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Updated: Nov 15 2021

TKA Patellar Prosthesis Loosening

  • summary
    • TKA Patellar Prosthesis Loosening is a complication following TKA that is more common with metal-backed patellar components.
    • Diagnosis is made with plain radiographs of the knee.
    • Treatment is generally revision arthroplasty of the patellar component. 
  • Epidemiology
    • Incidence
      • 0.6-5% of cases
        • more common with metal-backed patellae
  • Etiology
    • Cause
      • subclinical infection
      • maltracking or overstuffing, leading to high shear
    • Risks
      • obesity
      • lateral release
      • joint-line elevation
      • postoperative flexion >100°
      • poor bone stock
      • asymmetric patellar resection
      • inadequate implant fixation (small pegs)
      • secondary osteonecrosis and osteolysis
  • Presentation
    • Symptoms
      • persistnent knee pain
  • Imaging
    • Radiographs
      • recommended views
        • lateral
        • tangential
      • findings
        • loss of radiolucent space in patellofemoral joint with contact between patella bone and femoral component
          • seen on lateral view
        • dissociated patellar component
          • patellar component adjacent/superficial to patella
          • seen on lateral and tangential views
      • thinning of polyethylene
        • seen on tangential view
  • Treatment
    • Operative
      • revision of patellar component
        • if revision fails, resection of patellar component
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