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  • Summary
    • A metal-on-metal (MoM) THA pseudotumor, also known as aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL), is a mass-forming tissue reaction caused by metal-on-metal wear
    • Diagnosis involves obtain meta-subtraction MRI studies in the setting of elevated serum metal ion levels (cobalt, chromium)
    • Treatment is typically revision arthroplasty for symptomatic pseudotumor with elevated metal ions
  • Epidemiology
    • Incidence
      • 10-15% of patients with MoM THA have a pseudotumor
      • 45-50% of revisions in patients with MoM THA are due to pseudotumor or adverse local tissue reaction
    • Risk factors
      • elevated cobalt and chromium levels
      • female gender
      • high acetabulum inclination angle > 55°
  • Etiology
    • Pathophysiology
      • mechanism
        • two different mechanisms have been proposed for formation of pseudotumors:
          • hypersensitivity to metal ions
          • local high wear debris
      • variability in distribution of metal debris, degree of necrosis, and number, type, and arrangement of inflammatory cells
        • macrophages and lymphocytes are present in all cases with lymphocytes being predominant
          • patient's with high wear have more macrophages than those with primarily hypersensitivity to metal ions
          • patients with extensive infiltrates of macrophages tend to have smaller lymphocytic aggregates.
  • Presentation
    • History
      • patient may complain of gradual onset of symptoms or a sudden inciting pain in the groin
    • Symptoms
      • common symptoms
        • may be asymptomatic
        • groin pain
        • trendelenburg gait
    • Physical Exam
      • inspection
        • soft tissue masses around the hip may be present
      • neurovascular
        • usually normal
      • provocative tests
        • groin pain with flexion, IR and adduction
        • groin pain with rising from a chair
  • Imaging
    • Radiographs
      • recommended views
        • AP pelvis, AP and lateral of affected hip
      • findings
        • will show metal-on-metal THA
        • necessary to rule out peri-prosthetic fractures as source of pain
        • may show peri-prosthetic bony erosion, commonly seen in calcar region
    • MRI with Metal Artifact Reduction Sequence (MARS)
      • indications
        • normal radiographs in the setting of elevated metal ion levels (cobalt, chromium)
      • findings
        • a pseudotumor will appear like a fluid collection or solid mass in periprosthetic soft tissues
        • T1 weighted images will show signal similar to bladder contents (transudate)
        • T2 weighted images will generally show hyperintensity as compared to muscle and may be heterogenous or homogenous
          • the hypointense content observed in T2 sequences may be related to the presence of necrosis or metal deposition
  • Studies
    • Serum labs
      • WBC, ESR and CRP
      • metal ion levels (cobalt, chromium)
        • serum metal ion concentration highest at 12-24 months following index surgery
          • correlates with the initial "wear in" or "run-in" phase of increased particle generation, but then followed by a "steady state" phase of decreased particle generation
        • values > 7 parts per billion (ppb, or ug/L) generally an indication for advanced imaging with MRI
    • Invasive studies
      • Hip aspiration
        • synovial fluid analysis will allow for differentiation of a metallosis from periprosthetic infection
        • gross appearance of metallosis generally described as "dishwater fluid" with watery, grayish and hazy appearance
        • manual cell count necessary
          • fibrinous debris from metal-on-metal reactions will falsely elevate automated cell counts
  • Treatment
    • Nonoperative
      • observation
        • indications
          • well functioning THA with low metal ions and no pseudotumor on MRI
        • outcomes
          • studies show that around 40% of patients with a pseudotumor are asymptomatic
    • Operative
      • revision THA to ceramic-on-polyethelyne components
        • indications
          • painful metal on metal THA, elevated metal ions, pseudotumor on MRI
            • rate of revision THA due to symptomatic pseudotumor is only 1.7–5.6%
          • most patients with pain, elevated ions or a psudotumor on MRI require operative intervention
        • outcomes
          • significant bone loss, soft tissue destruction, degree of abductor muscle deficiency and poorlocal environment for healing corresponds to difficulty of revision and functional outcomes
            • if severely compromised abductor function or damaged soft-tissue affects implant stability, may require the use of a contrained liner
              • gluteus maximus transfer can be used to reconstruct deficient abductor mechanism 
            • higher rates of dislocation and infection
  • Techniques
    • Observation
      • technique
        • in the asymptomatic patient, serial hip radiographs to assess for wear, or component loosening can be performed
    • Revision THA to ceramic-on-polyethelyne components
      • approach
        • depends on location of tumor and surgeon preferene
          • direct lateral and direct anterior commonly cited
      • technique
        • can be single stage or 2 stages depending on surgeon preference or presence/concern of infection
        • depend on bone loss, abductor defiency and soft tissue damage
        • constraint liners may be required if severe abductor deficiency is present
      • complications
        • instability
        • deep infection
        • aseptic loosening
        • persistent iliopsoas tendonitis
        • persistent metal related reaction
  • Complications
    • Repeat revision THA
      • incidence
        • 14-20% of revision THAs performed due to a MoM pseudotumor require a 2nd operation within 5 years
      • treatment
        • revision THA to address reason for repeat failure
    • Pseudotumor induced femoral nerve palsy
      • incidence
        • rare, only case reports noted
      • treatment
        • decompression and revision THA to ceramic-on polyethelyne components
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