Enhancing Biomedical Implant Design to Improve Performance

Assessments of different kinds of stems by experiments and FEM analysis: Appropriate stress distribution on a hip prosthesisRina Sakai, Moritoshi Itoman, Kiyoshi Mabuchi

Journal of Clinical Biomechanics (2006) Vol. 21- pages 8268336/15/2015Paper Objective:Establishment of a method for the evaluation of the quality of initial fixation with various prosthetic stems by defining the change rate of the fixation area.6/15/2015Egypt-Japan University of Science and Technology (E-Just)2Contents:Introduction.Methods.Results.Discussion.Conclusions.Critique.

6/15/20153Egypt-Japan University of Science and Technology (E-Just)Introduction (Initial Fixation)In the initial fixation before biological adhesion occurs, it is necessary to provide a stable distribution of stress in appropriate regions. Prosthetic stems with a design that maintains a stress distribution in the proximal regions independent of loading conditions are considered to contribute to initial fixation.6/15/2015Egypt-Japan University of Science and Technology (E-Just)4MethodsThe femoral stems that were modeled were: PSV stem (PerFix SV 910 series, Japan Medical Materials).IMC stem (Intra-Medullary cruciate stem, Japan).VS stem (VerSys Fiber Metal Taper, Zimmer, USA).

6/15/2015Egypt-Japan University of Science and Technology (E-Just)5Methods (FEA)A three-dimensional mesh model of the contour of an adult femur was built from the CT data.A nonlinear structural analysis program (LS-DYNA Ver. 950) was used for finite element analysis.Hexahedral solid elements filled the contour models. The mass density of bone tissue was derived from the value obtained by experiment in another paper.6/15/2015Egypt-Japan University of Science and Technology (E-Just)6Methods (Material Properties)They defined the stem and bone tissue as a rigid material and an elasticplastic material, respectively.The material properties of the stem elements were assumed to be an isotropic titanium alloy with an elastic modulus of 110 GPa and Poissons ratio of 0.29.The femur was assumed to be isotropic material with an elastic modulus of 15.5 GPa and Poissons ratio of 0.30.6/15/2015Egypt-Japan University of Science and Technology (E-Just)7Methods (boundary conditions )Rigid contact of the distal end of the femur with the rigid base. Load of 1800 N was applied to the proximal top of the stem.The flexion angle was changed from 0o to 20o.Load of 1400 N was applied by the greater trochanter of the femur as a muscle force.The automated contact is defined as a slip between the bone and the stem with a coefficient of friction of 0.1.6/15/2015Egypt-Japan University of Science and Technology (E-Just)8Methods (Experiments with pressure-sensitive films)The authors developed a system to assess the fixation method of a femoral stem, using a loading machine and pressure-sensitive films.The material of the bone model was self curing acrylic resin.Firstly, the joint prosthesis was inserted in the bisected model bones with the pressure sensitive films. Two-dimensional pressure distribution was mapped on films (Pressure-sensitive film, Fuji Photo Film, Japan) that were attached to the stem. 6/15/2015Egypt-Japan University of Science and Technology (E-Just)9Methods (Experiments with pressure-sensitive films)Pressure range of this film is from 0 to 30.0 MPa. These pressure-sensitive films are stained to red by pressurizing and the intensity of stained color changes according to the magnitude of pressure. The stress values of over 10 MPa determined on the pressure sensitive tape were obtained using the stress measure.6/15/2015Egypt-Japan University of Science and Technology (E-Just)10Methods (Experiments with pressure-sensitive films)Secondly, the bisected model bones were firmly fixed to each other by twelve screws. Thirdly, a static load of 1800 N was applied to the model bone by a loading machine. Load of 1400 N was applied by the greater trochanter of the femur as a muscle force (How?). Lastly, to examine the maximal stress, a film with a wide measuring range was used. Stress on the three kinds of stems was measured five times.6/15/2015Egypt-Japan University of Science and Technology (E-Just)11Methods (Experiments with tactile sensors)The tactile sensor system was built using a PCI interface board, a sensor connector, and a sensor sheet with a thickness of about 0.1 mm.The measurements were repeated 30 times for each stem under the same loading conditions.Two sensors were used located on both the proximal medial and distal lateral sides.6/15/2015Egypt-Japan University of Science and Technology (E-Just)12Discussion (VS Stem)In the VS stem, high stress was distributed in the proximal medial areas, and the distribution fluctuated, suggesting that the mechanical condition of the interface between the bone and prosthetic stem was unstable in different loading conditions.6/15/2015Egypt-Japan University of Science and Technology (E-Just)13