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Ceramic on Metal

The world's first ceramic on metal hip implant has been given approval by the FDA (USA Food and Drug Administration). Manufactured by DePuy, a subsidiary of Johnson& Johnson, it's called The Pinnacle CoMplete Acetabular Hip System.

Like other total hip replacement systems the device comes in two parts but now for the first time the femoral component will made from ceramic and the pelvis side from metal.

Previously hip implants had been made from: -

  • Metal-on-metal or metal-on-polyethylene
  • Ceramic-on-ceramic or ceramic-on-polyethylene

Why a New System?

Metal-on-metal hip implants are cheaper than ceramic and longer wearing than metal-on-polyethylene and that is what DePuy have been manufacturing until now.

However, in the last year they have been forced to recall their entire ASR system.

What's the Problem with Metal?

Metal-on-metal hip implants suffer from one major problem - they are made of metal! When the two metal surfaces of the implant rub together they shed minute bits of metal that can cause metallosis. In turn this can lead to damage to soft tissue and rejection of the new hip. Furthermore the metal ions are known to enter the blood stream and so be transported around the body and even across the placenta and so may affect the foetus.

The Recalls

The DePuy recall of its ASR system is affecting over 93,000 patients. Many of these people have been in excruciating pain, unable to walk or even weight bear on the affected leg and are now having to endure further surgery to remove and replace the faulty implant.

A British study has stated that up to 49% of ASR patients may need to undergo such revision surgery.

But the ASR system is not the only metal-on-metal system manufactured by DePuy - they also manufacturer the Pinnacle System.

How Safe is the Existing Pinnacle System?

Good question.

Over the last year there has been growing concerned expressed from patients and their representatives about the safety of this system. Concerns which have been reported to the FDA,

The Pinnacle system has also been found to shed metal ions with similar consequences to the ASR system and there is talk in legal circles about a possible recall during 2011 or 2012.

Is the New System Safe?

Patients as Guinea Pigs

Guinea Pig

It's never easy to test out a new implant. Whether it works or not and how safe it is can really only be determined after it has been implanted in a large group of people and used over a number of years. But waiting for the results of such a trial delays implantation. This not only hits profit margins but may also deny patients the choice of a better implant. As a consequence the current system allows a manufacturer to claim that a new device is safe simply by demonstrating that it is similar to an existing licensed product.

In effect the patients are testing out the hip implants for the manufacturers.

Comparison Studies

An alternative approach is to implant the new device in a smaller group of people (say a couple of hundred willing patients) and compare it with an existing system. Fewer guinea pigs but hopefully good results. This is what DePuy chose to do with its new ceramic on metal system.

The new device was implanted into 194 patients and the outcomes compared with 196 people who had received an existing metal-on-metal implant. After two years of use no clinical difference was found between the two groups. Sounds like good news.

The problem is with the design of the study, which raises two important questions: -

Firstly; why did DePuy chose (and the FDA allow)the comparison to be made with a metal-on-metal system? A system which is known to cause serious health problems. Why wasn't it compared with a metal-on-poly or ceramic-on ceramic system?

Secondly; two years isn't long in the life of a hip replacement. Is that sufficient time to really test out this new system? Again a difficult decision but should DePuy's need to bring out an alternative take priority over a longer study?

Into The Future

It is not particularly reassuring to learn that one of the conditions imposed by the FDA is that DePuy closely monitors its ceramic on metal patients for adverse events and regularly measures the levels of metal ion concentration in their blood.

From a patient's perspective that just means that the signs of a failing hip may be picked up earlier but it won't prevent the need for revision work should the hip fail.

All patients ask for is a safe, well-designed hip implant that will last a life time. Let's home DePuy's ceramic on metal system will be what the patient ordered.




Related Links: 

Metallosis 
The Depuy Recall


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