Updated: 1/29/2020

THA Trunnionosis

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https://upload.orthobullets.com/topic/422821/images/trunnionosis_example_2.jpg
https://upload.orthobullets.com/topic/422821/images/pseudotumor.jpg
https://upload.orthobullets.com/topic/422821/images/trunnion_wear.jpg
Introduction
  • Overview 
    • metal ion released from tribocorrosion at the femoral head-neck interface morse taper leading to adverse local tissue reactions (ALTRs)
  • Risk factors
    • Modular designs
    • Large cobalt chrome femoral heads
      • larger heads may put more torsional forces on the trunnion.
    • Taper design
      • shorter taper length may afford less interference fit and more micromotion
      • greater rigidity of the taper may lead to less wear
    • Metal on metal 
      • serum metal ions may contribute to taper wear
      • no pathognomonic serum metal ion level for trunnionosis
      • serum cobalt >1 ng/ml (ppm) should lead to consideration for mechanically assisted crevice corrosion (MACC)
  • Pathophysiology 
    • Galvanic corrosion
      • corrosion caused by an electrochemical transfer of electrons between dissimilar metals
        •  i.e. cobalt-chromium (CoCr) alloy femoral head on a titanium alloy stem
    • Fretting corrosion
      • corrosion from relative micromotion between two materials causing wear
        • i.e. tolerance between male and female morse taper allows for micromotion and wear
    • Crevice corrosion
      • physicochemical interaction between a metal and environment leading to altered mehcanical properties
Presentation
  • History
    • pain and limp are the most common complaints
  • Physical exam
    • occasionally if ALTR is large enough a palpable pseudocyst can be felt
    • abduction weakness if ALTR has caused soft tissue destruction of abductors
 Imaging
  • AP and lateral hip views should be obtained
    • imaging studies may be normal in the setting of trunnnionosis
  • Judet views and/or CT scan may be obtained if advanced osteolysis is present
  • MARS MRI 
    • findings may include periarticular pseudotumors and/or soft tissue destruction
Studies
  • Infection should be ruled out
    • ESR, CRP, WBC
    • Aspiration
      • consider manual cell count as metal debris can cause a false elevation of automated cell count
  • Metal ion levels
    • cobalt and chromium ion levels
    • cobalt levels may be elevated more substantially (4-5x) than chromium levels
Treatment
  • Operative
    • revision total hip
      • indications
        • painful THA with the above risk factors and elevated serum cobalt level compared to serum chromium level elevation
      • technique
        • frozen-sections and intraoperative cultures
        • extensive synovectomy
        • inspection of the taper and decision for retention of stem versus revision stem  
        • to ceramic head with titanium sleeve and new polyethylene liner  
 

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