Tuesday, April 12, 2011

Polyethylene (poly) materials reviewed for use in revised Depuy hips: the risk and rewards (2 of 3).


Overview:
The bearing component most commonly used for total hip replacement in the United States is a metal femoral head (ball) made of either stainless steel, cast or wrought cobalt, a metal-base alloy against a polyethylene (plastic)-lined acetabular cup.

Benefits
  • Durable and versatile
  • Long, successful clinical history
  • Not toxic to the human body
  • Adequate toughness for most lifestyles
Limitations
  • May wear down over time, which can lead to inflammation, bone loss, and/or a revision procedure
What do the studies say?

Please refer to the chart in part one of three of this series for other risks and rewards.

I chose to print out a few conclusions from 2008-2010.

(1)

Distribution of polyethylene wear particles and bone fragments in periprosthetic tissue around total hip joint replacements. 

Zolotarevova E, Entlicher G, Pavlova E, Slouf M, Pokorny D, Vesely F, Gallo J, Sosna A. Acta Biomater. 2010 Sep;6(9):3595-600. Epub 2010 Apr 22.  Faculty of Science, Charles University, Hlavova 8, 128 40 Prague 2, Czech Republic. ezolotarevova@gmail.com

Bottom Line:

Ultra-high molecular weight polyethylene (UHMWPE) wear particles play a significant role in failures of total joint replacements (TJRs). In this work, we investigated the distribution of these wear particles in periprosthetic tissues from 9 revisions and found that the there is a statistically significant relationship between the numbers of wear particles in the individual zones and the extent of tissue damage in these zones.  It can be concluded with certainty that wear particles associated with this ulta-high molecular weight poly are one of the main causes of aseptic joint implant failure
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(2)

Reduction of osteolysis with use of Marathon cross-linked polyethylene. A concise follow-up, at a minimum of five years, of a previous report.

Stiftung Orthopädische Universitätsklinik, Schlierbacher Landstrasse 200A, 69118 Heidelberg, Germany.

Abstract

We previously reported wear data at a minimum of two years following thirty-four total hip replacements with a Marathon cross-linked polyethylene liner and twenty-four replacements with a conventional (gamma-sterilized-in-air) Enduron polyethylene liner. In this current study, with sequential five-year radiographs, wear rates were determined with use of linear regression analysis. The Marathon polyethylene had average wear rates of 15.4 mm(3)/yr and 8.0 mm(3)/million cycles. The Enduron polyethylene had average wear rates of 55.5 mm(3)/yr and 29.9 mm(3)/million cycles. The adjusted volumetric wear rate of the Marathon polyethylene was 73% lower than that of the Enduron polyethylene (p = 0.001). Osteolysis developed in eight of the twenty-four hips with an Enduron liner but was not apparent in any hip with a Marathon liner.

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Why did I choose to show you these studies?  All of these materials have issues and you should have a conversation with your ortho surgeon to determine why he/she has chosen this new material for you.  Lots of options.  Risk/ reward is an appropriate consideration.   There is no perfect implant which has no risks.  You as a patient should be informed on your choices.

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