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Acetabular shell deformation as a function of shell stiffness and bone strength

Lookup NU author(s): Dr Martin Bone, Professor Tom Joyce, Professor David Deehan

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Abstract

Press-fit acetabular shells used for hip replacement rely upon an interference fit with the bone to provide initial stability. This process may result in deformation of the shell. This study aimed to model shell deformation as a process of shell stiffness and bone strength. A cohort of 32 shells with two different wall thicknesses (3 and 4 mm) and 10 different shell sizes (44- to 62-mm outer diameter) were implanted into eight cadavers. Shell deformation was then measured in the cadavers using a previously validated ATOS Triple Scan III optical system. The shell–bone interface was then considered as a spring system according to Hooke’s law and from this the force exerted on the shell by the bone was calculated using a combined stiffness consisting of the measured shell stiffness and a calculated bone stiffness. The median radial stiffness for the 3-mm wall thickness was 4192 N/mm (range, 2920–6257 N/mm), while for the 4-mm wall thickness the median was 9633 N/mm (range, 6875–14,341 N/mm). The median deformation was 48mm (range, 3–187mm), while the median force was 256 N (range, 26–916 N). No statistically significant correlation was found between shell stiffness and deformation. Deformation was also found to be not fully symmetric (centres 180 apart), with a median angle discrepancy of 11.5 between the two maximum positive points of deformation. Further work is still required to understand how the bone influences acetabular shell deformation.


Publication metadata

Author(s): Dold P, Pandorf T, Flohr M, Preuss R, Bone MC, Joyce TJ, Holland J, Deehan D

Publication type: Article

Journal: Proceeding of the Institute of Mechanical Engineers Part H: Journal of Engineering in Medicine

Year: 2016

Pages: 1-6

Online publication date: 17/02/2016

Acceptance date: 21/12/2015

ISSN (print): 0954-4119

ISSN (electronic): 2041-3033

Publisher: Sage Publications Ltd.

URL: http://dx.doi.org/10.1177/0954411916632792

DOI: 10.1177/0954411916632792


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