UKA (Complete)

Question 1

What are the advantages of a UKA vs. TKA?

[JAAOS 2007;15:9-18]

Answer 1

1. Preservation of normal knee kinematics
2. Lower perioperative morbidity
3. Less blood loss
4. Accelerated patient rehabilitation and recovery

Question 2

What are the indications for UKA?

[JAAOS 2007;15:9-18]

Answer 2

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***No longer valid

Question 3

What are the indications for the Oxford UKA?

[Orthop Clin N Am 46 (2015) 113–124]

Answer 3

• Bone-on-bone anteromedial OA
• Ligamentously normal knee with intact ACL
• Correctable varus deformity
• Normal lateral joint space on valgus stress view

Question 4

What are the contraindications for UKA?

[JAAOS 2007;15:9-18]

Answer 4

1. 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

2. Other contraindications
   * Osteonecrosis due to corticosteroid use (risk of osteonecrosis of adjacent compartments)

Question 5

What are the contraindications for the Oxford UKA?

[Orthop Clin N Am 46 (2015) 113–124]

Answer 5

• 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

Question 6

What pattern of osteoarthritis is the primary indication for medial Oxford UKA?

[Orthop Clin N Am 46 (2015) 113–124]

Answer 6

Medial compartment OA with an anteromedial pattern

• Anteromedial OA is associated with an intact ACL where as posteromedial OA is associated with ACL deficiency

Question 7

What are the main causes of mobile-bearing failure vs. fixed-bearing failure?

[Joints 5(1) 2017: 44-50]

Answer 7

1. Mobile-bearing = bearing dislocation
2. Fixed-bearing = polyethylene wear and aseptic loosening

Question 8

What are the main causes of failure of UKA?

[Joints 5(1) 2017: 44-50]

Answer 8

1. 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
    
    2. 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

3. 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

4. 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

5. Infection

• Incidence lower than TKA (~0.2-1%)
• Treatment options:
  
  • Acute – I&D and liner exchange
  • Chronic – one or two stage revision to TKA

6. Impingement
7. 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

8. Retaining of cement debris
9. Arthrofibrosis

• Incidence lower than TKA
• Treatment options:
  
  • MUA +/- arthroscopic debridement

10. Unexplained pain

Question 9

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]

Answer 9

1. Directly visualize the ACL and contralateral compartment for disease – convert to TKA if affected
2. Tibial component should be perpendicular to the long axis of the tibia in the coronal plane
3. Tibial slope should match the native tibial slope (some recommend slope <7° to protect the ACL from degeneration/rupture)
4. Femoral component should be perpendicular to the tibial component in the coronal plane
5. Soft tissue releases should never be performed
6. Restore ligament tension and balance by positioning the components accurately and inserting the appropriate thickness poly
7. Avoid overcorrection/undercorrection of the deformity

• Goal in medial UKA = 1-4° varus
• Goal in lateral UKA = 3-7° valgus

Question 10

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]

Answer 10

1. Valgus stress – demonstrates if the deformity is correctable and if the lateral compartment cartilage is maintained
2. Varus stress – demonstrates if the medial compartment is bone-on-bone OA