Logo

CALL TOLL FREE TODAY

1.800.814.4540

Lawyers ⋅ Nurses ⋅ Doctors
Protecting Your Rights for Decades

Medical Devices Defective Drugs Transvaginal Mesh

 The Hip Joint and Development of Hip Implants

The hip joint is a ball-and-socket joint with the ball of the hip joint, known as the femoral head fitting into the socket, known as the acetabulum, of the hip bone or  pelvis. The bone of the femoral head and acetabulum of the pelvis are separated by spongy cartilage and by a sac of synovial fluid, both which lubricate the joint.

A properly functioning hip joint is critical for normal everyday activities of walking, running and climbing. The cartilage or bones that make up the hip joint can deteriorate for a variety of reasons, leading to pain, stiffness or difficulty walking. Painful hip conditions can be treated in several ways including physical therapy, exercise and medications. If these symptoms do not respond to these treatments, an orthopaedic surgeon may recommend traditional hip replacement surgery or hip resurfacing surgery.

Prosthetic Hip Implants

Hip implants are medical devices intended to restore mobility and relieve pain associated with arthritis and other hip diseases or injuries. Every hip implant has a distinct set of benefits and risks. The key design features of each implant including size, material and dimensions make each system unique. In addition, the same hip implant system will have different outcomes in different patients. It is also important to recognize that hip implants may need to be replaced eventually. Factors that influence the longevity of the device include the patient’s age, sex, weight, diagnosis, activity level, conditions of the surgery, and the type of implant chosen.

In the United States, there are currently five types of total hip replacement devices available with different bearing surfaces. These are:

  • Metal-on-Polyethylene: The ball is made of metal and the socket is made of plastic (polyethylene) or has a plastic lining.
  • Ceramic-on-Polyethylene: The ball is made of ceramic and the socket is made of plastic (polyethylene) or has a plastic lining.
  • Metal-on-Metal: The ball and socket are both made of metal.
  • Ceramic-on-Ceramic: The ball is made of ceramic and the socket has a ceramic lining.
  • Ceramic-on-Metal: The ball is made of ceramic and the socket has a metal lining.

An orthopaedic surgeon should determine which hip implant will offer the most benefit and least risk for each patient. When making a recommendation, orthopaedic surgeons should consider several factors such as the patient’s age, weight, height, activity level, and cause of hip pain. Hip surgery may involve total hip replacement or it may involve hip resurfacing.

Hip Replacement vs. Hip Resurfacing

During total hip replacement surgery, the damaged portions of the hip joint are removed. The ball portion, called the femoral head, is removed and replaced with a prosthetic ball made of metal or ceramic, and the socket, called the acetabulum, is removed and replaced with a prosthetic cup. This cup consists of one or two components made of metal, ceramic or plastic. A stem is also hammered into the femur and the femoral head is attached to it.

In contrast, in hip resurfacing surgery, the femoral head is not removed. Instead the femoral head is trimmed and capped with a metal covering. Any damaged bone and cartilage within the socket are removed and replaced with a metal shell. In hip resurfacing surgery, both components are made of metal.

Hip surgery, like any medical procedure, carries risks. The risks of surgery include:

  • A reaction to the anesthesia
  • Heart attack
  • Wound infection
  • Excessive bleeding
  • Blood clots

There may be adverse events after surgery, regardless of the type of hip system implanted including:

  • Hip dislocation, when the ball of the thighbone (femur) slips out of its socket in the hip bone (pelvis)
  • Bone fracture
  • Joint infection
  • Local nerve damage with numbness/weakness
  • Device loosening or breakage
  • Difference in leg lengths
  • Bone loss (osteolysis)

Patients with hip implants should be aware of potential symptoms that may occur after 3 or more months after surgery that may indicate that their device is not functioning properly. Symptoms may include:

  • Pain in the groin, hip or leg
  • Swelling at or near the hip joint
  • A limp or change in walking ability
  • Noise (popping, grinding, clicking or squeaking) from the hip joint
  • Infection

Depending on the severity of the adverse event(s), additional surgery may be necessary. Many of the recommendations, warnings and contraindications outlined appear from the manufacturers’ labeling.

Metal-on-Metal Hip Implant Systems

Metal-on-Metal (MoM) hip implants consist of a ball, stem and shell, all made of metal materials. Manufacturers claim that MoM hip implants were designed to offer the following benefits:

  • Less device material wear is generated when the ball and socket rub against each other in comparison to other hip implants
  • Decreased chance of dislocation when the ball of the thighbone (femur) slips out of its socket in the hip bone (pelvis)
  • Decreased chance of device fracture  

There are two types of MoM hip implants:

  • Traditional total hip replacement systems
  • Resurfacing hip systems

Traditional Metal-on-Metal Total Hip Replacement Systems

Metal-on-metal total hip replacement systems consist of a metal ball as the femoral head, a metal femoral stem hammered in the thighbone, and a metal cup in the hip bone, acetabular component. The ball attaches to the taper of the stem hammered in the femur.

At this time there are five manufacturers of metal-on-metal total hip replacement systems in the U.S.

Metal-on-Metal Resurfacing Hip Systems

Metal-on-metal resurfacing hip systems consist of a trimmed femoral head capped with a metal covering. Any damaged bone and cartilage within the socket are removed and replaced with a metal acetabular component.

The FDA has approved three metal-on-metal hip resurfacing implants. Links to the Summary of Safety and Effectiveness Data (SSEDs) for each of the three approved PreMarket Approval (PMAs) are available below:

  1. Corin USA Limited Cormet Hip Resurfacing System
  2. Smith & Nephew, Inc. Birmingham Hip Resurfacing (BHR) System
  3. Wright Medical Technology, Inc. CONSERVE® Plus Total Resurfacing Hip System

Metal-on-Metal Total Hip Replacement Systems

In June 2012, the FDA’s Orthopaedic and Rehabilitation Devices Advisory Panel discussed data from Orthopaedic device registries and other sources. Data from the Australian1 and United Kingdom2 Orthopaedic device registries, both of which contain the largest number of patients and the longest length of follow-up time, indicate that approximately 95 percent of patients with any kind of total hip replacement have not undergone revision surgery wherein the hip implant is removed and another is put in its place, for seven years after the initial implant.

These Orthopaedic device registries note differences in revision rates by primary diagnosis, sex and age. These registries also noted that the use of cement and the type of bearing surfaces had an impact on revision rates. More than 85 percent of patients with MoM total hip replacements from the U.K registry and more than 92 percent of patients with MoM total hip replacements from the Australian registry did not have a revision for seven years after the initial implant.

Note that registry data shows that MoM hip patients with larger head sizes of 36 mm or larger, had more revisions than those with smaller head sizes.

When comparing outcomes of different bearing surfaces, limitations in any registry data make it difficult to draw definitive conclusions. In order to obtain additional data to address safety concerns related to MoM total hip replacement systems, the FDA is requiring manufacturers of MoM total hip replacement systems marketed in the U.S. to conduct postmarket surveillance studies.

Metal-on-Metal Resurfacing Hip Systems

Hip resurfacing is intended to be a bone preserving procedure on the femoral side, since failure of a resurfacing implant on the femoral side typically allows for revision to a conventional primary femoral component. Hip resurfacing implants are only available with metal-on-metal (MoM) bearings in the U.S.

At the June 2012 Orthopaedic and Rehabilitation Devices Advisory Panel meeting, two of the three hip resurfacing manufacturers in the U.S. discussed the clinical performance of their systems. Manufacturers Smith & Nephew, Inc. and Corin USA Limited said that their resurfacing implants had at least a 90 percent survivorship rate with no revision surgery seven years after follow-up. They also reported on survivorship from their PMA post approval studies when considering various risk factors. Survivorship of the Wright Medical Technology CONSERVE Plus Total Resurfacing Hip System is available in their PMA Summary of Safety and Effectiveness Data (SSED).

The manufacturers of MoM resurfacing hip systems are still conducting long-term post-approval studies assessing device survivorship and metal ion levels; the data will be made available after completion of the studies.

Concerns about Metal-on-Metal Hip Implants

All artificial hip implants carry risks including wear of the component material. Metal-on-metal (MoM) hip implants have unique risks in addition to the general risks of all hip implants.

In MoM hip implants, the metal ball and the metal cup slide against each other during walking or running. Metal can also be released from other parts of the implant where two implant components connect. Metal release will cause some tiny metal particles to wear off of the device into the space around the implant. Wear and corrosion at the connection between the metal ball and taper of the stem may also occur. Some of the metal ions – cobalt and chromium – from the metal implant or from the metal particles will enter the bloodstream.

Orthopaedic surgeons take several precautions before and during hip replacement surgery to try to optimize the way in which the ball and socket rub against each other so that fewer wear particles are produced. However, there is no way to fully avoid the production of some metal particles.

Over time, the metal particles around some implants can cause damage to bone and/or tissue surrounding the implant and joint. This is sometimes referred to as an “adverse local tissue reaction (ALTR)” or an “adverse reaction to metal debris (ARMD).” Soft tissue damage may lead to pain, implant loosening, device failure, and the need for revision surgery wherein the old device is removed and replaced with another one. Patients with a progressing ALTR may be considered for earlier revision to prevent extensive damage to bone, muscle and nerves.

Note: International regulatory agencies have issued alerts and safety communications related to MoM hip implants.

  • In April 2010, the United Kingdom’s (U.K.) Medicines and Healthcare products Regulatory Agency (MHRA) issued a medical device alert that included specific follow-up recommendations for patients with MoM hip replacements. The recommendations included blood tests and imaging for patients with painful MoM hip implants.
  • In February 2012, MHRA published a medical device alert and updated it in June 2012 with advice on the management and monitoring of patients with MoM hip systems.
  • In May 2012 Health Canada issued a public health communication to orthopaedic surgeons and patients regarding MoM hip implants.
  • The Therapeutic Goods Administration of Australia published their safety information for healthcare professionals on MoM hips in September 2012.

There are also reports in orthopaedic literature, data from international orthopaedic implant registries and presentations from professional/scientific meetings that have increasingly noted complications and potential problems of early failure of MoM hip systems, often requiring revision surgery. Much of the available data are from countries outside the U.S., and the data may not be directly applicable to the experience in the U.S. For example, some of the devices available outside of the U.S. are not marketed in the U.S. For this reason, recommendations from international regulatory agencies may not necessarily apply to U.S. patients with MoM hip systems.

If patients with MoM hip implants develop any symptoms that may indicate that their device is not functioning properly, it is very important for them to make an appointment with their orthopaedic surgeons promptly for further evaluation. Aside from a physical exam of the hip, the orthopaedic surgeon may consider several tests to evaluate these symptoms including:

  • Using a needle to remove fluid from around the joint (joint aspiration)
  • Soft tissue imaging

Patients who receive MoM hip implants should also pay close attention to changes in their general health including new or worsening symptoms outside their hip. If they are referred to a doctor to evaluate new conditions, they should let their physician know they have a MoM hip implant. There have been some case reports and articles in the medical literature that suggest patients with a MoM hip implant may have certain symptoms or illnesses elsewhere in the body (systemic reactions). These include:

  • General hypersensitivity reaction (skin rash)
  • Cardiomyopathy
  • Neurological changes including sensory changes (auditory, or visual impairments)
  • Psychological status change (including depression or cognitive impairment)
  • Renal function impairment
  • Thyroid dysfunction (including neck discomfort, fatigue, weight gain or feeling cold

At the current time,  medical legal attorneys recommend the routine need for checking metal ion levels in the blood or soft tissue imaging if patients with MoM hip implants have signs or symptoms described above and the orthopaedic surgeon agrees. The FDA is recommending that asymptomatic patients with MoM hip implants continue to follow-up with their orthopaedic surgeon every 1 to 2 years to monitor for early signs of change in hip status. 

Please feel free to contact us for a free medical legal consultation toll free at 800-814-4540 or  fill out the contact form.

Information for Orthopaedic Surgeons

Attorney Note: If you and your patient are working with an attorney, please contact the attorney for a hip implant testing kit. There are certain protocols and procedures recommended to preserve the evidence and testing.

The following recommendations are advised by the Food and Drug Administration. These are the minimum recommendations, however, more testing may be indicated.General

Recommendations for Orthopaedic Surgeons BEFORE Metal-on-Metal Hip Replacement Surgery

  • Consider your patient’s individual characteristics. Each implant has a unique set of benefits and risks which will result in different outcomes in different patient populations.
  • Select a metal-on-metal (MoM) hip implant for your patient only after determining that the benefits of using a MoM hip implant outweigh the risks, in comparison to using alternative hip systems (metal-on-polyethylene, ceramic-on-polyethylene, ceramic-on-ceramic or ceramic-on-metal).

Use careful consideration in identifying best candidates for MoM total hip replacement. Members of the FDA’s Orthopaedic and Rehabilitation Devices Advisory Panel identified young males with larger femoral heads as the best candidates for MoM hip resurfacing systems.

Get adequate training in the technical aspects of each individual implant and the surgical instruments needed. The success of MoM hip systems is highly dependent on correct placement and implantation. Contact the manufacturer for device specific information on proper placement. Do not implant MoM hip systems in:

  • Patients with known moderate to severe renal insufficiency
  • Patients with known metal sensitivity (e.g. cobalt, chromium, nickel)
  • Patients with suppressed immune systems
  • Patients currently receiving high doses of corticosteroids
  • Females of childbearing age

When discussing the implant and procedure with the patient, make sure the patient understands that there are hip implants available with different bearing surfaces and each hip implant has unique benefits and risks. All hip implants will need to be replaced eventually, and implant longevity is influenced by a patient’s age, sex, weight, diagnosis, activity level, condition of the surgery, and the type of implant. The potential risks associated with MoM hip implants include, but are not limited to:

  •   Infection
  •   Dislocation
  •   Osteolysis
  •   Bone or device fracture
  •   Elevated metal ion levels in the joint and blood
  •   Transplacental transport of metal ions
  •   Development of local inflammatory reactions and lesions including soft tissue    masses and tissue necrosis
  •   Development of potential systemic events related to elevated metal ion levels
  •   Revision surgery
  •   Femoral neck fracture (for hip resurfacing)

Certain patients have an increased risk for greater wear of the device or for an adverse local tissue reaction (ALTR) and require closer follow-up. These patients may include:

  •     Patients with implants in bilateral implants
  •     Patients with resurfacing systems with small femoral heads (less than or equal to 44 mm)
  •    Female patients
  •    Patients receiving high doses of corticosteroids
  •    Patients with evidence renal insufficiency
  •    Patients with suppressed immune systems
  •    Patients with suboptimal alignment of device components
  •    Patients with suspected metal sensitivity (e.g. cobalt, chromium, nickel)
  •    Patients who are severely overweight
  •    Patients with high levels of physical activity

Previously implanted hardware at or near the hip joint may increase wear of the device or the amount of metal exposure to the patient who receives a MoM implant or revision. There is currently no evidence to support the use of pre-operative skin patch testing or other tests to predict implant sensitivity prior to surgery.

General Recommendations for Orthopaedic Surgeons DURING Metal-on-Metal Hip Replacement Surgery

  • Be aware that suboptimal placement may cause excess wear and early failure.
  • Pay particular attention to the angles of inclination and anteversion of the acetabular cup.
  • For resurfacing systems, make sure of appropriate orientation of the femoral stem-shaft angle before cementing into place (all resurfacing femoral heads are intended for cemented use only).
  • Do not mix components from different hip implant systems. Each hip implant system has different metallurgy and design specifications and it is imperative that all implanted components and their associated instruments be from the SAME manufacturer’s marketed hip implant system.

General Recommendations for Orthopaedic Surgeons AFTER Metal-on-Metal Hip Replacement Surgery (Follow-up)

  • At the time of hospital discharge, schedule the patient for routine office follow-up and review with the patient or caregiver the signs/symptoms of adverse events.
  • The FDA recommends routine long-term follow-up of patients with metal-on-metal (MoM) hip implants, typically to occur every 1 to 2 years.
  • If the patient experiences any pain or decreased hip function approximately 3 or more months after surgery, instruct the patient to contact you for a follow-up exam.
  • Patient follow-up visits should include:
  • Physical exam with functional assessment;
  • Check for asymptomatic local swelling or masses; and
  • Assessment of organs and systems for changes including systemic adverse events in cardiovascular, nervous, endocrine (especially thyroid) and renal systems.
  • Schedule certain patients with increased risk of device wear or adverse local tissue reaction (ALTR) for closer follow-up. These may include:
  • Patients with bilateral implants
  • Patients with resurfacing systems with small femoral heads (less than or equal to 44 mm)
  • Female patients
  • Patients receiving high doses of corticosteroids
  • Patients with evidence of renal insufficiency
  • Patients with suppressed immune systems
  • Patients with suboptimal alignment of device components
  • Patients with suspected metal sensitivity (e.g. cobalt, chromium, nickel)
  • Patients who are severely overweight
  • Patients with high levels of physical activity

Pay close attention to signs of the following local and systemic symptoms or complications associated with metal-on-metal (MoM) hip implants:

  • Hypersensitivity (allergic type reaction)
  • Loosening
  • Infection
  • Osteolysis (bone loss)
  • Aseptic lymphocytic vasculitis-associated lesions (ALVAL) (histologic reaction in surrounding tissue)
  • Soft tissue mass (fluid-filled or solid soft tissue mass around the replaced joint that is diagnosed radiologically)
  • Femoral neck fracture (for resurfacing systems)
  • Systemic symptoms or complications:
  • General hypersensitivity reaction (skin rash)
  • Cardiomyopathy
  • Neurological changes including sensory changes (auditory, or visual impairments)
  • Psychological status change (including depression or cognitive impairment)
  • Renal function impairment
  • Thyroid dysfunction (including neck discomfort, fatigue, weight gain or feeling col

Follow-Up for Symptomatic Patients

Clinical Evaluation

  • If a patient experiences local symptoms (i.e. pain or swelling at or near the hip, a change in walking ability, or a noise from the hip joint) more than three months after metal-on-metal (MoM) hip implant surgery, conduct a thorough evaluation.
  • Follow-up of symptomatic patients with MoM hip implants should occur at least every six months.
  • Guide your clinical evaluation by the symptoms and physical findings, including an assessment for well-known emergent complications including joint infection, implant loosening, peri-prosthetic facture and dislocation.
  • Recognize that localized lesions associated with reactions to metal debris may also present with pain or a variety signs and symptoms including:
  • Local nerve palsy
  • Palpable mass
  • Local swelling
  • Joint dislocation or subluxation

Additional Testing for Symptomatic Patients

  • In some patients with symptoms, plain radiograph findings (e.g. osteolysis, femoral neck narrowing, component suboptimal positioning, fracture), in conjunction with other non-imaging information, are sufficient to indicate a need for revision surgery.
  • In other symptomatic patients, cross-sectional imaging should be considered to diagnose and assess soft tissue findings surrounding an implant.
  • Patients with MoM hip implants who develop any symptoms or physical findings that indicate their device may not be functioning properly, should be considered for metal ion testing. It is important to note that at the current time, the FDA believes there is not enough evidence in the U.S. to demonstrate a correlation between a metal ion level and the presence of localized lesions, clinical outcomes and/or the need for revision surgery.

Assessment for Systemic Effects

  • Evaluate patients with new systemic symptoms in collaboration with their primary medical physicians or specialists to determine the cause of their symptoms or findings.
  • Patients with evidence of excessive device wear or a localized adverse local tissue reaction (ALTR) should be assessed for potential systemic effects of exposure to metal ions.

A thorough physical examination should be performed by the patient’s health care team, which include primary medical physicians and/or specialists, with particular focus on cardiovascular, neurological, endocrinological (especially thyroid), and renal systems.

Because metal ions are cleared through the kidneys, a patient who has renal insufficiency may be at higher risk for systemic adverse eventsBlood urea nitrogen (BUN) and creatinine levels may be measured to evaluate a patient’s renal function.

Device Revisions

  • At this time, there is not enough evidence to provide a science-based recommendation for a threshold value of metal ion levels in the blood that would serve as a trigger for revision.
  • The decision to revise a patient’s metal-on-metal (MoM) hip implant should be made in response to the overall clinical scenario and results of diagnostic testing.

In extreme cases, adverse local tissue reactions (ALTR) may significantly damage periprosthetic bone, muscle, and nerves. Therefore patients with progressing ALTR, may be considered for earlier revision to prevent extensive damage.

  • If you recommend revision, advise patients of the surgical risks of revision as well as the expected outcomes, including:
  • Revision procedures are complicated and may not fully resolve a patient’s pain nor restore complete function;
  • In case of ALTR, revision of a MoM hip may have a worse prognosis than revision of other types of bearing surfaces;
  • Possible need for an additional revision procedure in the future; and
  • Metal ion levels should be expected to decrease after revision.
  • In selecting components for revision:
  • Check the specific device labeling for compatibility of device components.
  • Some failed hip resurfacing devices may be revised to a total MoM hip replacement system.
  • Consider the benefits and risks of all bearing surfaces for each patient.
  • If a patient is suspected to have developed metal sensitivity, carefully select the materials of the revision components (potentially avoiding materials with nickel or chromium).
  • In order to better understand the performance of these devices and causes of failure, a retrieval analysis is recommended, especially in cases where there is no obvious cause for implant failure such as suboptimal positioning.

Attorney Note: If you are working with a patient and attorney, contact the attorney about the preservation of the implant procedure. The removed implant is evidence and should not be returned to the implant manufacturer. 

Talk to the patient about returning the implant for retrieval analysis. A retrieval analysis is a vital part of a manufacturer’s quality system allowing them to assess manufacturing and quality processes through their Corrective and Preventative Action (CAPA) system. If the patient agrees, contact the manufacturer prior to revision surgery for instructions on returning the implant for analysis. Along with the implant, provide non-identifying information about the patient, the date of procedure, observations from the revision surgery and the histopathology report from any tissue sent to the hospital pathologist. Report any adverse events believed to be related to the MoM system to FDA through MedWatch, the FDA Safety Information and Adverse Event Reporting Program.

Soft Tissue Imaging and Metal Ion Testing

In certain clinical situations, orthopaedic surgeons should consider additional testing including soft tissue imaging and metal ion testing to assess patients with metal-on-metal (MoM) hip implants. Please see the General Recommendations for Orthopaedic Surgeons AFTER Metal-on-Metal Hip Replacement Surgery for recommendations on which patients may require additional diagnostic testing. When conducting soft tissue imaging or metal ion testing in MoM patients, please consider the following :

Soft Tissue Imaging

For some patients, cross-sectional imaging is required to assess and diagnose soft tissue findings surrounding an implant. The benefits and risks of using different types of diagnostic imaging procedures should be considered when determining the most appropriate imaging modality for each patient. MoM hip implants can create metal artifacts (distortions of the image due to the presence of metal in the imaging field) in some imaging modalities. The most utilized methods of imaging soft tissue surrounding MoM hip implants include:

Magnetic Resonance Imaging (MRI) with metal artifact reduction

  • Strengths: MRI offers the best visualization of soft tissue surrounding a MoM hip implant and uses non-ionizing radiation.
  • Weaknesses: MRI is contraindicated for some patients with implants. Most MoM h
  • Hip implants in the U.S. have not been evaluated for safety in an MR environment so the likelihood of adverse events, such as heating of the tissue near the implant, may not be known.

Computed Tomography Scan (CT)

  • Strength: CT offers the best visualization of implant positioning and bony tissue
  • Weaknesses: CT uses ionizing radiation and provides lower soft tissue visualization. Image artifacts from the implant may distort the image.

Ultrasound

 

  •  Strengths: Ultrasound allows soft tissue visualization without metal artifacts and uses non-ionizing radiation.
  •  Weaknesses: Image quality in ultrasound is very operator dependent. Ultrasound provides a lower resolution soft tissue image than MRI and has a limited depth penetration.

During the June 2012 Orthopaedic and Rehabilitation Devices Advisory Panel meeting, panel members recommended imaging using MRI with metal artifact reduction.If it is determined that MRI imaging of a MoM hip implant patient is appropriate, the FDA recommends that the orthopaedic surgeon:

  • Consult with the radiologist to evaluate the benefits and risks of utilizing MRI with metal artifact reduction;
  • Use the available device-specific labeling to help determine appropriate scan sequences; and
  • Inform the MRI site that the patient has a MoM hip implant.

The FDA is working with the manufacturers of MoM hip systems to evaluate devices for safety in the MR environment and to develop MR Conditional labeling, which would help ensure safe scanning of patients with MoM hip implants. The FDA is also encouraging the development of metal artifact reduction technologies for MRI scanners to improve image quality around metal implants.

Metal Ion Testing

As described in “Concerns about Metal-on-Metal Hip Implants,” some patients with a metal-on-metal (MoM) hip implant may have elevated metal ion levels (e.g. cobalt and/or chromium) in their bloodstream. Depending on the clinical scenario, orthopaedic surgeons may recommend measuring metal ion levels.

Obtaining accurate and precise metal ion test results in patients can be difficult. For example, patient samples can become contaminated during the sample collection and processing. Needles and blood collection tubes (even trace element tubes) can potentially contaminate patient samples with metal ions. Serum samples may become contaminated with metal ions from the environment during harvesting especially since this would be done outside of the testing lab. There are also known interferences, including polyatomic interferences that can affect the accuracy of metal ion test results.

In addition, not all commercial labs can accurately and precisely measure trace (greater than 10 µg/L) or ultratrace (less than 10 µg/L) elements. These factors have important implications for the accuracy, reproducibility and clinical interpretation of the test results.

Who Should Be Tested?

As part of their overall clinical evaluation, orthopaedic surgeons should consider measuring and following serial measurements of metal ion levels in symptomatic patients with MoM hip implants.

  • The orthopaedic surgeon should consider testing patients with MoM hip implants who develop any symptoms that may indicate that their device may not be functioning properly.
  • At the current time, there is insufficient evidence to recommend metal ion testing in patients with MoM hip implants that have none of the signs or symptoms described above and the orthopaedic surgeon feels the hip is functioning properly.

What Should Be Tested?

Test Method:

  • Measure cobalt using an inductively coupled plasma mass spectrometer (ICP-MS), equipped with either a collision cell or dynamic reaction cell technology, or use a sector field inductively coupled plasma mass spectrometer (SF-ICP-MS). The FDA recommends testing cobalt in EDTA anti-coagulated whole blood using a validated method that meets the Clinical Laboratory Improvement Amendments (CLIA) validation criteria. The method should accurately and precisely measure concentrations as low as 1 µg/L cobalt.
  • If chromium is measured, use an ICP-MS, equipped with either a collision cell or dynamic reaction cell technology, or use SF-ICP-MS (in medium or high resolution mode) to resolve potential polyatomic interferences. The FDA recommends testing chromium in EDTA anti-coagulated whole blood using a validated method that meets the CLIA validation criteria. The method should accurately and precisely measure concentrations as low as 1 µg/L chromium.
  •  To minimize well known interferences and accurately measure chromium, the laboratory can use available techniques that can resolve interferences. If these techniques are used properly, accurate chromium measurements can be obtained. However, it is important that the testing laboratory carefully validate their method to make sure that it is working properly and producing accurate test results.

Selecting a Testing Lab:

  • Ensure the lab is CLIA-certified and is using a validated method that meets the CLIA validation criteria for EDTA anti-coagulated whole blood;
  • Ensure the lab has an ongoing quality assurance and quality control program for the measurand in EDTA anti-coagulated whole blood;
  • Ensure the lab provides collection kits (including all components necessary for sample collection and processing) that are free of significant metal contamination and fit for purpose (i.e., measuring trace and ultratrace cobalt and chromium). The lab is responsible for validating that all components within the collection kit are not contaminated;
  • Ensure the lab participates in a Centers for Medicare and Medicaid Services (CMS) approved trace element proficiency testing (PT) program (e.g. New York State Department of Health, Wadsworth Center) for that particular measurand. A lab’s results for that measurand should be within the defined acceptance criteria of the PT program.
  • Ensure that the lab has performed an appropriate study, or references appropriate data, to define valid reference range values.

Interpreting Test Results:

  • The metal ion concentration values should be considered in addition to the overall clinical scenario including symptoms, physical findings, and other diagnostic results when determining further actions.
  • When assessing metal ion concentration values, it is important to determine if the patient has any other reasons to have metal ion concentration values above reference range values including:
  • Other implanted metal hardware
  • Occupational exposure
  • Renal insufficiency
  • Dietary supplements
  • Metal ion concentration values should be interpreted in conjunction with blood urea nitrogen (BUN) and creatinine to concurrently evaluate the patient’s renal function.
  • Test results should be interpreted considering the measurement error of the method and the lab’s reference range. The measurement error can be estimated by reviewing the lab’s proficiency testing results and the imprecision of the method.
  • Follow test results serially in a patient, ensuring that the same sample type, measurement method and the same laboratory are utilized for each measurement. If a different laboratory was utilized, the ordering physician needs to consider the test results in light of potentially differing laboratory methods that may not have values that are interchangeable. The ordering physician should interpret the test results considering the total error of the method(s) to determine if metal ion levels are changing.

International regulatory agencies developed specific follow-up recommendations for patients with metal-on-metal (MoM) hip implants, including recommendations for blood tests including specific metal ion threshold values. There are differences between the usage and availability of metal-on-metal hip implants in the U.S. and those outside the U.S., as well as differences in laboratory practices. For this reason, these recommendations may not be appropriate for patients in the U.S. As noted above, several factors can impact the accuracy, reproducibility, and clinical interpretation of the test results.

At the current time, the FDA believes there is insufficient evidence in the U.S. demonstrating a correlation between a metal ion level and the presence of localized lesions, clinical outcomes and/or the need for revision surgery.

Information for All Health Care Professionals who Provide Treatment to Patients with a Metal-on-Metal Hip Implant

Case reports in the medical literature have suggested the potential for systemic effects of elevated metal ion levels resulting from device wear in metal-on-metal (MoM) hip implants. These effects have included:

  • General hypersensitivity reaction (skin rash)
  • Cardiomyopathy
  • Neurological changes including sensory changes (auditory, or visual impairments)
  • Psychological status change (including depression or cognitive impairment)
  • Renal function impairment
  • Thyroid dysfunction (including neck discomfort, fatigue, weight gain or feeling cold

Based on these limited number of case reports in published literature, the true incidence or prevalence of adverse systemic effects from MoM hip implants is not known at this time. A patient with systemic symptoms and a MoM hip implant is more likely to visit his or her general practitioner or medical specialist rather than his or her orthopaedic surgeon, it is imperative that all health care providers be aware of the potential role of metal ions during their evaluation of their patients with MoM hip implants

At the current time, the FDA believes there is not enough evidence in the U.S. demonstrating a correlation between a metal ion level and the presence of localized lesions, clinical outcomes and/or the need for revision surgery. If the patient’s systemic findings are thought to be related to the MoM hip implant, the patient should follow-up with his or her orthopaedic surgeon to determine the appropriate course of action.

Report any adverse systemic events which are believed to be related to MoM hip implants to the FDA through MedWatch, the FDA Safety Information and Adverse Event Reporting Program.

Follow-Up for Asymptomatic Patients

Clinical Evaluation

  • If a patient with a metal-on-metal (MoM) hip implant is asymptomatic and has a well functioning hip, follow-up should occur periodically (typically 1 to 2 years).
  • Be aware the following patients may experience increased wear of the implant and/or adverse reaction to metal debris and require closer monitoring. They include:
  • Patients with bilateral implants
  • Patients with resurfacing systems with small femoral heads (44mm or smaller)
  • Female patients
  • Patients receiving high doses of corticosteroids
  • Patients with evidence of renal insufficiency
  • Patients with suppressed immune systems
  • Patients with suboptimal alignment of device components
  • Patients with suspected metal sensitivity (e.g. cobalt, chromium, nickel)
  • Patients who are severely overweight
  • Patients with high levels of physical activity
  • Patient follow-up visits should include:
  • Physical exam with functional assessment;
  • Checking for asymptomatic local swelling or masses; and
  • Assessment for possible systemic adverse events in cardiovascular, nervous, endocrine (especially thyroid) and renal systems.

Additional Testing for Asymptomatic Patients

  • If the orthopaedic surgeon feels the hip is functioning properly and the patient is asymptomatic, the FDA does not believe there is a clear need to routinely check metal ion levels in the blood or perform soft tissue imaging.
  • Findings of lesions on soft tissue imaging, or of elevated blood metal ion levels in the absence of symptoms have been reported in a limited number of research studies for some MoM hip implant patients. These studies are difficult to interpret because:
  • The exact incidence or prevalence of asymptomatic lesions and their natural history is not known.
  • The correlation between elevated blood metal ion levels and development of future local or systemic system adverse reactions is not well established.
  • If the orthopaedic surgeon determines it is in the best interest of the patient to conduct soft tissue imaging, please review FDA’s recommendations.
  •  If the orthopaedic surgeon determines it is in the best interest of the patient to measure metal ion levels, please review FDA’s recommendations.
Share This Page: