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Research Papers

Design Optimization of a Total Hip Prosthesis for Wear Reduction

[+] Author and Article Information
George Matsoukas

Department of Mechanical and Materials Engineering, Queen’s University, McLaughlin Hall 305, 130 Stuart Street, Kingston, ON, K7L 3N6, Canadageorge@traxtal.com

Il Yong Kim1

Department of Mechanical and Materials Engineering, Queen’s University, McLaughlin Hall 305, 130 Stuart Street, Kingston, ON, K7L 3N6, Canadaiykim@me.queensu.ca

1

Corresponding author.

J Biomech Eng 131(5), 051003 (Mar 20, 2009) (12 pages) doi:10.1115/1.3049862 History: Received February 13, 2008; Revised November 04, 2008; Published March 20, 2009

Aseptic loosening from polyethylene debris is the leading cause of failure for metal-on-polyethylene hip implants. The accumulation of wear debris can lead to osteolysis, the degradation of bone surrounding the implant components. In the present study, a parametric three-dimensional finite element model of an uncemented total hip replacement prosthesis was constructed and implanted into a femur model constructed from computed tomography (CT) scan data. Design optimization was performed considering volumetric wear as an objective function using a computational model validated in a previous study through in vitro wear assessment. Constraints were used to maintain the physiological range of motion of wear-optimum designs. Loading conditions for both walking and stair climbing were considered in the analysis. In addition, modification of the acetabular liner surface nodes was performed in discrete intervals to reflect the actual wear and creep damage occurring on the liner surface. Stair climbing was found to produce 49% higher volumetric wear than walking. Using a sensitivity analysis, it was found that the objective function sensitivity to the chosen design variables was identical for both walking and stair climbing. The greatest reduction in volumetric wear achieved while maintaining a physiological range of motion was 16%. It was found that including nodal modification in the sensitivity analysis produced little or no difference in the sensitivity analysis results due to the linear nature of volumetric wear progression. Thus, nodal modification was not used in optimization. An increase in the maximum contact pressure was observed for all wear-optimized designs, and an increase in head-liner penetration was found to be related to a reduction in volumetric wear.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Three dimensional model and mesh of an uncemented implant, femoral head, acetabular liner and shell, and right proximal femur constructed in ALTAIR HYPERMESH

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Figure 2

Hip contact forces and motions for walking (top) and stair climbing (bottom) (23)

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Figure 3

Muscle attachment sites on the proximal femur (left) defined according to Heller (25) with corresponding muscle loads (21)

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Figure 4

Nonlinear stress-strain material model for UHMWPE at 37°C adapted from Cripton (26) and used in the liner surface damage simulation

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Figure 5

Initial design variable selection

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Figure 6

Simulation procedure used to optimize for volumetric wear

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Figure 7

Wear, creep, and total damage depth distributions for walking and stair climbing shown from left to right without nodal modification. The top of the figure denotes the superior direction.

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Figure 8

A comparison between walking and stair climbing with nodal modification for wear and creep every 250,000 cycles

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Figure 9

Sensitivity analysis results for volumetric wear, maximum wear depth, and maximum creep depth during walking

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Figure 10

Sensitivity analysis results for volumetric wear, maximum wear depth, and maximum creep depth during stair climbing

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Figure 11

Sensitivity analysis results for volumetric wear, maximum wear depth, and maximum creep depth during walking with nodal modification every 250,000 cycles

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Figure 12

Sensitivity analysis results for flexion, abduction, and external rotation, the most likely types of motion in which impingement could occur without nodal modification

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Figure 13

Damage distribution comparison of the liner surfaces for initial design 6 and optimum design 6. Wear, creep, and total damage depth distributions are shown from left to right. The top of the figure denotes the superior direction.

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Figure 14

Damage distribution comparison of the liner surfaces for initial design 4 and optimum design 4. Wear, creep, and total damage depth distributions are shown from left to right. The top of the figure denotes the superior direction.

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Figure 15

The maximum contact pressure at each loadstep for initial and optimum designs

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Figure 16

Discretized muscle loading during walking

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Figure 17

Discretized muscle loading during stair climbing

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