title: Fixation techniques and stem dimensions in hinged total knee arthroplasty: a finite element study.
abstract: BACKGROUND
  No evidence-based guidelines are available to determine the appropriate stem length, and whether or not to cement stems in revision total knee arthroplasty (TKA). Therefore, the objective of this study was to compare stresses and relative movement of cemented and uncemented stems of different lengths using a finite element analysis.
  
  
  METHODS
  A finite element model was created for a synthetic tibia. Two stem lengths (95 and 160 mm) and two types of fixation (cemented or press fit) of a hinged TKA were examined. The average compressive stress distribution in different regions of interest, as well as implant micromotions, was determined and compared during lunge and squat motor tasks.
  
  
  RESULTS
  Both long and short stems in revision TKA lead to high stresses, primarily in the region around the stem tip. The presence of cement reduces the stresses in the bone in every region along the stem. Short stem configurations are less affected by the presence of cement than the long stem configuration. Press-fit stems showed higher micromotions compared to cemented stems.
  
  
  CONCLUSIONS
  Lowest stresses and micromotion were found for long cemented stems. Cementless stems showed more micromotion and increased stress levels especially at the level of the stem tip, which may explain the clinical phenomenon of stem-end pain following revision knee arthroplasty. These findings will help the surgeon with optimal individual implant choice.
authors.affiliation: Center of Orthopaedics and Traumatology, University Hospital Marburg, Baldingerstrasse, 35033, Marburg, Germany. elzayat@med.uni-marburg.de.
authors.forename: Bilal Farouk
authors.initials: BF
authors.lastname: El-Zayat
authors.affiliation: Center of Orthopaedics and Traumatology, University Hospital Marburg, Baldingerstrasse, 35033, Marburg, Germany.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Heyse
authors.affiliation: Department of Mechanics and Industrial Technology, University of Florence, Florence, Italy.
authors.forename: Nelson
authors.initials: N
authors.lastname: Fanciullacci
authors.affiliation: Mechanical Engineering Technology TC, KU Leuven, Geel, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Labey
authors.affiliation: Center of Orthopaedics and Traumatology, University Hospital Marburg, Baldingerstrasse, 35033, Marburg, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Fuchs-Winkelmann
authors.affiliation: BEAMS Department (Bio Electro and Mechanical Systems), Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Innocenti
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001843:Bone Cements; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007720:Knee Prosthesis; D011474:Prosthesis Design; D012086:Reoperation; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D001843:Bone Cements
keywords: Cemented; Finite element model; Hinged total knee arthroplasty; Press fit; Stem length