TKA THA Flashcards
DOF of knee
6 DOF
varus
knee out
valgus
knees in
causes of knee degeneration
osteoarthritis
fractures
torn cartilage/ligaments
more conforming implant
Higher stress across fixation surface
lower wear/stres on PE
less conforming implant
lower stress across fixation surface
higher wear/stres on PE
reduced radius
increasing radius near extension and decreasing radius at flexion
single radius
identical femoral radius from extension to flexion
advantages of UKA
preserves ACL
smaller incision and less blood loss
lesser bone removed
quicker recovery
disadvantages of UKA
short life
loosening risk
prosthetic wear
degeneration of opposite compartment
Causes for THA
arthritis
hip dysplasia
avascular necrosis
hip fracture
arthritis / dysplasia
wear of cartilage
bone on bone contact
joint becomes stiff, uneven, painful
avascular necrosis
disruption of blood supply to hip
bone tissues die and femoral head collapses
intracapsular fracture
subcaptial neck fracture
transcervical neck frac
basicervical neck frac
extracapsular fractures
trochanteric
subtrochanteric
garden 1
incomplete fracture of the femoral neck
garden 2
complete fracture without displacement
garden 3
complete fracture with partial displacement
garden 4
complete fracture with full displacement
as the fracture angle increases there is a greater risk of a non union due to ….
increasing shear stresses across the fracture
cannulated hip screws
multiple screws in parallel
used for un-displaced femoral neck fractures
good for fracture which no shear stress (horizontal)
dynamic hip screws
-extra-capsular fractures
-adequate for fracture with shear stress
-resist angular deformation while allowing compression along the lag screws axis
l-ag screw is inserted into the head of the femur and held in place by a plate positioned on the side of the femur
Cephalo-medullary device
- intramedullary nails designed for the fixation of the femoral head and neck
- complex proximal femoral fractures
- nail is closer to the central axis of the femur
-act as load sharing device
hemiarthroplasty hip
-replaces one half of the joint
-recommended only for elderly due to their low life span
- tends to loosen or to erode acetabulum
THA components
femoral head
femoral stem
acetabular cup
polyethylene between liner and ball
THR
resurfacing
preserves more bone
removes cartilage and damaged tissues
places a metal cap and cup over the femoral hear and acetabulum
small stem
THR advantages
head size is more natural to fem head
less wear due to advanced bearing
bone conservation
stability is sustained by…
bony impingement, muscle and ligaments tension force
hip implant design considerations
ROM
stability
wear resistance
lifestyle
gender
age
weight
severity of wear
Metal on poly - pros/cons
pros:
options
toughness
cons:
wear of standard poly
xlpe sensitivity
cer on poly - pros /cons
pros:
reduced wear
abrasion resistance
cons:
fracture risks
fewer sizes
metal on metal - pros /cons
pros:
reduced wear
head size options
strength and toughness
cons:
high ion levels
sensitive to abrasion
