DOI: 10.21276/sjet.2016.4.10.6

Pages: 507-511

One of the major factors that determine the success of hip replacement is the primary stability which is the function of the micromotion on the bone-implant interface. Failure of hips replacement may arise from excessive motion at the implant-bone interface under the weight bearing loads. Minimizing the micromotion of the cementless prosthetic components is a key requirement for obtaining bone in-growth. If the initial movement is excessive, bone in-growth into the porous surface will not occur. Few experimental studies are available on implant micromotion largely due to difficulty of simulating loads in-vitro and in-vivo. Due to this reason, this research derived a theoretical model that relates the micro-velocity at which the implant moves down in the bone at the implant-bone surface at a specific time, the axial force applied on the head of the implant and the stiffness of the implants and the bones. The implant-bone interface (fibrous tissues) was taken as elastic surface that obeys Hooke’s law using spring analysis. Here, the displacement of the implant equals the micromotion depending on the stiffness of both cortical and trabecular (cancellous) bones. When the implant is axially loaded, due to the elastic modulus of the bone when compared to that of the implant (stainless steel), the deformation of the implant is neglected. That is, Ei >> (EC,ET) where Ei ,EC and ET are the elastic moduli of the implant, cortical part of the bone and the trabecular part of the bone respectively.