UKA updated Flashcards
What are the advantages of a UKA vs. TKA?
[JAAOS 2007;15:9-18]
- less invasive surgical expsoure
- bone conserving
- retains cruciate ligaments
- lower periop morbidity and mortality
- enhanced postop recovery
- improved patient satisfaction
- cost effective
- preservation of normal knee kinematics
- less blood loss
What are the traditional indications for UKA?
[JAAOS 2007;15:9-18]
Classic indications (proposed by Kozinn and Scott):
- Unicompartmental OA or osteonecrosis of the medial or lateral compartments
- Age >60
- Low activity demand
- Minimal pain at rest
- ROM arc >90°
- <5° flexion contracture
- Angular deformity <15° that is passively correctable to neutral
***No longer valid
What are the indications for the Oxford UKA?
[Orthop Clin N Am 46 (2015) 113–124]
- Bone-on-bone anteromedial OA
- Ligamentously normal knee with intact ACL
- Correctable varus deformity
- Normal lateral joint space on valgus stress view
What are the contraindications for UKA?
[JAAOS 2007;15:9-18]
- Classic contraindications:
- Inflammatory arthritis
- Age <60
- Weight >81kg (181 lbs)
- High activity level
- Pain at rest (suggesting inflammatory arthritis)
- Patellofemoral pain
- Exposed bone in the patellofemoral or opposite compartment
- Other contraindications
* Osteonecrosis due to corticosteroid use (risk of osteonecrosis of adjacent compartments)
What are the contraindications for the Oxford UKA?
[Orthop Clin N Am 46 (2015) 113–124]
- Inflammatory arthritis
- Previous HTO
- ACL deficiency
- MCL contracture with inability to correct varus deformity
- Weightbearing cartilage wear of the lateral compartment
- Severe patellofemoral arthrosis with lateral facet disease, lateral subluxation, and trochlear grooving
***NOTE – mild to moderate PF disease is not considered a contraindication
***NOTE – obesity is not considered a contraindication
What pattern of osteoarthritis is the primary indication for medial Oxford UKA?
[Orthop Clin N Am 46 (2015) 113–124]
Medial compartment OA with an anteromedial pattern
- Anteromedial OA is associated with an intact ACL where as posteromedial OA is associated with ACL deficiency
What are the main causes of mobile-bearing failure vs. fixed-bearing failure?
[Joints 5(1) 2017: 44-50]
- Mobile-bearing = bearing dislocation
- Fixed-bearing = polyethylene wear and aseptic loosening
What are the main causes of failure of UKA?
[Joints 5(1) 2017: 44-50]
- Bearing dislocation
- Major complication of mobile bearing
- Causes:
- Malposition of components
- Unbalanced flexion-extension gaps
- Impingement of the insert on adjacent bone or tibial/femoral component
- Instability due to MCL injury
- Secondary to femoral or tibial component loosening
- Treatment options for bearing dislocation
- Bearing exchange
- Revision UKA or conversion to TKA
- Aseptic mechanical loosening
- Causes:
- Undercorrection of the deformity
- Component malalignment
- ACL deficiency
- Excessive tibial slope
- Bearing dislocation
- Treatment options
- Revision UKA or conversion to TKA
- Polyethylene wear
- More common in fixed-bearing designs
- Causes:
- Component malposition
- Undercorrection of deformity
- Poly thickness <6mm
- Reduced conformity in the design
- Manufacturing process and sterilization method
- Treatment options?
- Insert exchange or conversion to TKA
- Progression of OA in unreplaced compartments
- Causes:
- Overcorrection of deformity, inflammatory arthritis
- PF degeneration can occur with impingement of the patellar cartilage on the femoral component
- Avoid by sizing appropriately and avoid placing femoral component beyond the sulcus terminalis [JAAOS 2007;15:9-18]
- Treatment options for progression of OA?
- Conversion to TKA or replacement of affected compartment
- Infection
- Incidence lower than TKA (~0.2-1%)
- Treatment options:
- Acute – I&D and liner exchange
- Chronic – one or two stage revision to TKA
- Impingement
- Periprosthetic fracture
- More commonly involve the tibial condyles
- Treatment options for tibial periprosthetic fracture:
- Nonop – minimal translation or varus deformity
- ORIF – unacceptable translation or deformity
- Conversion to TKA – tibial component loosening, severe displacement or nonunion
- Retaining of cement debris
- Arthrofibrosis
- Incidence lower than TKA
- Treatment options:
- MUA +/- arthroscopic debridement
- Unexplained pain
What are the surgical principles of performing a UKA?
[JAAOS 2007;15:9-18] [Orthop Clin N Am 46 (2015) 113–124][JISAKOS 2017;0:1–11]
- Directly visualize the ACL and contralateral compartment for disease – convert to TKA if affected
- Tibial component
- horizontal tibial cut should be minimal and match native tibial slope (some recommend slope <7° to protect the aCL from degeneration/rupture)
- saggital cut should be as close to the tibial spine to maximize tibial surface area
- tibial component should be perpendicular to the long axis of the tibia in the coronal plane
- avoid under sizing the tibial component (risk of tibial fractur or implant subsidence)
- avoid posterior cortex penetration
- avoid excessive tibial implant impactoin (risk of fracture)
- Femoral component
- should be perpendicular to the tibial component in the coronal plane
- in the center or slightly lateral on the medial femoral condyle
- Soft tissue releases should never be performed
- Restore ligament tension and balance by positioning the components accurately and inserting the appropriate thickness poly
- Avoid overcorrection/undercorrection of the deformity
* Goal in medial UKA = 1-4° varus
* Goal in lateral UKA = 3-7° valgus
What is the role for valgus and varus stress radiographs in planning UKA in a varus knee with medial compartment OA?
[Orthop Clin N Am 46 (2015) 113–124]
- Valgus stress – demonstrates if the deformity is correctable and if the lateral compartment cartilage is maintained
- Varus stress – demonstrates if the medial compartment is bone-on-bone OA
what are the outcomes of conversion of failed medial UKA to TKA
- outcomes are worse than primary TKa but comparable or better than revision TKA
- complications are smimily to primary TKA and bettern than revision TKA
