The Research Of Simulation Of Bone Cement Interface Morphology And Biomechanisms After The Changes Morphology Of Inner Wall Of Bone Medullary Canal

Background and Purpose:The failure of artificial joint caused by bone-cement interface is common,mainly due to aseptic loosening. The fixation strength of cemented artificial joint dependents on good interlocking between the cement and the bone ie the interlocking strength of the bone-cement interface. Bone-cement interface interlocking strength is positively correlated with contact area and interlocking depth of interface. By increasing the bone-cement interface contact area and interlocking depth, artificial joint replacement surgery can be ensured to get better initial fixation strength, resulting in extended life of artificial joint and reduced complications. This study is to identify whether the strength of bone-cement interface could be increased by changing the morphology of inner wall of bone medullary canal with grooves.Methods:Self-developed new reamer was used to process fresh pig reamed femoral canal,resulting in two cortical grooves at 20 mm and 40 mm in the canal wall of experimental group(new bone-cement interface). When simulated prosthetic replacement, cement under pressure can be better infiltration to the cortical grooves of femoral. We use the Micro-CT to scanned the all models, and observed the infiltration of cement and to determined the difference between the new bone-cement interface and the traditional interface. Then, we used the Biomechanical testing instrument to tested the new and traditional bone-cement- prosthesis model(tensile testing and rotation testing), until the model to failure. Compare the biomechanical strength of both models. Finally, we analysed the correlation between the results ofmicroscopic detection and biomechanical testing. In order to understand the influence which the inner wall of the marrow cavity of the femur bone to the bone-cement-prosthesis composite, we performed a simple finite element analysis.Result:First, compared with the control group, bone cement in the specimens of experimental group had better penetration and better interlock between cement and bone, due to annular grooves of inner wall of bone medullary canal. The contact area of the bone-cement interface was greater(P<0.05) for the experimental group(5470 ± 265mm2) when compared to the specimens of control group(5289 ±299mm2). However, the porosity for the experimental group(1.50 ± 0.382%) was similar( P > 0.05) to the control group(1.59 ± 0.496%). In addition, in the tensile testing, the failure of all specimens occurred at the bone-cement interface. There was a macroscopic displacement between bone and cement. In 20 models of rotary testing, the failure of 17 specimens occurred at the bone-cement interface. The mechanical responses to tensile loading showed that the specimens of experimental group(7337±1825N) had stronger strains(P<0.05) at the bone-cement interface compared to the control group(5564±1359N). The anti-rotation capability was greater(P<0.05) for the experimental group(65.70±4.83N*m) when compared to the control group(60.60±4.43N*m). In the tensile testing, including the experimental group and control group, the contact area of bone-cement interface and the tensile force of models had strong significant positive correlation(R2=0.85,P<0.0001). In the rotational testing, the contact area of bone-cement interface andthe maximal torsion had a strong correlation(R2=0.77, P<0.0001). The relationships between the tensile force and the porosity and the maximal torsion and the porosity were observed.(R2=0.57, P<0.0001 and R2=0.43, P<0.0001). In the Finite element analysis, we found the new groove does not produce stress concentration. And the femoral shaft did not significantly affect the overall stress both the stretch and rotation tests. In tensile testing, however, the bone cement shell increased 36.86% of stress compare with control group. Rotating the test, 4.8%reduction in stress compare with control group.Conclusion:Converting the standard reaming process from a smooth boring cortical tube to one with grooves permits the cement to interlock with the reamed bony wall. This would increase the strength of the bone-cement interface. We believe that the addition of such grooves has potential to enhance cement fixation to the bone, provide better initial fixation and extend potential longevity of the bone-cement-implant composite.