title: Numeric simulation of bone remodelling patterns after implantation of a cementless straight stem.
abstract: OBJECTIVE
  For further development of better bone-preserving implants in total hip arthroplasty (THA), we need to look back and analyse established and clinically approved implants to find out what made them successful. Finite element analysis can help do this by simulating periprosthetic bone remodelling under different conditions. Our aim was thus to establish a numerical model of the cementless straight stem for which good long-term results have been obtained.
  
  
  METHODS
  We performed a numeric simulation of a cementless straight stem, which has been successfully used in its unaltered form since 1986/1987. We have 20 years of experience with this THA system and implanted it 555 times in 2012. We performed qualitative and quantitative validation using bone density data derived from a prospective dual-energy X-ray absorptiometry (DEXA) investigation.
  
  
  RESULTS
  Bone mass loss converged to 9.25% for the entire femur. No change in bone density was calculated distal to the tip of the prosthesis. Bone mass decreased by 46.2% around the proximal half of the implant and by 7.6% in the diaphysis. The numeric model was in excellent agreement with DEXA data except for the calcar region, where deviation was 67.7%.
  
  
  CONCLUSIONS
  The higher deviation in the calcar region is possibly a sign of the complex interactions between the titanium coating on the stem and the surrounding bone. We developed a validated numeric model to simulate bone remodelling for different stem-design modifications. We recommend that new THA implants undergo critical numeric simulation before clinical application.
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries Str. 1-7, 30625, Hannover, Germany, matthias.lerch@ddh-gruppe.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Lerch
authors.forename: Henning
authors.initials: H
authors.lastname: Windhagen
authors.forename: Christina M
authors.initials: CM
authors.lastname: Stukenborg-Colsman
authors.forename: Agnes
authors.initials: A
authors.lastname: Kurtz
authors.forename: Bernd A
authors.initials: BA
authors.lastname: Behrens
authors.forename: Amer
authors.initials: A
authors.lastname: Almohallami
authors.forename: Anas
authors.initials: A
authors.lastname: Bouguecha
mesh_terms: D015502:Absorptiometry, Photon; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation; D001843:Bone Cements; D015519:Bone Density / Q000502:physiology; D016723:Bone Remodeling / Q000502:physiology*; D005269:Femur / Q000502:physiology* / Q000601:surgery*; D020342:Finite Element Analysis; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D011474:Prosthesis Design; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
chemical_list: D001843:Bone Cements