Cobalt Chromium Toxicity

The Latest Research

The 510 (k) process and metal on metal hip implants


Currently, various medical devices enter the marketplace via a regulatory pathway, the 510(k) process, monitored by the Food and Drug Administration (FDA). The 510(k) process loosely evaluates for safety and effectiveness, and approves the clearance of new medical devices based on ones that are substantially similar and previously cleared.

There are 3 classes of devices:

  1. Class 1: low-risk devices (e.g. toothbrushes, dental floss, band aids). Class 1 devices are subject to minimal regulatory controls. 
  2. Class 2: moderate- risk devices (e.g. powered wheelchairs). Class 2 devices require greater regulatory controls. 
  3. Class 3: highest-risk devices (e.g. metal on metal hips, replacement heart valves). Class 3 devices are supposed to undergo the highest level of regulatory control known as Premarket Approval, or PMA. 

According to the FDA, Premarket Approval (PMA) requires manufacturers to submit an application if they intend to market any new products containing new materials or differing in design from products already on the market. A PMA submission must provide valid scientific evidence collected from human clinical trials showing the device is safe and effective for its intended use.

However, many class 3 devices do not undergo PMA. They are cleared through the 510 (k) process, claiming substantial equivalence to preamendment devices, or comparable devices already on the market. Unfortunately, this allows companies a means of avoidance in testing their products for safety and effectiveness before releasing them on the market.

 

Closer Look between Metal on Metal Hip Prostheses and Cobalt-Chromium Toxicity


There is recent interest in the health consequences attributed to metal on metal hip implants and toxic levels of chromium and cobalt released from bearing surfaces and metallic junctions. There are various sources of cobalt and chromium exposure such as occupational and environmental.  Nowadays, concern over cobalt and chromium toxicity is focused on the corrosion of biomedical implants, like metal on metal (MoM) prostheses. The effect of toxicity from these metal ions is dependent on a multitude of factors. For instance, in an industrial setting, toxicity is influenced by the duration of exposure, ion concentration, and entry routes into the body (i.e. skin or respiration). On the other hand, the release of cobalt and chromium ions from MoM devices is an internal exposure rather than external. However, toxicity from MoM implants is contingent on duration of exposure and chemical composition of the implant. According to the article, “It has been determined that these implants release particulate metal debris in the form of corrosion with or without abrasion particles.”

Patients who underwent MoM hip replacement have a range of 5-100 parts per billion of chromium and 5-300 parts per billion of cobalt present in their blood and tissues. In addition, patients also suffer from adverse local tissue reactions (ALTR) and adverse reaction to metallic debris (ARMD) leading to tissue necrosis, pseudotumors, and lesions. The reactions are caused by a combination of metal toxicity and a hypersensitivity reaction. Analysis of tissue recovered from patient with MoM implants revealed necrosis from metal wear debris and corrosion products in the surrounding tissue. Elevated levels of cobalt and chromium ions were also detected in the collected tissue samples in comparison to controls. The study demonstrated a 2.5 fold increase of tissue cobalt levels and a 9 fold increase of tissue chromium levels in patients with MoM hips compared to the controls.

It is natural to have trace amounts of chromium and cobalt because they are required for certain metabolic functions. Glucose metabolism requires chromium to increase the effects of insulin on carbohydrates. Cobalt is involved with Vitamin B12’s biological activity. Only a few specific proteins use the metals and therefore require only trace amounts. However, cobalt and chromium are extremely toxic at high concentrations. The study indicates the effects of cobalt toxicity include irreversible cardiomyopathy, vision or hearing impairments, hypothyroidism, and polycythemia. The effects of chromium toxicity are associated with damage to multiple tissues and kidney and liver failure. Patients implanted with MoM hip prostheses develop an “accelerated inflammatory reaction frequently associated with tissue necrosis and cellular toxicity”. This is known to cause necrotic tissue and formation of pseudotumors.  Furthermore, cobalt and chromium toxicity can interfere and impair certain biological mechanisms and functions and lead to necrotic and apoptotic cell death.

Source: Molecular analysis of chromium and cobalt-related toxicity

Risk of Infection From Metal on Metal Wear


There is literature and research suggesting a risk of infection from wear products in metal on metal (MOM) hip implants. According to this article, wear products may hinder the immune system via accelerating bacterial growth, possible antibiotic resistance, and a heavy metal reaction. MOM implants were popularized as a result of their supposed longevity. However, metals employed in MOM hip implants degrade from wear, corrosion, and over time. MOM bearings release small amounts of metal ions or particles, and in relatively high numbers results in corrosion. Metal debris in the body prompts an inflammatory response. An inflammatory response stems from various pathological changes in the body. Metal debris can cause adverse local tissue reactions (ALTR), hypersensitivity, and osteolysis (destruction of bone). Recent studies found metal debris presents an ideal environment for bacterial growth.

A major concern for patients is the release of metal into the tissues secondary to wear and corrosion from MOM hip devices. Specifically, rough particles from MOM implants cause local damage, such as ALTR. This results in an increase of metal particles and ions released into the blood stream and surrounding tissues. The article highlights that the nature, size, and amount of particles can determine the effects it has on the body, and subsequently, the body’s reaction to those effects. Metal ions are generated even in MOM implants with corrosion-resistant alloys. Different types of corrosion cause metal particle release. For instance, fretting corrosion causes damage on the surfaces of articulating structures from movement. Cobalt- chromium alloys release metal ions which can produce toxic effects in the body. The article states that cobalt levels were approximately 6 fold higher in patients post MOM implantation compared to pre-implantation. There is a correlation between wear rates and the amount of metal ion levels; the higher the wear rate, the higher the level of metal ions.

Corrosion from MOM implants can influence the immune system and the immune response via different organs and their immune related mechanisms. Metal ions travel in the body through lymph and blood hindering the immune response. The study reveals that simply having a foreign body is enough to require only a small amount of bacteria to cause an infection. Ion release may damage DNA. Cobalt chromium particles can actually damage DNA via its cellular barrier. Metal particles pose the possibility for carcinogenesis. Patients with MOM implants also have a decrease in the immune cells responsible for destroying tumor cells.

The spleen and liver are vital organs regarding immunological mechanisms.  The spleen is vulnerable to corrosion byproducts which alter the number of immunocompetent cells. This illustrates how metal ions reduce the defense against immunocompromising organisms like bacteria. A recent study indicates that chromium ions can collect in the liver. Elevated metal ions in the liver may stimulate hepatocellular necrosis (death of liver cells). Corrosion products from cobalt chromium implants inhibit the release of cells necessary to kill bacteria. The cobalt chromium particles produce toxicity because they create a low pH concentration in the cells that try to destroy bacteria. In addition, bacteria have developed mechanisms to resist metal toxicity, and as a result, are also becoming resistant to antibiotics. This has significant consequences since patients with MOM prostheses are more susceptible to infection at the implant site.

Source: Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

The correlation between prostheses failure and elevated metal ion levels in patients


This study focuses on whether or not higher metal ions in the blood could help determine the likelihood of prostheses failure in patients with metal on metal (MOM) implants or total hip arthroplasty. The study involved 597 patients who received hip implants approximately one year prior. Patients with failed prostheses and patients with non-failed prostheses were compared via their blood metal ion levels. A prosthetic was considered a failure if they were revised, a revision was pending, or the patient reported poor hip function.

Patients with failed implants had elevated cobalt and chromium blood levels compared to patients with non-failed hips.  Patients with failed hip resurfacing (replacement of the joint’s articular surface) had less blood cobalt levels than patients with failed total hip arthroplasty (surgical removal of the femur’s neck and insertion of a stem deep within the bone connecting with the pelvic socket and liner). There was not a significant difference in blood chromium levels between the two procedures.

The presence and amount of the metal ions were good indicators of whether or not a hip would fail. There was a 23% increase in failure among patients with a total hip arthroplasty for each increase in 1 part per billion (µg/L) of metal ions. Whereas, patients with hip resurfacing had a 5% increase in failure with each increase in 1 part per billion (µg/L ) of metal ions.

In conclusion, there was a direct correlation between higher levels of blood metal ions and metal on metal hip resurfacing and total hip arthroplasty failures.

Source: Surveillance of Patients with Metal-on-metal hip resurfacing and total hip prostheses

Modularity and Total Hip Arthroplasty


Total hip arthroplasty (THA), also known as a hip replacement, involves replacing the hip joint with a prosthetic implant. The surgical procedure is supposed to improve a patient’s quality of life and function. The outdated method of hip replacements was called monoblock. Modularity, implants with at least one modular junction, is employed for total hip arthroplasty. Modularity involves prosthetic hip implant components available in multiple segments, or parts, rather than a single piece (monoblock implants). The popularity of modular implants results from their variations in leg length and size, degree of offset, and version. Modular implants are meant to accommodate a patient’s unique anatomy.

Unfortunately, corrosion, fretting, and fatigue failure of the implants are progressively occurring in the dual modular implants. Evidence suggests a revision rate of 8% to 15% among metal on metal total hip arthroplasty. As a result, modular implants are now under close supervision.

Modularity evolved with the development of the modular femoral head-neck junction. The modular head-neck junction utilizes metallic alloys head alternatives, leg length and offset adjustment, and bearing replacement resulting from wear. Modularity of the head-neck junction occurs at a taper functioning by joining two rotating components in the hip implant. The two components of the taper are a trunnion and bore. The trunnion compresses the bore when it expands, interlocking the two parts, creating stability. A larger head-neck taper may lead to an increased dislocation rate because the prosthesis is impacted faster by different range of motions. However, smaller tapers may lead to increased junction fretting and corrosion.

The article differentiates between two design features: metaphyseal neck-stem modularity (DePuy), and modular neck or proximal modular stems (Stryker). A metaphyseal modular stem has an implant with a distal junction placed distal to the femoral neck. Whereas the proximal modular stem has the distal junction proximal to the femoral neck. The taper connections undergo various physiological stresses depending on the location of the modular junction. Both tapers have the potential to cause neck-body dissociation, elevated levels of metal debris, fretting, and corrosion. Corrosion is the main source for modular implant failure.

Many modular femoral stems are composed of a cobalt-chromium or titanium alloy. The metal implant can corrode from stresses and disruptions. Metal ions are released secondary to the corrosion resulting in elevated serum metal ion levels. Corrosion and fretting cause loss of mechanical integrity of the implant, local tissue infiltration, and adverse local tissue reactions (ALTR). There are multiple sources for head-neck taper corrosion including crevice, fretting, and galvanic. Fluid can enter a gap between the trunnion and bore causing crevice taper corrosion. Fretting corrosion can occur from movement of the head relative to the neck; this is the main source for failure at the modular junctions. Crevice corrosion is reported in 35% to 40% of mixed-metal tapers, and 9% to 28% in single- alloy tapers.

Corrosion is time-sensitive and accelerated with mechanical stresses. Increased local and systemic metal particle exposure is connected to increased corrosion at the taper. Even in properly working metal on metal hip implants, cobalt chromium levels are roughly five fold higher than in patients with other hips. Head-neck interface corrosion results in inflammatory responses, local osteolysis and synovitis. Subsequently, metal particles were found in various organs. Corrosion byproducts stem from adversely affected metals at the taper junctions. Chromium phosphate is one such byproduct associated with femoral head-neck junction corrosion and substantial inflammation. This inflammation causes bone resorption and osteolytic reactions (bone loss). Corrosion and metallosis results in elevated cobalt levels in synovial fluid; this is linked to thyroiditis, auditory disturbances, and granulomatous lesions. Arthroprosthetic cobaltism, increased cobalt levels, is connected to systemic symptoms from malfunctioning hip implants.

Source: Modularity of the Femoral Component in Total Hip Arthroplasty 

Adverse local tissue responses in hip implants with dual-taper stems


Within the last two decades, modularity in hip implants became the prevalent paradigm. Modularity means prosthetic hip implant components are available in multiple segments, or parts, as opposed to a single piece (monoblock implants). Modular components generally consist of a femoral stem with an extra modular junction between the neck and stem body, known as a dual-taper stem. Dual-taper stems are popular since they allow for variations in length, shape, size, degree of offset, and rotation of the implant. Most hip replacement manufacturers have models with the modular neck design option.

However, this extra modular junction is under scrutiny for potentially causing corrosion between the neck and body stem. Studies show metal debris and adverse local tissue reactions (ALTR) secondary to taper corrosion at the head-neck junction analogous to patients with failed metal on metal hips. This study highlights patients with ALTR from modular neck-body junction corrosion.

The study involves eleven patients, eight women and three men; with a total of twelve hips (one patient had bilateral total hip arthroplasty). The patients were evaluated for ALTR secondary to modular femoral neck-body taper junction corrosion. According to the study, the patients presented with pain approximately 8 months after their initial surgery. The pain among the patients was mainly localized in the groin. However, some patients pain radiated to their buttocks, trochanters (parts of the femur), or thighs. Others experienced severe limps, weakness, and significant leg swelling. Stryker rejuvenate was among the models of implanted metal on metal hips in the patients. Patients were all implanted with hips constructed with a cobalt-chromium alloy modular neck and a titanium-alloy stem.

Before undergoing revision surgery, patients had a preoperative workup. The preoperative workup included blood tests which analyzed elevated white blood cells (checking for inflammation), erythrocyte sedimentation rate (reveals inflammatory activity), and serum metal ion levels (checking for metal sensitivity). Additionally, patients underwent a metal artifact reduction sequence (MARS) MRI to evaluate for any abnormalities.

Serum metal ion lab results demonstrated considerable elevation in serum cobalt and serum chromium levels (cobalt was worse than chromium). The MARS MRI indicated large fluid collections and hypertrophic soft-tissue reactions (pseudotumor formation) in ten of the eleven patients (90.9% of patients). Patients were later diagnosed with taper corrosion and underwent revision surgery roughly 9 months after their symptoms first appeared. Revision surgery in the patients revealed capsular hypertrophy (increased tissue growth) and necrosis (death) of the soft-tissue structures involving the hip joint. Several patients had large soft-tissue masses. The modular junction between the femoral component neck and body established marked corrosion, with taper fretting and black, flaky material deposits at the base of each hip. Microscopic testing showed obvious corrosion at the modular femoral neck-body junction in all devices along with fretting and metal debris.

This study confirms dual-taper stem designs with modular cobalt-chromium-alloy necks may cause pain and significant soft-tissue destruction and death surrounding the implanted hip eventually leading to joint failure. Adverse local tissue reactions and metal debris result from fretting and corrosion at the head-neck junction of the cobalt-chromium alloy head and cobalt-chromium alloy stem. Extensive pitting corrosion and fretting was found in many patients. Head-neck taper corrosion resulted in elevated serum cobalt and serum chromium levels. The cobalt levels were much higher than chromium in the cobalt-chromium alloy.  Blood tests also determined inflammation due to adverse local tissue responses secondary to taper corrosion. The study establishes substantial soft tissue damage from corrosion at the modular neck-body taper of a dual-taper femoral model.

Source: Adverse Local Tissue Reaction Arising from Corrosion at the Femoral Neck-Body Junction in a Dual- Taper Stem with a Cobalt-Chromium Modular Neck, The Journal Of Bone and Joint Surgery

METAL ON METAL CORROSION FROM ACETABULAR LINER TAPER


Metal on metal (MoM) hip replacements and resurfacings are under increasing criticism because of high revision rates and poor patient outcomes. Metal on metal wear and corrosion particles causes adverse local tissue reactions (ALTR). ALTR is associated with elevated levels of metal ions, such as cobalt and chromium, in the blood, and pseudotumors.

Many metal on metal joints, like Stryker and Depuy, are recalled as a result of ALTR to metal on metal wear and corrosion particles. MoM hip replacement issues are correlated with the release of metal ions, metal on metal wear, and corrosion from the implant. Corrosion damage of femoral head-neck tapers and stem-neck junction are well-known sources for these issues. Recently, reports indicated the acetabular liner-shell taper as an additional source of corrosion and fretting wear. These sources are considered in vivo, “within the living”, metal corrosion products. This study focuses primarily on the liner-shell taper.

Data for the study was collected from 36 patients with MoM hips, and modular acetabular cups, undergoing revision surgery between 2011 and 2013. Twenty two percent (8 of the 36) cobalt-chromium alloy liners exhibited obvious and extensive corrosion of the liner-shell taper and material removal. Blood samples were collected from the patients to analyze the presence of cobalt and chromium metal ions. In addition, the liner taper junction was evaluated and scored for damage and severity of corrosion.

The articulating surfaces of metal on metal implants are possibly the main source of elevated metal ion levels. As aforementioned, the head-neck taper connection and wear at the articulating surface are also known to cause metal on metal corrosion, wear and elevated ion levels. The taper junctions of modular femoral heads cause corrosion product release. Corrosion product release results in ALTR and systemic toxicity from metal ion accumulation. The corrosion rates are similar between these taper junctions. Evidence suggests that liner-shell tapers and head-neck taper corrosion pose the same risk to patients.

In recent years, the use of MoM hips has significantly declined.  However, liner corrosion is a present concern for other implants where the modular acetabular shell and liner are joined by a taper junction.

Metal on metal corrosion from acetabular liner taper              Hip implant joints

 

Source: The Journal of Arthroplasty Corrosion on the Acetabular Liner Taper from Retrieved Modular Metal-on-Metal Total Hip Replacements

Correlation between Smoking and Risk of Revision Among Patients with Hip Replacements


Significant Correlation between Smoking and Risk of Revision Among Patients with Metal on metal (MOM) hip replacements

World wide, an estimated one million people are implanted with metal on metal (MOM) hip prostheses. It was originally believed that the MOM prosthesis would have a decrease in implant wear over time. However, recent studies and case reports demonstrate the contrary. MOM total hip arthroplasties indicate a higher failure rate in comparison to other types of hip prostheses. Some prominent effects that result in an elevated failure of the MOM bearings include aseptic loosening (loosening of the total joint replacement) and a hypersensitivity to the metals.

Metal hypersensitivity can cause a myriad of health issues such as osteolysis, severe and chronic pain, infection, and periarticular tissue reactions, which is aptly named an adverse local tissue reaction (ALTR). These all subsequently contribute to the high rate of failure of the MOM prostheses. In addition to the ALTR, there are reported cases of massive bone and tissue necrosis (death) along with the formation of periprosthetic pseudo-tumors. In terms of hip implant revisions, those patients suffering from pseudo-tumors had worse revision rates than those that did not.

Metal hypersensitivity, or metal sensitization and allergy, stems from the release of cobalt and chromium found within the metal bearings. In this study, it is also found that smoking patients with MOM hip prostheses led to poorer results of the hip prostheses than non-smokers. This is due to the association between the traces of cobalt and other metal elements found in cigarette smoke, and the elevated metal ions from the prosthesis. These two sources of metal are potential triggers for an increase in metal hypersensitivity and contribution to a higher risk for revision.

In this study, patients were separated into two groups: never-smokers and ever-smokers. The ever-smokers were further subdivided into current smokers and former smokers. The main concern with the study focused on an all-cause revision, known as any change or removal of a single or multiple prosthetic components. The causes of revision were divided into the following categories: aseptic loosening, infection, dislocation, periprosthetic fracture, impingement, or implant migration. During the revision, findings for ALTR were also recorded. These findings included metallosis, presence of pseudo-tumors, and tissue necrosis (death). In addition to the aforementioned subdivisions, the study was further divided into two sub-cohorts among patients with MOM, cobalt-chromium alloy hip prostheses versus patients with non-metal, ceramic-on-polyethylene (COP) hip prostheses.

The results of the study indicated that ever-smokers in both the MOM and COP cohorts suffered from secondary arthritis as a result of surgery. Among ever-smokers and never-smokers with MOM prostheses, the revision rate was more than tripled for the ever-smokers (8.7 revisions per 1,000 persons) compared to the never-smokers (1.5 revisions per 1,000 persons). The reason for such a discernible difference between never-smokers and ever-smokers with MOM prostheses was an increase in an adverse local tissue reaction (ALTR) among the ever-smokers. In conclusion, there is a strong correlation between smoking and an increase failure rate of MOM hip replacements. This association was not definitively evident among never-smokers and ever-smokers with COP hip arthroplasties.

Source: Strong Association between Smoking and the Risk of Revision in a Cohort Study of Patients with Metal-on-Metal Total Hip Arthroplasty http://onlinelibrary.wiley.com/doi/10.1002/jor.22603/pdf

 

Metal Implants and Hypersensitivity


Metal Hypersensitivity

Metal hypersensitivity is an immune mediated response resulting from exposure to certain metals such as cobalt and chromium. An immune mediated response occurs when there is a trigger, like a foreign agent, that causes an immune reaction. These triggers can range from seasonal allergies to specific cells responding to an exposure of metals. It is important to differentiate between the immune reaction from an allergen, like pollen, and a metalloid material. Whereas a seasonal allergy generates immediate symptoms, like itching, watery eyes, and sneezing, a metal allergy induces a delayed response to the exposure of these elements.

Once your immune system is exposed to new metals, your body creates an immunological memory. This occurs because certain cells called T-lymphocytes recognize the metals as a foreign body and want to create a memory in order to activate immune responses. This is the body’s defense mechanism if the metals continue to be present, or are reintroduced, in the body. After formation of immunological memory, if you are exposed to the metal again, the body will activate an inflammatory reaction in order to better defend against this foreign object. This gives the delayed response of metal hypersensitivity. The symptoms of delayed hypersensitivity are analogous to the reaction you would get from a food allergy or insect sting.

 

Symptoms of Metal Hypersensitivity

Contact dermatitis, most commonly known as a skin rash, is the most suitable way to describe the main symptom of metal hypersensitivity. Other symptoms include but are not limited to: blisters, vesicles, erythema (redness), pruritis (itching), and inflammation around the area of exposure. Due to its delayed nature, symptoms may not appear until a day after contact with the metal and may take many days to return back to normal.

Metal implant devices, such as Metal on metal (MOM) hip prostheses, lead to a more complicated metal hypersensitivity. It is difficult to describe the effects of a MOM implant because the field of visualization is restricted since the device is implanted within the body. However, studies demonstrated an immune response and hypersensitivity in the tissue areas interacting with the debris from implanted devices. Wear debris is the result of movement, friction, metal corrosion (metal oxidation), and metal ions released from the device. This can cause severe pain, swelling, limited range of motion, joint effusion (abnormal buildup of fluid between layers of tissue in or around joints), inflammation, and osteolysis (bone loss).

What happens to my device if I have a metal hypersensitivity?

Wear debris is a by product of corrosion of the implant material. Metal ions and particles are released into the surrounding tissue over time. People with a hypersensitivity to the metals of their implant will react differently compared to those who don’t have an allergy due to the triggering of an adverse response. As previously mentioned, an inflammatory response is triggered when the immune cells are exposed to the metals like cobalt and chromium. The response ranges from mild to severe depending on the extent of the sensitivity, levels of metals within the body, and wear debris. Persistent inflammation, due to the MOM implant, can cause muscle spasms, myofascial pain, headaches, tinnitus (ringing in the ear), vertigo (dizziness), and angioedema (swelling under the skin). A chronic inflammatory reaction from continued exposure, from a MOM device, can lead to loss of bone strength, implant loosening or fracturing, and osteolysis (bone loss).

Testing for Metal Hypersensitivity

It is difficult to test because the environment on the skin is different than the periprosthetic area deep within the tissues. There is a blood test called lymphocyte transformation test (LTT) which determines if a patient suffers from metal hypersensitivity. The LTT measures the proliferation of T lymphocytes which are the immune specific cells that form the immunological memory in response to metal exposure. The blood is collected and put within special tubes in order to decrease the risk of contamination. Similarly, it is tested within a laboratory that follows strict procedural protocols and standards to avoid contaminating the sample.

 Metal Hypersensitivity and Implant Performance

Approximately 25% of people with properly functioning MOM devices have a metal hypersensitivity and more than 60% of people with malfunctioning MOM devices have a metal hypersensitivity. This is a stark and alarming contrast which is attributed to the poor implantation. There is also a greater failure rate as a result of metallosis, hypersensitivity, and adverse local tissue reactions (ALTR). Hypersensitivity is strongly correlated with poor implant performance and generally makes revision difficult and risky as a result of the body’s reaction.

Source: Metal Hypersensitivity to Implant Materials By: Marco Caicedo, Ph.D

http://www.tmj.org/site/pdf/Metal_Hypersensitivity.pdf

Metal on Metal Hip Prostheses and Total Hip Arthroplasty Effects on Auditory and Visual Health


In the United States, there are over half a million patients implanted with metal on metal (MOM) hip prostheses. The typical elements released by the metal on metal hip prostheses are cobalt and chromium. The normal levels of cobalt and chromium within the body are below a microgram per liter of blood, or below a part per billion. The term microgram per liter is analogous to parts per billion. There are studies demonstrating that a normal range is within 0.1 to 0.3 micrograms per liter. According to this study, patients with well functioning MOM hips, had cobalt-chromium blood levels between 1.5 and 2.3 micrograms per liter. This is ten times higher than normal physiological levels and significantly contributes to the potential for cobalt-chromium toxicity, or metallosis. In association with metallosis, the study indicates that failure with prostheses was connected to visual and auditory issues resulting from elevated cobalt-chromium levels. There is a strong correlation between device failure with visual and auditory dysfunction.

In addition to the aforementioned findings, the study determines whether or not chronic low levels of metal exposure result in obvious physiological effects on the auditory and visual systems as well. In order to determine the effects of chronic low levels of cobalt-chromium, participants met with both an otolaryngologist and an ophthalmologist in order to determine primary or pre-existing pathologies within the ears and eyes, respectively. Subjects then underwent objective and subjective audiometric testing in order to assess auditory health and function. Similarly, the subjects demonstrated their visual health and functioning via subjective and objective visual testing. There were two types of participants in this study: those with MOMHR and those with total hip arthroplasty (THA). The participants in this study were then separated into groups based on their age and time since surgery. The participant’s blood tests also revealed that those with MOMHR had a blood, plasma, urinary cobalt and chromium levels that were 5 to 10 times higher than the THA participants. In terms of objective audiometric and visual findings between the MOMHR and THA groups, there was no observable difference, and patients in each group had similar auditory and visual function.

There is no conceivable evidence between MOMHR and altered brain stem responses for patients with exposure to chronic low metal levels. However, there is optic nerve atrophy (damage) in patients with exposure to high metal levels in their system  which reflects visual loss among this specific population. Whereas patients with long term exposure to low metal levels had no obvious association with auditory or visual defects, the patients with malfunctioning hip prostheses and elevated metal levels (up to hundreds in micrograms per liter) suggested visual and auditory defects.

Source: Auditory and Visual Health after Ten Years of Exposure to Metal-on-Metal Hip Prostheses: A Cross-Sectional Study Follow Up http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0090838

 

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