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Updated: Oct 19 2023

Wear & Osteolysis Basic Science

Images
https://upload.orthobullets.com/topic/5001/images/xray.knee.ap.shows osteolysis.jpg
  • Overview
    • Osteolysis represents a histiocytic response to wear debris
    • Steps in the process include (see below)
      • particulate debris formation
      • macrophage activated osteoclastogenesis and osteolysis
      • prosthesis micromotion
      • particulate debris dissemination
    • Evaluation
      • radiostereometric analysis
        • 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 the radius² of the femoral head
        • volumetric wear more or less creates a cylinder
          • V = 3.14r² x w
            • 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
        • 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/year
            • linear wear rates >0.1 mm/year have 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 UHMWPE)
            • factors increasing wear in THA
              • thickness <6 mm
              • malalignment of components
              • patients <50 y/o
              • men
              • higher activity level
          • femoral head size between 22-46 mm 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.
          • unique complication of stripe wear occurring from lift-off separation of the head gait
          • recurrent dislocations or incidental contact of femoral head with a 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 and lower wear rates compared to 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 poor resistance to wear and notch sensitivity
          • metal-on-metal wear stimulates lymphocytes
          • metal-on-metal serum ion levels are greater with cup abduction angle >55° and smaller component size
    • Particulate type
      • UHMWPE most common
      • PMMA
      • Co-Cr
      • Ti
      • third-body
  • 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 enhances 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 an increase in particle wear and further prosthesis loosening
      • N-telopeptide urine level is a marker for bone turnover and is elevated in osteolysis
  • Step 4: Debris Dissemination
    • Increase in hydrostatic pressure leads to dissemination of debris into effective joint space
      • increased hydrostatic pressure is the result of inflammatory response
      • dissemination of debris into effective joint space further propagates osteolysis
      • a circumferentially coated prosthesis limits osteolysis in the distal femur
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