Fluid-structure interactions in micro-interlocked regions of the cement-bone interface

Area of Science:

• Biomedical Engineering
• Biomechanics
• Fluid Dynamics

Background:

• Total knee replacements (TKRs) involve cementing a tibial component to the proximal tibia.
• The interface between the cement and the bone's trabecular structure is crucial for implant stability.
• Understanding fluid dynamics at this interface is key to preventing implant loosening and bone loss.

Purpose of the Study:

• To investigate fluid dynamics and bone resorption at the trabeculae-cement interface in TKRs.
• To determine the relationship between gap size, fluid shear stress, and bone resorption.
• To correlate computational findings with post-mortem observations of retrieved implants.

Main Methods:

• Experimental testing and computational modeling of cement-bone constructs.
• Fluid-structure interaction analysis with parametric evaluation of gap dimensions, loading conditions, and fluid properties.
• Development of a bone resorption model based on fluid shear rate.

Main Results:

• Trabeculae-cement gaps ranged from 0 to 50.4 μm, with mean micro-motions of 0.56–4.7 μm under load.
• Fluid shear stresses up to 926 Pa were observed, significantly exceeding physiological levels (~1–5 Pa).
• Simulated bone resorption occurred in high shear stress regions, consistent with morphologies in retrieved TKRs.

Conclusions:

• Supra-physiological fluid shear stresses generated by small post-operative gaps can induce trabecular bone lysis.
• This fluid-induced lysis may be a primary mechanism for bone resorption at the TKR interface.
• Findings suggest that minimizing initial gaps could improve long-term TKR stability and bone integration.