Trabecular bone remodeling around smooth and porous implants in an equine patellar model.

The research paper examines the relationship between stress and morphology in trabecular bone (spongy bone typically found at the end of long bones), when implants of different surface characteristics are applied. The study used horse kneecaps as a model and discovered that smooth implants caused more bone remodeling than porous implants that allowed bone to grow into them. However, the study found that current theories may not accurately explain why this differential in remodeling occurs.

Research Methodology

• The study employed the use of stainless steel spheres as the model implants. These spheres either had a polished surface or a porous, sintered-bead coating.
• The implants were inserted into one side of the kneecaps of horses and left in place for six months.
• After the time period, stereological methods were applied to precisely measure the trabecular bone morphology quantitatively.
• Furthermore, finite element analyses were applied to predict the stresses on the trabecular bone.

Findings

• The remodeling response of the trabecular bone was found to be significantly greater around the smooth implants compared to the porous implants.
• The finite analysis models showed greater changes in stress adjacent to the smooth implants due to nonlinear boundary conditions.
• However, the study revealed that the simplest form of the trajectory theory (which would suggest trabecular bone architecture adjusts in response to implant-induced stresses) may not be applicable to predict remodeling behaviors induced by the implants.

Implications

• A robust correlation was noted between change in bone density and change in von Mises effective stress: an established method used in the study of bone strength and fracture mechanics, this implies that trabecular bone architecture might correspond to an optimal structure.
• The findings also indicate that under particular circumstances, small changes in the stress state may initiate significant changes in the primal material orientation. This can potentially alter the direction or arrangement of the bone material.
• The study’s results may potentially guide improvements in implant design and understanding the biological responses to varied implant surfaces, impacting orthopedic surgeries and the field of biomedical engineering.