Metallosis is a type of metal poisoning that can occur as a side effect of joint replacement devices with metal components, such as metal-on-metal hip implants or some knee implants. These devices are made from a blend of several different metals, including chromium, cobalt, nickel, titanium and molybdenum. When the metal parts rub against each other, they release microscopic metal particles into the blood and surrounding tissues.
Metal poisoning occurs when toxic levels of metal build up in the body. This can cause damage to tissue, bone and the nervous system. People can be exposed to high levels of metal through their environment and diet. Unapproved or counterfeit medications and natural remedies may also contain aluminum, mercury, lead or uranium. But people can also get metal poisoning from metal-on-metal hip or knee replacements.
A small number of people may have sensitivities to these materials. Allergies to nickel are the most common causes of metal poisoning. Exposure to metal in the blood and surrounding tissues can lead to several complications, including implant failure, tissue and bone death, and organ damage that may require revision surgery.
People who smoke may have a greater risk of metallosis. A study reported at the American Academy of Orthopaedic Surgeons 2012 annual meeting in San Francisco found the metal-on-metal implant failure rate for smokers was 9.1 percent compared with 3.4 percent for nonsmokers.
Some metal-on-metal hip implants, such as the DePuy ASR, use a metal ball and cup. Others, such as the Stryker Rejuvenate and ABG II, use a metal neck and stem. Each of these components is made of cobalt and chromium. Both total hip replacement and hip resurfacing systems can cause metallosis, though the rate is higher with resurfacing components.
What are Common Symptoms of Metallosis?
Hip replacement surgery resulting in metallosis can lead to serious complications affecting the nervous system, skin and other organs. One report by Dr. James Pritchett found that symptoms evolved over several months and were present within the first four years after surgery.
Pain is not always an indicator of metallosis. For example, 18 percent of hip resurfacing patients had groin pain, but only 2 to 5 percent had metallosis.
Metallosis often causes the following symptoms:
- Cardiomyopathy (heart problems), including heart failure
- Depression, anxiety and other mental problems
- Visual impairment that may lead to blindness
- Cognitive impairment
- Nerve problems
- Thyroid problems
- Auditory impairment that may lead to deafness
- Skin rashes
- Noise coming from the hip
- Implant loosening
Because each person can react differently to high levels of cobalt, the symptoms of metallosis may vary. The symptoms of metallosis correspond to the level of metal ions in the blood and become more severe as the levels rise.
Symptoms of Metallosis Specific to Serum Cobalt Levels:
|Cobalt Level in Micrograms per Liter of Blood (>µg/L)||Possible Symptoms|
|1 – 5||Heart and memory problems|
|> 7||Hip pain, tissue necrosis, pseudotumors|
|23||Hip pain, mental problems (concentration, memory), vertigo, some deafness|
|> 66||Blindness, hip pain, deafness, seizures, tremor, heart failure, goiter, rashes, abnormal blood pressure, depression, weakness|
One of the most common is tissue or bone death (necrosis). With tissue or bone necrosis, the tissue around the implant turns gray or black from being exposed to the metal debris. This creates pain and instability, which can lead to spontaneous dislocation, bone loss and fracture.
On occasion, non-cancerous pockets of fluid called pseudotumors will form around the affected tissue. The fluid from these pockets or effusions contains gray, rust or cloudy yellow fluid. In addition to tissue reactions around the joint, high levels of cobalt in the blood can also cause other symptoms.
Metallosis and Cancer
A metallosis link to cancer has not been proven, but the World Health Organization International Agency for Research on Cancer lists cobalt and trivalent, a type of chromium, as potential carcinogens. After thousands of metal-on-metal implants failed, the London Implant Retrieval Centre released test results confirming that the implants released trivalent chromium ions. Thus, metal-on-metal hip implants may contain particles that cause cancer.
Cobalt & Chromium Hip Implants
Naturally, the body stores a certain level of cobalt and chromium for healthy cellular function. But when metal implant components rub together, they release cobalt and chromium ions into the surrounding tissues and into the bloodstream. This creates toxic levels in the body, leading to metallosis.
Metallosis is similar to cobalt poisoning, which a person can get by breathing in too much cobalt, swallowing too much of it or having prolonged skin contact with it. Manufacturers use cobalt in products such as dyes, batteries, alloys and machine tools.
Ingesting or inhaling too much cobalt may lead to deafness, thyroid problems, nerve problems and heart problems. The same problems can occur in hip implant patients if the amount of metal ions in the blood is excessive.
When excessive metal builds up near the joint, the lymph nodes and surrounding joint fluid attempt to “clean” the body by absorbing the ions and transporting them to the kidneys, where they are removed from the body in the urine. However, the body can be overwhelmed by the amount of metal.
Cobalt-chromium (CoCr) implants are the most corrosion-resistant implants. Doctors began using them in the 1950s. Hip patients developed pain and instability in the joint less than five years after hip replacement surgery – some as early as nine months after receiving the implant.
Doctors found the tissue surrounding the implant was stained green or grey and surrounded with a paste-like material. Joint fluid tests revealed high levels of cobalt.
The first published reports of metallosis surfaced in the 1970s. The studies revealed that these prostheses released cobalt and chromium ions into tissues, joint fluid, blood and urine, but it wasn’t until recently that metallosis became more widespread because of increased metal-on-metal implant use.
The studies did not deter manufacturers from making these implants, and in the early 2000s metal-on-metal total hip replacement and hip resurfacing implants grew in popularity.
Manufacturers claimed that newer metal-on-metal hips were designed with larger articulation surfaces to cut down on dislocation. The companies said the metal implants lasted longer. Studies showed they were more durable. But the new prostheses had a large surface that created metal debris and had a higher failure rate. Those injured filed lawsuits against hip replacement manufacturers for failing to warn them about metallosis and for defective design.
Severe Metallosis Cases
One orthopedic doctor, Stephen S. Tower, wrote about two cases of metallosis in the 2010 State of Alaska Epidemiology Bulletin. Both patients were fit, healthy 49-year-old men who received metal-on-metal implants.
Within a year of receiving the implants, both men suffered from:
- Groin pain
- Skin rashes
- Poor memory and mental fogginess
- Vertigo headaches
- Hearing loss
Despite normal kidney function, both men had toxic levels of cobalt in the blood. Each patient had revision surgery, which revealed tissue necrosis around the implants.
Doctors usually diagnose metallosis by doing a blood test in patients who complain of symptoms. The U.S. Food and Drug Administration has not recommended a safe level of metal ions in the blood because there are few studies.
Every person with a metal-on-metal implant has elevated levels of cobalt. The normal measurement for cobalt in joint fluid (serum) is typically less than 2 micrograms per liter (µg/L).
A 2012 report in the British Medical Journal stated that the Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) limit for cobalt in the blood was 5 µg/L.
Patients with some metal-on-metal hip implants showed levels above 5 µg/L a few months after implantation. The two severely poisoned patients from Dr. Tower’s Alaskan study had levels at 122 µg/L and 23 µg/L.
Imaging tests, such as X-rays and MRIs, may also help find tissue damage before pain occurs. Dr. Hollis Potter of the Hospital for Special Surgery in New York City advocated for using an MRI to detect tissue damage early.
Who is at Risk of Developing Metallosis?
Anyone who receives a metal-on-metal hip implant is at risk of developing metallosis. However, some people might be at greater risk for suffering problems from excessive amounts of metal ions in the blood.
According to the FDA, these factors are associated with a higher risk of suffering adverse events from metal ions:
- Women are at a higher risk than men
- Bilateral implants
- Femoral heads 44mm or smaller
- High doses of corticosteroids
- Renal insufficiency
- Suppressed immune systems
- Suboptimal alignment of device components
- Suspected metal sensitivity
- Severely overweight
- High levels of physical activity
People with any of those risk factors should talk to their doctor about testing for high levels of metals.
Aside from revision surgery, there are few treatments for metallosis. There have been some studies on chelation therapy to remove excess metal from the body. Chelating agents are administered orally, intravenously or intramuscularly. They bind metal ions and remove them from the body. Chelation therapy is used to treat lead, arsenic, iron and mercury poisoning.
However, excess cobalt cannot be chelated from the joint or fluid, so this type of treatment does not work well with metallosis. The only proven treatment is revision surgery, and early diagnosis leads to a better surgical outcome. Dr. Tower’s Alaskan patients with severe metallosis had surgery to remove the metal implants, and both patients showed improvement.
With severe metallosis, the amount of tissue and bone necrosis determines the outcome of the surgery. Some patients suffer fractures during revision surgery because of weak bones and extensive tissue damage. During revision surgery, surgeons replace the metal-on-metal implant with a ceramic-on-metal or plastic-on-metal implant to minimize future problems with metal ions.
Metallosis and the FDA
The FDA refers to metallosis as “adverse local tissue reaction” or “adverse reaction to metal debris.” According to the FDA, metal-on-metal implants pose more risks than other hip implants because of the metal ions that enter the tissue.
In 2012, after two days of hearings to investigate the safety of metal-on-metal hip implants, an 18-member FDA panel found little reason for doctors to continue using the devices.
The opinion came after reports of nearly 17,000 patient injuries caused by hip implants made by medical device companies, such as DePuy Orthopaedics and Zimmer Holdings.
The chief complaint was that as the devices wear, they release metallic particles into the body that cause muscle and tissue damage among other serious complications.
The FDA warned that these ions can cause implant loosening, pain and illness. The agency recommended that patients with metal-on-metal implants follow up with their doctors if they had symptoms. It also recommended that patients with extreme symptoms be considered for earlier revision surgery to minimize tissue, muscle and bone damage.
Patients without symptoms were encouraged to see their doctor every one to two years. The FDA does not recommend routine blood tests to check metal levels. The FDA has yet to determine the full extent of the damage caused by metal ions.
Most manufacturers recalled or discontinued metal-on-metal hip implant products after thousands of patients were injured by the devices. However, the FDA has not banned the devices despite the risks associated with them.