A finite element analysis of the push‐out test: Influence of test conditions

Abstract

The commonly used method for quantitative evaluation of the strength of a boneimplant interface is the push-out test. In order to give an impulse to standardization and t o g a i n more insight in t h e biomechanics of the push-out test, a finite element analysis of this test was performed. This study focused on the influence of test conditions on the push-out results. The influence of the following four parameters on the interface stress distribution was tested: (a) clearance of the hole in the support jig, (b) Young's modulus of the implant; (c) cortical thickness; and (d) implant diameter. The distance between the implant and the support jig turned out to be very critical for the occurrence of peak stresses in the interface. Variations of the Young's modulus of the implants resulted in a wide range of interface shear stresses. Variation of the cortical thickness showed a reciprocal relationship between cortical thickness and interface shear stress. However, the interface stress distribution remained uniform under the specific test circumstances. These findings also hold for variations in implant diameter. The present investigation shows that the clearance of the hole in the support jig, and the Young's modulus of the implant are parameters which most strongly influence the interface stress distribution. The clearance of the hole in the support jig is the most critical parameter, but also the parameter that can be controlled most easily. Lack of standardization with regard to these parameters can lead to uninterpretable test results. It is recommended that the clearance of the hole in the support jig is at least 0.7 mm and that push-out results are only compared with each other when materials with similar Young's modulus are concerned.

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“…It is accepted that such tests are able to estimate the mechanical interlocking between bone and implant 21 . The results of push-out tests demonstrated that a considerably high force was required to disrupt the boneimplant interface, and that it was increasingly higher as the period elapsed between surgery and sacrifice grew, reaching values around 100N.…”

Additive manufactured push‐fit implant fixation with screw‐strength pull out

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