Updated: 9/6/2018

TKA Aseptic Loosening

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Introduction
  • Macrophage-induced inflammatory response resulting in bone loss
    • steps in the process include    
      • particulate debris formation
      • macrophage activated osteolysis 
      • prosthesis micromotion
      • particulate debris dissemination
    • see wear and osteolysis basic science for full description 
  • Pathophysiology
    • factors affecting wear rate of polyethylene in TKA
      • sterilization method
      • manufacturing method (conventional vs. crosslinked)
      • presence of third-body debris
      • motion between modular tibial insert and metal tray (i.e., backside wear)
      • roughness of femoral component counterface
      • alignment and stability of the TKA
        • malalignment causes asymmetric loading causes early loosening
        • more frequent with varus rather than valgus malalignment
      • demand or activity level of patient
Presentation
  • Symptoms
    • painless
      • early disease
    • pain
      • location
        • localized to the tissues around the loose components
      • aggrevating factors
        • weightbearing
        • often activity related
  • Physical exam
    • may have minimal pain with ROM
    • increased pain with weight bearing
Imaging
  • Radiographs 
    • recommended views
      • AP
        • tibial osteolysis readily visible on AP
        • femoral osteolysis may be difficult to detect on AP as lesions are typically located in posterior condyles and are obscured by the femoral component
      • lateral
      • oblique
        • often more helpful for identifying femoral osteolysis 
    • findings  
      • radiolucent area around implant or cement with sclerotic border
        • especially radiolucencies > 2 mm
      • change in position of the implant
        • varus or valgus subsidence of tibial component
      • progressive widening of cement-bone or bone-prosthesis interface
      • cement cracking or fragmentation
  • CT Scan & MRI 
    • viable options for assessing larger osteolytic lesions to aid in preoperative planning 
Studies
  • Serum labs
    • ESR normal
    • CRP normal
Differential
  • Critical to rule out periprosthetic joint infection
Treatment
  • Nonoperative
    • observation
      • indications
        • stable implant with minimal symptoms
  • Operative
    • revision TKA 
      • indications  
        • pain due to aseptic loosening
        • pain with evidence of osteolysis  
        • extensive osteolysis that would compromise revision surgery in the future
      • technique
        • bone graft
          • indicated for defects > 10 mm
          • often used in younger patients to preserve bone stock
        • prosthetic metal wedges/augments
          • indicated for defects > 10 mm
          • often used in elderly, low activity patients 
        • bone cement
          • indicated for smaller defects
          • heat released can cause thermal necrosis of surrounding bone and vascular tissue which can potential lead to aseptic loosening
Techniques
  • Revision TKA  
 

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