Prediction of bone ingrowth into the porous swelling bone anchors using an osteoconnectivity-based adaptive finite element algorithm.

In this study, a bone ingrowth framework was developed, which was integrated with a hygro-elastic swelling simulation, to evaluate the ingrowth of bone into porous co-polymeric swelling bone anchors. The aim was to investigate the impact of swelling-induced radial stress on bone ingrowth and the improvement in the mechanical properties and fixation strength of the anchors. Using the finite element method coupled with the osteoconnectivity matrix, the model successfully predicted the sequential bone formation within the porous bone anchor. The bone ingrowth framework was validated based on available experimental data, closely aligning with empirical observations. The results show that owing to radial stresses generated in the bone-anchor interface by swelling, considerable bone ingrowth could be stimulated. Moreover, among the three finite element models incorporating porosity within the recommended pore size range (300-600 $\mu m$ ), smaller pore sizes seem to promote faster and more extensive bone ingrowth, while larger pores exhibit slower ingrowth rates. Regardless of the pore sizes, the mechanical integrity and fixation strength of the anchors significantly improved. These findings strengthen the hypotheses that swelling of such anchors can stimulate bone ingrowth, and highlight the importance of pore geometry, size and interconnectivity in optimizing bone ingrowth and improving their performance.