Biomechanical effects of morphological variations of the cortical wall at the bone-cement interface

BACKGROUND The integrity of bone-cement interface is very important for the stabilization and long-term sustain of cemented prosthesis. Variations in the bone-cement interface morphology may affect the mechanical response of the shape-closed interlock. METHODS Self-developed new reamer was used to process fresh pig reamed femoral canal, creating cortical grooves in the canal wall of experimental group. The biomechanical effects of varying the morphology with grooves of the bone-cement interface were investigated using finite element analysis (FEA) and validated using companion experimental data. Micro-CT scans were used to document interlock morphology. RESULTS The contact area of the bone-cement interface was greater (P < 0.05) for the experimental group (5470 ± 265 mm(2)) when compared to the specimens of control group (5289 ± 299 mm(2)). The mechanical responses to tensile loading and anti-torsion showed that the specimens with grooves were stronger (P < 0.05) at the bone-cement interface than the specimens without grooves. There were positively significant correlation between the contact area and the tensile force (r (2) = 0.85) and the maximal torsion (r (2) = 0.77) at the bone-cement interface. The volume of cement of the experimental group (7688 ± 278 mm(3)) was greater (P < 0.05) than of the control group (5764 ± 186 mm(3)). There were positively significant correlations between the volume of cement and the tensile force (r (2) = 0.90) and the maximal torsion (r (2) = 0.97) at the bone-cement interface. The FEA results compared favorably to the tensile and torsion relationships determined experimentally. More cracks occurred in the cement than in the bone. CONCLUSIONS Converting the standard reaming process from a smooth bore cortical tube to the one with grooves permits the cement to interlock with the reamed bony wall. This would increase the strength of the bone-cement interface.