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Research Papers

Study of Micromotion in Modular Acetabular Components During Gait and Subluxation: A Finite Element Investigation

[+] Author and Article Information
F. Amirouche1

Biomechanics Laboratory, and Department of Orthopedics,  University of Illinois at Chicago, Chicago, IL 60607

F. Romero

Biomechanics Laboratory,  University of Illinois at Chicago, Chicago, IL 60607

M. Gonzalez

Biomechanics Laboratory, and Department of Orthopedics,  University of Illinois at Chicago, Chicago, IL 60607

L. Aram

 Depuy (Johnson & Johnson), Warsaw, IN 46581-0988

1

Corresponding author.

J Biomech Eng 130(2), 021002 (Mar 25, 2008) (9 pages) doi:10.1115/1.2898715 History: Received February 08, 2006; Revised July 05, 2007; Published March 25, 2008

Polyethylene wear after total hip arthroplasty may occur as a result of normal gait and as a result of subluxation and relocation with impact. Relocation of a subluxed hip may impart a moment to the cup creating sliding as well as compression at the cup liner interface. The purpose of the current study is to quantify, by a validated finite element model, the forces generated in a hip arthroplasty as a result of subluxation relocation and compare them to the forces generated during normal gait. The micromotion between the liner and acetabular shell was quantified by computing the sliding track and the deformation at several points of the interface. A finite element analysis of polyethylene liner stress and liner/cup micromotion in total hip arthroplasty was performed under two dynamic profiles. The first profile was a gait loading profile simulating the force vectors developed in the hip arthroplasty during normal gait. The second profile is generated during subluxation and subsequent relocation of the femoral head. The forces generated by subluxation relocation of a total hip arthroplasty can exceed those forces generated during normal gait. The induced micromotion at the cup polyethylene interface as a result of subluxation can exceed micromotion as a result of the normal gait cycle. This may play a significant role in the generation of backsided wear. Minimizing joint subluxation by restoring balance to the hip joint after arthroplasty should be explored as a strategy to minimize backsided wear.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 4

Loading profile during gait. The resultant force was computed as R=Fx2+Fy2+Fz2 to show the maximum force occurring in the hip during gait.

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Figure 3

Experimental setup of validation experiment

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Figure 2

Contacting areas (acetabular shell/liner and liner/femoral head) involved in the FE model

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Figure 1

FE Model of the acetabular shell, liner, and femoral head. The liner locking mechanism was simulated constraining all degrees of freedom of the nodes located at the same positions as locking tabs of the real-life liner.

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Figure 5

Separation orientations during subluxation. Δx represents the radial separation and Δy represents the axial separation.

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Figure 6

Backside liner micromotion vectors when subjected to gait loading profile. The graph represents the resultant force applied to the femoral head during gait. The reference line represents a reference of the liner position with respect to the resultant force. All images are shown with the same orientation.

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Figure 7

Front-side liner micromotion vectors when subjected to gait loading profile. The graph represents the resultant force applied to the femoral head during gait. The reference line represents a reference of the liner position with respect to the resultant force. All images are shown with the same orientation.

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Figure 8

Liner stress distribution during all the steps analyzed during the gait loading profile. The values shown for the stress are given in MPa.

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Figure 9

FE results for maximum stresses occurred in the liner for each subluxation case

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Figure 10

FE results for maximum micromotion occurred in the liner for each subluxation case

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Figure 11

Micromotion tracks in the liner’s front and back-side surfaces during relocation of the femoral head within the liner after subluxation ((a) and (b)) and ((c) and (d)) during gait.

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Figure 12

Maximum stresses occurred in the liner during the relocation of the femoral head after subluxation. The results shown correspond to the average subluxation case (y=3.3mm, x=0.3mm). During the relocation process, the femoral head impacts and bounces against the liner. The first three peak stress values represent the moments when the femoral head impacts against the liner. After t=0.06s, the femoral head is relocated within the liner.

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