Depuy Hip Replacement Recall

Depuy, a Johnson and Johnson company, issued a voluntary recall of their ASR hip replacement system in September of 2010.  The ASR hip replacement is a large metal ball that rotates inside a thin metal shell.  The recall was in response to findings in the British joint registry of an unusually high rate of revisions.  There are multiple possible explanations for this higher than normal revision rate, which I will address below.  The ASR hip replacement has been available in the United States for about 3 years, so if your hip replacement was preformed before 2007, you are unaffected by this recall. 

The term "recall" to me suggest that some sort of defect was discovered with this ASR implant.  However, that is not the case.  The cause of the poor outcomes is not completely clear.  There are patients that have done and continue to do very well with their ASR hip replacement, but an unusually high number of patients are having problems with their ASR hip replacement.

What does a patient with an ASR hip replacement need to do?

If you have an ASR hip replacement from Depuy, you should have been notified by your surgeon.  Depuy sent out a mailing to all orthopedic physicians with the name of every ASR patient that physician had performed and the physicians are expected to notify their patients.  If you have not been notified and are not certain what type of implant you have, then contact your surgeon or the hospital where the surgery was preformed. 

If you have an ASR hip replacement, you need to contact Depuy and get a patient reference number so that the cost of the work up of your ASR hip replacement is covered by Depuy.  If you do not file the paperwork with Depuy, it is possible that your health insurance company may refuse to pay for your medical bills. 

You then need to see an orthopedic surgeon and have your blood tested for metal ion levels.  If the metal ion levels in your blood are high (>7), then you probably need to consider getting your hip revised.  If your metal ion levels are normal, but you are having considerable pain, then an ultrasound or metal suppressed MRI may be ordered to see if you have any fluid around your hip replacement.  If you have fluid around your hip replacement, you should consider a hip revision.  A hip aspiration may also be preformed.  If you have normal metal ion levels and are not having hip pain, then you should recheck your metal ion levels in a year or sooner if you develop pain.

Why is the ASR failing at a higher rate than other hip replacements?

This is a million dollar question that every trial attorney is trying to answer.  I have a few theories, but little facts to back them up.

First, I think that the problem with the ASR is probably not isolated to Depuy's large metal on metal components.  The whole family of monoblock acetabular components with a large metal on metal bearing surface have had some reported problems.  About a year or so ago, Dr. Larry Dorr, a prominent orthopedic physician from San Diego, sounded the alarm about the Zimmer Durom monoblock acetabular components.  He was seeing a higher than expected rate of loosening of the acetabular shell.  Zimmer initially said they were not seeing a high failure rate; however, Dr. Dorr sent out a memo to every orthopedic surgeon in AAHKS stating his concern with the Durom cup.  Zimmer then said that the problem was with the surgical technique and operating surgeon, but if Dr. Dorr, who is a world expert at hip replacement, was having problems, then every orthopedic surgeon would have problems.  Zimmer finally restricted the use of the Durom cup to physicians that attended a special cadaver lab, which along with the swarm of trial attorneys basically ended the use of the Durom acetabular shell in the United States.  The Biomet M2M cup also had some reported problems.  This cup has been redesigned, but the earlier acetabular shell had little cut outs that allowed the cup to be attached to the insertion handle.  These cut outs decreased the effective articular surface.

These monoblock acetabular cups (Depuy's ASR, Stryker's Cormet, Smith & Nephew's Birmingham, Zimmer's Durom, Biomet's M2M, Wright's Conserve) have a couple things in common which could explain some of their potential problems.  First, the acetabular cups are less than a hemisphere.  Most of them are around 158 to 169 degrees, which is necessary for hip resurfacing.  This means there is less material or acetabular shell to bear the load of the joint.  Less surface area means greater pressure which means more wear.  This increased wear may not be an issue if the components are in perfect position, but slight changes in the angle of the acetabular cup may have grave consequences.  The reissued Durom cup is now a full hemisphere.  The wear in a metal on metal monoblock cup is obviously metal ions.  Second, these monoblock cups offer the surgeon great hip stability, which may make surgeons less concerned with their cup angles because they would not have to worry about hip dislocations.  Third, all of these cups do not offer additional fixation with screws.  The modular acetabular components allow the surgeon to screw the acetabular cup into the acetabular bone so that the cup can not move while the bone grows into the acetabular cup.  The monoblock acetabular components can not have screw holes.  Fourth, these monoblock shells are thinner and more flexible than the modular shells.  It is possible that the shells deform when they are impacted into hard bone.  The tolerance on these monoblock shells is around 60 to 200 microns to improve wear rates.  If the shell deforms more than 60 microns or so, then the bearing surface would experience equatorial seizing and the motion of the hip joint would cause considerable shear stress at the bone / acetabular shell interface and loosen the implants.

Another possibility includes a theoretical problem with the way that Depuy manufactured the surface of the cup or femoral head.  The polishing of the metal could have been different than other companies or their tolerance (the difference between the inner diameter of the cup and the outer diameter of the femoral head) could have been a little off.

Summary

I am impressed with Depuy's handling of this recall.  They have taken responsibility for the poor outcomes of their implant and refrained from blaming the surgeon or surgical technique.  These sorts of problems can arise with any new product, but I feel they have responded in an ethical manner.