title: [Bone adaptation changes mechanical stress in the femur--a prospective two years follow up after Hüft-TEP implantation].
abstract: OBJECTIVE
  Periprosthetic adaptive bone remodeling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodeling theory with finite element analysis. Unfortunately, there is still a lack of clinical validation data. The collection of prospective volumetric bone density data with a clinical computerized tomography study after THA was previously conducted. The objective of the study presented here is an additional evaluation of femoral strain.
  
  
  METHODS
  In a prospective clinical trial with 7 female patients after THA computerized tomography (CT) and finite element (FE) modeling was patient specifically combined immediately after surgery, as well as at three and 24 months postoperatively. Mechanical strain was expressed by strain energy density.
  
  
  RESULTS
  Corresponding to a bone density decrease, a decrease of the femoral strain energy density was observed during the two year follow-up after surgery (approximately 20 %). The predominant change occurred within the first three months and was found to be distally stronger than proximally.
  
  
  CONCLUSIONS
  As far as we are aware, this is the first combination of fully prospective 3D CT density data in vivo with patient-specific finite element modeling. The assessment of mechanical strain data during a follow-up trial should be a new approach for analyzing hip stems in clinical biomechanics. A future confirmative study based on a statistical case number calculation would increase the evidence of the results presented here.
authors.affiliation: Klinik für Orthopädie und Rheumatologie, Philipps-Universität Marburg. lengsfel@post.med.uni-marburg.de
authors.forename: M
authors.initials: M
authors.lastname: Lengsfeld
authors.forename: D
authors.initials: D
authors.lastname: Günther
authors.forename: T
authors.initials: T
authors.lastname: Pressel
authors.forename: R
authors.initials: R
authors.lastname: Leppek
authors.forename: J
authors.initials: J
authors.lastname: Schmitt
authors.forename: P
authors.initials: P
authors.lastname: Griss
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D001862:Bone Resorption / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004548:Elasticity; D019544:Equipment Failure Analysis / Q000379:methods; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D020342:Finite Element Analysis; D005500:Follow-Up Studies; D006622:Hip Prosthesis; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D013314:Stress, Mechanical