Quantification of Wear and Deformation in Different Configurations of Polyethylene Acetabular Cups Using Micro X-ray Computed Tomography

Abstract

Wear is currently quantified as mass loss of the bearing materials measured using gravimetric methods. However, this method does not provide other information, such as volumetric loss or surface deviation. In this work, we validated a technique to quantify polyethylene wear in three different batches of ultrahigh-molecular-polyethylene acetabular cups used for hip implants using nondestructive microcomputed tomography. Three different configurations of polyethylene acetabular cups, previously tested under the ISO 14242 parameters, were tested on a hip simulator for an additional 2 million cycles using a modified ISO 14242 load waveform. In this context, a new approach was proposed in order to simulate, on a hip joint simulator, high-demand activities. In addition, the effects of these activities were analyzed in terms of wear and deformations of those polyethylenes by means of gravimetric method and micro X-ray computed tomography. In particular, while the gravimetric method was used for weight loss assessment, microcomputed tomography allowed for acquisition of additional quantitative information about the evolution of local wear and deformation through three-dimensional surface deviation maps for the entire cups’ surface. Experimental results showed that the wear and deformation behavior of these materials change according to different mechanical simulations.

Simulation of Wear in a Spherical Joint With a Polymeric Component of the Total Hip Replacement Considering Activities of Daily Living

“…[1] shows the results of the THR's wear tests on the simulator taking into account the next main typical normal activities of the patient's daily living: level walking, stair ascending and stair descending, chair sitting and rising, and deep squatting. In the same study, based on the frequency of the cycle of each activity, the relative duration of each type of activity, reduced to the same cycle duration for 1 s, is determined, and is distributed as follows: 44% -level walking, 24% -stair ascending-stair descending, 12% -chair sitting, 12% -chair rising, and 8% -deep squatting.…”

“…In the current study, numerical wear simulation of the THR's spherical polymeric component is conducted, based on the activities indicated in [1] and their duration. At the same time, the wear during the level walking activity is evaluated using parameters regulated by ISO 14242-1.…”

“…In the same study, based on the frequency of the cycle of each activity, the relative duration of each type of activity, reduced to the same cycle duration for 1 s, is determined, and is distributed as follows: 44% -level walking, 24% -stair ascending-stair descending, 12% -chair sitting, 12% -chair rising, and 8% -deep squatting. The tests during level walking presented in [1] are carried out in accordance with the ISO 14242-1 demands for angular movements of the femoral joint component and the applied force. For other activities, only the resulting vector of the applied force is shown for the worst case load when the patient's weight force is of 1000 N, but no kinematic profiles of the angular displacements are presented.…”

“…And ref. [1] describes similar studies of a THR's spherical joint with a polymeric element, but on a specialized device for wear testing spherical sliding couples. It is clear that for successful implementation of such tests it is necessary to know the real kinematic motion dependencies in the joint, including angular displacements in three planes for the full step cycle for all the activities used, and also their kinetics, i.e.…”

“…In addition to level walking, these activities can include the most frequent ones, such as stair climbing, chair sitting and squatting [1].…”