A simple fully integrated contact-coupled wear prediction for ultra-high molecular weight polyethylene hip implants

Abstract

A fully coupled contact and wear model was developed in the present study for hip implants employing an ultra-high molecular weight polyethylene (UHMWPE) cup in combination with a metallic or ceramic femoral head. A simple elasticity equation based on the concept of constrained column model was employed to solve the contact mechanics between the acetabular cup and the femoral head under the three-dimensional physiological loading condition. The wear model was based on the classical Archard-Lancaster equation in common with all other studies reported in the literature. The fully coupled contact and wear model was applied to both conventional and cross-linked UHMWPE cups under a wide range of design parameters such as the clearance and the femoral head radius. The predicted linear and volumetric wear as well as their rates for conventional UHMWPE cups were found to be in good agreement with those obtained from a similar analysis by Maxian but using the finite element method for the contact mechanics analysis. The predicted maximum contact pressure was found to decrease rapidly within the first 10(6) cycles, and below the limit to cause plastic deformation within the UHMWPE cup with a nominal radial clearance of 0.2 mm. The effect of the clearance between the head and the cup on the predicted wear was found to be negligible. For the cross-linked UHMWPE cup with relatively large diameters up to 48 mm and a fixed outside diameter of 50 mm, the predicted wear, which was found to increase with increasing femoral head radius, remained small owing to the small wear factor associated with these materials. Furthermore, if the head diameter increases beyond 42 mm, a rapid increase in the contact pressure was predicted, owing to the decrease in the wall thickness of the cross-linked UHMWPE cup.

Modifying and Expanding the Simulation of Wear in the Spherical Joint With a Polymeric Component of the Total Hip Prosthesis

“…The radial clearance between them makes up 0.15 mm. The elasticity modulus and Poisson's ratio were chosen as 1.4 GPa and 0.46, respectively, for the cup and 210 GPa and 0.3, respectively, for the head [7]. The right hip joint, that corresponds to ISO 14242-1 test standard, is defined in anatomically fixed coordinates x ' y ' z ' and shown in Fig.…”

“…3. The wear simulation was based on the classical Archard equation [6,7]. Until now, the total interaction for ideal uniformly loaded isotropic surfaces with a nominal contact pressure in the linear elastic condition is usually adopted for description by the relation:…”

“…In particular, for the THR with a UHMWPE polymeric component the wear simulation is based on the classical Archard equation together with all other studies reported in literature referred to, for example, in [6,7,8], where the wear factor is taken as a constant value. In [5], the polymer wear in terms of cumulative linear and volume wear when the wear factor is chosen to be a function of contact pressure was first evaluated.…”

“…Loading and displacement parameters for wear-testing machines and corresponding environmental conditions for test are regulated in the given standard. At the same time, in [7], at a constant wear factor, there was performed the research for the head of 32 mm and also for standard head diameter of 28 mm. Also, it was conducted under conditions during walking gait when the hip implant experiences three-dimensional load and motion patterns at a gait cycle according to the angular positions measured by Jonhston and Smidt, and load measured by Paul [7].…”

“…The objective of this work is to modify the existing wear model and expand the results obtained in [5] by performing simulations using the finite element analysis for the ISO 14242-1 demands and additionally for the conditions during walking gait [7]. Likewise, it is to be carried out for a head diameter of 28 mm in terms of cumulative linear and volumetric wear at a constant and variable wear factor, where the variable wear factor is adopted from the modified formula for the dependence on the contact pressure.…”