Sunday, December 26, 2010

Part Two of Two: How was it designed? Excerpts from the HarrisMartin Conference ( on the issues surrounding the Depuy hip recall held in November

I think this first section Part One: Development of the Product/How it was designed,  is nicely presented in language that is easy to follow. The course is worth purchasing for those of you who want to study the different implications and ramifications of the hip recall issues.

1.       The Depuy ASR hip has an “open back” design which means the acetabular component is designed to fit snugly without the use of screws or adhesive (cement.)  The outer surface of the hip cup is rough and porous allowing for the patient’s bone to grow into the back of the cup and secure it in place.
·         This feature is supposed to have the advantage of being a very strong and secure bond when the surface combines with the bone.
2.       One of the designers of the hip allegedly stated that the hip design of the Depuy hip which  was based on the Birmingham hip replacement (BHR), did not have the same characteristics as the Depuy hip.  The Depuy hip turned out to have a SMALLER acetabular cup so the suction tool used to place them was ineffective in implanting them. 
3.       A new tool had to be designed to put this piece in place but in order to accommodate this new tool, Depuy reportedly decided to reduce the rim size of the cup by about 5 degrees, making the ASR less forgiving for implanting surgeons and thus more prone to failure.
4.       The ASR design may be flawed because it uses the lowest tolerances in the industry.
·         The ASR design contains a size difference between the ball and cup of 80 and 120 microns vs the other MoM implants which have tolerances between 100 and 240 microns.
5.       When the size difference between the ball and cup becomes too small, the edge of the femoral ball purportedly wears against the edge of the cup because the fluid film barrier that provides the lubrication to the two surfaces is too thin.
6.       One of the inventors on the design team for the hip (Dr. Schmalzried) stated in an interview in Feb of 2010 in the NY Times article that he and the Depuy officials realized within the last two years, the ASR cup might be more challenging to implant properly than the competing cup.
7.       Dr. Schmalzried received $3.4 million in payments for his design and related fees between 2008-2010.
8.       In a study conducted by Schmalzried in 2005, he and another investigator asserted that metal ion levels are well within safe levels laid down by toxicologists.  They did admit that there are limitations to the measurement of these levels since the tests measure the free circulating ions in the blood rather than the total ion levels.
·         Metal particles have been shown to spread through the reticuloendothelial system (lymph nodes, liver, spleen) in patients with MOM implants.
·         If the implants were not positioned properly however, the ware rates can increase significantly and the metal levels can exceed the normal limits and cause tissue necrosis.

Excerpts from the HarrisMartin Conference ( on the issues surrounding the Depuy hip recall held in November. You can purchase this full course directly from HarrisMartin Publishing.

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