A Study on the Relationship Between Contact Pressures in a Grade2 TDN–UHMWPE Hip Implant: Young’s Modulus and Poisson’s Ratio

Statistical data show that over 90% hip implants have the acetabular cup made of ultra-high molecular weight polyethylene (UHMWPE), while the femoral head is made of stainless steel, CoCrMo alloy, titanium and ceramics. The values of Young's modulus for stainless steel, CoCrMo alloy and titanium differ from that for UHMWPE by 100–200 times, while Young's modulus of ceramics differs from the Young's modulus value of UHMWPE by up to 400 times. Young's modulus of UHMWPE can also differ by up to 3 times, which considerably affects contact parameters. Therefore, the problem of assessing the impact of the elastic characteristics of UHMVE on the contact pressure in the prostheses of the hip joint is relevant. A new calculation method is used to determine the effect of Young's modulus and Poisson's ratio (UHMWPE) on maximum contact pressures in a hip implant. This study undertakes an analysis of the relationship between elastic properties of UHMWPE and contact pressures, considering a Grade2 TDN (thermo-diffusion nitrided titanium) femoral head diameter and radial clearance. Quantitative and qualitative relationships are established between contact pressures and Young's modulus and Poisson's ratio for the UHMWPE acetabular cup. The proposed calculation method can be used at the stage of hip implant selection to estimate contact pressures depending on the implant load (patient's weight and muscular force) and geometry (femoral head diameter and radial clearance in the implant). Contact pressures also have a significant impact on the wear rate of an UHMWPE acetabular cup, as well as on hip implant service life.