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 as many as 1 million of these implants 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 linked to MoM implants vary. “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,” William J. Maloney, MD, professor of orthopedic surgery, Stanford University, Stanford, Calif., told Orthopedics Today.

The most publicized problem has been metal ion release and adverse local tissue reactions. These issues led to the recall of several MoM devices.

However, some surgeons continue to use MoM implants — their practice backed by high long-term survivorship rates. Problems, they note, derive from inferior implant designs and component orientation. MoM hip resurfacing is the best option for patients with osteoarthritis of the hip, Harlan C. Amstutz, MD, the founding director of the Joint Replacement Institute at St. Vincent’s Hospital and emeritus professor at the University of California Los Angeles, told Orthopedics Today.

The procedure is appropriate for patients of all ages and etiologies, Amstutz said.

In the more than 1,350 MoM hip resurfacings he has done during the last 16 years, Amstutz has 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 dysplasia of the hip), 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 and, in his practice, the socket loosening rate is 1%.

In addition, 0.5% of his patients have demonstrated adverse local tissue reactions. “Those are all in malpositioned sockets,” he said. “The socket does have its limitations. You cannot put it in at ranges that we did not prescribe.”

Amstutz said the problems with metal implants have not been caused by the bearing. “It is due to poor [implant] design and poor component orientation,” Amstutz said. “If you get a good design, which the Conserve Plus is [Wright Medical Technology], 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.

For some, the early luster of MoM has dulled and the use of these devices has significantly decreased. This can be especially true for the case of the MoM big femoral head total hip replacements, Amstutz said. “We have seen in the marketplace a dramatic decrease in the use of metal-on-metal implants,” Joshua J. Jacobs, MD, chairman of the department of orthopedic surgery at Rush University Medical Center, Chicago told Orthopedics Today. “At their peak in the mid-2000s, nearly a third of the primary total hip market was metal-on-metal. Now, it is diminished substantially, so that it is [less than] 5%.”

How should orthopedic surgeons manage those patients who still have metal bearings? Orthopedics Today talked with top U.S. and European surgeons about this, and they agree: All patients with MoM hip implants require vigilant, systematic and sometimes more aggressive follow-up.

“We are much more vigilant in terms of reacting to any symptom that is unusual for total hip replacement,” Keith R. Berend, MD, of Joint Implant Surgeons Inc., in New Albany, Ohio, said. Multiple studies have shown that even patients with conventional hip bearings will still have pain postoperatively; however, “if a patient has a metal-on-metal bearing, we are going to start a more aggressive work-up to ensure that the pain is normal for them as opposed to something that might be related to a metal-on-metal problem that could result in more concerning reactions.”

In the United States, the American Academy of Orthopaedic Surgeons (AAOS), the American Association of Hip and Knee Surgeons and the Hip Society collaborated on a consensus statement with recommendations and risk stratification designed to help orthopedic surgeons manage patients with metal bearings. In Europe, members of the European Federation of National Associations of Orthopaedics and Traumatology, the European Hip Society and the German Arbeitsgemeinschaft Endoprothetik and the Deutsche Arthrosehilfe developed a similar consensus statement, prompted by the 2010 Medicines and Healthcare Products Regulatory Agency (MHRA) alert, Klaus-Peter Günther, MD, chairman of the department of orthopedic surgery at the Universitätsklinik Carl-Gustav Carus, Dresden, Germany, told Orthopedics Today.

Frequency of follow-up

The frequency of follow-up will vary from patient to patient; however, as a general rule, annual follow-up is recommended for all patients with metal bearings. However, Amstutz noted that 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.

According to the European consensus statement, MoM articulations with 32-mm heads or smaller should be followed in a manner similar to patients with conventional hip arthroplasties.

“Of course, if they have pain, you have to investigate more, but in general, this group of patients does not need special follow-up,” Karl Knahr, MD, of Orthopaedic Hospital Vienna-Speising, told Orthopedics Today.

For large head implants, 36 mm or larger, the European consensus statement recommended life-long annual check-ups, he said.

Knahr, 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.

A thorough history and exam

When patients with MoM implants present at the office, the first step is to reassure them that they are most likely okay. “The majority of patients with metal-on-metal are doing fine; it is just reassuring them that they are okay,” Maloney said.

To assess how the patient is doing, the surgeon must get a history and perform a physical exam, Jacobs said.

“I get a thorough history, so that I understand how their hip is feeling [and] whether there is been any change in their general health,” Jacobs said. “That is number one.”

All patients should receive serial plain radiographs, so that the surgeon can assess the condition of the bone and the implant, Jacobs said.

If there are abnormalities on the initial imaging, the patient should undergo ultrasound, CT or metal artifact reduction sequence (MARS) MRI, Knahr said.

It is important to look for radiographic signs of impingement in patients who underwent resurfacing, according to the AAOS consensus statement.

As for the typical lab work, following erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in patients with MoM is unnecessary. “Typically, white blood counts, CRP and ESR rates are not utilized in following adverse tissue reactions,” Maloney said.

However, Maloney and Berend routinely run labs for infection, serum and whole-blood cobalt as well as chromium and titanium levels as part of the initial patient evaluation.

Metal-ion level threshold

There is a lot of debate about the threshold for metal ion levels. “There are multiple reasons for that debate,” Berend said. “The testing, the actual physical way that it is tested, the blood draw, the testing facility and the storage can vary,” he said. There are also variations in whole-blood vs. serum testing.

With the type of testing used in his office, Berend starts to get concerned with a level of 6 ppb or 7 ppb. “[In] someone who is relatively asymptomatic, has a normal MRI or ultrasound with an elevated serum ion level of 6 ppb or 7 ppb, I would probably repeat the level in 6 months to make sure that it is not elevated and make sure that their symptoms do not change,” he said.

In a 2012 medical device alert, the MHRA identified the threshold as 7 ppb, which is somewhat different from the level determined by Günther and colleagues.

“We think the future threshold may lie between 2 µg/L and 7 µg,/L” Günther, an Orthopaedics Today Europe Editorial Board member, said. “This is the point where future research should strengthen to deliver more information about a reasonable threshold level for local and systemic adverse events.”

Benchmarks for revision

Ultimately, the primary goal of the revision surgery is to intervene before there is severe tissue damage, Jacobs said. “If there is a lot of metal released, we know that in some cases that can lead to damage to the tissue around the hip,” he said. “You certainly want to intervene before there is so much damage that it compromises the results of revision surgery.”

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

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.”

Revising these patients is not without peril, and the patients must be informed about the risks. “The outcome of revision can be suboptimal in these patients, depending on the level of soft tissue necrosis that they have and damage to the pericapsular soft tissues, including the muscles,” Maloney said. “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 got 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, Maloney 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 boney necrosis, the outcomes are fair at best.”

As for asymptomatic patients, they 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. “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.”

Special revision technique

There is no special surgical technique required to revise patients with MoM implants.

“Revision surgery is variable for any bearing, whether it is metal-metal, ceramic-ceramic, ceramic-poly or metal-poly,” Jacobs said. “Each revision case presents different challenges. In some cases, the bearing surface is an issue and, in some cases, the taper connection is an issue. In some cases, the components are not well-fixed. You have to tailor revision surgery to what you find intraoperatively; there is no set protocol, if you will, for what is done in a revision. Many metal-on-metal revisions can be done with simple bearing surface exchange,” Jacobs continued. “Sometimes, the situation dictates the removal of a device that is well-fixed. Sometimes, you have to remove a device because it is not well-fixed.”

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.”

“Routinely, [the procedure] includes a straightforward revision,” Berend said. “It is taking out an acetabular component that may or may not be well-fixed. Most of these in our practice are going to be large-diameter heads. I routinely use a so-called active articulation or bipolar nonconstrained tripolar combination to allow for a large-diameter femoral head to be replaced, but getting rid of all cobalt chromium, titanium trunnions and getting rid of as much cobalt chromium as possible.”

The reason for the revision plays an important role in determining outcome, Berend said. “If they have a large pseudotumor and significant soft tissue damage — those are way more problematic. The literature would suggest a higher rate of infection and a higher rate of dislocation or instability. Some early evidence would suggest that perhaps, even modern porous metals may not fare as well in the revision setting for metal-on-metal failure.”

Analyze retrieved implants

Once the implant is removed, the surgeon should send it to a retrieval center for analysis. “When a retrieved device is sent to an implant retrieval center or a manufacturer, [that] is an opportunity for us to learn how this device has performed and to understand what factors led to success and what factors have led to the failure of the reconstruction,” Jacobs said.

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 and the levels should decrease over time.

“Normally, they are eliminated from the patient by the renal function, which is why metal-on-metal is not recommended in patients with reduced renal functioning,” Knahr said.

There is some debate about whether to follow metal ion levels after revision surgery.

“I do not think you necessarily need to obtain metal ion levels on all these patients unless there is some specific reason,” Jacobs said. “If the patient is having a good response to his or her revision surgery, he or she has no significant symptoms in his hip and no significant systemic symptoms; I do not think it is necessary to do metal ion levels.”

Knahr said it makes sense to follow up on metal ion levels post revision to see that the levels are going down. The main problem is that usually, the surgeon does not know what the patient’s level was prior to the primary procedure.

Future of MoM implants

Interview sources for Orthopedics Today had differing views on the future of MoM implants.

Maloney 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.”

Berend said MoM bearings no longer represent the state of the art. “Technology has sort of leapfrogged metal-on-metal with some of the newer bearing surfaces. With minimally invasive approaches to total hip, instability is rare, so we do not need big heads, and with the newer generation of cross-linked and vitamin E-enhanced polyethylene, wear characteristics are tremendous with polyethylene now. If [MoM] is not dead, it is certainly on life support.”

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

Jacobs urged surgeons to not lump all MoM implants together; each class of metal bearings has different clinical results. For resurfacing in men younger than 50 years, MoM implants have had a good track record, he said. The marketplace has clearly voted on large-head metal bearings; few are being implanted now, he noted.

But there is always room for improvement, Jacobs said. Through additional research, he said we will better understand why certain implants performed more poorly than others, which may reveal strategies for better implant designs.

“There have been previous generations of polyethylene that did not perform well,” Jacobs said. Over time and through research — at the bench, in post-retrieval implant analysis and in modeling — investigators have determined which factors were associated with success and failure.

“As we learned more about the mechanistic basis of polyethylene performance, better polyethylenes were developed. I see no reason why the same cannot be true for metal-on-metal bearings in the future.” – by Colleen Owens

Should metal-on-metal implants be banned?

They should not be banned

Banishing metal-on-metal (MoM) hip implants would be a classic example of “throwing the baby out with the bath water.” That means that many of the benefits of a MoM implant would be lost simply because there have been problems with a certain subset of products. To take an example from consumer goods, if one brand of hybrid car has had product recalls and problems, should we ban the use of all hybrid cars? Certainly not; this would be a drastic action that overlooks the fact that many hybrid vehicles are successful and continue to work. It is a similar situation with MoM hip implants. Let us examine the history and literature.

MoM bearings were first used in the hip joint because the material properties allow the attainment of fluid film lubrication, a scenario that leads to a low rate of wear, thereby potentially lasting a long time. Later, it was realized that the strength of the metals allowed the construction of larger head sizes and thinner sockets, creating additional hip joint stability, reducing the dislocation risk. Hip resurfacing represented the ideal marriage of these two benefits, while also preserving proximal femoral bone. Therefore, a MoM bearing has been favored for active patients who require a stable joint and low wear because of their activity level, and for those patients who fit the criteria for hip resurfacing.

It is important to realize that not all MoM implants are the same. The most important distinction is that a MoM hip resurfacing is different than a MoM total hip replacement (THR). The reason for this difference is the additional parts and junctions that are used to construct the THR implant. A hip resurfacing has two metal components: the head and the socket. A MoM THR has at least three, and up to five different components: a stem, a socket and a head. It may also have an acetabular liner, and many times, there is also a sleeve adapter for the femoral head. These additional pieces and junctions can lead to fretting, corrosion and additional metal production, a fact that was first noted by Garbuz and colleagues in their comparison of 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 has been recalled because of an unexpectedly high failure rate. Langton and colleagues have found a failure rate of up to 49% at 5 years due to problems arising from a 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 an in vivo setting.

The results of MoM bearings have been variable, depending upon the implant design, accuracy of surgical implantation, patient characteristics and whether the bearing was used in hip resurfacing or THR. Several papers have shown that a 28-mm MoM THR can have a 94% survival rate at 12 years to 13 years, comparable to that of traditional metal-on-poly THR. Hip resurfacings have also been shown to have a 95% survival in male patients at 10-year follow-up.

I believe that 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 its use in hip resurfacing, where there are no alternatives to the MoM articulation. In THR, however, because there are good alternatives such as highly cross-linked polyethylene, I agree that MoM should not be used routinely. Nevertheless, I would rather see us spend more time and energy to understand the problems of MoM implants so that 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 Inc., the manufacturer of the Birmingham Hip Resurfacing Implant. They have also provided institutional support for research studies pertaining to this implant.

 

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 run, fewer revisions. The companies produced the product in order 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 definitely 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 orthopedic 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. There is too much. We have to learn more about the long-term prognoses. We have other, safer articulations to be used today.

Søren Overgaard, MD, DmSc, PhD, is Professor and Head of Research at the Department of Orthopaedics and Traumatology Odense, Norway.
Disclosure: Overgaard has received research funding from DePuy and Biomet.