TKR revision

Question 1

What are the causes of failure in TKR?

Answer 1

• Aseptic failure
• septic failure- 1%

Question 2

What are the causes of aseptic failure in TKR?

Answer 2

• Patellofemoral mal tracking (8-35%)
  
  • most common cause of revision TKR
• Abnormal joint line
  
  • elevated
    
    • patella baja
    • PF tracking problems
    • low knee scores
  • lowered
    
    • flexion instability
• Component loosening
  
  • tibial loosening more common cf femoral
  • femoral loosening more difficult to detect due to obscured view of posterior femoral condyles where lesions typically occur- oblique xray may help
• Osteolytic wear
  
  • ​uncemented
  • tibial insert and metal tray ( backside wear)
• ​Ligament instability (6%)
• periprosthetic fx
• catastrophic wear
• patella clunk
• arthrofibrosis

Question 3

What are the goals of revision surgery?

Answer 3

• Extraction of components with minimal bone loss and destruction
• restoration of bone deficiencies
• restoration of joint line
• balance knee ligaments
• stable revision implants

Question 4

How is the metaphyseal bone loss in revision TKR addressed?

Answer 4

• Local sharing to diaphysis
  
  • usually done with a long intramedullary stem
• Cavity defect filling
  
  • cement for cavity <1cm
    
    • almost all TKR are cemented at the metaphyseal surface
  • Structural bone allografts, cones and wedges
    
    • include metal augments, modular endoprosthetic devices
    • indicated for segemental defect >1cm

Question 5

Describe the general technique for revision TKR?

Answer 5

• Surgical exposure
  
  • extensile
  • tibial tubercle ostoetomy- esp patella baja
• Remove implants
  
  • tibial side first
  • tibial joint line should be 1.5-2cm above head of fibula ( use xay contral knee to determine exactly
• Balance flexion-extension gap
• balance medial - lateral gap
• address patellofemoral tracking
  
  • keep patella thickness >12mm to avoid fx

Question 6

What are the complications of revision TKR?

Answer 6

• Pain
  
  • pain scores less favourable than primary TKR
  • activity related pain expected for 6 months
• Stiffness
• Neurovascular problems
  
  • peroneal nerve subject to injury with correction of valgus and flexion deformity
• Infection
• Skin necrosis
  
  • prior scars should be incoporated into skin incision whenever possible
  • blood supply to skin is medially based so lateral skin edge is more hypoxic- if multiple scars use most lateral skin incision
  • skin grafts, gastronemius muscle coverage
• Extensor mechansim disruption
  
  • ​can use allograft- achilles tendon