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The effect of geometry and abduction angle on the stresses in cemented UHMWPE acetabular cups--finite element simulations and experimental tests.

Korhonen RK, Koistinen A, Konttinen YT, Santavirta SS, Lappalainen R - Biomed Eng Online (2005)

Bottom Line: An increase in the abduction angle increased contact pressure in the IP model, but this did not occur to any major extent with the Lubinus eccentric model.FE results were consistent with experimental tests and acetabular cup deformations.FE analyses showed that geometrical design, thickness and abduction angle of the acetabular cup, as well as the clearance between the cup and head do change significantly the mechanical stresses experienced by a cemented UHMWPE acetabular cup.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Applied Physics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland. rami.korhonen@uku.fi

ABSTRACT

Background: Contact pressure of UHMWPE acetabular cup has been shown to correlate with wear in total hip replacement (THR). The aim of the present study was to test the hypotheses that the cup geometry, abduction angle, thickness and clearance can modify the stresses in cemented polyethylene cups.

Methods: Acetabular cups with different geometries (Link: IP and Lubinus eccentric) were tested cyclically in a simulator at 45 degrees and 60 degrees abduction angles. Finite element (FE) meshes were generated and two additional designs were reconstructed to test the effects of the cup clearance and thickness. Contact pressures at cup-head and cup-cement interfaces were calculated as a function of loading force at 45 degrees, 60 degrees and 80 degrees abduction angles.

Results: At the cup-head interface, IP experienced lower contact pressures than the Lubinus eccentric at low loading forces. However, at higher loading forces, much higher contact pressures were produced on the surface of IP cup. An increase in the abduction angle increased contact pressure in the IP model, but this did not occur to any major extent with the Lubinus eccentric model. At the cup-cement interface, IP experienced lower contact pressures. Increased clearance between cup and head increased contact pressure both at cup-head and cup-cement interfaces, whereas a decreased thickness of polyethylene layer increased contact pressure only at the cup-cement interface. FE results were consistent with experimental tests and acetabular cup deformations.

Conclusion: FE analyses showed that geometrical design, thickness and abduction angle of the acetabular cup, as well as the clearance between the cup and head do change significantly the mechanical stresses experienced by a cemented UHMWPE acetabular cup. These factors should be taken into account in future development of THR prostheses. FE technique is a useful tool with which to address these issues.

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Peak contact pressure at cup-cement interface as a function of loading force and abduction angle. a) Lubinus eccentric and IP1, b) Lubinus concentric and IP2.
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Figure 8: Peak contact pressure at cup-cement interface as a function of loading force and abduction angle. a) Lubinus eccentric and IP1, b) Lubinus concentric and IP2.

Mentions: At the interface between the acetabular cup and the cement, the contact pressure increased as a function of abduction angle in all models (Figs. 7 and 8). Due to the larger contact area between cup and head and the smaller deformation of the cup, the contact pressure remained lower on the outer surface of the IP cup at all abduction angles (Figs. 7a, b and 8a). A decreased thickness of the acetabular cup (Lubinus eccentric → concentric) (Figs. 7a,c and 8) and the increased clearance between IP cup and femoral head (Figs. 7b,d and 8) elevated contact pressures on the outer surfaces of the cups.


The effect of geometry and abduction angle on the stresses in cemented UHMWPE acetabular cups--finite element simulations and experimental tests.

Korhonen RK, Koistinen A, Konttinen YT, Santavirta SS, Lappalainen R - Biomed Eng Online (2005)

Peak contact pressure at cup-cement interface as a function of loading force and abduction angle. a) Lubinus eccentric and IP1, b) Lubinus concentric and IP2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1173123&req=5

Figure 8: Peak contact pressure at cup-cement interface as a function of loading force and abduction angle. a) Lubinus eccentric and IP1, b) Lubinus concentric and IP2.
Mentions: At the interface between the acetabular cup and the cement, the contact pressure increased as a function of abduction angle in all models (Figs. 7 and 8). Due to the larger contact area between cup and head and the smaller deformation of the cup, the contact pressure remained lower on the outer surface of the IP cup at all abduction angles (Figs. 7a, b and 8a). A decreased thickness of the acetabular cup (Lubinus eccentric → concentric) (Figs. 7a,c and 8) and the increased clearance between IP cup and femoral head (Figs. 7b,d and 8) elevated contact pressures on the outer surfaces of the cups.

Bottom Line: An increase in the abduction angle increased contact pressure in the IP model, but this did not occur to any major extent with the Lubinus eccentric model.FE results were consistent with experimental tests and acetabular cup deformations.FE analyses showed that geometrical design, thickness and abduction angle of the acetabular cup, as well as the clearance between the cup and head do change significantly the mechanical stresses experienced by a cemented UHMWPE acetabular cup.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Applied Physics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland. rami.korhonen@uku.fi

ABSTRACT

Background: Contact pressure of UHMWPE acetabular cup has been shown to correlate with wear in total hip replacement (THR). The aim of the present study was to test the hypotheses that the cup geometry, abduction angle, thickness and clearance can modify the stresses in cemented polyethylene cups.

Methods: Acetabular cups with different geometries (Link: IP and Lubinus eccentric) were tested cyclically in a simulator at 45 degrees and 60 degrees abduction angles. Finite element (FE) meshes were generated and two additional designs were reconstructed to test the effects of the cup clearance and thickness. Contact pressures at cup-head and cup-cement interfaces were calculated as a function of loading force at 45 degrees, 60 degrees and 80 degrees abduction angles.

Results: At the cup-head interface, IP experienced lower contact pressures than the Lubinus eccentric at low loading forces. However, at higher loading forces, much higher contact pressures were produced on the surface of IP cup. An increase in the abduction angle increased contact pressure in the IP model, but this did not occur to any major extent with the Lubinus eccentric model. At the cup-cement interface, IP experienced lower contact pressures. Increased clearance between cup and head increased contact pressure both at cup-head and cup-cement interfaces, whereas a decreased thickness of polyethylene layer increased contact pressure only at the cup-cement interface. FE results were consistent with experimental tests and acetabular cup deformations.

Conclusion: FE analyses showed that geometrical design, thickness and abduction angle of the acetabular cup, as well as the clearance between the cup and head do change significantly the mechanical stresses experienced by a cemented UHMWPE acetabular cup. These factors should be taken into account in future development of THR prostheses. FE technique is a useful tool with which to address these issues.

Show MeSH
Related in: MedlinePlus