Recon Flashcards
acetabular dysplasia quantitative definition
anterior or lateral CE angle less than 20, acetabular index greater than 5
measured on the false profile view
anterior CE angle
besides crossover sign, often see this in acetabular dysplasia on the AP
ischial spine sign
abnormal acetabular contact point in FAI
anterosuperior labrum, leads to contracoup at the posteroinferior acetabulum
lesion described by a high ALPHA angle
Cam lesion of FAI. Normal alpha is ~40*
distinguish the tissues affected by the two types of FAI
in cam impingement the neck travels under the labrum rather than hitting it, so affects the chondral surface of the pelvis more than in pincer, where the labrum itself gets trapped
this is most common reason for conversion of hip fusion to THA, and a technical reason it can occur
disabling back pain, which is more common when there is hip abduction component to the fusion
preop planning for takedown of a hip fusion and conversion to THA
need to know if the gluteus medius works: EMG. If it doesn’t there will be a severe lurching gait and you will need constrained liner
can be used for medical mgmt of precollapse AVN
bisphosphonates. Have to be started before stage 3 (crescent +)
these 3 pts don’t have as good of an outcome with core decompression for AVN
pts with crescent sign, pts on chronic steroids, or pts that have larger than 15% head involvement (go on to collapse)
deciding between core decompression or fibular strut graft
grafting done for the pts that wouldn’t do well with decompression: lesion more than 15%, those with a crescent sign (prefer not to have one though)
ingrowth surface
porous coating
ongrowth surface
grit blasted coating
why do cemented cups fail when cemented stems don’t
stems are loaded mainly in compression, whereas cups see shear and tension forces
optimal ingrowth of metallic components based on these 6 factors
viable bone, implant in contact with cortical bone, micromotion less than 30 microns, gap less than 50 microns, metal pore size between 50 and 150 microns, with 50% porosity
algorithm for for acetabular fx while implanting THA cup
Cup is stable? Then add screws. If cup is unstable, take it out, fix the fx, then put it back in and add screws
algorithm for for femoral fx while implanting stem
If the crack is small and stem is stable, just limit weightbearing, keeping the stem. If the stem is unstable, take it out, fix the fx, and replace with same stem or revision stem.
linear relationship between this and implant ongrowth fixation strength
surface roughness, Ra. Difference between peaks and valleys.
two complications of bone ongrowth implants
fracture and aseptic loosening (initial rigid fixation not strong enough to allow osteointegration)
osseous properties of hydroxyapatite
osteoconductive only; no biology
purpose of HA on implants
shortens time to biologic fixation
optimal thickness of HA coating on implants
Any thicker than 50 microns will crack and shear off
indications for cementless femoral stem
young male patient and higher-activity level pt. Both instances related to mechanical properties of the cement. Activity because of cyclic failure, young male bc of higher stress-loading
this is more to blame for stress shielding than the amount of porous coating
the modulus mismatch, i.e. stem stiffness
worst scenario for proximal femoral stress shielding in THA
round, solid, large diameter, extensively-coated, cobalt stem
segmental deficiency in the context of cup fixation
loss of the main bony supports: acetabular rims or columns, or the medial wall
why cementing a poly into a damaged cup is less than optimal
higher dislocation rate
“safe zone” of acetabular screw placement
posterior-superior quadrant
“zone of death” for acetabular screw placement
anterior-superior, external iliac arteries
major artery injury during THA
pack, flip if need be, anterior incision and control/repair
mgmt of femoral segmental defect in revision THA
cementless, extensively porous-coated revision stem that bypasses the most distal defect by 2 cortical diameters is preferred
why a longer femoral revision stem provides better initial rigid fixation
increased resistance to torsional loads
This is mainly to blame for PE-related osteolysis, and the process that causes it
submicron-sized particles are generated by adhesive wear, that get phagocytosed by macrophages and then become activated
The molecular basis for PE-related osteolysis
submicron particles eaten by macrophages. Macrophages activated, then release TNFa, IL1, TGFb, PDGF. PDGF is activator of RANKL. Leads to osteoclast activation. No other cell besides osteoclasts eat bone…
mechanism for PE distribution through the effective joint space
PE particle generation and the resultant biologic response creates hydrostatic pressure that pushes fluid into the effective joint space
the main determinant of the number of PE particles generated
volumetric wear, which is directly related to head size
volumetric wear determinant
directly related to the square of the radius of the head
These wear rates of X are associated with osteolysis
Linear wear rates more than 0.1mm per year
why 28mm heads are common size
Older 22mm heads had too much linear wear and failed through the cup. Larger heads, 32mm, have more volumetric wear and failed by osteolysis
non-technique ways to reduce osteolysis
alternative bearings, bisphosphonates, or OPG
this is associated with acetabular fx while performing THA
cementless cup, underreaming more than 2mm
fracture patterns of intraop femoral fxs during THA
wedge-taper designs break proximally, cylindrical fully-coated stems break distally
vancouver B class
B1 - well-fixed, good bone. B2 - loose, good bone. B3 - loose, shitty bone.
the periprosthetic fx where extensively-coated long-stem prosthesis is the ONLY answer
Vancouver B in CEMENTED stem that compromises the cement mantle
contraindication for THR
coxa vara
% of pts with nerve injury after THA that will recover strength
35-40%
where the sciatic nerve is closest to the acetabulum (THA)
at the level of the ischium
4 risk factors for sciatic nerve injury in THA
female, post-traumatic, revision, DDH
risk for nerve injury increases with lengthening of nerve over X
3.5 cm
positional foot-drop after THA
flat in bed, knee on a pillow
Two explanations for sciatic palsy after THA that was not complicated by intraop nerve injury
Hematoma (evacuate it) and spinal stenosis (image it, MRI Lspine)
Retractor placement under the TAL during THA
obturator artery at risk down there
THA in sickle cell
early loosening
THA in psoriatics
infection
THA in ankylosing spondylitis
HO formation. Increased risk for anterior dislocation.
THA in Parkinsons
higher dislocation, mortality, medical complications, and reoperation rates
intraoperative hypotension
fat emboli syndrome, pressure from femoral stem insertion
Which 7 pts dislocate the most after THA?
female, post-AVN, posterior approach, small head-size, alcoholics, neuromuscular dz, revisions
lever range in THA
after the neck hits the cup, the arc allowed before the hip dislocates
excursion distance in THA
distance the head must travel to dislocate. Equal to radius of the head.
primary arc range in THA, and its determinant
Controlled by the head/neck ratio, the arc a femur travels before impinging on the cup. Anything that decreases the head/neck ratio decreases the primary arc range.
4 problems with decreased THA offset
weakened abductor moment, increased JRF, increased risk of dislocation, trendelenberg gait
4 assessments of the unstable THA
design, position, soft tissue tension, soft tissue function
4 indications for constraint in THA
Components well aligned #1, then: elderly, abductor-deficient, CNS decline, or revision with a cage (approach causes soft tissue damage)
when a THA would get converted to a hemi
recurrent dislocator that has no segmental bone loss and good bone density
this type of PE manufacturing has the best wear properties
direct compression molding, because there is no machining involved
what is cross-linked poly and how is it better than non-cross-linked
when irradiated in a vacuum, the free radicals produced will bond with an adjacent PE chain. Improves resistance to adhesive and abrasive wear
what causes oxidized PE, and the term for its molecular basis
after formation of free-radicals by irradiation, presence of oxygen will allow bonding between O2 and the free radicals. Called “chain scission”.
why is oxygen bad for PE manufacture
O2 bonds with free radicals, causing oxidation. Oxidation makes poly more vulnerable to pitting, delamination and fracture. (more brittle, less strong, less ductile)
how is standard PE better than cross-linked poly
although the cross-linking improves the wear properties, it makes nearly all the mechanical ones worse.
why does the dose matter in sterilizing PE by radiation
the higher the dose of radiation, the more free radicals are formed. The more free radicals, the higher the chance that some bond with oxygen and cause oxidation
irradiation in PE production essentially targets this structure
the amorphous phase is the only part of a poly that cross-links, however it forms free-radicals throughout the poly
the mechanical properties of PE are related to this structure
the crystalline phase provides the mechanical strength of a poly. Free radicals are not able to cross-link here.
why does melting a poly reduce the mechanical properties and annealing does not
melting further increases the cross-linking, but that prevents recrystallization. Since the mechanical properties are related to the crystalline phase, they decrease.
this process creates free radicals and causes cross-linking
irradiation in vacuum
this process eliminates all free radicals
melting
this process eliminates some free radicals
annealing, which does not remove them from the crystalline phase of a poly. Oxidation risk, but with less reduction in mechanical properties than melting.
rationale for vit E treatments with poly production
free radical scavenger
this has the largest effect on “on-the-shelf” poly wear
type of packaging
MoM wear
nanometer-sized particles, low volumetric and linear wear, but the number of particles is actually higher than PE wear
responsible for the biologic response to metal debris
T cell mediated. Contrast with PE wear which is due to macrophages
why women are more likely to get MoM PITR
Co-Cr ions bind with a serum protein seen as antigen by the T-cells, the inflammatory cascade of which includes RANK/RANKL system. This process is already influenced by sex hormones
2 contraindications for MoM bearings
women of child-bearing age (DOES cross placenta) and pts with renal failure
bearing used in revision of ceramic THA failure
have to use ceramic again; microscopic particles of ceramic that remain would destroy a poly bearing too quickly
osteotomy for knee arthritis indications
young active pt under ~45
osteotomy for mgmt of varus knee arthritis
valgus-producing tibial
osteotomy for mgmt of valgus knee arthritis
varus-producing femoral
3 contraindications for osteotomy as mgmt of varus knee arthritis
inflammatory, less than 90* of flexion or flexion contracture more than 10*, varus thrust gait. NOT contraindicated in cruciate-deficient knees
4 contraindications for osteotomy as mgmt of valgus knee arthritis
inflammatory, flexion contracture more than 10, prior medial menisectomy, or more than 15 valgus
4 contraindications for UKA
inflammatory, ACL deficient, FIXED deformity, flexion contracture more than 10*
these TKA candidates get full-length standing AP legs
very tall, very short, or angular bony deformity
the distal femoral cut is perpendicular to this
the mechanical axis of the femur, not the anatomic axis
the valgus cut angle
usually between 4-7, it is the difference between the MAF and the AAF. Affected by the length of the femur, as hip offset is pretty standard
sequence of release for varus malalignment of TKA
osteophytes, deep MCL, posteromedial corner, superficial MCL
medial structure tight in flexion during balancing of TKA
anterior portion of the superficial MCL
medial structure tight in extension during balancing of TKA
posterior oblique portion of the superficial MCL
lateral structure tight in flexion during balancing of TKA
popliteus
lateral structure tight in extension during balancing of TKA
IT band
sequence of release for valgus malalignment of TKA
osteophytes, capsule, popliteus, IT band, LCL
instance where LCL is released first in valgus malaligned TKA
something to do with if only tight in flexion or extension? might be esoteric…
sequence of release for flexion contracture of TKA
osteophytes, posterior capsule, gastroc origin. All performed with knee flexed to protect vessel
fracture patterns with anterior nothing of a TKA
in torsional loads there is no difference, but in bending loads the fx starts at the notch. DON’T MUA a notched femur…
mgmt of most common nerve palsy after TKA
peroneal nerve palsy. Most resolve on own in 3 mos. If doesn’t and nerve is intact by EMG, explore and decompress.
artery at risk with lateral retinacular release for patellar maltracking
lateral superior geniculate artery
intraoperative MCL injury
Convert to revision prosthesis, then primary repair is acceptable. postop brace x6wks.
the only thing i can’t fix if you fuck it up during a TKA
extensor tendon disruption can’t be repaired intraop, nor does nonop mgmt work. Fresh frozen allograft is close to the best shot.
this can be done in extra-articular femoral deformities (TKA)
can add distal femoral angular osteotomy at the time of TKA if cuts would be extreme
this influences femoral rollback in TKA
PCL tension
3 causes of loose flexion gap
over-release of popliteus, anterior portion of the superficial MCL, or anterior translation of the femoral component
maximal joint line elevation in TKA
8mm, or risk patella baja
specific indications for PS TKA
inflammatory (erosive chg if you leave PCL), post-traumatic PCL rupture or attenuation, after patellectomy (anterior subluxation with a flat CR poly)
3 advantages and 1 disadvantage of anterior stabilization in CR TKA
Has to be more highly congruent, which decreases the contact stresses. This results in less poly wear, lower fracture rate, and less delamination. BUT there is increased shear stress but it takes away the femoral rollback.
this is a debated relative indication for use of constrained TKA in primary setting
charcot arthropathy
polio in TKA
hyperextension instability, absolute indication for a hinge
diagnosis of metal hypersensitivity
made with serum lymphocyte T-cell proliferation test NOT skin patch testing
after 2 yrs from TKA most common cause for TKA failure
poly wear
most common complications in TKA
patellar maltracking
causes of patellar maltracking in TKA
internal rotation or medialization of either side, lateralization of the patellar component
proximal tibial closed wedge osteotomy
patella baja: loss of knee flexion
contraindications to shoulder arthroplasty
deltoid AND cuff deficiency (?), and charcot arthropathy
requirements for TSA
Intact cuff, although isolated infraspinatus tear without retraction at surgery isn’t reason to convert to something else
incidence of full thickness RTC tears at time of TSA
5-10%
better pain relief long term, hemi or TSA?
TSA. Conversion from hemi to TSA not as successful (issues with glenoid bone loss)
humeral stem position in TSA
35* of RETROversion
glenoid position in TSA
neutral. Avoid retroversion
why are passive ER exercises avoided after TSA
risk of subscap tear
result of subscap tear after TSA
anterior instability
critical to success of hemi if done for RTCA
preservation of the CA ligament; if disrupted can lead to anterior-superior escape
deltoid power and effiency are improved by this in RTSA
medialization of the center of rotation, which increases the humeral head offset
biofilm is 85% this
polysaccharide matrix
within 2-4 weeks after a TJA this fluid WBC is suggestive of infxn
~11,000
in the chronic setting after a TJA this bug is most common pathogen
staph epi
in the acute setting after a TJA this bug is most common pathogen
staph aureus
Routine use of this in TKA may be associated with aseptic loosening
antibiotic-impregnated cement
blood supply to the medial gastroc flap
medial sural artery. Has good excursion.
blood supply to the lateral gastroc flap
lateral sural artery. Not as much excursion, so not used for anterior deficiencies. Can have peroneal palsy from tension.
