Stress shielding at the bone-implant interface: influence of surface roughness and of the bone-implant contact ratio

TL;DR

This study investigates how surface roughness and contact ratio influence stress distribution at the bone-implant interface, highlighting shear stress effects and implications for implant stability.

Contribution

It introduces a microscale 2-D finite element model to analyze the impact of surface roughness and contact ratio on stress shielding in bone-implant interfaces.

Findings

Shear stresses are influenced by surface roughness and geometry.

Stress shielding is more significant at low contact ratios.

Shear stress peaks near the interface, within 0.1 wavelength.

Abstract

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.