METAL ALLERGY DETAILS

Patient's immune response against products of metal wear from artificial joints.

Metal allergy and failure of total joints

The mechanism of allergic reaction against metals

Harmful effects of allergic reaction against metal.

Metal allergy

Skin allergy against metals is a well recognized condition. Most often occurs skin allergy against nickel; it occurs mainly in women who use the cheap earrings or other jewelry made from high-nickel alloys. Some reports say that about 10% of the population suffers of this form of metal allergy. These patients suffer skin rash and eczema with every close contact with objects containing high concentrations of nickel, may it be bearing nickel containing jewelry or grasping door knobs and handles made from nickel containing alloys. See also http://www.corrosion-doctors.org/Allergies/nickelallergy.htm

It has been acknowledged since long that allergic skin reaction against metal is also occurring, although very rarely, in patients who have implanted metallic plates for repair of fractures or artificial metallic joints inside their bodies. These rare patients may be suffering skin rashes and eczemas that disappear after removal of the metallic devices (Hallab 2001) .

As yet, the discussion dealt with allergic immune reaction on the surface of the body, skin reaction against metals – rash, eczema. Can allergy against metal produce changes also in deeper organs?

Three questions arise:

First, can patients with some form of skin allergy against metal (usually against nickel) still have a total joint made from a nickel containing alloy implanted?

Second, can patients develop metal allergy against metals contained in the total joint that will damage the tissues around the total joint and eventually cause its failure?

Third, can patients with total joints develop skin allergy against metals contained in the total joint and develop difficult allergic skin changes (rashes, eczemas)? Before giving answer to these questions first some facts:

What metals make part of orthopaedic alloys, especially alloys used for production of total hip joints.

The bulk of artificial hip joint device is made from orthopaedic metal alloys. See also the chapter Metal alloys for total joints. All metallic alloys used for manufacture of total joints corrode in contact with body fluids. Even titanium alloys, proclaimed to be exceptionally corrosion resistant, corrode. Eventually, corrosion products of metals enter circulation in the patient's body.

The only parts of total hip joint that are in some models manufactured from non metallic materials, and thus do not corrode and do not enter circulation, are bearing surfaces made from polyethylene and ceramic materials. See also the chapter Bearing surfaces of TH

What is corrosion?

Corrosion is a process that gnaws away bites of metal from the metal’s surface. Rusting is a form of corrosion that leaves visible stain on the iron materials. But there are other forms of corrosion that leave no visible hallmarks on the surface of the metal. See also the website: http://www.corrosion-doctors.org/Implants/Corrosion.htm

The metal surfaces corrode more easily if subjected to friction, or when two different metal alloys are in close contact.

In total hip devices, the place where there may occur friction between two different metals is the taper junction. See the Mechanics of the Morse taper.

Usually, the shaft component of a total hip is made from a titanium alloy and the ball component is made from cobalt-chrome based alloy. Both components are put together in a Morse taper junction. If the junction is not perfect, there may appear friction between the two components and corrosion ensues.

Another condition that facilitates corrosion of the metal alloy is when the metal alloy is divided into very small particles. Small particles have very large surface together that corrode easily. Metallic bearing surfaces of artificial hip joints produce very tiny metallic wear particles that corrode easily. The corrosion products then enter into the circulation. It is known that patients with metal-on-metal artificial hip joints have elevated blood levels of mainly cobalt and chrome, the metals that enter the metal alloy used for manufacture of these artificial hip joints.

How is the allergy against metals tested:

The generally used test is called patch testing:

The salts of the studied metal are mixed with a non-allergic ointment and then applied direct on the skin and the reaction of the skin is evaluated after 48 hours.

More about patch testing is on http://www.netdoctor.co.uk/health_advice/examinations/patchtesting.htm

The skin patch test is a very simple and cheap test, which, however, is not very precise. Several authors believe that this test is not specific enough to study the development of allergic reaction against metals in patient with artificial joints.

There are better, more specific and more reliable laboratory methods to measure the patient’s hypersensitivity against the metals. These laboratory methods measure directly the response of the patient’s T-lymphocytes on contact with the studied metals (most often cobalt, chrome, titanium, nickel). “These methods remain a labor-intensive and clinically unpopular means of assessment” of metal allergy says one renowned scientist (Youn-Soo Park 2005).

Thus, to date (Mars 2007) there are no standardized and generally acknowledged methods for testing patient’s allergy against metal implants.

Metal allergy and failure of total joints

It is well known that patients with metal-on –metal total hips have high blood levels of the metals cobalt and chrome. The question arises whether these patients with high blood levels of metals are also more prone to develop allergy against the metals that circulate in the blood. Can such allergy lead to the failure of the total hip or to other complications, such as severe pain around the total hip?

The surgeons are divided about the question whether artificial total joints, which are manufactured from metals, may produce allergic immune reaction in the patient's body against the artificial joints. The discussion is at present concentrated on metal-on-metal total and superficial hip joints because patients with these joints have high levels of metals (mainly cobalt and chrome) in their blood and urine.

The mechanism of allergic reaction against metals

The products of corrosion of metals combine with patient’s own proteins. These complex substances (called haptens) may eventually sensitize the patient against the specific metal that circulates in the patient’s blood. When the patients immune system is once triggered (sensitized) it then may go to attack also against the artificial hip joint itself, because it perceives the artificial joint as an “alien” - which it actually is.

Such an allergic attack is against surgeons desires, because the surgeons strive to produce a "biocompatible" artificial joint. The patient's body should perceive the artificial joint as a "compatible" with other parts of the body; the artificial joint should be "biocompatible".

The body’s immune system has patrolling polices called T-lymphocytes, a special kind of white blood cells that execute body’s defense against intruders. These cells have excellent “memory" that is placed on their surfaces.

In sensitized patients the T-lymphocytes are specifically pointed against the metals. Masses of T-lymphocytes are produced in lymph glands and wander within the blood stream to the places where metallic particles are: tissues around the artificial joint but also to organs that store the small metallic wear particles (liver, spleen, lymphatic glands in the pelvis). On these places the white bloods form round clusters, small and large. From these clusters are then released enzymes that produce inflammation in the soft tissues that should “destroy” the metallic particles.

Picture:

A cluster of T-lymphocytes assembled around a small blood vessel in the soft tissues around a metal-on-metal total hip joint. This is a microscopic picture and the cluster is small. The black dots in the picture are individual T-lymphocytes. The cells inside such cluster may produce substances that start inflammation.

Many small clusters may also coalesce and form large tumors that need surgical removal. :

The question is: Can this inflammatory reaction dissolve the bone tissue around the metal-on-metal total joint and cause its failure?

Harmful effects of allergic reaction against metal.

There are many ways how the allergic reaction against metal may damage the artificial metal-on-metal hip joint:

First, the T-lymphocytes assembled around the artificial hip joint may start bone dissolving process (osteolysis) so that the artificial joint will become loose and fail or the skeleton around it will break (Boehler 2002,Youn-Soo Park 2005). As yet there are only indirect proofs that this action is possible.

Second, the clustered T-lymphocytes may form very large masses that propagate to the pelvis that need operative removal (Boardman 2006). Such rare complications were really published. Together with the removal of these large masses the surgeon was forced to remove the metal-on-metal bearing surfaces of the artificial hip joint that started the inflammatory reaction and replace them with ceramic-on-ceramic or ceramic-on-polyethylene bearing surfaces.

Third, the allergic reaction against metal may cause unexplained pain in the artificial hip joint area. The pain disappeared only when the metal-on-metal joint was removed and replaced by a total joint with non-metallic surfaces (Willert H-G 2005). Again, there are surgeons denying that such complication is possible, although such rare complications were published.

Fourth, in some patients the allergic reaction may cause troublesome skin changes- rash and eczema (Hallal 2001, Niki 2005).

Large clusters of T-lymphocytes were also found in liver and spleen around the tiny metallic wear particles that are deposed in these organs in patients with metal-on-metal artificial hip joints. The significance and consequences of these findings is not clear (Willert 2005)

Conclusion

Answers on the three questions asked at the start of this page are at present (April 2007) still much like the answers and opinions held in the 2001 by the American scientist Nadim Hallab:

When a patient is known to be allergic to nickel the majority of surgeons believe today that such patient should have an artificial hip made from alloys devoid of nickel (practically only titanium alloys fulfill this condition) because metal sensitivity can be a contributing factor in implant failure.

It is unclear whether allergic reactions to metallic total joints cause unclear pain in other than a few highly predisposed people. But it is clear that some patients have excessive eczematous skin reactions directly associated with implanted metallic materials. Removal of the implants (change to ceramic total joint) will heal these skin changes.

Some scientists believe that metal sensitivity may exist as an extremely rare complication that causes total joint / implant failure in only a few highly susceptible patients (that is, less than 1% of joint-replacement patients), or it may be a more common risk factor to total joint / implant failure according to other scientists.

It is likely that cases involving total joint /implant-related metal sensitivity have been underreported because of the difficulty of diagnosis. Thus, the degree to which a known skin metal hypersensitivity may elicit an overaggressive immune response in patients receiving metal-on-metal artificial hip joint remains unpredictable. At this time, there is no evidence that there is an increased risk of an allergic reaction to an implanted device in patients who have skin patch metal sensitivity but no history of reaction to metallic materials.

The question whether patients should be tested for metal sensitivity before the artificial joint replacement operation has as yet no definite answer.

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References:

Boardman, D.R et al: A benign psoas mass following metal-on-metal resurfacing of the hip. J Bone Joint Surg-Br 2006; 88-B: 402- 4

Boehler M. et al: Adverse tissue reactions to wear particles from Co-alloy articulations.. J Bone Joint Surg-Br 2002; 84-B: 128 -36

Hallab N et al: Metal sensitivity in patients with orthopaedic implants. J Bone Joint Surg-Am 2001; 83-A: 428-36.

Niki et al: Screening for symptomatic metal sensitivity: a prospective study of 92 patients undergoing total knee arthroplasty. Biomaterials. 2005 Mar;26(9):1019-26

Willert H-G et al: Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints. J Bone Joint Surg-Am 2005; 87-A: 28 – 36

Youn-Soo Park: Early osteolysis following second-generation metal-on-metal hip replacement. J Bone Joint Surg-Am 2005; 87-A: 1515- 21

Last revised March 2007