  Short and long-term stabilities of cementless implants are strongly
determined by the interfacial load transfer between implants and bone tissue.
Stress-shielding effects arise from shear stresses due to the difference of
material properties between bone and the implant. It remains difficult to
measure the stress field in periprosthetic bone tissue. This study proposes to
investigate the dependence of the stress field in periprosthetic bone tissue on
i) the implant surface roughness, ii) material properties of bone and of the
implant, iii) the bone-implant contact ratio. To do so, a microscale 2-D finite
element model of an osseointegrated boneimplant interface was developed where
the surface roughness was modeled by a sinusoidal surface. The results show
that the isostatic pressure is not affected by the presence of the bone-implant
interface while shear stresses arise due to the combined effects of a
geometrical singularity (for low surface roughness) and of shear stresses at
the bone-implant interface (for high surface roughness). Stress-shielding
effects are likely to be more important when the bone-implant contact ratio
value is low, which corresponds to a case of relatively low implant stability.
Shear stress reach a maximum value at a distance from the interface comprised
between 0 and 0.1 time roughness wavelength $\lambda$ and tend to 0 at a
distance from the implant surface higher than $\lambda$, independently from
bone-implant contact ratio and waviness ratio. A comparison with an analytical
model allows validating the numerical results. Future work should use the
present approach to model osseointegration phenomena.
