Updated: 9/6/2018

TKA Patellar Prosthesis Loosening

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Introduction
  • Epidemiology
    • 0.6-5% of cases
      • more common with metal-backed patellae 
  • Etiology
    • 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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