title: Do obesity and/or stripe wear increase ceramic liner fracture risk? An XFEM analysis.
abstract: BACKGROUND
  Hypothesized risk factors for fracture of ceramic liners include impingement, edge-loading, and cup malpositioning. These risk factors are similar to those for generation of stripe wear. However, it is unclear whether the biomechanical conditions contributing to stripe wear generation also increase the risk for ceramic liner fracture
  
  
  OBJECTIVE
  We asked whether (1) head stripe wear propensity; and (2) cup orientation would correlate with alumina liner fracture risk for instances of normal and elevated body weight.
  
  
  METHODS
  An eXtended Finite Element Method (XFEM) model was developed to investigate these mechanisms. Liner fracture risk for 36-mm alumina bearings was studied by simulating two fracture-prone motions: stooping and squatting. Twenty-five distinct cup orientations were considered with variants of both acetabular inclination and anteversion. Four separate body mass indices were considered: normal (25 kg/m(2)) and three levels of obesity (33, 42, and 50 kg/m(2)). Material properties were modified to simulate alumina with and without the presence of dispersed microflaws. The model was validated by corroboration with two previously published ceramic liner fracture studies.
  
  
  RESULTS
  Of 200 XFEM simulations with flaw-free alumina, fracture occurred in eight instances, all of them involving obesity. Each of these occurred with cups in ≤ 37° inclination and in 0° anteversion. For 200 corresponding simulations with microflawed alumina, fracture propensity was greatest for cups with higher (edge loading-associated) scraping wear. Fracture risk was greatest for cups with lower inclination (average 42° for fractured cases versus 48° for nonfractured cases) and lower anteversion (9° versus 20°).
  
  
  CONCLUSIONS
  Fracture propensity for 36-mm liners was elevated for cups with decreased anteversion and/or inclination and under conditions of patient obesity.
  
  
  CONCLUSIONS
  Factors causing stripe wear, including obesity and cup malpositioning, also involve increased risk of ceramic liner fracture and merit heightened concern.
authors.affiliation: Department of Orthopaedics and Rehabilitation, Orthopaedic Biomechanics Laboratory, University of Iowa, 2181 Westlawn, Iowa City, IA 52242, USA.
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Elkins
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Pedersen
authors.forename: John J
authors.initials: JJ
authors.lastname: Callaghan
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Brown
mesh_terms: D000077:Acetabulum / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip; D002516:Ceramics; D003198:Computer Simulation; D019544:Equipment Failure Analysis; D006622:Hip Prosthesis; D006801:Humans; D008962:Models, Theoretical; D009765:Obesity / Q000150:complications*; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology*; D012307:Risk Factors