Chapter 49 - Primary Knee Arthroplasty Flashcards
What is a possible advantage of the midvastus or subvastus approach
possible more rapid restoration of extensor mechanism function (accelerated rehabilitation)
possible improvement in patellar tracking limiting need for lateral release
relative contraindications for mis vastus or subvastus approaches
- lack of pre-op flexion
- v large osteophytes
- obesity
- previous HTO
- revision
- extremely mm quads
indication for lateral parapatellar approach
fixed severe valgus deformity
standard coronal plane cuts
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
anatomic coronal plane cuts
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
what is the difference in sagittal cuts for cruciate sacrificing implants?
less posterior slope cut for the cruciate sacrificing, bc resecting the pcl tends to loosen the flexion space
what alignment correction places the peroneal nerve at highest risk of injury?
valgus with a flexion contracture
when to use a PCL substituting TKA
inflammatory arthritis
previous PCL injury
excessive pcl release intraop
pcl sparing knees have what kinematic disadvantage>
paradoxical motion - eg no roll back, and poor flexion
which knee design is associated with patellar clunk?
posterior stabilized
cross linked patellar buttons are associated with what?
increased risk of poly fracture compared to standard buttons
what is the only proven difference between commercially mixed antibiotic cement and non-antibniotic cement?
increased in cost in antibiotic cement
Most common late complication of non-cemented TKA
osteolysis
when is an absolute indication to use a resurfaced patella?
inflammatory arthritis
what percentage of extension power is lost after patellectomy
25-60%
- also causes substantial increase in tibiofemoral joint reactive forces
if a TKA is performed after patellectomy, what kind of implant design should be used?
posterior stabilized
most common technical complication following TKA?
patellar maltracking
how should you orient the femoral component relative to the transepicondylar axis?
slightly externally rotated (like 3-5 degrees)
how should the femoral component be oriented
externally rotated, slightly lateralized
internal rotation of the tibial component leads to what?
external rotation of the tibial tubercle, increased q angle
** DO NOT DO IT
how should the tibial component be oriented
slightly externally rotated
midpoint of the component should be in the middle 1/3 of the plateau
how should the patellar component be oriented
medial and slightly superior (remember when you have the patella everted, medializing the patella actually looks like you are placing it lateral)
instability accounts for what percentage of TKA revisions overall?
10-20%
how to address axial instability
if symmetric in both flexion and extension - insert bigger poly
if asymmetric, need to remove components and do full revision
