title: Stem micromotion after femoral impaction grafting using irradiated allograft bone: a time zero in vitro study.
abstract: BACKGROUND
  A gamma irradiation dose of 15kGy has been shown to adequately sterilise allograft bone, commonly used in femoral impaction bone grafting to treat bone loss at revision hip replacement, without significantly affecting its mechanical properties. The objective of this study was to evaluate whether use of 15kGy irradiated bone affects the initial mechanical stability of the femoral stem prosthesis, as determined by micromotion in a comprehensive testing apparatus, in a clinically relevant time zero in vitro model of revision hip replacement.
  
  
  METHODS
  Morselised ovine bone was nonirradiated (control), or irradiated at 15kGy or 60kGy. For each dose, six ovine femurs were implanted with a cemented polished taper stem following femoral impaction bone grafting. Using testing apparatus that reproduces stem loading, stems were cyclically loaded and triaxial micromotion of the stem relative to the bone was measured at the proximal and distal stem regions using non-contact laser transducers and linear variable differential transformers.
  
  
  RESULTS
  There were no significant differences in proximal or distal stem micromotion between groups for all directions (p≤0.80), apart for significantly greater distal stem medial-lateral micromotion in the 60kGy group compared to the 15kGy group (P=0.03), and near-significance in the anterior-posterior direction (P=0.08, power=0.85).
  
  
  CONCLUSIONS
  Using a clinically relevant model and loading apparatus, irradiation of bone at 15kGy does not affect initial femoral stem stability following femoral impaction bone grafting.
authors.affiliation: Biomechanics & Implants Research Group, The Medical Device Research Institute, Flinders University, South Australia, Australia. Electronic address: john.costi@flinders.edu.au.
authors.forename: John J
authors.initials: JJ
authors.lastname: Costi
authors.forename: Rohan H
authors.initials: RH
authors.lastname: Edmonds-Wilson
authors.forename: Donald W
authors.initials: DW
authors.lastname: Howie
authors.forename: Roumen
authors.initials: R
authors.lastname: Stamenkov
authors.forename: John R
authors.initials: JR
authors.lastname: Field
authors.forename: Richard M
authors.initials: RM
authors.lastname: Stanley
authors.forename: Trevor C
authors.initials: TC
authors.lastname: Hearn
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Callary
authors.forename: Margaret A
authors.initials: MA
authors.lastname: McGee
mesh_terms: D064591:Allografts; D000704:Analysis of Variance; D000818:Animals; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D001696:Biomechanical Phenomena; D016025:Bone Transplantation; D005269:Femur / Q000528:radiation effects* / Q000601:surgery / Q000637:transplantation*; D006622:Hip Prosthesis; D009068:Movement; D011475:Prosthesis Failure; D012086:Reoperation; D012756:Sheep; D014184:Transplantation, Homologous
keywords: Biomechanics; Femoral revision; Impaction grafting; Irradiation; Micromotion