Homogenized finite element models can accurately predict screw pull-out in continuum materials, but not in porous materials

Bone screw fixation can be estimated with several test methods such as insertion torque, pull-out, push-in and bending tests. A basic understanding of the relationship between bone microstructure is still lacking. Computational models help clarify this relationship. The objective paper to evaluate homogenized finite element (hFE) pull-out. Experimental pull-out tests were performed on three materials: two polyurethane (PU) foams having a porous microstructure, high density polyethylene (HDPE) which continuum material. Forty-five titanium pedicle screws inserted 10, 20, 30 mm in equally sized blocks all materials (N = 5/group). Pull-out characteristics i.e. stiffness (S), yield force (Fy), peak (Fult) displacement at Fult (dult) measured. hFE created replicating experiments. was modeled rigid body 5 axial applied head screw. Simulations evaluating different conditions bone-screw interface; once fitted pilot hole exactly ("free-stressed") interface stresses resulting from process taken into account ("pre-stressed"). simulations representing pre-stressed condition HDPE matched experimental data well; S, Fy, differed less than 11%, 2% 0.5% data, respectively, whereas dult 16%. free-stressed accurate, especially (158% higher condition) (30% lower affected. PU did not match experiments well. For 20 depth, Fy by more 104%, 89% 66%, respectively values. Agreement improve for 10 depths. We found that accurately quantify HDPE, but structure, PU. Pre-stresses induced cannot neglected need included simulations.