TKR Design Flashcards
1
Q
Describe the designs of a TKR?
A
-
Unconstrained
- Posterior cruciate retaining (PCR)
- Posterior crucitate subsituting (PS)
-
Constrained
- Non hinged
- hinged
- fixed vs mobile bearing
2
Q
What is femoral rollback?
A
- The posterior translation of the femur with progressive flexion
3
Q
What is the important of femoral rollback and what controls it?
A
- Improves quadriceps function and range of knee flexion by preventing posterior impingment during deep flexion
- controlled iin native knee by acl and pcl
4
Q
How is rollback implicated into design of prothesis?
A
- Both PCL retaining and PCL subsituting designs allow for femoral rollback
- PCL retaining
- native PCL promotes posterior displacement of femoral condyles similar to native knee
- PCL substituting
- tibial post contacts the femoral cam causing posterior displacment of the femur
5
Q
What is constraint?
A
- The ability of a prosthesis to provide varus -valgus and flexion-extension stability in the face of ligamentous laxity or bone loss
- NB in ligamenotus laxity/bone loss normal crucite retaining or posterior stabilising implants may not provide enough stability
6
Q
Can you descibe the least to the most constraint TKR?
A
- Cruciate retaining ( PCL)
- PCL sacrificing
- Non hinged- (varus-valgus constrained)
- rotating- hinge
7
Q
What is modularity?
A
- The ability to augment a standard prosthesis to balance soft tissue and or restore bone loss
8
Q
How can modularity be achieved in TKR?
A
-
Metal tibial baseplate with modular polyethylene inserts
- more expensive then all poly tibial component
- has an equivalent rate of aseptic loosening cf all PE tibial components
- Metal augmentation for bone loss
- modular femoral and tibial stems
9
Q
what are the adv and dis to modularity iin TKR?
A
- ADV
- ability to customise implant intraoperatively
- DIS
- increased rates of osteolysis in modular components
- backside PE wear
- micromotion between tibial baseplate and undersurface of PE insert that occurs during loading
10
Q
Describe the cruciate retaining TKR?
A
- Minimal constraint device that relies on intact PCL to provide stability
- Indications
- arthritis with minimal bone loss, minimal soft tissue laxity . intact PCL.
- Varus <15o, valgus <10o
- Xrays no box cut is seen on lateral cf PS
11
Q
What are the adv/dis of cruciate retaining TKR?
A
ADV
- Avoids tibial post cam impingement/dislocation that may occur in PS knee
- more closely resembles normal knee kinematics
- less distal femur needs to be cut cf PS
- Imporved proprioception with preservation of native PCL
DIS
- Tight PCL may cause accelerated polyethylene wear
- loose or ruptured PCL -> flexion instability and subluxation
12
Q
Describe the Posterior stabilised knee replacement?
A
- PCL subsitiuting
- Slightly more constrained that sacrificised the PCL
- femoral component contains a cam that engages the tibial PE post during flexion
- PE inserts are more congruent or deeply dishes
13
Q
What are the indications for posterior stabilised TKR?
A
- Previous patellectomy
- reduced risk of potential anteroposterior instability in setting of weak extensor mechanism
- Infammatory arthritis
- infammatory arthritis may lead to late PCL rupture
- Deficient or absnet PCL
- xrays
- show outline ot box on lateral xray
14
Q
What are the adv/dis of a posterior stabilised TKR?
A
ADV
- easier to balance the knee with absent PCL
- arguably more ROM
- easier surgical exposure
DIS
-
CAM Jump
- with loose flexion gap or hyperextension, the cam can rotate over the post and dislocate
- tx with closed reduction using anterior draw
- revise to address loose flexion gap
- Tibial post PE wear
-
Patellar clunk syndrome
- scar tissue gets caught in box as knee moves into extension
- tx with arthroscopic vs open resection of scar tissue
- additional bone is cut from distal femur to balance extension gap
15
Q
Describe the design of the constrained non hinged TKR?
A
- Constrained prosthesis without axle connecting tibial and femoral components ( non hinged)
- large tibial post and deep femoral box provide
- varus-valgus stability
- rotational stability
- Indications for use
- LCL attenutation/deficiency
- MCL attenutation/deficiency
- flexion gap laxity
- moderate bone loss in the setting of neuropathic arthropathy
17
Q
Describe the design of a constrained hinged tkr?
A
- most constrained device with linked femoral and tibial components
-
tibial bearing rotates around a yoke on the tibial platform ( rotating hinge)
- decreases overall level of constraint
- Indication
- Global ligamentous deficiency
-
hyperextension instability
- polio and tumour resections
- resection of tumour
- massive bone loss in setting of neuropathic joint
18
Q
What are the adv and dis of constrained hinged tkr?
A
Adv
- Prothesis allows stability in the face of soft tissue ligamentous or bony deficiency
Dis
-
aseptic loosening
- as a result of increased constraint
- large amount of bone resection required
19
Q
Can you describe the design of a mobile bearing TKR?
A
- Minimally constrained prosthesis where the polyethylene can rotate on the tibial baseplate
- PCL is removed at time of surgery
- indications
- young, active
