Micromotion-induced peri-prosthetic fluid flow around a cementless femoral stem

Abstract

Micromotion-induced interstitial fluid flow at the bone-implant interface has been proposed to play an important role in aseptic loosening of cementless implants. High fluid velocities are thought to promote aseptic loosening through activation of osteoclasts, shear stress induced control of mesenchymal stem cells differentiation, or transport of molecules. In this study, our objectives were to characterize and quantify micromotion-induced fluid flow around a cementless femoral stem using finite element modeling. With a 2D model of the bone-implant interface and full-factorial design, we first evaluated the relative influence of material properties, and bone-implant micromotion and gap on fluid velocity. Transverse sections around a femoral stem were built from computed tomography images, while boundary conditions were obtained from experimental measurements on the same femur. In a second step, a 3D model was built from the same data-set to estimate the shear stress experienced by cells hosted in the peri-implant tissues. The full-factorial design analysis showed that local micromotion had the most influence on peak fluid velocity at the interface. Remarkable variations in fluid velocity were observed in the macrostructures at the surface of the implant in the 2D transverse sections of the stem. The 3D model predicted peak fluid velocities extending up to 2.2 mm/s in the granulation tissue and to 3.9 mm/s in the trabecular bone. Peak shear stresses on the cells hosted in these tissues ranged from 0.1 to 12.5 Pa. These results offer insight into mechanical stimuli encountered at the bone-implant interface.

Comparison of different three dimensional-printed resorbable materials: In vitro biocompatibility, In vitro degradation rate, and cell differentiation support

“…Mathematical models suggest the fluid flow at the implant-bone interface to be 2–4 mm/s. 42,44 Therefore, it is essential to predict the degradation behavior and rate under dynamic conditions. Degradation behavior of the materials across the three experimental set-ups was quite similar.…”

Effects of interfacial micromotions on vitality and differentiation of human osteoblasts

“…Micromotions of an implant act on bone cells by exerting pressure and shear stress forces. 20 The impact of shear stress on orientation of osteoblast cell clusters, cell morphology, and elongation has been previously reported. 21 To gain a better understanding of how micromotions influence bone cell activity, an in vitro system, which allows application of defined micromotions in a range of 0 µm to 100 µm under static pressure loading conditions, was developed.…”

Femoral stem sagittal balance - Do we need a new entry point?

“…Data from studies by Hoenders et al 8 and Greenfield et al 9 , regard initial stem micro movement and early stage migration, as an independent negative predictive factor of implant loosening, acting as osteoclast differentiation stimuli. Camine et al 10 have also announced similar results about the negative effects of stem micro motion and migration, using a parametric model. Finally, femoral stem positioning is regarded as a predisposing factor of periprosthetic fractures acting as a "stress riser" 11,12 .…”