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TECHNICAL BRIEFS

# Preclinical Testing of Femoral Hip Components: An Experimental Investigation With Four Prostheses

[+] Author and Article Information
John R. Britton

Center for Bioengineering, Department of Mechanical Engineering,  Trinity College, Dublin 2, Ireland

Patrick J. Prendergast

Center for Bioengineering, Department of Mechanical Engineering,  Trinity College, Dublin 2, Irelandpprender@tcd.ie

J Biomech Eng 127(5), 872-880 (Apr 18, 2005) (9 pages) doi:10.1115/1.1992531 History: Received July 28, 2004; Revised April 18, 2005

## Abstract

Existing standards for the preclinical testing of femoral hip implants have been successful in the objective of guaranteeing the implant’s fatigue strength. There is a need for an experimental test which could ensure prostheses were not susceptible to aseptic loosening. In this study we measure the relative movement between the prosthesis and the bone of four different cemented femoral component designs in in vitro tests. The aim is to determine if differences can be distinguished and whether the differences correlate with clinical performance. The four designs are the Charnley (DePuy International Ltd., UK), the Exeter (Stryker Osteonics Howmedica Corp., USA), the Lubinus SPII (Waldemar-Link GmbH, Germany), and the Müller Curved (JRI Ltd, UK). Five tests were carried out for each femoral component type, giving a total of 20 tests, and their permanent relative displacement (termed migration) and recoverable (i.e., elastic) relative displacement (termed inducible displacement) monitored over one million loading cycles. Considerable variation occurred in the tests. Nonetheless, most femoral components migrated medially, posteriorly, and distally. Most also rotated into varus. Translations of the Charnley $(64microns)$ and Lubinus $(67microns)$ implants were less than the Müller $(72microns)$ and Exeter $(94microns)$ implants, but this difference is not statistically significant. Most of the femoral components had rapid early migration followed by slower steady-state migration. With regard to the steady state inducible displacements of the prostheses, those of the Charnley, Exeter, and Lubinus decreased or were stable with respect to time, whilst those of the Müller typically increased with respect to time. It is concluded that migration is not a suitable basis for in vitro comparison of prosthesis designs. However, inducible displacement trends provide a clinically comparable performance ranking.

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## Figures

Figure 1

Lateral-posterior view of experimental rig with the migration measurement device removed for clarity. Rig consists of two linked levers.

Figure 2

Close-up view of the migration measurement device attached to an implanted composite femur

Figure 3

Time series curves of the femoral components’ translations during the course of the experimental tests. (Negative values imply translation in the opposite sense to that labeled.)

Figure 4

Time series curves of the femoral components’ rotations during the course of the experimental tests. Positive rotation direction defined as follows: Θx, head translates posteriorly and tip anteriorly; Θy, into valgus (head translates laterally, tip medially); and Θz, longitudinal rotation (medial face translates posteriorly and lateral face translates anteriorly).

Figure 5

Mean translations and rotations at one million cycles for the four prosthesis designs tested. Error bars give 90% confidence intervals.

Figure 6

Mean resultant translations and rotations at one million cycles with 90% confidence intervals. (Bars are in order of magnitude.)

Figure 7

Survival curves of the four prosthesis designs tested in this study taken from the Swedish Hip Register (7,46). Adapted from Stolk (47).

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