This study was aimed at investigating the effect of the bone compositions on the fracture toughness of bovine cortical bone. A series of the SENB bovine cortical bone specimens were tested to assess the fracture toughness. Dual energy X-ray absorptiometry (DEXA) was applied to determine the mineral content of each bovine cortical specimen and hence the porosity and bone mineral fraction were measured. Current results indicate that the mean value fracture toughness is 9.37 MNm3/2. Moreover, the fracture toughness was found to be significantly correlated with the apparent wet bone density and porosity of bone structure. No apparent correlations are found among clinical BMD and mechanical properties, implying that the BMD is an invalid indicator of the bone properties. Additionally, the tested data were fitted to the relationship, based on power law model, that the fracture toughness increase as a power (1.526) of increasing volume fraction and as a power of increasing bone mineral fraction (0.8195). These data indicate that small changes in the amount or density of compact bone tissue exert a more pronounced influence on fracture property.
Clinical studies have proved that artificial joints may fail under prolonged gait load, which failure mechanism includes mechanical loosening and infectious loosening. Infectious loosening can be prevented by avoiding osteomyelitis, caused by bacterial infection arising from the marrow cavity, which affects the fixation function of the bone handle. As a result, use of bone cement containing various antibiotics has become an important method for prevention and treatment of infection after artificial joint replacement. This study was aimed to investigate the mechanical properties of bone cement after the addition of antibiotics through the mechanical tests. With the measurements we can then assessed the variations of mechanical strength with the dosage of antibiotics. The results showed that the dose of antibiotics directly affected the compression strength and elastic modulus of antibiotic bone cement. When the antibiotics was added more than 4.8 wt %, the cement strength was obviously affected and reduced, by 27%, indicating that during artificial hip joint replacement, the dose of antibiotics should be concerned, in order to avoid affecting the strength of bone cement and stability of the entire implant.
In this paper, a crack analysis model based on finite element method and virtual crack extension technique was proposed to investigate the occurrence of surface fracture of polyethylene acetabular cup under gait loadings. To this, a simplified hip joint model was created for facture analysis. The stress intensity factor (SIF) at crack site was estimated and used to evaluate the propagation of the surface crack. Current results show that under normal gait loading, the SIF at crack tip within polyethylene cup was predicted to be lower than the fatigue threshold of polyethylene material. However, under the heel strike instant, the crack tip SIF exceeds the fracture strength of polyethylene subject to gamma radiation, which may drive the crack to propagate to final fracture. Overall, the presented analysis model has demonstrated the probability of severe surface damage occurring in polyethylene cup under impact walking conditions. This provides a valuable reference to the improvement of the mechanical properties or design of bearing materials in clinical orthopedic application.
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