Do Stryker Hip Implants Cause Increased Metal Levels? Recalled Stryker Rejuvenate and ABGII May Cause Cobalt Metal Poisoning

An FDA warning was issued in February, 2011 which cautioned the public and physicians that metal-on-metal hip implants carried unique risks due to the potential of cobalt and chromium ion shear. Stryker Orthopedics issued an Urgent Safety Alert to all healthcare providers outlining these potential hazards in April, 2012 then issued a voluntary recall of the Rejuvenate and ABGII hip implant devices in July, 2012. One of the primary concerns centers around cobalt metal poisoning from the recalled Stryker Rejuvenate and ABGII hip systems. The symptoms of cobalt and chromium poisoning include:

·         Neurological, cardiovascular, renal and thyroid disorders

·         Disruptions in DNA

·         Bone loss, tissue destruction and death

·         Chronic or serious pain

·         Anxiety, depression, irritability

·         Loss of vision and hearing

·         Chronic headaches

·         Balance disruption, vertigo, dizziness

·         Gastrointestinal disorders

·         Memory loss

·         Skin disorders

Differences in Cobalt Toxicity between the Stryker and DePuy Hip Implants

While both the Stryker recalled hip implants and the DePuy ASR recalled implant can lead to metal toxicity, the Stryker implants are constructed differently and patients may be advised to undergo revision surgery when the levels of cobalt are much lower than those of a DePuy patient—even at levels of 2-3 parts per billion.  If a person without a metal hip implant were to go to their doctor and request a blood test to measure metal in the bloodstream the amount found in a healthy person would range from .19 to .4 parts per billion—an amount smaller than a grain of sand. An amount of 7 parts per billion or higher are definite cause for concern and, aside from the symptoms listed above, can cause constant pain in the hip region, the destruction of bone, tissue and muscle and muscle masses under the skin known as pseudotumors.

A revision will generally be recommended for a patient with a metal-on-metal hip implant who measures cobalt concentrations of 19 parts per billion. The difference between the DePuy ASR and the Stryker ABGII and Rejuvenate as far as levels of cobalt and chromium is that in a DePuy patient if the cobalt level is 20, 30, 40 or any other number, the chromium level is likely to be much the same. Stryker patients, however, are seeing a much greater disparity between the chromium and cobalt levels with the cobalt levels being much higher. The theory behind the higher cobalt levels in Stryker Rejuvenate or ABGII patients ties to the design of the Stryker models.

The “wear” in the Rejuvenate and ABGII comes from the stem and neck rather than the cup and ball portion of the joint—a surface which was not supposed to undergo wear. A Morse taper—a slightly angular junction which the physician hammers into the stem until snug and locked tightly—is implemented into the design of these two hip devices. At the location the Morse taper meets the stem, cobalt and chromium ions are released which in turn leads to cross ionization between the titanium stem and the cobalt and chromium neck. It is believed the neck portion is releasing more cobalt than chromium ions although scientists are not entirely certain why. In any case, the Morse taper has apparently created an added stress location which sends cobalt ion debris into the body of the patients.

Why the Loss of Muscle is More Serious than Loss of Bone

While the loss of bone, muscle or tissue is always a serious event, bone can be recreated using bone stock and cement. Muscles, however, cannot be artificially recreated therefore when any of the roughly 640 muscles in the body are killed through cobalt exposure, the muscle is gone forever. While the surrounding muscles can be strengthened through exercise enough to carry the loads placed on them as a result of the destroyed muscles, this extra load can also potentially lead to a burning sensation, a constant limp or gait, or, in extreme cases, the necessity of a walker or wheelchair for the remainder of the person’s life.  

FDA Approval for the Rejuvenate and ABGII

Both the Rejuvenate and ABGII gained FDA approval in 2009 through a process known as the 510k. This approval process requires minimal testing and must only meet the criteria of being substantially equivalent to a product already on the market. Stryker had no idea the Morse taper would wear in the way it has once implanted, causing cobalt ions to flood the body because there was very little in-depth research prior to marketing. Once the cobalt levels have become elevated in a patient with a Stryker recalled hip implant, it is likely the patient’s doctor will recommend revision surgery to remove the dangerous implant and replace it with a safer alternative.