Chapter 49 - Primary Knee Arthroplasty

Question 1

What is a possible advantage of the midvastus or subvastus approach

Answer 1

possible more rapid restoration of extensor mechanism function (accelerated rehabilitation)

possible improvement in patellar tracking limiting need for lateral release

Question 2

relative contraindications for mis vastus or subvastus approaches

Answer 2

1. lack of pre-op flexion
2. v large osteophytes
3. obesity
4. previous HTO
5. revision
6. extremely mm quads

Question 3

indication for lateral parapatellar approach

Answer 3

fixed severe valgus deformity

Question 4

standard coronal plane cuts

Answer 4

standard tibia cut is perpendicular to the mechanical axis of the tibia (0 degrees varus/valgus)

standard femur cut is 5-7 degrees of valgus

standard cuts result in a horizontal joint line - more even wear across the joint - possible long term survivorship benefit

Question 5

anatomic coronal plane cuts

Answer 5

anatomic tibial cut is in 3 degrees of varus

anatomic femoral cut is in 8-10 degrees of valgus

more varus tibial cut places more strain on the bone cement interface -> early aseptic loosening

Question 6

what is the difference in sagittal cuts for cruciate sacrificing implants?

Answer 6

less posterior slope cut for the cruciate sacrificing, bc resecting the pcl tends to loosen the flexion space

Question 7

what alignment correction places the peroneal nerve at highest risk of injury?

Answer 7

valgus with a flexion contracture

Question 8

when to use a PCL substituting TKA

Answer 8

inflammatory arthritis
previous PCL injury
excessive pcl release intraop

Question 9

pcl sparing knees have what kinematic disadvantage>

Answer 9

paradoxical motion - eg no roll back, and poor flexion

Question 10

which knee design is associated with patellar clunk?

Answer 10

posterior stabilized

Question 11

cross linked patellar buttons are associated with what?

Answer 11

increased risk of poly fracture compared to standard buttons

Question 12

what is the only proven difference between commercially mixed antibiotic cement and non-antibniotic cement?

Answer 12

increased in cost in antibiotic cement

Question 13

Most common late complication of non-cemented TKA

Answer 13

osteolysis

Question 14

when is an absolute indication to use a resurfaced patella?

Answer 14

inflammatory arthritis

Question 15

what percentage of extension power is lost after patellectomy

Answer 15

25-60%

• also causes substantial increase in tibiofemoral joint reactive forces

Question 16

if a TKA is performed after patellectomy, what kind of implant design should be used?

Answer 16

posterior stabilized

Question 17

most common technical complication following TKA?

Answer 17

patellar maltracking

Question 18

how should you orient the femoral component relative to the transepicondylar axis?

Answer 18

slightly externally rotated (like 3-5 degrees)

Question 19

how should the femoral component be oriented

Answer 19

externally rotated, slightly lateralized

Question 20

internal rotation of the tibial component leads to what?

Answer 20

external rotation of the tibial tubercle, increased q angle
** DO NOT DO IT

Question 21

how should the tibial component be oriented

Answer 21

slightly externally rotated
midpoint of the component should be in the middle 1/3 of the plateau

Question 22

how should the patellar component be oriented

Answer 22

medial and slightly superior (remember when you have the patella everted, medializing the patella actually looks like you are placing it lateral)

Question 23

instability accounts for what percentage of TKA revisions overall?

Answer 23

10-20%

Question 24

how to address axial instability

Answer 24

if symmetric in both flexion and extension - insert bigger poly

if asymmetric, need to remove components and do full revision

Question 25

dislocation of a TKA is most likely to occur in what position

Answer 25

flexion

Question 26

how should posterior knee retractors be aimed intraop

Answer 26

bias them medially - away from the popliteal artery which lies lateral in the knee (eg just medial to the lateral femoral condyle)

Question 27

peroneal nerve palsy highest in correction of what pre-op deformity?

Answer 27

valgus and flexion contracture

Question 28

how to manage acute peroneal n palsy post op

Answer 28

loosen dressings, flex the knee

Question 29

when should a MUA be performed in decreased ROM post op TKA

Answer 29

between 6-12 weeks

increased risk, diminished benefits if you do it after 3 months

Question 30

absolute contraindication for unicompartmental knee replacement?

Answer 30

inflammatory arthritis

Question 31

true/false: you need an intact ACL for uni?

Answer 31

true

Question 32

true/false: you can do a uni in concurrent severe patellofemoral arthritis as long as it is asymptomatic

Answer 32

true

Question 33

causes of late failure of unicompartmental knee arthroplasty

Answer 33

opposite compartment degeneration
component loosening
poly wear

Question 34

mobile bearing uni for medial compartment

Answer 34

improves survivorship

Question 35

mobile bearing uni for lateral compartment

Answer 35

terrible idea - increased poly dislocation