Translated Abstract
Wear of Ultra high molecular weight polyethylene (UHMWPE) hip prosthesis can cause osteolysis, leading to aseptic loosening of the artificial joints. Therefore, wear resistance property is an important indicator of the clinical reliability for such artificial hip joint. Wear testing in simulators is a preclinical method to evaluate the wear resistance property of hip prosthesis. However, this method has certain disadvantages such as highly costing and long periods, thus not appropriate for parametric analysis. Instead, computer simulation model can take its advantage to deal with this situation. Moreover, the wear property difference among the domestic hip prostheses with different material pairs and sizes is still not clear, thus it is necessary to explore this issue through wear testing and simulation. Besides, it is not known that how different daily gaits affect the wear of hip. Research on this issue has some academic value and pratical meaning. Therefore, a wear prediction model for artificial hip joint was established in this study at first. Then two kinds of joint prosthesis including a group of MoP (Metal-on-Polyethylene) and a group of CoP (Ceramic-on-Polyethylene) were tested and the corresponding wear results were measured. Moreover, the effects of ball diameter and redial clearance as well as different daily activities on the wear of artificial hip joint were investigated by the developed wear prediction model.
The finite element explicit dynamic analysis method was adopted in the wear prediction model. In the model, two different contact algorithms including deformable cup setting and rigid body cup setting were provided. Compared with the former, the latter could accelerate computation efficiency by sacrificing the accuracy. And the cross shear effect and creep of UHMWPE was considered, which made the model closer to actual situation. In addition, all the key results include slide tracks, the distribution of cross shear ratio, wear factor K and wear depth were visualized and saved by figures. The predicted wear results were validated by literature.
Two kinds of domestic artificial hip joint with different head materials were tested and the wear was evaluated. The test specimen included a group of CoCrMo-UHMWPE coupled hip prosthesis with 28 mm in diameter and the other group of BIOLOX-UHMWPE coupled prosthesis with 28 mm and 36 mm in diameter. And both gravimetric and volumetric method were adopted to measure the wear for the CoP prosthesis, and the results agreed well. The wear rates for the samples were 54.8 mm3/MC (28 mm MoP prosthesis), 21.9 mm3/MC (36 mm CoP prosthesis) and 16.8 mm3/MC (28 mm CoP prosthesis) seperately. And the results from prediction and wear testing were compared. Under the deformable cup setting, the predicted value was close to the measured value, and the trend of wear for the samples with two different sizes was consistent. Besides, the surface roughness and micromorphologies of the samples were observed and measured, the roughness of metal heads was significantly higher than that of ceramic heads, which was thought to be the main cause of the wear difference.
The effect of two design parameters, diameter and radial clearance, on the wear of artificial hip joint was investigated though the prediction model. Both the contact mechanics and wear prediction results were analyzed. In summary, wear increased with the increase of the diameter, and decreased with the increase of the radial clearance. The effect of four different activities including walking, stair climbing, chair down/up and knee bending on the hip prosthesis wear were investigated. The predicted results showed that: the stair climbing ranked the first with the wear rate of 18.9 mm3/MC, then chair down/up (16.1 mm3/MC), followed by walking (12.8 mm3/MC), and the last was knee bending (7.9 mm3/MC). In addition, the combined effect of the four gaits on the hip wear was simulated using a simplified protocol, and the predicted wear rate was 15 mm3/MC, which showed that combined gaits caused more wear than walking gait alone.
Corresponding authors email
