title: Influence of prosthesis design and implantation technique on implant stresses after cementless revision THR.
abstract: BACKGROUND
  Femoral offset influences the forces at the hip and the implant stresses after revision THR. For extended bone defects, these forces may cause considerable bending moments within the implant, possibly leading to implant failure. This study investigates the influences of femoral anteversion and offset on stresses in the Wagner SL revision stem implant under varying extents of bone defect conditions.
  
  
  METHODS
  Wagner SL revision stems with standard (34 mm) and increased offset (44 mm) were virtually implanted in a model femur with bone defects of variable extent (Paprosky I to IIIb). Variations in surgical technique were simulated by implanting the stems each at 4° or 14° of anteversion. Muscle and joint contact forces were applied to the reconstruction and implant stresses were determined using finite element analyses.
  
  
  RESULTS
  Whilst increasing the implant's offset by 10 mm led to increased implant stresses (16.7% in peak tensile stresses), altering anteversion played a lesser role (5%). Generally, larger stresses were observed with reduced bone support: implant stresses increased by as much as 59% for a type IIIb defect. With increased offset, the maximum tensile stress was 225 MPa.
  
  
  CONCLUSIONS
  Although increased stresses were observed within the stem with larger offset and increased anteversion, these findings indicate that restoration of offset, key to restoring joint function, is unlikely to result in excessive implant stresses under routine activities if appropriate fixation can be achieved.
authors.affiliation: Julius Wolff Institute and Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Germany. markus.heller@charite.de
authors.forename: Markus O
authors.initials: MO
authors.lastname: Heller
authors.forename: Manav
authors.initials: M
authors.lastname: Mehta
authors.forename: William R
authors.initials: WR
authors.lastname: Taylor
authors.forename: Dong-Yeong
authors.initials: DY
authors.lastname: Kim
authors.forename: Andrew
authors.initials: A
authors.lastname: Speirs
authors.forename: Georg N
authors.initials: GN
authors.lastname: Duda
authors.forename: Carsten
authors.initials: C
authors.lastname: Perka
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005269:Femur / Q000601:surgery; D020342:Finite Element Analysis; D006621:Hip Joint / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation; D013314:Stress, Mechanical; D013718:Tensile Strength