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Dr. Swanson
MDM Total Hip
Sat Aug 11, 2012 10:25pm

Hi Gino,

The MDM total hip refers to the bearing surface ("Modular Dual Mobility"). It is produced by Stryker Orthopedics and has some potential advantages over conventional bearing surfaces. It is comprised of a small metal or ceramic ball articulating inside a larger polyethylene ball that articulates with an all metal socket that has no polyethylene. Most total hips, in contrast, fix the polyethylene liner to the metal socket and use a large metal or ceramic ball that articulates with the polyethylene liner. (MDM refers only to the ball and socket articulation and has nothing to do with the surgery itself.)

The greatest potential advantage of a dual mobility cup (MDM) is reduction in the risk of dislocation. Before the advent of 32mm and 36mm heads and improved surgical techniques (such as the Capsular Noose Technique), this design served a very important function in reducing the risk of dislocation. However, with dislocation rates using standard designs approaching 0, it is pretty hard to improve on hip stability using the MDM.

There are some potential downsides of a dual mobility cup, the most worrisome being that there are 2 polyethylene articulations (i.e. polyethylene surfaces that rub against metal or ceramic) vs. only 1 articulation in a standard design. This may lead to more wear particles and the possibility of osteolysis (holes in the bone resulting from excessive polyethylene particles). Additionally, there are more (modular) parts and pieces to fit together, which always raises a concern for failure of the modular components.

Overall, the MDM is a reasonable design that has potential advantages, particularly in the hands of surgeons that do not do many total hip replacements and may have a higher dislocation rate. However, for higher volume surgeons usng improved surgical techniques with dislocation rates approaching 0, the MDM has little to offer and may have some disadvantages.

As we see too often, sometimes new implant designs are hyped in the media without data to back the claims. And occasionally, these new designs can lead to catastrophic failures (such as we are now seeing with the large diameter metal on metal hips). So caveat emptor. And remember, MDM has nothing to do with the surgical technique itself.

I hope that this helps.

  • MDM?Gino, Tue Aug 7 6:35pm
    Hi Paulina, I had my 2nd visit the other day at LV DOG / NW, just a six month check-up, pending a hip replacement. Everything good so far, but the pain is starting to increase a bit. I'm still full... more
    • MDM Total Hip — Dr. Swanson, Sat Aug 11 10:25pm
      • Re: MDM Total HipGino, Sun Aug 12 4:21pm
        Thank you Dr. Swanson, yes that helped alot. See you soon. Have a great weekend. Gino
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