title: Femoral component loosening after hip resurfacing arthroplasty.
abstract: OBJECTIVE
  Before the re-introduction of the current generation of total hip resurfacing arthroplasty, component loosening and osteolysis were of great concern to the orthopaedic community. Early, mid- and long-term clinical results are encouraging, but component loosening still exists.
  
  
  METHODS
  Macroscopic, contact radiographic and histopathological analyses after undecalcified preparation of bone tissue specimens were performed. To investigate the frequency and morphological patterns of the loosening of the femoral component, we analysed a series of 190 retrieved femoral remnants that were revised for aseptic failures.
  
  
  RESULTS
  Thirty-five (18.4%) hips were revised for clinical and/or radiographic loosening of the femoral component. Pseudoarthrosis (n = 17; median in situ time: 16 weeks, interquartile range [IQR]: 9 to 34), collapsed osteonecrosis (n = 5; median in situ time: 79 weeks, IQR: 63 to 97), cement-socket debonding (n = 3; median in situ time: 89 weeks, IQR: 54 to 97) and at later follow-up bone-cement loosening (n = 10; median in situ time: 175 weeks; IQR 112 to 198; p =0.005) were distinct patterns of the femoral remnant-implant loosening. Fibrocartilaginous metaplasia of interface bone trabeculae (n = 38; median in situ time: 61 weeks, IQR: 32 to 138) was strongly associated with femoral component loosening (p = 0.009). Both the trabecular hyperosteoidosis (n = 32; median in situ time: 71 weeks, IQR 50 to 129) and excessive intraosseous lymphocyte infiltration (n = 12; median in situ time: 75 weeks, IQR 51 to 98) at the bone-cement interface correlated strongly with fibrocartilaginous metaplasia (p = 0.001 and p = 0.016 respectively) and all three lesions were associated with the female gender (p = 0.021, p = 0.009, and p = 0.051).
  
  
  CONCLUSIONS
  Femoral component loosening at early follow-up was mostly caused by pathological changes of the femoral remnant bone tissue: pseudoarthrosis and collapsed osteonecrosis. Fibrocartilaginous metaplasia was frequently observed in hips with femoral component loosening. The potential role of interface hyperosteoidosis as a precursor lesion of bone-cement loosening and its possible association with delayed type hypersensitivity reaction are discussed.
authors.affiliation: Institute of Pathology, University Medical Centre Hamburg-Eppendorf, Martinistrasse 52, 20246, Hamburg, Germany. j.zustin@uke.uni-hamburg.de
authors.forename: Jozef
authors.initials: J
authors.lastname: Zustin
authors.forename: Michael
authors.initials: M
authors.lastname: Hahn
authors.forename: Michael M
authors.initials: MM
authors.lastname: Morlock
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Rüther
authors.forename: Michael
authors.initials: M
authors.lastname: Amling
authors.forename: Guido
authors.initials: G
authors.lastname: Sauter
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000145:classification; D005260:Female; D005269:Femur / Q000473:pathology* / Q000601:surgery; D006801:Humans; D008297:Male; D015207:Osteoarthritis, Hip / Q000601:surgery* / Q000628:therapy; D011475:Prosthesis Failure