In a previous blog, I talked about the mounting concerns for patients who have been implanted with metal-on-metal hip prostheses during total hip replacement surgery. These devices have ball-and-socket joints made from metals including chromium and cobalt, and originally were thought to be more durable and lasting when first devised.
Now, serious problems associated with use of metal-on-metal hip replacements have led to a myriad of medical complications including tissue and bone damage, and in some cases, infection. All artificial joints shed tiny pieces of debris and researchers believe that particles released by all-metal hips cause the body’s protective tracking cells to convert the debris into metallic ions, which ultimately can cause a chain reaction and destroy tissue and muscle. These metal ions potentially can trigger a hypersensitivity reaction and cause problems around the hip and throughout the body.
However, metal-on-metal hip components may be just the tip of the iceberg. With full metal on metal hip implants, the metal ball and cup slide against each other during movement causing debris to be released into the body. However, metal also can be released from other parts of the implant where two implant components connect, such as between the taper which is the upper part of the stem and the metal ball.
Traditionally, the taper has been made from the same piece of metal as the rest of the stem (moneblock). Normally, the stem is coated with an oxide layer which helps protect the metal surface. The effects of crevices, stress and movement at these metal-on-metal taper connections can damage or fracture the oxide layer and lead to corrosion. Recently, a number of stems have been developed that also have a metal-on-metal connection between a separate or modular neckpiece and the stem. Because of the eccentric forces on this neck-stem connection, the development of corrosion is even more problematic.
When corrosion develops at this metal on metal junction, cobalt and to a lesser degree chromium are absorbed into the blood circulation. These levels can be measured with a blood test. Some people seem to tolerate abnormally high metal ion levels and others do not. Symptoms related to the elevation of these metal ions are extremely varied and along with the concerns of what is happening to the tissues around the hip vary from subtle to disabling or severe. Reported symptoms can affect all the major organs including cardiac (cardiomyopathy), hematologic (blood cell suppression), neurologic (depression, cognitive impairment, visual or auditory impairment), renal (kidney impairment) and endocrine (thyroid dysfunction with weight gain, neck discomfort and fatigue). I have seen several patients develop skin problems (dermatologic) including acne and rashes.
Generally, the level of metal ions in the body is extremely low. Unfortunately, we do not yet know what level is too high so that it becomes dangerous for patients. We also do not yet fully understand all of the short- and long-term consequences of having these elevated metal levels. We do know that some people are very sensitive while others don’t seem to be.
Because of each person’s unique genetics, individuals react differently to metal corrosion and ions, making it impossible to predict. I use an analysis with my patients that most can relate to: some people can wear costume jewelry and others cannot because it will turn their skin dark. We only learn who is sensitive and who is not after they wear it. Similarly, some don’t seem to react to the corrosion byproducts while others develop hypersensitivity much like an allergy. There is a great concern if a patient develops a local reaction round the prosthesis, called an “abnormal local tissue response” or ALTR because it leads to tissue destruction. These reactions range from mild to extremely severe and can result in large abnormal fluid collections and/or solid masses pushing and eroding into tissues. We call these masses or fluid collections pseudo tumors or false tumors because of the way they can extend out in all quadrants from the joint and destroy tissue, bone and potentially nerves.
Traditionally, MRI scans have not allowed us to visualize tissues if there is a metal prosthesis or hardware. Recently, new software called MARS or Metal Artifact Reducing Sequence has greatly improved our ability to visualize the tissues around the prosthesis and assess if a patient is having an ALTR.
We encourage even asymptomatic patients who have had an all-metal hip replacement, or were implanted with components with metal-on-metal junctions (particularly with modular neck-stem junctions), to be evaluated with blood studies and a MARS MRI. I repeatedly have seen people who are 100 percent asymptomatic and functioning at an extremely high level still develop problems. It is best to treat any potential problem sooner rather than later. Also, by having these tests done, it provides a baseline and comparison for the future. Hopefully, it also will provide peace of mind if tests results are favorable.
At the Leone Center we are prepared to treat people suffering from problems associated with metal-on-metal components and provide solutions with safer, more durable outcomes.
In my next blog I will discuss how to know when you need a revision and how to find the right surgeon for you.