Types TKR Flashcards
what are the different types of total knee replacement?
primary and revision protheses
Primary:
* Cruciate retaining
* posterior stabilising
revision implants:
* unhinged
* hinged
what is a cruciate retaining implant?
advantages
* lower shear forces at tibial component fixation interface
* less bone loss of dital femur
* greater stability in stair climbing
* avoids patella clunk syndrome and tibial post/ cam impingment
* improved proprioception
* allows roll-back
disadvantages
* slide from roll-back increases contact stresses and polyethylene delamination
* more difficult to balance
* flexion instability - if PCL loose or ruptured
* less conforming
what is a posterior stabilising implant? when would you use it?
PCL sacrificed with cam-post mechanism
Indications:
* post patellectomy - AP instability
* inflammatory arthritis - risk of PCL rupture
* deficient PCL
* stiff knee post traumatic OA
* previous HTO
Advantages
* conforming surfaces - allows roll-back and less wear than CR
* easier to balance
* better rom
* better AP stability
disadvantages
* increased loosening - high stresses at fixation
* femoral bone loss - for box
* patella clunk syndrome
* tibial post dislocation - cam jump
* tibial post increases wear
what is roll-back and why is it important?
what is it?
* roll-back is the posterior translation of the femur in flexion
* CR TKR - the PCL allows posterior displacement of the femoral condyles in rollback
why important?
* permits clearance of tibia in deep flexion
* improves mechanical efficiency of extensor mechanism
advantages and disadvantages of a hinged TKR?
what is it?
stemmed linked prothesis
tibial bearing rotates around the tibial platform
indications:
* global ligament deficiency
* hyperextension instability - polio
* tumour resection
* severe bone loss +/- neuropathic joint
advantage
provides stability in presence of large bone loss and instability
disadvantages
* risk of periprosthetic fractures - due to stress risers
* loosening - large forces going through the implant - 90% at 15yrs all ages, <55yrs its 84% at 10yrs
* large bone resection for implant
Advantages and disadvantages of using an unhinged TKR (LCCK)?
**unhinged TKR - LCCK **
constrained TKR with large tibial post, deep femoral box and no link bwn tibial and femoral components
indications
* Moderate bone loss (charcot)
* mild MCL/LCL deficiency
* flexion gap laxity - PCL rupture
Advantages:
* provides AP, varus/ valgus and rotational stability
* 95% survivorship at 15yrs
*Disdvantages: *
* increased femoral bone resection
* Asceptic loosening (large forces going through the prothesis)
what type of knee replacement would you use for a patient with a patellectomy?
Posterior stabilising TKR
- it provides greater anterior/posterior stability in the presence of weak extensor mechanism
some case series for UKR in the presence of medial compartment OA only
NJR data for triathlon
3.5% revision rate at 15yrs
ODEP rating 15A*
