title: Can wear explain the histological variation around metal-on-metal total hips?
abstract: BACKGROUND
  There is a general perception that adverse local tissue reactions in metal-on-metal hip arthroplasties are caused by wear, but the degree to which this is the case remains controversial.
  
  
  OBJECTIVE
  To what extent is the magnitude of wear associated with (1) the histological changes; (2) presence of metallosis; and (3) likelihood of pseudotumor formation in the periprosthetic tissues?
  
  
  METHODS
  One hundred nineteen metal-on-metal total hip arthroplasties and hip resurfacings were selected from a retrieval collection of over 500 implants (collected between 2004 and 2012) based on the availability of periprosthetic tissues collected during revision, clinical data including presence or absence of pseudotumor or metallosis observed intraoperatively, and wear depth measured using a coordinate measurement machine. Histological features of tissues were scored for aseptic lymphocytic vasculitis-associated lesions (ALVAL). Correlation analysis was performed on the three endpoints of interest.
  
  
  RESULTS
  With the sample size available, no association was found between wear magnitude and ALVAL score (ρ=-0.092, p=0.423). Median wear depth (ball and cup) was greater in hips with metallosis (137 μm; range, 8-873 μm) than in those without (18 μm; range, 8-174 μm; p<0.0001). With the numbers available, no statistically significant association between wear depth and pseudotumor formation could be identified; median wear depth was 74 μm in hips with pseudotumors and 26 μm in those without (p=0.741).
  
  
  CONCLUSIONS
  Wear alone did not explain the histopathological changes in the periprosthetic tissues. A larger sample size and more sensitive outcome variable assessments may have revealed a correlation. However, wear depth has been inconsistently associated with pseudotumor formation, perhaps because some patients with hypersensitivity may develop pseudotumors despite low wear.
  
  
  CONCLUSIONS
  Metal wear alone may not explain the histological reactions and pseudotumors around metal-on-metal hip implants.
authors.affiliation: The J. Vernon Luck, Sr, MD Orthopaedic Research Center, UCLA, Los Angeles, CA, USA, edward.ebramzadeh@ucla.edu.
authors.forename: Edward
authors.initials: E
authors.lastname: Ebramzadeh
authors.forename: Patricia
authors.initials: P
authors.lastname: Campbell
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Tan
authors.forename: Scott D
authors.initials: SD
authors.lastname: Nelson
authors.forename: Sophia N
authors.initials: SN
authors.lastname: Sangiorgio
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D005549:Foreign-Body Reaction / Q000473:pathology*; D006622:Hip Prosthesis; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D011475:Prosthesis Failure; D012189:Retrospective Studies; D013583:Synovial Membrane / Q000473:pathology; D055815:Young Adult