TXA CI
Active DVT or renal failure
Why do you want to avoid transfusion in total joint patients?
Increases risk PJI
What is the mechanism of dual mobility increasing stability?
Who should you use it for?
Increases head diameter + jump distance even in small cups
High risk patients:
- Hip frx
- L spine pathology (fusion)
- Revision
Vancouver classification femur fractures
A: troch
B: diaphyseal
1 - stable
2 - loose, good bone
3 - loose, bad bone
C: distal
Treat an intraop calcar fracture
Remove stem
Does not go past LT - cable, re-press fit
Past LT - revision implants
Imaging + treat transient osteoporosis of hip
Signal everywhere in prox fem (not just neck/head)
Protected WB
What are the deformities of DDH
Tab + fem neck are AV
Hip COR lateralized
Less shallow socket
Trt = PAO as long as posterior col intact
Describe trendelenburg gait
Weak abductors
Lean TOWARDS the weak side
Put the cane in the CL hand
What is the goal abduction and anteversion for tab component
30-50deg abd
5-25deg anteversion
Too high - risk ant dislocation w/ ext
Too low - risk post dislocation w/ flex
What head size for MOM vs THA increases risk of ALTR?
MOM <46mm - small
- Larger brings more fluid in the articulation
THA >32mm
How do Co/Cr levels differ for hip resurfacing vs taper corrosion
Resurfacing - both high TOGETHER (equally)
Taper/fretting - Co > Cr
