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

Abstract

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.

Keywords: Biomechanics; Bone cement; Interface; Morphology.

Fig. 1

The reamers and the relevant diagram of 3-D components (a1 traditional reamer, a2 self-developed reamer, b1 diagram of component without grooves, b2 diagram of component with grooves)

Fig. 2

The model of bone-cement-prosthesis component

Fig. 3

Tensile strength of the experimental group was significantly higher than the control group (a). Maximum torque in the experimental group was significantly higher than the control group (b). The contact area of bone-cement interface in the experimental group was significantly higher than the control group (c). There was no significantly different between the porosity of experimental and control groups (d)

Fig. 4

Linear regression models: tensile stress and contact area, r ² = 0.85 (a); tensile stress and porosity, r ² = 0.57 (b); maximum torque and contact area, r ² = 0.77 (c); maximum torque and porosity, r ² = 0.43 (d); P < 0.05

Fig. 5

The responses after biomechanical test: before tensile test (a1), after tensile test—the stretched displacement occurred at the bone-cement interface of all the samples and the cement-prosthesis interface did not have a displacement (a2); before torsion test (b1), after torsion test—cortical bone fractures occurred in the samples, and significant loosening of the bone-cement interface was observed, while loosening of the cement-prosthesis interface was not observed (b2)

Fig. 6

Under the tension and rotation loads, the von Mises stress in the components of the experimental group was lower than that in the components of the control group

Fig. 7

Under the tension and rotation loads, the von Mises stress in the femur of the experimental group was lower than that in the femur of the control group

Fig. 8

The high correlation between FEA and biomechanical experimental findings found for the strength–stiffness relation in tension (a) has also been noted in torsion (b)