Three-dimensional friction measurement during hip simulation

Robert Sonntag,J Philippe Kretzer,Steffen Braun,Joern Reinders,Loay Al-Salehi,Ulrike Mueller,John Leicester Williams

doi:10.1371/journal.pone.0184043

Robert Sonntag, J Philippe Kretzer + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0184043

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Journal: PloS one	Publication Date: Sep 8, 2017
Citations: 13	License type: CC BY 4.0

Affiliation: University Hospital Heidelberg, Heidelberg University

Abstract

ObjectivesWear of total hip replacements has been the focus of many studies. However, frictional effects, such as high loading on intramodular connections or the interface to the bone, as well as friction associated squeaking have recently increased interest about the amount of friction that is generated during daily activities. The aim of this study was thus to establish and validate a three-dimensional friction setup under standardized conditions.Materials and methodsA standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation. The setup was verified by an ideal hydrostatic bearing and validated with a static-load physical pendulum and an extension-flexion rotation with a dynamic load profile. Additionally, a pendulum model was proposed for screening measurement of frictional effects based on the damping behavior of the angular oscillation without the need for any force/moment transducer. Finally, three-dimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm).ResultsA precision of less than 0.2 Nm during three-dimensional friction measurements was reported, while increased frictional torque (resultant as well as taper torque) was measured for larger head diameters. These effects have been confirmed by simple pendulum tests and the theoretical model. A comparison with current literature about friction measurements is presented.ConclusionsThis investigation of friction is able to provide more information about a field that has been dominated by the reduction of wear. It should be considered in future pre-clinical testing protocols given by international organizations of standardization.

Highlights

To date, wear of total joint replacements has been the focus of many clinical evaluations and pre-clinical testing which is commonly conducted by joint simulators that can replicate standardized walking cycles
A standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation
Threedimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm)

Summary

Introduction

Wear of total joint replacements has been the focus of many clinical evaluations and pre-clinical testing which is commonly conducted by joint simulators that can replicate standardized walking cycles. With the osteolytic potential of UHMWPE wear particles, the evaluation of new bearing materials and implant designs was addressed by wear measurements from mechanical in vitro simulation. Using these methods, the conventional UHMWPE has been improved as our modern form of cross-linked and stabilized polyethylene (XPE) within the past few decades [2]. The design and dimensions of the intermodular taper interfaces have not been adapted to fit the larger head diameters and to incorporate modern material combinations. This can cause micromotions in the taper connection, which may lead to fretting. There is an increasing number of reports on taper wear for implant systems that use large head hard-on-hard bearings, which are associated with tribo-corrosion in the connective interface [6, 8, 9]

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