Abstract
The subsurface fatigue that occurs in the Ultra-High Molecular Weight Polyethylene (UHMWPE) hip joint cup has been identified to be correlated with the contact stress at that cup. This cup stress is known to be affected by the implant design, dimensions and materials. In this study, a 3D finite element modeling has been used to investigate the effects on the cup contact stress when using low stiffness Titanium alloy (Ti) as a femur head. Also, the effects on the cup contact stress due to using different sizes of femur heads, and the presence of metal backing shell with different thicknesses are studied. The finite element results show that the use of low stiffness Ti alloy femur head results in a significant decrease in the cup contact stress compared with Stainless Steel (SS) and Cobalt Chromium (Co Cr Mo) femur heads. The presence of metal backing shell up to 1 mm thickness results in a remarkable decrease in the cup contact stresses especially for small femur heads. Finally, the use of larger femur heads, up to 32 mm diameter, results in significant decrease in the overall predicted hip joint contact. The present results indicate that any changes in design and geometrical parameters of the hip joint have significant consequences in the long term behaviour of the artificial hip joint and should be taken into consideration.
Highlights
The artificial hip joint arthroplasty involves the replacement of the natural femoral head by a ball made of metallic alloy or ceramic material, and the acetabulum by a polymeric hemispherical lining (Figure 1) [1]
The results indicate that the maximum Von Mises stress at the Ultra-High Molecular Weight Polyethylene (UHMWPE) cup decreases significantly by increasing the femur head diameter for all types of femur head materials
The significant decrease in the UHMWPE cup stress due to using larger femur heads can be attributed to the increase in the contact area between the femur head and the cup Elastic Modulus GPa Poisson’s Ratio
Summary
The artificial hip joint arthroplasty involves the replacement of the natural femoral head by a ball made of metallic alloy or ceramic material, and the acetabulum by a polymeric hemispherical lining (Figure 1) [1]. Over the past few decades, different artificial hip joint designs have been demonstrated to modulate implant survival [26,27,28]. The combined effects of the hip joint design parameters on the resultant contact pressure on the polymeric cup are still unclear. Studying the combined effects of all these hip joint design parameters at the same time may result in modification of UHMWPE contact pressure, and affect the long term performance of the hip implant
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