Saturday, December 25, 2010

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.) I think this first section (Part One: Development of the Product) is very 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.

Part One of Two:  The ASR hip Product/What is it?

1.       Depuy ASR hip implants are part of a class of large diameter, monoblock (single piece in which the femoral head and stem are attached as one.)
1.      Large diameter ball purportedly has the advantage of being more stable and has a better range of motion so less likely to dislocate.
2.      The panelists point out however that  as the diameter of the femoral ball increases, the surface area of the bearing increases apparently resulting in increased contact and faster wearing of the bearing
·         THR (total hip replacement) consists of 3 parts:
1.      femoral stem
2.      femoral head/ball (usually plastic)
3.      Acetabular cup or socket
·         Surgeon hollows out the patient’s femur and implants the femoral stem into the patient’s femor which has a head mounted on top of it.
·         The patient’s femoral head is removed and replaced with a new head implant.
·         The cup is fitted into the existing acetabular socket.
·         When the ball is inserted into the liner, the hip joint is formed.

2.       In the MoM (metal of metal) implant, the metal femoral ball is placed in direct contact with the metal acetabular cap WITHOUT USING A LINER.
·         Removing the plastic liner allegedly allows for the use of the femoral heads that are close to the size of the natural hip.  Thus, there should be less friction. Wear and the chance of dislocation are reduced. 
·         Theoretically, these MoM implants are considerably more durable than other implant materials like ceramic-on-ceramic or meal-on-polyethylene and thus more appropriate for younger patients who need a long lasting replacement.
·         The problem arises because the MoM implant generates:
1.      Greater wear debris
2.      This debris can cause complications
3.      Complications can result in
1)      poor functioning of the current implant
2)      future surgeries
3)      systemic disease risk

Watch for part two: How was the product designed?


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