title: Wear characteristics of WSU total ankle replacement devices under shear and torsion loads.
abstract: BACKGROUND
  There are several factors that contribute to the failure of total ankle replacement (TAR). Aseptic loosening is one of the primary mechanisms of failure in TAR. Since a cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is used as liner material, there is a need to quantify and develop methods to estimate the wear rates of the liners. High contact stresses develop during the gait generates wear debris resulting in osteolysis and early loosening of the prostheses.
  
  
  METHODS
  In this paper wear characteristics of Wright State University (WSU) TARs were determined by applying shear and torsion loads. Viscoelastic properties were used to model the liner component. Finite element analysis was conducted to determine the wear rate by deriving Von Mises and contact stresses generated in the liner and wear rate equation was used to predict the wear rate.
  
  
  RESULTS
  Titanium alloy has shown less resistance towards shear forces when compared with other metal alloys. Under torsion, rotation angle plays a significant role in affecting the peak stress values. The maximum average contact stress was 14.46 MPa under torsion load which contributes to a wear rate of 0.67 (mm(3)/year) for one of the mobile bearing models. The maximum average contact stress and wear rate obtained from the analytical study were 10.55 MPa and 0.33 (mm(3)/year), respectively for mobile bearing models. When compared with mobile bearing model, fixed bearing model has shown higher stresses at different degrees of rotation.
  
  
  CONCLUSIONS
  Both shear and torsion loads cause significantly lower contact stresses and wear when compared to the axial load. Further studies are necessary to accurately determine the wear behavior of fixed bearing TAR models.
authors: Department of Biomedical, Industrial and Human Factors Engineering, Wright State University, Dayton, OH 45435, USA.
authors: Dinesh
authors: D
authors: Gundapaneni
authors: Department of Radiology, Miami Valley Hospital, Dayton, OH 45409, USA.
authors: James T
authors: JT
authors: Tsatalis
authors: Department of Orthopedic Surgery, Sports Medicine and Rehabilitation, Miami Valley Hospital, Dayton, OH 45409, USA.
authors: Richard T
authors: RT
authors: Laughlin
authors: Department of Biomedical, Industrial and Human Factors Engineering, Wright State University, Dayton, OH 45435, USA; Department of Orthopedic Surgery, Sports Medicine and Rehabilitation, Miami Valley Hospital, Dayton, OH 45409, USA; Mechanical Engineering and Economic Sciences, Institute for Materials Science and Welding, Graz University of Technology, Kopernikusgasse 24/I, A-8010 Graz, Austria. Electronic address: tarun.goswami@wright.edu.
authors: Tarun
authors: T
authors: Goswami
mesh_terms: D000497:Alloys; D058737:Arthroplasty, Replacement, Ankle / Q000295:instrumentation*; D020342:Finite Element Analysis; D005684:Gait; D006801:Humans; D008422:Materials Testing; D011475:Prosthesis Failure; D012399:Rotation; D033081:Shear Strength; D013314:Stress, Mechanical; D016474:Weight-Bearing
chemical_list: D000497:Alloys
keywords: Ankle replacement; Contact stress; FEA; Gait; Wear