Sunday, April 10, 2011

Considering the “Wear” rates of alternative materials for hip revision vs Metal on Metal used in the Depuy hip (1 of 3)


Wear rates matter when you are selecting an alternative material to the metal on metal involved in the recent recalls. One of the most important factors in any hip replacement is the rate of wear. Wear rate is important because the process of wear leads to the production of debris. This debris sets up a reaction locally in the joint that leads to the aseptic loosening of the prosthesis. In turn that causes pain and the probability of revision surgery.

 A metal–on-poly implant wears out about 10 times faster than a metal-on-metal one (0.1 and 0.01 mm per year respectively). In either case this is higher than found in ceramic-on-ceramic implants. The table below shows the comparative wear rates.  So Why not chose a ceramic on ceramic hip…or why not use the newest poly with metal?  Seems like an easy choice doesn’t it?  I thought I would look at the medical studies on these options.

 I will look at several of the options (especially the liners) over the next few days. 
The chart below was developed to highlight the characteristics and issues of each option from various resources.  This chart can be used to stimulate a discussion with your orthopedic surgeon re various options that might be available to you if you have decided to undertake a revision.



Wear rate per year
Newer materials
Issues
Metal ball and poly liner
.1mm  (highest wear rates)
.01 with highly crosslinked polyethylene. Polyethylene has been the dominant bearing surface for many years.Highly crosslinked polyethylene, an advancement in this material, is now one of the preeminent alternative bearing
materials available today. This advanced material is highly wear-resistant. It also
offers flexibility and options for surgeons not found in other liner materials

Marathon ploy  liners had average wear rates of 15.4 mm over 3 years in some studies.  Enduron poly had average wear rates reported as  55.5 mm over the same time frame.  That is, the marathon poly had average wear rates 73% below the Enduron poly.

The highest proportion of loosening occurs due to osteoylysis produced by the ultra high molecular weight poly.
Ceramic ball and poly liner
.05mm
Less prone to fracture vs the older ones
More likely to require removal of healthy bone due to size limitations.
Metal ball and metal liner
.01mm
Depuy hip
Depuy Hip with Ion wear debris found locally and systemically.  Recalled from the market.
Ceramic ball and ceramic liner
.0001 mm  (least wear rates)
While early ceramic implants tended to chip and break more easily, they now have dramatically lower fracture rates.

Squeaking noise present which is troublesome to patients in many studies I read from 2010


One thing is certain from the materials I reviewed.  There are issues with every one of the hips and liners.  It seems as though you have to carefully choose the risks you are willing to undertake in relation to the benefits.

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