Dear Christian

The potential systemic risks due to accumulation of metal ions its a reality and the American Academy of Orthopedic Surgeons has participated in numerous seminars,conferences and publications to verify this real possibility.

Since 2007, AAOS has offered numerous educational papers, posters and scientific exhibits with the latest research and studies on metal-on-metal (MoM) arthroplasty at each AAOS Annual Meeting. The AAOS website (www.aaos.org) has more than 400 references (AAOS Now articles, information statements, member alerts, orthopaedic journal articles, etc) on MoM-related information

In February 2011, AAOS sent a letter to more than a dozen medical specialty societies informing them of the latest communication released from the FDA and encouraging them to share it with their membership.

Created two areas on the public education website www.orthoinfo.org citing potential questions and answers for patients who may have a metal on metal hip. Content continues to be updated as appropriate. Provides links to the FDA, media materials, and patient information created by a consortium of specialty societies and AAOS.

dear Nelson

I know that, but the problem is that North American orthopaedics surgeons are mostly experienced with resurfacing and large head MoM THA. Experience in Europe with 2d generation MoM is much longer, began in 1988 with Weber 28mm MoM Metasul introduction in the market, with no big problems for more than 20 years like ARMD or pseudotumors that appeared in the mid 2000 with resurfacing... The question is that MoM hip replacement must not be treated as a whole, but by design family (28 and 32 mm THA versus resurfacing versus large head MoM THA) and the question is "are health authorities in EU in capacity to discriminate or not"?

Dear Christian

i agree with your comment .

The experience is very important in decision making

Thank you very much

Best regards

Dear Christian :

I agree to you . There are many Departments in Europe employing MoM for many years without significant problems. In my personal opinion the problems have appeared with prosthesis of resurfacing , and more specifically to a specific model. I consider that good indication and an appropriate model MoM is an alternative as arthroplasty reliably

I have worked in orthopedic implant materials r&d for 40+ years. MOM implants were around when I started, and were phased out because they caused a variety of problems. How and why MOM hips got resurrected in recent years is a mystery. It suggests a lack of information and lack of understanding of design principles for low-speed high-load articulations. If anyone would like a list of the fundamental problems MOM designs pose, feel free to ask and I will provide one.

I agree entirely with the considerations of Dr. Daniels. It is a real "mystery" to see how drugs, procedures, implants, etc. are rediscovered periodically in an ondulating line (i.e. 30-40 years) after their failure in the past. I was a young resident in the 60s when McKee-Farrar (MoM) prosthesis was introduced and rejected in favour of Charnley prosthesis (poly-metal), then in the 70s the Wagner resurfacing prosthesis (let me remind you of Smith-Petersen cup in the 40s !) followed the same road of rejection. In earlier years the Judet short stem has been a disaster (in the 50s). Renaissance is a wonderful phenomenon. However, in the medical practice we must explore not only the benefits but also the drawbacks of the past. I do not believe we have learned the lessons of the past well.

@Panayot Tanchev - Well said! A couple of thoughts:

1. Any engineer with experience in design of articulating or rotating bearings knows that "like on like" (e.g. MOM) usually results in high friction and wear--unless there is a lubricant present AND the relative surface speeds are high enough to provide hydrodynamic effects. The latter is certainly not the case in the hip, where in addition the loads across the joint are several times body weight during walking, and the lubricant is just a water solution of proteins.

2. In walking, the loads across the hip are not only high, they are in the form of a series of impacts. A MOM hip has no ability to dissipate these loads and instead passes them on directly to the bone implant interface, increasing the potential for loosening. In an implant with a metal ball and a UHMWPE cup, the cup deforms under such loads and partly absorbs and dissipates them due to the viscoelasticity of the polymer.

3. In addition the low stiffness of UHMWPE allows it to deform under load and ensure better congruency across the interface with the metal hip ball than is possible with MOM. In contrast, a MOM hip must have and retain near-perfect congruency in order to prevent the occurrence of locally concentrated loads which obviously contribute to wear.

There are more things wrong with MOM, but those are three of the mechanical considerations. By the way, a hip with UHMWPE ball and a metal cup would also be a disaster--again for reasons of mechanics of materials at articulating interfaces.

In my opinion the future of MOM prosthesis is to follow the "deja vu" fiasco of McKee-Farrar's one in the 60's. One can only prophetize that in 20 years a "novel MOM" will appear once again following the ondulating curve of renaissance and oblivion.

@Brian Derbyshire - If the hip joint simulator studies you mention suggest MOM hip designs are a good idea, then the simulation is a poor one. GIGO, as the saying goes. First, do the simulators employ cyclic (e.g 1/s) impact loads of ca. 3X body weight (as is the case in human gait)? If not the load cycle is a poor simulation. Are the studies done at body temperature? Is the lubricant used an accurate simulation of synovial fluid including proper levels of dissolved oxygen? Even if the answers are all yes, I doubt the simulation assesses the effect of the high modulus MOM interface transmitting undissipated impact loads to the interface between implants and bone and fostering interface loosening. Or is that covered too? Finally, the extensive long-term data (e.g. the Swedish Hip Registry) indicate the survival of classic Co alloy vs UHMWPE hips is ca. 90% at 15 years. Does this suggest to you that replacing the classic design with a new one is an urgent clinical need?

I agree entirely with Dr. Daniels. In my opinion the answer to the last question is - no. It does not mean that evidence-based studies should not be carried out. Science must develop giving new solutions and improving the weakest points of the known products.

@Brian Derbyshire

I suspect that major pitfalls of Leeds simulator were:

- not taking into account 'microseparation'

- not considering the 'whole system' (it seems that often problems arise from loose coupling betwwen the head and the neck)

I would like to have your opinion about that!

I think metal-on metal designs no longer have a chance to be first or second trend of hip surgeons.

there is no future in MoM hip

I agree with Dr Picardi, I do not think there is a future for the friction pair MoM