Metal Ion Issues

Larger cups and optimal positioning produced lowest ion levels and wear

In a review of 585 blood serum evaluations following hip resurfacing, only femoral size and cup inclination were found to have an effect on ion levels, according a study by orthopedic investigators.

The findings were presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons.

David J. Langton, MRCS, and his colleagues also found that the size of the coverage angle of the acetabular component contributed significantly to its tolerance of suboptimal positioning.

"Larger joints, it must be emphasized, tolerated suboptimal cup position," he said. "This must be taken into account in all analyses."

Inverse relationships

Using routinely obtained blood serum metal ion levels from patients under the care of the two senior authors of the paper being presented - both highly experienced hip resurfacing surgeons - metal ion results were analyzed regarding their relationship to femoral and acetabular component size and orientation, UCLA activity score, age, time post surgery and postoperative femoral head/neck ratios.

Langton reported an inverse relationship between metal ion levels and femoral size. A smaller acetabular coverage arc was associated with higher metal ion levels.

Another significant inverse correlation was noted by Langton between metal ion levels and contact patch to rim (CPR) distance. CPR is a measurement that relates the position of the articular contact patch with the patient in standing position to the cup rim. According to the abstract, CPR less than 5 mm is associated with a 50% chance of ion levels greater than 30 mg/L.

Words of warning

Langton warned the audience, "To increase metal ion levels as quickly as possible, use as small a bearing diameter as possible, use a cup with the smallest coverage arc, and combine very high anteversion with high inclination."
He concluded, "Cups placed with angles between 40° and 50° inclination and 10° to 20° anteversion have the lowest ion levels and the lowest rates of volumetric wear."

Reference:

Langton D, Jameson S, Joyce T, et al. A review of 585 serum metal ion results post hip resurfacing: cup design and position is critical. Paper 006. Presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons. March 9-13. New Orleans.

Langton has received research or institutional support from DePuy, a Johnson & Johnson Company, DJ Orthopaedics; he has also received miscellaneous non-income support (e.g., equipment or services) from DePuy, a Johnson & Johnson Company.

• DePuy makes patient safety and health a top priority and is continually evaluating data about its products. Most ASR hip replacement surgeries have been successful. However, data recently received by the company shows that more people than expected who received the ASR hip experienced pain and other symptoms that lead to a second hip replacement surgery, called a revision surgery.
• For this reason, DePuy Orthopaedics is recalling its ASR™ XL Acetabular Head System and DePuy ASR™ Hip Resurfacing System. This recall means additional testing and monitoring may be necessary in hip replacement patients.  In some cases, patients may need additional surgery.
• DePuy is working closely with health care professionals worldwide to contact patients with ASR hip implants.  Most people with ASR Hip System implants do not experience problems, but it is important that patients with ASR Hip System implants be evaluated with by a surgeon. Patients with problems reported different symptoms with their ASR hip implant, including pain, swelling, and problems walking. 

• DePuy intends to cover reasonable and customary costs of monitoring and treatment for services, including revision surgeries, associated with the recall of ASR.

Click here for the press release

Click here for the patient information page on our web site

Click here for an image of the ASR Hip System

Medical Release Form:

Patients with an ASR Hip are asked to complete the form and bring it with them to the appointment to give their surgeons permission to share information directly with DePuy.

Click here for the recall notice

This notice was shared with hospitals and surgeons regarding the ASR recall.

Reference:
Langton D, Jameson S, Joyce T, et al. The incidence of adverse reactions to metal debris (ARMD) following hip resurfacing with the articular surface replacement (ASR) and Birmingham Hip Resurfacing systems (BHR). Presented at the British Orthopaedic Association Annual Congress 2009. Sept. 15-18, 2009. Manchester.

Patients and prospective patients are always concerned about the complications that could occur after a hip resurfacing surgery. The typical problems include femur neck fractures, dislocations, loose acetabular cups, improperly positioned acetabular cups, high metal ions, infections, pseudotumors, ALVAL and metalosis.

There has been a lot of discussion among patients on discussion groups about the high metal ion issue and pseudotumors.  I am not a doctor or medically trained.  I am a Patient Advocate, Hip Resurfacing Patient and Mechanical Engineer.  I had the opportunity to attend the  Second Annual U.S. Comprehensive Course on Total Hip Resurfacing Arthroplasty October 24–25, 2008 Los Angeles, CA.  I listened to discussions about the metal ion issues and pseudotumors. I am going to explain what I learned in simple, non-medical terms since that is all I can do.

As an observer, I learned that the high metal ion issue has occurred in a small number of cases as a post op problem after a hip resurfacing. One of the most likely reasons, according to the experienced surgeons and presenters at the course, was the incorrect placement of the acetabular cup which resulted in additional wear on the bearing surface between the acetabular cup and the femur cap component.  The hip resurfacing device is really a metal bearing made of  High Carbon Cobalt-Chromium alloys.  A bearing is designed to equally spread out the load over the load bearing components.  If the components are not aligned properly, then only part of the bearing is loaded resulting in much more wear in that area possibly causing a high metal ion level. It was also explained that women seem to have more problems with high metal ions than men. Perhaps, this is due to the fact that most women use smaller sized hip resurfacing devices which causes more loading on the bearing surfaces than the men's larger sized devices.

When there is an abnormally high metal ion release from misplaced components, it seems to cause the surrounding tissue and bone to react adversely.  The surrounding tissue and bone tends to become abnormal.  Some doctors call the tissue reaction pseudotumors, AVAL (aseptic lymphocyte dominated vasculitis associated lesion), & others call it metalosis.  Whatever name given to the abnormal reaction, it is not good to have this happening around the hip device since it could become loose, pain could result  and possibly more severe medical reactions could happen. 

There is concern among the hip resurfacing community about the reactions to the very high metal ion issue.  At this time, to my understanding, there is not a standardized blood test available.  Different labs use different methods and tests.  There are not yet any specific guidelines as to what levels are too high for metal ions.  There is a lot of research being done, but there are no standards yet. 

This makes a surgeon's job to define and solve problems due to high metal ions difficult.  Some doctors feel that patients with very high metal ions should have a revision of their hip resurfacing to a ceramic on ceramic THR.  They don't want to take chances that even more serious problems could develop due to the high metal ions.  Normally, from what I understand, the high metal ions are probably due either to the incorrect position of the acetabular cup causing very high wear on the hip resurfacing bearing device or due to the use of a small hip resurfacing device causing excessive loading on the bearing surfaces. So once again, the learning curve and experience of hip resurfacing surgeons is very important to prospective patients along with proper patient selection.  It takes a great deal of experience to consistently place the acetabular cups at the proper angle and to know which smaller patients can successfully receive a hip resurfacing.

That is my layman's explanation of the high metal ion issue.  I am posting a number of abstracts below by surgeons attending the Second Annual U.S. Comprehensive Course on Total Hip Resurfacing Arthroplasty October 24–25, 2008 Los Angeles, CA. Their articles will help explain more about the high metal ion issue, the small device issue used in many women and the acetabular cup placement issue.