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Metallosis and Metal-on-Metal Implants

Hip-replacement surgeries ease pain and increase mobility for thousands of patients each year. But an unexpected side effect from some devices is metallosis, a type of metal poisoning. The condition, linked to metal-on-metal hip implants, causes muscle pain, tissue death, bone damage and other problems. Patients may face other risks from hip-replacement surgeries.

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What Causes Metallosis?

Metal-on-metal hip implants were introduced as more durable than other types of implants. But metal debris — usually chromium or cobalt — can be released into a patient’s body as the implant’s ball and socket rub against each other.

This can lead to reactions such as inflammation and pain, often forcing patients to have a procedure to replace the implant, known as revision surgery.

Hip implants are comprised of three components: the ball-shaped femoral head, femoral stem and acetabular socket. The ball and socket slide against each other during everyday use, causing friction that wears off tiny particles of debris.

While your surgeon will take precautions to minimize risks and potential wear between implant bearing surfaces, all artificial hips — regardless of construction, material and attention to design — undergo some degree of wear and break down over time.

Metal-on-metal implants are no exception. During normal use of the hip joint, metal ions and debris are released into the area of the implant due to movement of the two metal surfaces against each other. This can also occur at the interface or junction of the modular components of the device. Metal ions can also circulate and affect other parts of the body. Implant debris of any kind can lead to complications such as osteolysis, or bone loss.

However, the effects can be more varied, severe and widespread with metal-on-metal implants, in part because of the smaller size and larger surface area of the particles. Because different people respond in different ways to the metal-wear debris, it can be difficult to predict what reactions might occur.

What are the Symptoms of Metallosis?

Metallosis can lead to serious complications affecting the nervous system, skin and other organs. Symptoms typically evolve over several months and they are always present within the first four years after surgery, a study found. Metallosis often involves the following symptoms:

  • Cardiomyopathy (heart problems), including heart failure
  • Psychological status change (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
  • Infection
  • Implant loosening

Metallosis Risk Varies by Individual

Populations with a High Risk of Metallosis

Certain patient populations have a higher risk of suffering from the disease. These may include patients with

  • Bilateral implants

  • High levels of physical activity

  • Evidence of renal insufficiency

  • Suppressed immune system

  • Suboptimal alignment of device components

  • Suspected metal sensitivity

Because each person can react differently to high levels of cobalt, the symptoms of metallosis may vary. One of the most common symptoms of metallosis is tissue or bone death – called necrosis. With this condition, the tissue around the implant turns gray or black from being exposed to the metal debris flaking off the implant. 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. When excessive metals build 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, sometimes the body is overwhelmed by the amount of metal, and this can cause a number of complications.

Metallosis Found in Men with Metal-on-Metal Implants

One orthopaedic 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
  • Breathlessness
  • 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 that led to these symptoms. Both patients had revision surgery, which revealed tissue necrosis around the implants.

Symptoms of Metallosis Specific to Cobalt Levels

The symptoms of metallosis correspond to the level of metal ions in the blood and become more severe as the levels rise, as this study shows: Cobalt level in micrograms per liter of blood (>µg/L)

Levels, 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

While a metallosis link to cancer has not been proven, the World Health Organization (WHO) International Agency for Research on Cancer lists one type of chromium — trivalent — and cobalt as potential carcinogens.

Metal-on-metal Implant Recalls, Failures

Metal-on-metal hip replacements have experienced an unusually high failure rate, as high as 43 percent for one model. Several models have been subject to voluntary recalls. The U.S., UK, Australia and Canada have each issued health warnings related to the failure of metal-on-metal hip replacements.

Metal-on-metal (MoM) implants were marketed as more durable than other types of implants, with less wear and tear. They were said to decrease the chance of dislocation (when the ball of the femur slips out of its socket) or device fracture.

However, MoM implants have proven prone to a number of unexpected and severe side effects and experience a higher failure rate than other types of implants. Several models of metal-on-metal hip replacement have been recalled by regulating agencies and manufacturers.

Metal-on-metal hip replacements have experienced an unusually high failure rate, as high as 43 percent for one model. Several models have been subject to voluntary recalls. The U.S., UK, Australia and Canada have each issued health warnings related to the failure of metal-on-metal hip replacements.

In the U.S., there are currently five types of hip implants available, classified based on the materials used for each surface. Some implants are better suited to younger, active individuals, while others are more commonly used in older recipients. Factors that influence how long the implant lasts depend on the needs and characteristics of the individual as well as the type of implant chosen.

Hip-replacement Surgeries on the Rise

Hip pain is a harsh reality of aging. One out of every four men over 50 will suffer from a painful bone fracture caused by osteoporosis, a progressive loss of bone density.

The chances of bone fractures for women are higher: One out of every two women over 50 will experience bone-fracture agony. The most serious osteoporotic fractures develop at the hip, a joint essential for walking and standing. Patients experiencing hip pain have numerous non-surgical options, but depending on the type of damage and effectiveness of treatments like physical therapy and medication, a hip resurfacing or replacement may be necessary. Your doctor or an orthopedic specialist can help you determine the best course of action to manage hip pain.

Aging, heredity, diet and lifestyle are all factors in osteoporosis, as are certain medications and medical conditions. Osteoporosis is often a factor in hip fractures, which frequently lead to hip-replacement surgery. Total hip replacements are increasingly popular.

Roughly 310,800 inpatient procedures on individuals ages 45 and older were performed in 2010, up from 138,700 in 2000, according to the National Center for Health Statistics. Due to an aging population and a lack of focus on bone health in the past, the number of hip fractures in the United States could double or triple by 2020.

Hip replacement, also known as hip arthroplasty, is one of the most common surgical procedures in the United States as a way to correct a variety of types of hip pain. Reasons for hip-replacement surgeries include:

Roughly 310,800 inpatient procedures on individuals ages 45 and older were performed in 2010, up from 138,700 in 2000, according to the National Center for Health Statistics. Due to an aging population and a lack of focus on bone health in the past, the number of hip fractures in the United States could double or triple by 2020.

Osteoarthritis is age-related wear and tear on the knee joint and usually occurs in people older than 50.

Rheumatoid arthritis causes the immune system to attack the membranes in the knee and creates damage and cartilage wear.

Traumatic arthritis results from a serious knee injury (fracture, ligament damage, meniscus tear). This weakens the joint.

Avascular necrosis (AVN) is a condition that affects teenagers and young adults. The bones in the knee become soft, causing the bone and cartilage to wear down. This usually resolves during adulthood, but in some cases the wear on the bone is extensive and arthritis sets in.

Abnormal formation or alignment, sometimes called being “knock-kneed” or “bow-legged,” creates high stress on joint and causes abnormal wear.

Childhood Hip Disease, even when treated successfully, hip problems in children can cause the hips to heal irregularly or develop improperly, leading to pain later in life.

Osteoporosis and Hip Fracture can make hip-replacement surgery more difficult in cases when the bone has deteriorated so much that it can’t support the weight of the implant. It can also contribute to implant failure. Hip replacements that utilize a cementless femoral stem have a higher incidence of periprosthetic fracture in patients with osteoporosis, and total hip arthroplasty after a hip fracture may make dislocation more common.

Revision Surgeries After Metal-on-Metal Implants

If complications from a hip replacement procedure persist, or your implant fails, corrective surgery may be necessary to make the hip stable again. Corrective surgery is also a treatment for metallosis through the removal of the implant linked to metal buildups. Drugs are also an option for treating metal poisoning. Certain medications bind to metals, allowing release through urination.

Corrective surgery may include tightening the muscles and ligaments in the area. In some cases, it may require replacing the entire device. Metal-on-metal hip implants are more prone to this than other types of hip replacement.

Series of Tests used to Diagnosis Implant Problems

If you are exhibiting implant-problem symptoms, a series of tests will help determine if the implant is failing for any reason.

X-rays are useful for detecting bone loss and implant wear and tear. Comparison to previous X-ray results can often determine whether an implant has failed due to loosening. For this reason, regular follow-up radiography is often recommended after a hip implant procedure, so potential problems can be identified early.

A complete blood count, erythrocyte sedimentation rate (ESR), and a C-reactive protein test (CRP) can all help determine if an infection is present. Doctors may remove joint fluid for analysis or perform a variety of imaging tests.

Revision Surgeries More Complex Than Initial Replacement Procedure

A revision surgery procedure will vary depending on a variety of factors, including what complications the surgery is meant to address, whether the entire implant needs to be replaced, and the condition of the remaining bone. It is more complex than the initial replacement procedure, and has a higher risk of side effects.

Patients undergoing revision surgery will often require blood donation prior to the surgery to account for the more extensive dissection that the procedure requires. The incision may utilize the scar from the initial hip replacement, but is generally larger to simplify implant removal and replacement. Scar tissue will often need to be removed as well.

If some parts of the implant are still functioning properly, the surgeon may choose to leave them in place.

Revision Surgeries may Result in Various Outcomes

If the devices failed, the surgeon may use several methods to remove the implant, including specialized cutting tools or surgically splitting the femur to facilitate component removal. The method used depends on a variety of factors. In cases involving significant osteolysis, bone reconstruction may be needed before a new implant can be placed. This can be achieved through bone grafts, through the addition of artificial components such as metallic plates, or through a combination of the two.

Implants used for revision surgeries may be larger than those used for a first replacement to compensate for bone loss. In particular, the femoral stem is often longer. Patients who dislocate their hip implant are at risk of repetitive dislocations because the initial dislocation can distort the musculature around the joint. Patients who are very old, or who had their hip replaced after a fracture, are also more prone to this complication.

The surgeon has several options to prevent further dislocations. They may adjust the components of the implant, replace one or more components, or utilize a device known as a constrained socket that helps hold the implant ball in place.

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