Introduction:
Cobalt poisoning refers to the intoxication of cobalt metal in excessive amounts than needed by the body. The estimated quantity of cobalt required to prevent pernicious anemia is in the range of 150 to 500 mg/kg. But, excessive cobalt can prevent cell mechanisms. Cobalt poisoning has been discussed since 1948.
Cobalt poisoning can happen from long-term cobalt dust exposure from a living or working environment, beer drinking (cobalt adulteration), or wear and tear of arthroplasty (an artificial substitute placed surgically as a joint replacement) implants made from cobalt metal.
What Is Arthroprosthetic Cobaltism?
Orthopedic implants made of metal components have been used as joint replacements for more than 50 years. Cobalt has been one of the most important alloys in those metal structures. Cobalt poisoning related to arthroplasty implants is known as arthroprosthetic cobaltism. Chrome-cobalt alloys have been used as a material of choice in prosthetic implants for long years.
In general, the liver and the kidney eliminate excess cobalt from the body through excretion. However, chronic exposure to cobalt metal can lead to significant damage to the vital organs of the body.
How Does Arthroprosthetic Cobaltism Develop?
Arthroprosthetic cobaltism is a major concern, especially in hip replacement surgery using chrome-cobalt alloys. Naturally, the hip joint is a ball and socket type of joint between the cup-shaped cavity of the hip bone and the ball head of the thigh bone. Therefore, during replacement, the ball and socket form is maintained to preserve the joint’s range of motion. A metal sphere is used as a ball head, and a metal cup is used as a socket, thus providing a metal-on-metal (MOM) gliding action during hip and leg movements.
In the long run, the metal on the metal surface starts to wear and corrode, leading to periprosthetic metallosis (local inflammatory changes around the metal-replaced joint) and hypercobaltemia (increased level of cobalt in the blood).
What Are the Manifestations of Arthroprosthetic Cobaltism?
The clinical manifestation of arthroprosthetic cobaltism includes:
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Altered brain function and neurological problems like headache, mental disturbances, anxiety, depression, dizziness, visual impairment, and hearing loss.
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Cardiological issues explicit various heart failure symptoms that are non-coronary artery disease-related.
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Hypothyroidism (the decreased activity of the thyroid gland).
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Generalized body weakness and fatigue.
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Sleep and mood disturbances.
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Increased risk of cancer.
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Genetical changes.
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Reproductive dysfunction.
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Muscle wastage.
What Are the Grades of Arthroprosthetic Cobaltism?
The cardiovascular and neurological manifestations can be graded into five groups. They are:
What Are the Guidelines for Evaluating Arthroprosthetic Cobaltism?
Specific guidelines have been issued by two of the most important healthcare agencies to evaluate arthroprosthetic cobaltism.
- Food and Drug Administration (FDA) Guidelines: The Food and Drug Administration (FDA) has recommended a few follow-up investigations after placing metal orthopedic implants. These guidelines are issued for orthopedic surgeons pertaining to metal-on-metal hip replacement implants.
1. For Symptomatic Patients:
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Clinically evaluate the condition once in six months.
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Check for soft tissue changes using magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound.
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Monitor the level of serum metal ions, preferably with EDTA-anticoagulated blood (best for cobalt testing).
2. For Asymptomatic Patients:
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Even though the patients do not show any symptoms, it is advisable to have a clinical evaluation at least once a year or two.
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Other investigations like soft tissue imaging or metal ions testing are not necessary if the prosthetic implants are functioning properly.
If a general physician or other healthcare professionals find a patient with metal ion toxicity symptoms, they must immediately be redirected to the orthopedic surgeons to analyze the situation and take appropriate action.
- Medicines and Healthcare Products Regulatory Agency (MHRA) Guidelines:
The Medicines and Healthcare products Regulatory Agency (MHRA) recommendations provide threshold values to evaluate arthroprosthetic cobaltism.
1. For Symptomatic Patients:
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The patients must be evaluated every year for the rest of their lifetime.
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MARS MRI (metal artifact reduction sequences - magnetic resonance imaging) and ultrasound are recommended in all symptomatic patients.
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The patients should undergo a whole blood metal ion test.
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If the resultant level is above 7 ppb (parts per billion), it indicates a potential soft tissue reaction.
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The whole blood metal ion test is repeated after three months.
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If the result of the second metal ion test is also above 7 ppb, or higher than the previous test, the suspicion for soft tissue changes increases.
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Finally, it is advisable to consider a revision surgery if both imaging and metal ion levels are abnormal.
2. For Asymptomatic Patients: The recommendations for asymptomatic patients depend on the type and size of the metal prosthetic replacement.
How to Manage Arthroprosthetic Cobaltism?
The literature has not provided a specific treatment for arthroprosthetic cobaltism. Few scientific papers have demonstrated certain modalities for arthroprosthetic cobaltism. They are:
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Medications used are beta-blockers (manage abnormal heart rhythms), angiotensin converting enzymes (ACE) - inhibitors (manage high blood pressure and heart failure), and Diuretics (get rid of excess sodium and water from the body). These drugs have shown good clinical responses.
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The patients with high serum cobalt levels showed improvement in symptoms with the administration of Unithiol (2,3-dimercaptopropane 1-sulfonate) - a chelating agent.
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Hemodiafiltration (kidney replacement therapy) may be performed to remove the toxic metal from the blood.
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Ethylenediaminetetraacetic acid (EDTA) - a chelating agent, has been used to decline the blood cobalt value.
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Ultimately, hardware removal was performed in revision surgeries, and the metal was replaced with ceramic material with polyethylene liner.
Most of the signs and symptoms of arthroprosthetic cobaltism, like thyroid dysfunction, vertigo, cardiomyopathy, hearing loss, and anemia, have been reported to show improvement following hardware removal. However, neurological symptoms and optic atrophy have shown variable resolution.
Conclusion:
Arthroprosthetic cobaltism is a rare phenomenon, but when occurring, its consequences are devastating. The manifestations can be harmful both locally and systemically. There are no definitive treatment plans in the literature. The evidence-based treatment strategy is followed to manage arthroprosthetic cobaltism. Early diagnosis and intervention will give a better treatment outcome.
