OITE - Recon Flashcards
Effective joint space?
Any contigous area around the implant
Osteolytic process involves?
- phagocytosis of submicron PE particles by macrophages
- Bone reorption by osteoclasts
PE manufacturing, 4 methods?
1- ram bar extrusion (machine)
2- sheet molding (machine)
3 - compression molding (isostatic) - machine
4 - direct compress molding (is best option)
Good or bad, gamma irradiation in air?
Bad
Direct compression molding from PE powder to desired product has what advantage?
Lowest susceptibility to fatigue crack formation and propagation in joint bearing
McPherson’s Rule for sagittal plane (gap) balancing?
Symmetric problem - tinker with tibia
Asymmetrical problem - tinker with femur
Closed suction drain in TKA typically results in what?
Drain = increased rate of transfusion
meta-analysis study proves this
Peri-prosthetic fx key concepts (two)
1) Implant loose = REVISE + ORIF
2) Implant stable =
- non displaced – cast/brace
- displaced – ORIF vs nail (supracondylar), ORIF tibia
Paterllar clunk syndrome due to?
Internal rotation (femur or tibia component)
Medialization (femur or tibial component)
-investigate with CT scan
Anterior dislocation
ER + extension
posterior hip dislocation?
Flexion + IR
Highest patient factor for THA dislocation?
Female gender
Other, abductors
Head neck ratio and head size relevance to THA design?
If head-neck ratio is smaller will impinge sooner (ie more unstable)
Bigger head size = increased jump distance before dislocation
Trendelenburg sign in THA stability?
Weak abductors
turnk lurches to weakened side to keep level pelvis
Use of a skirted femoral head can lead to what?
Increase risk of hip dislocation
(smaller head to neck ratio), ie earlier impingement
Lowest values suggestive of infection of a joint aspirate (chronic)?
Chronic: WBC > 1,100 cells/ml PMN > 64 %
Acute (early post op): 27,800 cells PMN > 89% at 6wks
Inconclusive aspirate and peripheral lab data for joint infection, do what?
Repeat aspiration
What does inconclusive mean?
high inflam marker
hx concerning for infection (drainage)
unusual clinical presentation (early loosening)
additional imaging concerning for infection
THA peri-prosthetic fx, implant loose or not?
- question will lead you “no symptoms” = well fixed
- if loose - revise - cementless fully porous coated
- if stable - ORIF
Revision stem surgery (femur), cement or not cement?
Uncemented
Factors affecting fluid-film lubrication (metal on metal bearings)?
Radial clearance - defines contact area of bearing
- Want polar contact with high conformity.
- Dont want equatorial contact and seizing (complete congruence)
“Zone of death” in acetabular screw safe zone?
Anterior-superior zone (external iliac vessels)
Safe zone in acetab screw fixation?
Posterior superior zone
How can you look for polywear on xray of THA?
ECCENTRIC position of the femoral head
Osteolysis with well fixed implants, how to manage?
- No pain = well fixed implants
- Look at implant position
- -acceptable - exchange poly and bone graft
- -poor position - revise the shell
Indications for conversion arthrodesis to THA?
- painful pseudoarthrosis
- mechanical low back pain
- ipsilateral knee pain (hip fused with increased adduction)
Outcome of arthrodesis conversion to THA?
walking function depends on abductor function
pre-op glut strength predicts post-op ambulatory status
Increased Q angle leads to what?
=bad
Increased lateral patellar subluxation
Hypoplastic lateral femoral condyle will lead to what in a posterior condylar axis reference system?
Using posterior condylar axis will IR femoral implant
-Use the trans-epicondylar axis instead!
Advantages of UKA vs TKA
- faster rehab, preserve normal kinematics (ACL and PCL retained)
- better ROM short term, no difference at long term
- shorter LOS and less narcotic use
UKA-specific complication?
Stress fx - best visualized on bone scan
Contra indications to UKA?
- ACL def -fixed varus or valgus deformity > 10 deg
- restricted ROM (10 deg flexion contraction, or
What enhances bone-cement fixation?
- limit porosity of cement
- cement mantle > 2mm
- stiffer femoral stem
- smooth femoral stem (no sharp corners)
Bone-cement interface stronger or weaker in osteopenic bone?
Bone-cement interface is mechanically stronger in osteopenic bones due to deeper cement penetration into pore
Hydroxyapatite (HA) coated stems has what benefit?
- shorter time to biologic fixation in animal models, but no advantage clinically in humans
- osteoconductive
PE sterilization by radiation (during sterilization) can lead to what?
- free radical formation of PE
- if O2 rich environment — oxidized, delamination, wear, failure
- if O2 depleted env (argon/vacuum/nitrogen) - radicals cross link and lead IMPROVED wear, BUT decreased mechanical properties
Most common complication with hip resurfacing?
Femoral neck fx (peri-prosthetic) , 1-3 %
Hip resurfacing advantages?
- Low dislocation rate (preserved h-n ratio, ie larger head)
- preserve femoral bone stock
- maintains anatomic femoral neck offset and anteversion
Hip resurfacing disadvantages?
Requires larger exposure than conventional THA
-risk of peri-prosthetic femoral neck fx
What medical tx is shown to decrease hip AVN progression to collapse?
Bisphosphonates
- inhibits osteoclast formation, and slows down bone resorption
- Ficat stages 0 - 2 (pre-collapse AVN)
When do you see Crescent sign in AVN? implicates?
Transition from Stage 2 to Stage 3
Implicates impending collapse of head of femur
Risk factors for AVN?
-trauma, ETOH, steroids
What is femoral rollback?
Posterior transition of the femoral-tibial contact with progressive flexion
In non-constrained CR knee, what is relied on for rollback?
- Native PCL
- but rollback not anatomic
non-constrained PS (cruciate substituting) knee, what is relied on for rollback?
Tibial post engages on the femoral cam and forces mechanical roll back
Indication for a cruciate substituting TKA?
- previous patellectomy
- inflammatory arthritis
- deficient PCL
In a constrained non-hinged knee, what subs for MCL and LCL?
Large central post
-gives V/V stability and rotational stability
Indications for constrained non hinged?
Flexion gap laxity
MCL or LCL deficiency
THA, what most often leads to SCN palsy? What portion of SCN affected?
-Lengthening
-80% involve peroneal portion
risk factors: dysplasia, female gender, revision sgx
Optimal hip arthrodesis position?
25-30 deg flexion
0-5 deg adduction
0-5 deg ER
Hip arthrodesis expends how much more energy?
- 30% more nrg expenditure for ambulation
- accelerates degeneration of adjacent joints
Golfing following THA or TKA,
Rise in their handicap
decrease in driving distance
mild ache while playing
90% use a cart
Mechanical axis of a limb passes where relative to centre of the knee?
It passes slightly medial
Order of soft tissue release of valgus knee?
- osteophyte
- lateral capsule
- ITB if tight in extension -popliteus if tight in flexion
- release LCL if tight in BOTH
Abx-impregnated bone cement, most effective in who?
- Revision TKA
- most pronounced in pts whose risk of post-TKA infection is greatest
What ROM component is most important predictor of post-op TKA motion?
- Pre-op flexion is most important
- CPM not sown to improve outcome or longterm ROM
Patella Baja?
=shortened patellar tendon length
-limits flexion
Risk factors for patella baja?
- Proximal tibial osteotomy (both lat closing and medial opneing)–> tendon scarring
- tib tub shift or transfer
- prox tibia previous trauma
Highly cross linked UHMWPE vs conventional poly?
- more irradiation = better wear, but decreased mechanical strength
- increased resistance to abrasive wear
