Overview Osteolysis represents a histiocytic response to wear debris. Steps in the process include (see below) particulate debris formation macrophage activated osteolysis prosthesis micromotion 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 is < 1 micron 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