Assessment of head displacement and disassembly force with increasing assembly load at the modular head/trunnion junction of a total hip replacement prosthesis

Darryl Ramoutar, Emilie Crosnier, Faiz Shivji, Anthony Miles, Harinderjit Gill

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Abstract

Introduction
The aim of this study was to assess the effect of assembly force on the strength of head-trunnion interface and to measure the initial displacement of the head on the trunnion with different assembly forces.
Methods
Three assembly load levels were assessed (A:2kN, B:4kN, C:6kN). The stems were mounted in a custom rig and the respective assembly loads were applied to the head at a constant rate of 0.05kN/s (ISO7260-10:2003). Load levels were recorded during assembly. Head displacement was measured with a laser sensor. The disassembly force was determined by a standard pull-off test.
Results
The maximum head displacement on the trunnion was significantly different between the 2 kN group and the other two groups (4kN, 6kN, p=0.029), but not between the 4kN and 6kN groups (p=0.89). The disassembly forces between the three groups were significantly different (mean ± SD, A:1316±223kN; B:2224±151kN; C:3965±344kN; p= 0.007), with increasing assembly load leading to a higher pull-off force. For the 4kN and 6kN groups, a first peak of approximately 2.5kN was observed on the load recordings during assembly before the required assembly load was eventually reached corresponding to sudden increase in head displacement to approximately 150µm.
Discussion
An assembly force of 2kN may be too low to overcome the frictional forces needed to engage the head and achieve maximum displacement on the trunnion and thus an assembly load of greater than 2.5kN is recommended.
Original languageEnglish
Pages (from-to)1675-1678
JournalJournal of Arthroplasty
Volume32
Issue number5
Early online date14 Dec 2016
DOIs
Publication statusPublished - May 2017

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Hip Prosthesis
Hip Replacement Arthroplasties
Head
Lasers

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Assessment of head displacement and disassembly force with increasing assembly load at the modular head/trunnion junction of a total hip replacement prosthesis. / Ramoutar, Darryl; Crosnier, Emilie; Shivji, Faiz; Miles, Anthony; Gill, Harinderjit.

In: Journal of Arthroplasty, Vol. 32, No. 5, 05.2017, p. 1675-1678.

Research output: Contribution to journalArticle

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AU - Miles, Anthony

AU - Gill, Harinderjit

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N2 - IntroductionThe aim of this study was to assess the effect of assembly force on the strength of head-trunnion interface and to measure the initial displacement of the head on the trunnion with different assembly forces.MethodsThree assembly load levels were assessed (A:2kN, B:4kN, C:6kN). The stems were mounted in a custom rig and the respective assembly loads were applied to the head at a constant rate of 0.05kN/s (ISO7260-10:2003). Load levels were recorded during assembly. Head displacement was measured with a laser sensor. The disassembly force was determined by a standard pull-off test.ResultsThe maximum head displacement on the trunnion was significantly different between the 2 kN group and the other two groups (4kN, 6kN, p=0.029), but not between the 4kN and 6kN groups (p=0.89). The disassembly forces between the three groups were significantly different (mean ± SD, A:1316±223kN; B:2224±151kN; C:3965±344kN; p= 0.007), with increasing assembly load leading to a higher pull-off force. For the 4kN and 6kN groups, a first peak of approximately 2.5kN was observed on the load recordings during assembly before the required assembly load was eventually reached corresponding to sudden increase in head displacement to approximately 150µm. DiscussionAn assembly force of 2kN may be too low to overcome the frictional forces needed to engage the head and achieve maximum displacement on the trunnion and thus an assembly load of greater than 2.5kN is recommended.

AB - IntroductionThe aim of this study was to assess the effect of assembly force on the strength of head-trunnion interface and to measure the initial displacement of the head on the trunnion with different assembly forces.MethodsThree assembly load levels were assessed (A:2kN, B:4kN, C:6kN). The stems were mounted in a custom rig and the respective assembly loads were applied to the head at a constant rate of 0.05kN/s (ISO7260-10:2003). Load levels were recorded during assembly. Head displacement was measured with a laser sensor. The disassembly force was determined by a standard pull-off test.ResultsThe maximum head displacement on the trunnion was significantly different between the 2 kN group and the other two groups (4kN, 6kN, p=0.029), but not between the 4kN and 6kN groups (p=0.89). The disassembly forces between the three groups were significantly different (mean ± SD, A:1316±223kN; B:2224±151kN; C:3965±344kN; p= 0.007), with increasing assembly load leading to a higher pull-off force. For the 4kN and 6kN groups, a first peak of approximately 2.5kN was observed on the load recordings during assembly before the required assembly load was eventually reached corresponding to sudden increase in head displacement to approximately 150µm. DiscussionAn assembly force of 2kN may be too low to overcome the frictional forces needed to engage the head and achieve maximum displacement on the trunnion and thus an assembly load of greater than 2.5kN is recommended.

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