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Variability in reference point microindentation and recommendations for testing cortical bone: Maximum load, sample orientation, mode of use, sample preparation and measurement spacing.

Variability in reference point microindentation and recommendations for testing cortical bone: Maximum load, sample orientation, mode of use, sample preparation and measurement spacing.
Variability in reference point microindentation and recommendations for testing cortical bone: Maximum load, sample orientation, mode of use, sample preparation and measurement spacing.
Reference Point Indentation (RPI) is a novel microindentation tool that has emerging clinical potential for the assessment of fracture risk as well as use as a laboratory tool for straight-forward mechanical characterisation of bone. Despite increasing use of the tool, little research is available to advise the set-up of testing protocols or optimisation of testing parameters. Here we consider five such parameters: maximum load, sample orientation, mode of use, sample preparation and measurement spacing, to investigate how they affect the Indentation Distance Increase (IDI), the most published measurement parameter associated with the RPI device. The RPI tool was applied to bovine bone; indenting in the proximal midshaft of five femora and human bone; indenting five femoral heads and five femoral neck samples. Based on the findings of these studies we recommend the following as the best practice. (1) Repeat measurements should be utilised to reduce the coefficient of variation (e.g. 8-15 repeats to achieve a 5-10% error, however the 3-5 measurements used here gives a 15-20% error). (2) IDI is dependent on maximum load (r=0.45 on the periosteal surface and r=0.94 on the machined surface, p<0.05), mode of use (i.e. comparing the device held freehand compared to fixed in its stand, p=0.04) and surface preparation (p=0.004) so these should be kept consistent throughout testing. Though sample orientation appears to have minimal influence on IDI (p>0.05), care should also be taken in combining measurements from different orientations. (3) The coefficient of variation is higher (p=0.04) when holding the device freehand, so it should ideally be kept supported in its stand. (4) Removing the periosteum (p=0.04) and machining the surface of the bone (p=0.08) reduces the coefficient of variation, so should be performed where practical. (5) There is a hyperbolic relationship between thickness and IDI (p<0.001) with a sample thickness 10 fold greater than the maximum indentation depth recommended, to ensure a representative measurement. (6) Measurement spacing does not appear to influence the IDI (p>0.05), so it can be as low as 500µm. By following these recommendations, RPI users can minimise the potential confounding effects associated with the variables investigated here and reduce the coefficient of variation, hence achieving more consistent testing. This optimisation of the technique enhances both the clinical and laboratory potential of the tool.
bone, bone quality, femur, microindentation, reference point indentation
1751-6161
311-324
Jenkins, T.
e079f477-2bcf-41ea-bb7f-bcbbb5f5c945
Coutts, L.V.
90c9e532-5400-4ef8-853f-0e3c311b4f27
Dunlop, D.G.
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Oreffo, R.O.C.
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Cooper, C.
e05f5612-b493-4273-9b71-9e0ce32bdad6
Harvey, N.C.
ce487fb4-d360-4aac-9d17-9466d6cba145
Thurner, Philipp J.
ab711ddd-784e-48de-aaad-f56aec40f84f
Jenkins, T.
e079f477-2bcf-41ea-bb7f-bcbbb5f5c945
Coutts, L.V.
90c9e532-5400-4ef8-853f-0e3c311b4f27
Dunlop, D.G.
5f8d8b5c-e516-48b8-831f-c6e5529a52cc
Oreffo, R.O.C.
ff9fff72-6855-4d0f-bfb2-311d0e8f3778
Cooper, C.
e05f5612-b493-4273-9b71-9e0ce32bdad6
Harvey, N.C.
ce487fb4-d360-4aac-9d17-9466d6cba145
Thurner, Philipp J.
ab711ddd-784e-48de-aaad-f56aec40f84f

Jenkins, T., Coutts, L.V., Dunlop, D.G., Oreffo, R.O.C., Cooper, C., Harvey, N.C. and Thurner, Philipp J. (2015) Variability in reference point microindentation and recommendations for testing cortical bone: Maximum load, sample orientation, mode of use, sample preparation and measurement spacing. Journal of the Mechanical Behavior of Biomedical Materials, 42, 311-324. (doi:10.1016/j.jmbbm.2014.09.030). (PMID:25455607)

Record type: Article

Abstract

Reference Point Indentation (RPI) is a novel microindentation tool that has emerging clinical potential for the assessment of fracture risk as well as use as a laboratory tool for straight-forward mechanical characterisation of bone. Despite increasing use of the tool, little research is available to advise the set-up of testing protocols or optimisation of testing parameters. Here we consider five such parameters: maximum load, sample orientation, mode of use, sample preparation and measurement spacing, to investigate how they affect the Indentation Distance Increase (IDI), the most published measurement parameter associated with the RPI device. The RPI tool was applied to bovine bone; indenting in the proximal midshaft of five femora and human bone; indenting five femoral heads and five femoral neck samples. Based on the findings of these studies we recommend the following as the best practice. (1) Repeat measurements should be utilised to reduce the coefficient of variation (e.g. 8-15 repeats to achieve a 5-10% error, however the 3-5 measurements used here gives a 15-20% error). (2) IDI is dependent on maximum load (r=0.45 on the periosteal surface and r=0.94 on the machined surface, p<0.05), mode of use (i.e. comparing the device held freehand compared to fixed in its stand, p=0.04) and surface preparation (p=0.004) so these should be kept consistent throughout testing. Though sample orientation appears to have minimal influence on IDI (p>0.05), care should also be taken in combining measurements from different orientations. (3) The coefficient of variation is higher (p=0.04) when holding the device freehand, so it should ideally be kept supported in its stand. (4) Removing the periosteum (p=0.04) and machining the surface of the bone (p=0.08) reduces the coefficient of variation, so should be performed where practical. (5) There is a hyperbolic relationship between thickness and IDI (p<0.001) with a sample thickness 10 fold greater than the maximum indentation depth recommended, to ensure a representative measurement. (6) Measurement spacing does not appear to influence the IDI (p>0.05), so it can be as low as 500µm. By following these recommendations, RPI users can minimise the potential confounding effects associated with the variables investigated here and reduce the coefficient of variation, hence achieving more consistent testing. This optimisation of the technique enhances both the clinical and laboratory potential of the tool.

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e-pub ahead of print date: 24 October 2014
Published date: February 2015
Keywords: bone, bone quality, femur, microindentation, reference point indentation
Organisations: Human Development & Health

Identifiers

Local EPrints ID: 373343
URI: http://eprints.soton.ac.uk/id/eprint/373343
ISSN: 1751-6161
PURE UUID: 09c24d1d-d3d0-414f-93c4-9a6c7fdcc176
ORCID for R.O.C. Oreffo: ORCID iD orcid.org/0000-0001-5995-6726
ORCID for C. Cooper: ORCID iD orcid.org/0000-0003-3510-0709
ORCID for N.C. Harvey: ORCID iD orcid.org/0000-0002-8194-2512
ORCID for Philipp J. Thurner: ORCID iD orcid.org/0000-0001-7588-9041

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Date deposited: 15 Jan 2015 16:32
Last modified: 21 Nov 2021 02:54

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Contributors

Author: T. Jenkins
Author: L.V. Coutts
Author: D.G. Dunlop
Author: R.O.C. Oreffo ORCID iD
Author: C. Cooper ORCID iD
Author: N.C. Harvey ORCID iD

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