Technical note

Comparison of metal-on-metal hip simulator wear measured by gravimetric, CMM and optical profiling methods

L Russell Alberts, Vanesa Martinez-Nogues, Richard Baker Cook, Christian Maul, Paul Bills, Radu Racasan, Martin Stolz, Robert Wood

Research output: Contribution to journalArticle

Abstract

Simulation of wear in artificial joint implants is critical for evaluating implant designs and materials. Traditional protocols employ the gravimetric method to determine the loss of material by measuring the weight of the implant components before and after various test intervals and after the completed test. However, the gravimetric method cannot identify the location, area coverage or maximum depth of the wear and it has difficulties with proportionally small weight changes in relatively heavy implants. In this study, we compare the gravimetric method with two geometric surface methods; an optical light method (RedLux) and a coordinate measuring method (CMM). We tested ten Adept hips in a simulator for 2 million cycles (MC). Gravimetric and optical methods were performed at 0.33, 0.66, 1.00, 1.33 and 2 MC. CMM measurements were done before and after the test. A high correlation was found between the gravimetric and optical methods for both heads (R<sup>2</sup> = 0.997) and for cups (R<sup>2</sup> = 0.96). Both geometric methods (optical and CMM) measured more volume loss than the gravimetric method (for the heads, p = 0.004 (optical) and p = 0.08 (CMM); for the cups p = 0.01 (optical) and p = 0.003 (CMM)). Two cups recorded negative wear at 2 MC by the gravimetric method but none did by either the optical method or by CMM. The geometric methods were prone to confounding factors such as surface deformation and the gravimetric method could be confounded by protein absorption and backside wear. Both of the geometric methods were able to show the location, area covered and depth of the wear on the bearing surfaces, and track their changes during the test run; providing significant advantages to solely using the gravimetric method.
Original languageEnglish
Article number014002
Pages (from-to)1-8
Number of pages8
JournalSurface Topography: Metrology and Properties
Volume6
Issue number1
Early online date4 Jan 2018
DOIs
Publication statusPublished - 29 Jan 2018

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simulators
Simulators
Metals
Wear of materials
metals
optics
Bearings (structural)
cycles
Proteins
proteins
intervals
simulation

Cite this

Alberts, L Russell ; Martinez-Nogues, Vanesa ; Baker Cook, Richard ; Maul, Christian ; Bills, Paul ; Racasan, Radu ; Stolz, Martin ; Wood, Robert. / Technical note : Comparison of metal-on-metal hip simulator wear measured by gravimetric, CMM and optical profiling methods. In: Surface Topography: Metrology and Properties. 2018 ; Vol. 6, No. 1. pp. 1-8.
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Technical note : Comparison of metal-on-metal hip simulator wear measured by gravimetric, CMM and optical profiling methods. / Alberts, L Russell; Martinez-Nogues, Vanesa; Baker Cook, Richard ; Maul, Christian; Bills, Paul; Racasan, Radu; Stolz, Martin; Wood, Robert.

In: Surface Topography: Metrology and Properties, Vol. 6, No. 1, 014002, 29.01.2018, p. 1-8.

Research output: Contribution to journalArticle

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AB - Simulation of wear in artificial joint implants is critical for evaluating implant designs and materials. Traditional protocols employ the gravimetric method to determine the loss of material by measuring the weight of the implant components before and after various test intervals and after the completed test. However, the gravimetric method cannot identify the location, area coverage or maximum depth of the wear and it has difficulties with proportionally small weight changes in relatively heavy implants. In this study, we compare the gravimetric method with two geometric surface methods; an optical light method (RedLux) and a coordinate measuring method (CMM). We tested ten Adept hips in a simulator for 2 million cycles (MC). Gravimetric and optical methods were performed at 0.33, 0.66, 1.00, 1.33 and 2 MC. CMM measurements were done before and after the test. A high correlation was found between the gravimetric and optical methods for both heads (R<sup>2</sup> = 0.997) and for cups (R<sup>2</sup> = 0.96). Both geometric methods (optical and CMM) measured more volume loss than the gravimetric method (for the heads, p = 0.004 (optical) and p = 0.08 (CMM); for the cups p = 0.01 (optical) and p = 0.003 (CMM)). Two cups recorded negative wear at 2 MC by the gravimetric method but none did by either the optical method or by CMM. The geometric methods were prone to confounding factors such as surface deformation and the gravimetric method could be confounded by protein absorption and backside wear. Both of the geometric methods were able to show the location, area covered and depth of the wear on the bearing surfaces, and track their changes during the test run; providing significant advantages to solely using the gravimetric method.

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