Patients with metal-on-metal implants require systematic follow-up

When they were re-introduced on the market, metal-on-metal hip implants sparkled with the promise of lower volumetric wear rates, significantly less wear-induced osteolysis and improved implant stability. As a result, their popularity soared. Recent estimates list that up to 1 million of these devices have been used worldwide since 1996.

As clinical results emerged from national joint registries in the United Kingdom and Australia, a different image came into focus. The data revealed significantly higher revision rates for metal-on-metal (MoM) implants compared with their non-metal counterparts.

The adverse events now linked to some MoM implants vary. The most publicized problem has been metal ion release and adverse local tissue reactions, and these issues led to the recall of several MoM hip devices. However, some surgeons continue to use MoM resurfacing or total hip replacement (THR) implants — their practice backed by high long-term survivorship rates. Problems, they note, derive from inferior implant designs and component orientation.

It is widely agreed, however, that the follow-up of asymptomatic patients with a MoM resurfacing or THR is critical.

Karl Knahr, MD, of Orthopaedic Hospital Vienna-Speising, who is an Orthopaedics Today Europe Editorial Board member, said that resurfacing patients should be followed annually for the first 5 years. “If, after this period, they have normal ion levels, they should be followed up like standard procedures for conventional hip arthroplasty,” he said.

Reaching a consensus

According to the European consensus statement on the use and monitoring of MoM bearings for THR and hip resurfacing, patients with MoM articulations with 32-mm heads or smaller should be followed in a manner similar to patients with conventional hip arthroplasties.

“If they have pain, you have to investigate more, but in general, this group of patients does not need special follow-up,” Knahr told Orthopaedics Today Europe.

For implants with 36-mm or larger heads, the European consensus statement recommended life-long annual check-ups, he said. According to the consensus statement, for large-head implants follow-up should involve radiographs and whole blood cobalt metal ion measurement done with specific techniques. More involved imaging, such as ultrasound, CT or metal artifact reduction sequence-MRI, is required for patients with a clinical or radiographic abnormality.

“Cobalt values less than 2 µg/L are probably devoid of clinical concern, the threshold value for clinical concern is expected to be within the range of 2-7µg/L,” Hannemann and colleagues wrote in the European multidisciplinary consensus statement published in 2013.

William J. Maloney, MD, professor of orthopaedic surgery, Stanford University, Stanford, Calif., USA, told Orthopaedics Today Europe, “I have seen a spectrum of adverse events with metal-on-metal implants, which includes failure of the socket to osseointegrate and adverse local tissue reactions, including osteolysis and soft tissue destruction with pseudotumor formation.”

The European consensus statement, to which the European Federation of National Associations of Orthopaedics and Traumatology (EFORT), the European Hip Society and other organizations in Europe contributed, was prompted by the 2010 Medicines and Healthcare Products Regulatory Agency (MHRA) alert, Klaus-Peter Günther, MD, chairman of the department of orthopaedic surgery at the Universitätsklinik Carl-Gustav Carus, Dresden, Germany, told Orthopaedics Today Europe.

According to the American Academy of Orthopaedic Surgeons (AAOS) consensus statement on this topic, which was developed in collaboration with the American Association of Hip and Knee Surgeons and the Hip Society, it is important to look for radiographic signs of impingement in patients who underwent resurfacing.

That statement consists of recommendations and a risk stratification to help orthopaedic surgeons manage patients with metal hip bearings.

Günther, who is an Orthopaedics Today Europe Editorial Board member, said a European working group in place for the last year is now developing a document about the status of MoM implants, which was commissioned by the European Union (EU). He and Orthopaedics Today Europe Editorial Board member Luigi Zagra, MD, of Milan, represent EFORT in the group, which includes other orthopaedic surgeons and external experts.

“The goal of the group is to summarize the current available knowledge and to provide the EU authorities with a literature and expert-based opinion on the benefits and risks of metal-on-metal implants,” said Günther.

The report should be completed in about 3 or 4 months, he noted.

Günther said his department has not performed metal THR with small heads for several years.

“We do perform a very select number of resurfacings and have completely stopped large heads. Several institutions have announced a ‘time out’ for large heads, but still some surgeons do them. I am personally afraid of legal problems in the future when any patients with a large head operated on right now develop any problems,” he said.

Case for MoM resurfacing

Harlan C. Amstutz, MD, of the Joint Replacement Institute at St. Vincent’s Hospital and emeritus professor at University of California Los Angeles, USA, said MoM hip resurfacing is the best option for patients with osteoarthritis of the hip and is appropriate for patients of all ages and etiologies.

In the more than 1,350 MoM hip resurfacings he performed in the last 16 years, Amstutz told Orthopaedics Today Europe he recorded 99% 11-year survivorship rates in patients (irrespective of gender or large body mass index) who received large components (>46 mm) and had good bone quality. For more challenging cases (heads 46 mm and smaller, and including osteonecrosis with whole head disease and class III developmental hip dysplasia), technique improvements mean that 7-year survivorship is now 94.8%, he said.

Amstutz has not had a femoral neck fracture or femoral loosening in patients implanted after 2004. The socket loosening rate is 1% and 0.5% of patients have demonstrated adverse local tissue reactions.

“Those are all in malpositioned sockets.”

He contends the problems with metal implants have not been caused by the bearing but are due to poor implant design and poor component orientation.

“If you get a good design, which the Conserve Plus (Wright Medical Technology; Arlington, Tenn., USA) is, and you see what you are doing — no minimally invasive surgery — and if you put the socket in correctly, the MoM hip resurfacing bearing will continue to function optimally forever without adverse wear,” Amstutz said.

In terms of following patients with a MoM hip bearing, the orthopaedic surgeons interviewed for this article noted that all of them require vigilant, systematic and sometimes more aggressive follow-up. The frequency of follow-up will vary from patient to patient; however, as a general rule, annual follow-up is recommended.

Asymptomatic patients with well-implanted hip resurfacings with a contact patch to rim distance greater than 10 mm do not need annual follow-up or ion studies because the bearing will function well, Amstutz noted.

Revision benchmarks

It is critical that surgeons know the benchmarks for revising patients with MoM implants.

“Clinical data is the most important [benchmark],” Knahr said. Radiographic findings run a close second, he said.

Knahr will follow patients with small signs of osteolysis, opting to revise only if the osteolysis increases.

But, there are other reasons to revise patients who have MoM implants.

“Patients with soft tissue and bone destruction due to [adverse reaction to metal debris] ARMD are one reason for revision,” Günther said. “Patients with gross soft tissue and bone destruction with or without symptoms are a cause for revision.”

The most important benchmark for revision is the patient’s pain, Knahr said. “We do not treat X-rays. We treat patients,” he said. “The patients are the most important part.”

“For those patients who have elevated serum ion levels or some worrisome finding radiographically or a pseudotumor on MRI scan, we start to talk about revision with them,” Maloney said, noting that revising these patients is not without peril, and they must be informed about the risks.

“The outcome of revision can be suboptimal in these patients, depending on the level of soft tissue necrosis they have and damage to the pericapsular soft tissues, including the muscles,” according to Maloney. “In some cases, there is actual necrosis of the bone both on the pelvis and the proximal femur. When there is extensive tissue necrosis, both soft tissue and bone, you have to tell the patient upfront that their outcome is guarded.”

Further, patients with associated tissue damage tend to have a higher risk of post-revision complications, especially dislocation, he said. “You have got to prepare these patients for postoperative complications that can occur. If you get [the patients] late, and they have extensive soft tissue and bony necrosis, the outcomes are fair at best.”

Asymptomatic patients require only periodic surveillance.

“If a patient has a well-functioning implant clinically, their X-ray looks stable and they have normal serum ion levels, we normally just reassure them and tell them to come back in a year unless they have a problem,” Maloney said.

During a revision procedure, Knahr recommends doing a complete synovectomy because there may be metal particles. “[The surgeon] should try to remove as [many of the particles] as possible.”

Orthopaedists will send retrieved components away to be analyzed for issues related to performance, wear and other factors. The soft tissue should be examined, too.

“The tissue should be analyzed because you can find in the tissue inflammatory reactions and maybe some particles,” Knahr said. “[Tissue analysis] is the only way to make sure whether it is inflammation or just a reaction to the metal-on-metal.”

Once the metal bearing is removed, the body eliminates the excess metal ions in the blood by way of renal function and those levels should decrease over time. “[That] is why metal-on-metal is not recommended in patients with reduced renal functioning,” Knahr said.

Ion level follow-up

One area that is still debated is whether metal ion levels should be followed after revision surgery, particularly when the patient responded well to the procedure and it was uncomplicated.

Knahr said it makes sense to follow up on metal ion levels post-revision to ensure that those levels are going down. The main problem is that usually the revision surgeon does not know what the patient’s “normal” ion levels were prior to the primary procedure.

Interview sources for this Orthopaedics Today Europe article had differing views on the future of MoM implants.

Maloney said he sees no future for MoM bearings. “In my opinion, there is no indication for metal-on-metal conventional hip replacement. There is a small group of patients who might benefit from metal-on-metal resurfacing, but it is small. In my opinion, the potential risks outweigh the potential benefits.”

While Günther agreed that there is no indication for large-head MoM hip procedures, he said there still may be a role for resurfacing, provided it is performed by a well-trained surgeon in a properly selected patient. – by Colleen Owens and Susan M. Rapp

• References:
• Cohen D. BMJ. 2012; doi10.1136/bmj.e1410.
• Hannemann F. Orthop Traumatol Surg Res. 2013; doi10.1016/j.otsr.2013.01.005.
• www.aaos.org/about/papers/advistmt/1035.asp
• http://www.iss.it/binary/riap2/cont/2012_05_10_MoM_Consensus_statement.pdf.
• www.mhra.gov.uk/home/groups/dts-bs/documents/medicaldevicealert/con155767.pdf.

• For more information:
• Harlan C. Amstutz, MD, can be reached at 2200 West Third St., Suite 400, Los Angeles, CA 90057, USA; email: harlanamstutz@dochs.org.
• Klaus-Peter Günther, MD, can be reached at Fetserstrasse 74, 01307, Dresden, Germany; email: klaus-peter.guenther@uniklinikum-dresden.de.
• Karl Knahr, MD, can be reached at Speisinger Strasse 109, A – 1130 Vienna, Austria; email: karl.knahr@oss.at.
• William J. Maloney, MD, can be reached at Stanford University School of Medicine, 450 Broadway St., Pavilion A, Redwood City, CA 94063, USA; email: wmaloney@stanford.edu.

Disclosures: Amstutz receives royalties from Wright Medical Technology and receives some research support from St. Vincent’s Hospital. Günther receives funding for research projects from Zimmer and Smith & Nephew and financial support for oral presentations from Zimmer. He has no other disclosures on MoM. Knahr has no relevant financial disclosures. Maloney receives royalties from Pipeline Orthopaedics on hip products.

Should metal-on-metal implants be banned?

They should not be banned

Banishing metal-on-metal (MoM) hip implants means many benefits of a MoM implant would be lost simply because there have been problems with a certain subset of products. They were first used in the hip joint because the material properties allow the attainment of fluid film lubrication, which leads to a low rate of wear, thereby potentially lasting a long time. Later, it was realized the metal’s strength allowed constructing larger head sizes and thinner sockets, creating additional hip joint stability and reducing dislocation risk. Hip resurfacing represented the ideal marriage of these benefits, while preserving proximal femoral bone. Therefore, a MoM bearing has been favored for active patients who require a stable joint and low wear due to their activity level, and for those patients who fit the criteria for hip resurfacing.

Not all MoM implants are the same. The most important distinction is a MoM hip resurfacing is different than a MoM total hip replacement (THR) due to the additional parts and junctions of a THR implant. A hip resurfacing has two metal components: the head and the socket. MoM THR has at least three components: a stem, a socket and a head, but it may also have an acetabular liner and sometimes a sleeve adapter for the femoral head. These additional pieces and junctions can lead to fretting, corrosion and additional metal production, a fact that Garbuz and colleagues noted when they compared metal ion release from hip resurfacing and MoM THR.

Not all implants are designed or manufactured the same. We have heard a lot about the DePuy ASR implant that was recalled because of an unexpectedly high failure rate. Langton and colleagues found a failure rate of up to 49% at 5 years due to problems arising from reduced articular coverage of the acetabular component. This is a prime example of a design that made sense from an engineering and theoretical standpoint, but failed to perform in vivo.

The results of MoM bearings have been variable, depending upon the implant design, accuracy of surgical implantation, patient characteristics and whether they were used in hip resurfacing or THR. Several papers have shown that a 28-mm MoM THR can have 94% survival at up to 13 years, comparable to that of traditional metal-on-poly THR. Hip resurfacing was also shown to have 95% survival in men at 10-year follow-up.

MoM bearings in hip arthroplasty still have merit and should not be banned simply because a few implants have demonstrated problems. The creation of a stable joint and the ability to preserve bone justify their use in hip resurfacing, where there are no alternatives to MoM articulations. In THR, however, there are good alternatives like highly crosslinked polyethylene, so MoM should not be used routinely. Nevertheless, we should spend more time and energy to understand the problems of MoM implants so they can be improved rather than eliminated.

Edwin P. Su, MD, is associate professor of Clinical Orthopedics at Weill Cornell Medical College, Hospital for Special Surgery, New York.
Disclosure: Su is a consultant for Smith & Nephew, the manufacturer of the Birmingham Hip Resurfacing Implant. They have provided institutional support for research studies pertaining to this implant.

• References:
• Coulter G. J Bone Joint Surg Br. 2012;doi:10.1302/0301-620X.94B3.28185.
• Garbuz DS. Clin Orthop Relat Res. 2010;doi:10.1007/s11999-009-1029-x.
• Holland JP. J Bone Joint Surg Br. 2012;doi:10.1302/0301-620X.94B4.27895.
• Langton DJ. J Bone Joint Surg Br. 2011;doi:10.1302/0301-620X.93B8.26040.
• Randelli F. J Arthroplasty. 2012;doi:10.1016/j.arth.2011.04.015.
• Streit MR. Int Orthop. 2012;doi:10.1007/s00264-011-1399-z.

No current role

There are reasons why we began using large diameter metal-on-metal (MoM) hip arthroplasty. From the clinical point of view, we wanted to have reduced risk for hip dislocation, lower wear rates and, along with this, less concern about restrictions post-surgery and, in the long-term fewer revisions. The companies produced the product to get market share. The patients did not know better than [what] they were told or read.

To some extent, clinicians got what we wanted: Fewer dislocations and less volumetric wear. Unfortunately, revision rates increased in most studies. In addition, we did get some adverse reactions to metal debris.

I stopped using MoM hip arthroplasty implants because of the risks associated with them. There is uncertainty with regard to metal ions in the body and the risk for local reactions due to metal debris. In addition, there may be other risks not known today.

The easiest way to handle the situation is to say, “Stop.” This is what the national orthopaedic societies in Denmark and The Netherlands recommended in 2012 and 2011. The surgeons and authorities were happy. I am happy.

For safety reasons, I believe that MoM should not be used currently. We have to learn more about the long-term prognoses. We have other, safer articulations that can be used today.

Soren Overgaard, MD, DmSc, PhD, is Professor and Head of Research, the Department of Orthopaedics and Traumatology, Odense University Hospital, in Odense, Denmark.
Disclosure: Overgaard received research funding from DePuy Synthes and Biomet.