Updated: 2/23/2020

THA Pseudotumor (Metal Reactions)

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Questions
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Introduction
  • Overview
    • a metal-on-metal pseudotumor, also known as aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL), is a mass-forming tissue reaction caused by metal-on-metal wear   
    • the lesion is neither infective or neoplastic, and develops in the vicinity of a total hip replacement (THA)
  • Epidemiology
    • incidence
      • 10-15% of patients with metal-on-metal THA
    • risk factors
      • elevated cobalt and chromium levels
      • female gender
      • high acetabulum inclination angle > 55°
    • pathophysiology
      • two different mechanisms have been proposed for formation of pseudotumors:
        • hypersensitivity to metal ions and high wear debris 
      • there is variability in the distribution of metal debris, degree of necrosis, and the 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
  • Symptoms
    •  common symptoms
      • may be asymptomatic
      •  groin pain with ambulation
      •  trendelenburg gait due to abductor weakness
  • Physical Exam
    • inspection
      • soft tissue masses around the hip
    • palpation
      • areas of tenderness around hip
Imaging
  • Radiographs
    • 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) 
    • 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
  • Labs
    • WBC, ESR and CRP as initial diagnostic workup to evaluate for peri-prosthetic infection
    • with metal-on-metal THA, current recommendations are to obtain serum metal ion levels (cobalt, chromium) and follow them over time
      • 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 mg/L) generally an indication for advanced imaging with MRI
  • 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 painless THA with low metal ions and no pseudotumor on MRI
  • 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 
      • degree of abductor muscle involvement associated with pseudotumor 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 
        • higher rates of dislocation and infection
Techniques
  • Revision THA to ceramic-on-polyethelyne components
    • approach
      • tested concepts only (techniques steps go in outline)
    • technique
    • complications (ONLY if specific to this treatment)
Complications
  • Compliation A
    • incidence (only if pertinent)
    • risk factors
    • treatment
      • tested treatment in bold blue
        • indications
          • indication A
  • Compliation B
    • incidence
    • risk factors
    • treatment
      • tested treatment in bold blue
        • indications
          • indication A

 

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(OBQ13.270) Figure A shows a radiograph of a 62-year-old female that underwent a left total hip arthroplasty 5 years ago. She presents to your office with insidious onset of left groin and buttock pain. She denies trauma, fever or chills. On physical examination, her left hip has mild pain with range of motion. She has a normal gait cycle, normal power across the hip and her vitals signs are stable. A left hip aspirate was performed and results are shown in Figure B. What is the most likely cause of her hip pain? Review Topic | Tested Concept

QID: 4905
FIGURES:
1

Periprosthetic bacterial hip infection

9%

(291/3377)

2

Periprosthetic hip fracture

0%

(11/3377)

3

Large-particle wear debris disease

15%

(497/3377)

4

Pseudotumor hypersensitivity response

75%

(2523/3377)

5

Abductor tendon tear

1%

(33/3377)

L 3 B

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