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Updated: Oct 19 2023

Wear & Osteolysis Basic Science

Images osteolysis.jpg
  • Overview
    • Osteolysis represents a histiocytic response to wear debris.
    • Steps in the process include (see below)
      1. particulate debris formation
      2. macrophage activated osteolysis
      3. prosthesis micromotion
      4. particulate debris dissemination
    • Evaluation
      • radiostereometric analysis
        • is the most accurate and precise technique to evaluate polyethylene wear
        • uses radiopaque tantalum beads planted in the bone to follow the position of the components relative to the beads on radiographs.
  • Step 1: Particulate Debris Formation
    • Types of wear
      • adhesive wear
        • most important in osteolytic process
        • microscopically PE sticks to prosthesis and debris gets pulled off
      • abrasive wear
        • cheese grater effect of prosthesis scraping off particles
      • third body wear
        • particles in joint space cause abrasion and wear
      • volumetric wear
        • main determinant of number of particles created
        • directly related to square of the radius of the head
        • volumetric wear more or less creates a cylinder
          • V=3.14rsquaredw
          • V is volumetric wear, r is the radius of head, w is linear head wear
          • head size is most important factor in predicting particles generated
      • linear wear
        • is measured by the distance the prosthesis has penetrated into the liner
    • Wear leads to particulate debris formation
      • wear rates by material
        • polyethylene
          • non-cross linked UHMWPE wear rate is 0.1-0.2 mm/yr
            • linear wear rates greater than 0.1 mm/yr has been associated with osteolysis and subsequent component loosening
          • highly-cross linked UHMWPE generates smaller wear particles and is more resistant to wear (but has reduced mechanical properties compared to conventional non-highly cross-linked)
            • factors increasing wear in THA
              • thickness < 6mm
              • malalignment of components
              • patients < 50 yo
              • men
              • higher activity level
          • femoral head size between 22 and 46mm in diameter does not influence wear rates of UHMWPE
        • ceramics
          • ceramic bearings have the lowest wear rates of any bearing combination (0.5 to 2.5 µ per component per year)
          • ceramic-on-polyethylene bearings have varied, ranging from 0 to 150 µ.
          • has a unique complication of stripe wear occurring from lift-off separation of the head gait
          • recurrent dislocations or incidental contact of femoral head with metallic shell can cause "lead pencil-like" markings that lead to increased femoral head roughness and polyethylene wear rates.
        • metals
          • metal-on-metal produces smaller wear particles as well as lower wear rates than those for metal-on-polyethylene bearings (ranging from 2.5 to 5.0 µ per year)
          • titanium used for bearing surfaces has a high failure rate because of a poor resistance to wear and notch sensitivity.
          • metal-on-metal wear stimulates lymphocytes
          • metal-on-metal serum ion levels greater with cup abduction angle >55 degrees and smaller component size
    • Particulate Type
      • UHMWPE
        • most common
      • PMMA
      • Co-Cr
      • Ti
      • third-body
    • Particulate size
  • Step 2: Macrophage Activated Osteoclastogenesis and Osteolysis
    • Macrophage activation
      • results in macrophage activation and further macrophage recruitment
      • macrophage releases osteolytic factors (cytokines) including
        • TNF- alpha
        • osteoclast activating factor
        • oxide radicals
        • hydrogen peroxide
        • acid phosphatase
        • interleukins (Il-1, IL-6)
        • prostaglandins
    • Osteoclast activation and osteolysis
      • increase of TNF- alpha increases RANK
      • increase of VEGF with UHMWPE inhances RANK and RANKL activation
        • RANKL mediated bone resorption
          • an increase in production of RANK and RANKL gene transcripts leads to osteolysis
  • Step 3: Prosthesis Micromotion
    • Osteolysis surrounding the prosthesis leads to micromotion
      • micromotion leads to increase particle wear and further prosthesis loosening
      • N-telopeptide urine level is a marker for bone turnover and are elevated in osteolysis
  • Step 4: Debris Dissemination
    • Increase in hydrostatic pressure leads to dissemination of debris into effective joint space
      • increased hydrostatic pressure is result of inflammatory response
      • dissemination of debris into effective joint space further propagates osteolysis
      • circumferentially coated prosthesis limits osteolysis in the distal femur
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