Introduction to Metal on Metal Hip Implants

Image Courtesy of NIH

Millions of Americans suffer from chronic hip joint pain.  Whether from osteoarthritis, rheumatoid arthritis, or an injury, many of these individuals do not respond well to medication and therapy.  In order to resume a more normal life and level of activity, many of them turn to hip replacement.

There are several options when it comes to hip replacements.  One may opt for a full hip replacement, in which the both the ball and socket are replaced by the device.  The other option is hip resurfacing, in which the ball is shaved down and capped with a liner.  The joint is then fitted with a prosthesis as well.  This allows for more bone to be left in tact.

Materials used to make hip implants also vary.  There are two parts to a full hip implant: the femoral head, and the acetabular cup.  The implants can either be made of metal on metal, metal on plastic, or ceramic on ceramic.

Metal on metal hip implants were first hailed as huge progress for those in need of surgery.  Manufacturers claimed that metal on metal hip implants were longer-lasting and could allow patients to have more active lifestyles.  Unfortunately, the reality of metal on metal hip implants turned out to be very different.

In fact, these devices have turned out to be no superior to the older, ceramic devices, and actually cause more complications.  One of the most serious complications that has resulted from metal on metal hip implants is that the metal ions can flake off from the implant itself and then enter the bloodstream and the surrounding tissue and bone.  This metal toxicity is called metallosis, and is a very serious condition.  In the case of metal on metal hip implants, chromium and cobalt ions are released into the body.  Only a blood test from your doctor can definitely diagnose this condition.

In the most serious cases, metallosis can lead to cancer.  The following symptoms may also be observed:

• Adverse local tissue reaction, including inflammation and severe pain in the surrounding muscle and bone
• Infection
• Immobility
• Joint pain and stiffness, lack of range of motion
• Sensory complications such as tinnitus, blindness, or deafness
• Vertigo
• Nerve damage (peripheral neuropathy)
• Convulsions
• Cardiomyopathy
• Hypothyroidism
• Skin rashes
• Kidney damage
• Optic nerve damage
• Psychological changes, including depression and cognition changes

Metal on metal hip implants are associated with other serious side effects aside from metallosis, including:

• Decreased mobility
• Severe pain hip that radiates to groin and thigh
• Loosening of the device
• Inflammation and pain
• Infections
• Bone damage

There are many tests that your doctor may perform on you to gauge the status of your metal on metal implant.

First, he may perform joint aspiration, which is when a needle is used to remove fluid from around the joint.  Second, soft tissue imaging may be performed as well.  This includes MRI, CT scan, or an ultrasound.  Finally, the FDA is now recommending that doctors perform blood tests on patients presenting with complications to check the level of metal ions in the blood.

There are several manufacturers of metal on metal hip implants, each proclaiming its product to be long-lasting and complication-free.  Only after they were forced to confront the reality of thousands of patients and surgeons complaining of serious complications did many of these device manufacturers begin recalling their devices.  Manufacturers include:

• Stryker
• DePuy
• Zimmer
• Smith & Nephew
• Biomet
• Wright Medical Technologies

Please click on the above links for more information about each particular manufacturer, its products, and its complications.