Metal-on-metal bearings: Allow careful clinical experience to proceed

Introduction

There is a renewed focus on the utilization and compromise of metal-on-metal (MoM) articulations in total hip and surface replacement procedures. Clinical reports of tissue reactivity leading to early revision in some patients have gone hand-in-hand with a gathering storm of litigation. It is important to appreciate that reasonable care should be taken in the use of any evolving technology. The regulatory requirements making these articulations available for clinical use in the United States represent a pathway that over the nearly 4 decades of hip arthroplasty use have overwhelmingly improved the activities of daily living for millions of people. In this particular instance of metal-on-metal bearing utilization, it is important that the baby is not allowed to be thrown out with the bathwater, and that careful clinical experience is allowed to proceed.

Part 2 of this two-part Round Table discussion brings together experienced orthopedic surgeons whose collective background is intended to provide reader insight into the use of MoM articulations in hip arthroplasty and sets a tone for the requirements of their continued utilization.

– A. Seth Greenwald, DPhil (Oxon)
Moderator

Round Table Participants Moderator A. Seth Greenwald, DPhil (Oxon) Orthopaedic Research Laboratories Cleveland, Ohio Robert L. Barrack, MD Washington University School of Medicine St. Louis, Mo. Adolph V. Lombardi Jr., MD, FACS Mt. Carmel New Albany Surgical Hospital New Albany, Ohio John M. Cuckler, MD Alabama Spine and Joint Center Birmingham, Ala. David W. Murray, MD, FRCS Nuffield Orthopaedic Centre Oxford, United Kingdom Joshua J. Jacobs, MD Rush University Medical Center Chicago, Ill.

A. Seth Greenwald, DPhil(Oxon): What is your thinking in regards to the cause(s) of increased incidences of adverse local tissue reactions (ALTRs)? Are there further systemic effects you can identify?

Robert L. Barrack, MD: The vast majority of cases of adverse local tissue reaction is the direct result of edge loading and related to component positioning. The major risk factors are excessive verticality of the acetabular component or excessive anteversion. Combined anteversion of the acetabular and femoral components of 45· or more seems to be just as high of a risk factor as a vertical acetabular component. The design of some components makes the window of acceptable position very narrow, which probably was the major factor in leading to high failure rates with certain designs.

John M. Cuckler, MD: I need to take issue with your statement of “increased incidences” of ALTR with MoM. First, we do not know the prevalence of incidence of ALTR associated with MoM bearings. In fact, I suspect the incidence may vary with the specific implant design and materials combination.

I believe the ALTRs are associated with one of two situations: accelerated wear, due to the factors described earlier, which have been associated with pseudotumor formation, and hypersensitivity (T-cell – mediated) reactions which may or may not be associated with accelerated wear. Compelling evidence now exists for genetic predisposition to extreme immune response to polyethylene debris; I suspect the same phenomenon will be identified with regard to the predisposition to hyperimmune response to metallic debris or ion moieties associated with MoM wear.

It is important to remember that ALTRs are also associated with bearing couples such as metal-on-polyethylene and ceramic-on-ceramic; these reactions are also usually, but not always, associated with ALTRs. The difference, however, is that ALTRs associated with MoM appear to be associated with severe soft tissue damage, with relatively mild osteolysis. In contrast, the ALTRs associated with metal-on-polyethylene or ceramic-on-ceramic are usually associated with severe osteolysis, with relatively mild effect on the soft tissues. We have had 30 years experience with managing osteolysis, while the challenges of the soft tissue damage seen with MoM ALTRs are new to the orthopedic community.

Joshua J. Jacobs, MD: There is increasing evidence to suggest that ALTRs to metal-containing implants are directly related to the quantity of wear and corrosion debris released by the implants. In turn, the quantity of debris that is released is a complex function of the metallurgy, design and geometry of the implant and bearing surfaces, the orientation and fixation of the components, the performance of modular junctions, the presence of third bodies and perhaps patient factors such as body mass index (BMI) and activity level. There are now six hip replacement cases — two cases with MoM bearings and four cases with other bearing combinations, where there was a fractured ceramic component — in which systemic cobalt and/or chromium toxicity, in the form of neurologic, cardiac and/or endocrinologic effects, have been reported in patients with cobalt-chrome hip implants and very high levels of these metals in the bloodstream.

Adolph V. Lombardi Jr., MD, FACS: With respect to the etiology of ALTR to metal debris, it is my impression that this represents a soft tissue reaction to toxic levels of metallic debris. A recent report by Tower has outlined systemic effects from toxic levels of cobalt. This report described two patients with elevated levels of cobalt who developed significant neurological symptoms.

David W. Murray, MD, FRCS: I believe the adverse reactions are a response to cobalt-chrome particulate debris. This may come for various sites. It may come from the articulating surfaces as a result of edge loading which may be a result of impingement or the joint reaction force passing near the edge of the acetabular component. This is the primary cause of problems in resurfacing. With MoM conventional hip replacements the debris may also come for the Morse taper because of movement at the interface. This is probably the result of the high frictional torque generated by the large head when there is poor lubrication at the initiation of movement. Debris may also be released as the result of corrosion.

Greenwald: Specific to the previous question, is metal hypersensitivity a cause of implant compromise or does the prodigious production of particulate overwhelm an individual’s immune system, triggering this response? In either case, revision is the seeming endpoint.

Barrack: I think metal hypersensitivity is probably fairly rare and accounts for a small minority of cases of ALTR and/or persistent pain. Rarely, a component that is well-positioned and well-fixed may be associated with pain and an adverse tissue reaction and serum testing that indicates a high reactivity to cobalt-chromium or nickel. I suspect this represents less than 5% of these cases, possibly even less than 1%.

Cuckler: I believe either mechanism can be associated with MoM implant failure. As mentioned in the previous question, I suspect individual, genetically determined, immune response is the primary operative determinant in the ALTR; I suspect large quantities of metallic debris are more likely to produce the pseudotumor-type of clinical presentation — histologically appearing as a cellular response of both macrophages and lymphocytes — while elevated metal ion levels, even in the absence of “run-away” wear, will present clinically as loosening, mild osteolysis and intense lymphocytic response in the periarticular soft tissues (the hypersensitivity reaction). Of course, any immune-mediated response to any material could be considered a “hypersensitivity” reaction.

Jacobs: The precise role of metal hypersensitivity has yet to be defined. There may be a subset of patients who are more reactive to metal debris by virtue of an adaptive immune response such as a delayed-type hypersensitivity response (type 4), or by virtue of a genetic susceptibility that confers an exaggerated innate immune response. However, in the majority of cases of ALTR it is likely that the relatively high quantity of particulate, colloidal and ionic metal debris has a direct adverse effect on the cells in the periprosthetic milieu, including cells of the immune system.

Lombardi: The adverse tissue reaction to metal debris does not appear to be a metal hypersensitivity type reaction. Rather it is my impression that this is a response to toxic levels of metallic debris. Using lymphocytic proliferation assay a recent study by Kwon and colleagues found no difference in the reactivity to various metals in patients with MoM bearings who had pseudotumors and those who did not. If this indeed were a metal hypersensitivity then one would expect a high reactivity to various metals with the lymphocytic proliferation assay.

Murray: True metal hypersensitivity probably does occur, but rarely. In most cases the severe damage to soft tissue and occasionally bone is a toxic effect of the metal debris. The most likely mechanism is that the metal particles are taken up by macrophages and once in the acidic environment of the lysosome the particles corrode releasing high levels of cobalt ions which kill the cells. Other patient-related factors are important as reactions are particularly common in patients with bilateral MoM articulations.

Greenwald: Given the recent advisories regarding MoM articulations, how should the normal follow-up pattern be altered for patients with a MoM bearing and when do you consider surgical interdiction?

Barrack: When utilizing a component that has a good long-term track record, if the component is well-positioned and well-fixed based on radiographic criteria and the patient is asymptomatic, then the follow-up interval is the same as for any other total hip arthroplasty. The patients are told to follow-up at 1- and 5-year intervals unless there is a change in their symptoms, regardless of their hip arthroplasty. Our patients are followed more frequently than that, only because they are in various clinical study protocols.

Cuckler: I tell all of my implant patients, regardless of the bearing couple used, that regular follow-up is required for the remainder of their life. Young, active patients who are more demanding of the bearing couples should be seen at least every 2 years, if not annually; less active or older patients can be seen at 3 to 5 years. Importantly, patients need to be educated that a change in prosthetic joint function — onset of new pain, swelling, a feeling of “slippage” (subluxation) — should merit an earlier return for follow-up.

Jacobs: Routine periodic surveillance, as in annual follow-up visits, which would include a discussion of local hip symptoms as well as general health changes, is recommended for all patients with total hip replacements, including patients with MoM bearings. For the symptomatic patient, this surveillance should be more frequent. Depending on the symptoms, signs and plain radiographic findings, additional testing should be considered to address the differential diagnoses of loosening, whether septic or aseptic, sepsis, referred pain, local bursitis/tendonitis or ALTR. Metal ion testing, metal allergy testing and metal artifact reduction sequence MRI may also be useful in patient assessment. The findings from all these sources should be interpreted in concert when making a decision as to possible surgical intervention.

Lombardi: Historically we have advised all of our arthroplasty patients to return for annual follow-up. With respect to patients with a MoM articulation it is our impression that these patients should be seen annually and, more importantly, if they have any hip symptoms ascribable to the hip. The patient who is symptomatic should have baseline metal ion testing and should have either ultrasound or MRI to evaluate the soft tissues about the hip. In the symptomatic patient with any evidence of lysis and any evidence of soft tissue reaction, revision should be advised and performed.

Murray: The optimum follow-up remains controversial and depends in part upon the device; how long it has been in general usage and whether it has had problems. At a minimum, all patients should be regularly contacted and if they have any symptoms from the hip they should have cross-sectional imaging. We find ultrasound the best imaging modality but it does require an experienced operator. If patients have significant symptoms and a soft tissue lesion or have minimal symptoms and a large or expanding lesion we would recommend early revision so as to minimize the soft tissue damage.

Greenwald: Are the increased costs of MoM bearings a compromising factor in their selection as a solution for the hip arthritic patient despite perceived benefit?

Barrack: A component with increased cost should have some evidence of a clinical advantage. I believe our data on hip resurfacing patients from a number of centers evaluated by an independent survey center make a compelling case for a clinical advantage for surface replacement in selected patients. I am not aware of data as convincing for MoM total hip replacement. Some centers have reported a low dislocation rate compared to standard total hips, but now that large heads are being utilized with crosslinked polyethylene, this advantage may be less important.

Cuckler: Clearly, we as orthopedic surgeons need to make bearing decisions based on the individual need of the patient and the experience and skills of the surgeon. Given the high cost and risk to the patient of revision surgery, it is the job of the arthroplasty surgeon to make the judgment of the trade-off between cost and expected performance — longevity — of the chosen implant.

Lombardi: As responsible orthopedic surgeons, cost should always be a consideration. However, it is my impression that the costs of MoM bearings are not a compromising factor in their selection as a solution for the patient undergoing hip arthroplasty. These articulations can be extremely beneficial in high-demand individuals with providing enhanced stability.

Murray: I do not believe that the advantages of MoM bearings outweigh the risks for conventional hip replacements used in routine situations. The advantages do, however, outweigh the costs for appropriate patients needing resurfacing.

Greenwald: What influence do you believe the current advertisement of both individual and sought class-action litigation will have on the use of MoM technologies that on-balance have greatly assisted the patients they are advocated for?

Barrack: Certainly there has been a decline in the utilization of MoM bearings of certain designs that have not had a consistently good track record. There still exists enthusiasm for MoM surface replacement — and to a lesser degree, MoM total hip arthroplasty. Patients will become increasingly more selective in seeking out implant designs and centers that have a track record of success with their particular procedure, which is probably appropriate.

Cuckler: The litigious environment, particularly in the United States, will have a devastating impact on technology development and implementation of new medical technologies in general for our patients. The cost of medical care will be directly and adversely affected by the unbridled hunger of the tort lawyers. In my opinion, if the current legal environment existed during the introduction of the Charnley-type total hip replacement 40 years ago, one of the most cost-effective and successful medical interventions ever developed would have been summarily eliminated, as may happen with MoM bearing surfaces.

Unfortunately, our patients have been led to believe that medical interventions such as total joint replacement are now minor medical procedures without significant risk and with the potential to return them indefinitely to the activity status of a 21-year-old. If we as a medical community have learned nothing else over the past 40 years, it is that despite extensive in vitro and in vivo premarket trials, whether for implants or drugs, not all adverse effects can be identified, and with certainty, not all risks of the intervention can be eliminated.

Lombardi: The current advertisements of both individual and class-action litigation regarding MoM bearings will certainly have a negative effect on the utilization of this technology. However, it is my impression that we as physicians always want to do what is best for our patients. Recent literature has raised some concerns regarding MoM bearings and therefore, their use should be limited until further understanding is ascertained.

Murray: I expect the use of MoM bearings will continue to decrease. There is an urgent need for further research to understand the problems of MoM bearings so as to define the role of these articulations.

References:

• Kwon YM, Thomas P, Summer B, et al. Lymphocyte proliferation responses in patients with pseudotumors following metal-on-metal hip resurfacing arthroplasty. J Orthop Res. 2010;28(4):444-450.
• Tower SS. Arthroprosthetic cobaltism: Neurological and cardiac manifestations in two patients with metal-on-metal arthroplasty: A case report. J Bone Joint Surg (Am). 2010; Oct 29. [Epub ahead of print]

• Robert L. Barrack, MD, can be reached at Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8233, Department of Orthopedic Surgery, St. Louis, MO 63110; 314-727-2592; e-mail: barrackr@wustl.edu.
• John M. Cuckler, MD, can be reached at Suite 164, 100 Club Dr., Burnsville, AL 28714; 205-936-9199; e-mail: jcuckler@charter.net.
• A. Seth Greenwald, D Phil(Oxon), can be reached at Orthopaedic Research Laboratories, 2310 Superior Ave. East, Cleveland, OH 44114; 216-523-7004; e-mail: seth@orl-inc.com.
• Joshua J. Jacobs, MD, can be reached at Rush University Medical Center, 1725 Harrison St., No. 1063, Chicago, IL 60612; 312-432-2344; e-mail: joshua.jacobs@rushortho.com.
• Adolph V. Lombardi Jr., MD, FACS, can be reached at Joint Implant Surgeons Inc., 7277 Smith’s Mill Road-Suite 200, New Albany, OH 43054; 614-221-6331; e-mail: LombardiAV@joint-surgeons.com.
• David W. Murray, MD, FRCSC, can be reached at Nuffield Orthopaedic Centre, University of Oxford, Oxford, OX3 7LD, United Kingdom; e-mail: david.murray@ndorms.ox.ac.uk.
• Disclosures: Barrack is a consultant for and has intellectual property rights with Smith & Nephew. Cuckler receives grant and research support, royalties and is on the speakers bureau for Biomet Orthopedics. Greenwald has no relevant financial disclosures. Jacobs is a paid consultant for Zimmer and receives research and institutional support from Arthrex, Biomet, Cervitech, DePuy, Johnson & Johnson, Medtronic, Medtronic Sofmor Danek, National Institutes of Health, Smith & Nephew, Spinal motion, Stryker, Syntheses, Tornier, Wright Medical Technology, and Zimmer, and has stock options with Implant Protection. Lombardi is a consultant for and has intellectual property rights with Biomet. Murray receives support from Biomet, DePuy, Smith & Nephew, Stryker, Wright Medical and Zimmer.

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