Metallosis occurs when a foreign object—such as metal ions which are produced by a metal hip implant—enter the tissues of the body. The body reacts by sending special types of white blood cells called macrophages to attack the area and fight the metal ions. While the goal of the body is to trap the metal shards and prevent them spreading to other parts of the body, in this particular case it is somewhat of a lost cause. The body is, of course, unable to remove the metal shards and inflammation, pain, tissue destruction or death and bone loss are the potential results. The longer the metal ions remain in the body, the more potential damage.

Metal Shear and Corrosion

Any time metal components of a hip implant rub against one another during periods of activity by the implant recipient, that friction can cause metal ions to shear away. In the case of metal hip implants which implement a ceramic ball, there can still be a metal liner in use, or there can be corrosion and fretting at the neck juncture. In some hip implant models small metal trundles are located at either end of the neck piece, allowing it to snap into place—on one end into the stem, on the other into the ball. When body fluids become trapped under these trundles corrosion can occur, just as it does at the neck juncture. This corrosion, like the friction caused by metal-on-metal implants, sends microscopic metal ions of cobalt and chromium into the body.

Tolerance Levels to Cobalt and Chromium

Doctors are not certain why some people appear to have a fairly high tolerance for cobalt and chromium in the body while others are extremely sensitive to any level at all. In persons with acute metal sensitivity, the body essentially kicks into overdrive when it senses metals, mounting an all-out autoimmune response in an attempt to remove the metal ions from the body. Normal, healthy tissues can get caught in this war and become damaged.  The attack mounted by the macrophages produces specific secretions meant to wipe out the “invaders.”

The Body’s Futile Defense to Cobalt and Chromium

The metal hip implant, however, produces a never-ending stream of metal ions which causes the immune system to stay in a constant state of frenzy as it attempts—unsuccessfully—to eliminate the intruders. The longer the cobalt and chromium remain in the body, the more likely the body will suffer acute inflammation, tissue death and bone loss, all leading to a total failure of the implant. When fracturing of the hip bone, severe levels of infection or loosening of the implant occurs, revision surgery will likely be the only option and the patient will be fitted with an implant which is not metal-on-metal.

The Risks of a Metal Hip Implant

Many people who are recipients of a metal-on-metal hip implant, a hip implant which utilizes a metal liner, or a hip implant with a metal neck juncture or metal trundles, may wonder what their health risks actually are. A study in the Journal of Orthopedic Research studied 259 patients with all-metal hip implants. This group was compared to a control group of subjects. Compared with the age and gender-matched control group, the recipients of metal hip implants tested significantly higher in cobalt and chromium in the body with some hip implant patients testing as much as 50-100 times higher levels of these metals. Whatever the levels of the metals tested were, every single patient with an all-metal hip implant showed some level of metal debris in the body.

Metallosis and Metal Toxicity

Pseudo tumors are a very real risk in patients with a metal-on-metal hip implant. A pseudo-tumor is a mass of inflamed cells which, although they closely resemble a “regular” tumor, are filled with fluid. Pseudo-tumors must be surgically removed in order to prevent further damage to tissues. Other symptoms of metallosis such as deteriorating tissue and bone, pain in the hip or groin area, loosening of the hip implant, difficulty in standing or walking and even a rash in the area where tissues are slowly dying can be seen. Women tend to be at a much greater risk of metallosis. Any time additional stress is placed on the implant, more metal shards will find their way into the bloodstream and surrounding tissues, therefore those patients who are obese will also have a greater risk of metallosis.

Metal toxicity occurs when cobalt and chromium build up in the bloodstream and cause serious health problems. Cardiovascular, neurological, renal and thyroid issues have all been seen in patients with all-metal hip implants. Emotional disturbances including irritability, anxiety and depression are common as are skin rashes, recurring infection, memory loss, gastrointestinal disorders, loss of vision and hearing, chronic headaches, vertigo, burning and tingling in the extremities, the development of cancerous cells and even disruption of DNA.

Types of Metal Hip Implants Which Bring Considerable Risk to Patients

Although most hip implants and hip implant systems have some of the same issues, there are important differences as well. The “true” all-metal hip implant implements a metal acetabular cup and a metal ball; these components rub against one another during activity leading to metal shear. While the metal hip implants which utilized a ceramic ball were believed to avoid this metal-on-metal friction and resulting metal shear, it was found they have their own risks of metallosis due to corrosion at the neck juncture and under the metal trundles. At this point, only the DePuy ASR XL, the DePuy ASR Hip Resurfacing System, the Stryker Rejuvenate, the Stryker ABGII and the Smith and Nephew R3 metal liner have been recalled. It is widely believed that more recalls are in the works. The current list of high-risk metal-on-metal hip implants includes:

• Metal-on-Metal Smith & Nephew R3 Acetabular Hip System
• Metal-on-Metal Wright-Conserve Total Hip System
• Metal-on-Metal Wright-Conserve Profemur Total Hip System
• Metal-on-Metal Zimmer Durom Acetabular Hip Component
• Metal-on-Metal DePuy ASR XL Acetabular Hip System
• Metal-on-Metal DePuy ASR Hip Resurfacing System
• Metal-on-Metal DePuy Pinnacle Acetabular Cup System
• Ceramic-on-Metal Stryker Rejuvenate Hip Implant
• Ceramic-on-Metal ABGII Hip Implant 
• Metal-on-Metal Biomet M2A Magnum Hip Implant

If you believe you are a recipient of one of these hip implants, it is important to contact your doctor as soon as possible. You will want to ensure you receive regular monitoring of your blood work to test for increased levels of cobalt and chromium. Your doctor may also order x-rays, an MRI or a bone scan to check for implant failure. If you have any pain at all in the hip or groin area, see your doctor at once. Even if you’ve not yet experienced any ill effects from your hip implant, it is crucial that you take steps to minimize the potential damage.  If you are uncertain which implant you received, you can contact the hospital where your surgery took place and ask for the implant type.