Cobalt poisoning from hips is
becoming more and more common among those recipients of a metal-on-metal hip implant
device. Stryker Rejuvenate and ABGII were placed on the market in 2009, yet
shortly after adverse reports began coming in regarding side effects of these
two Stryker models. The Rejuvenate and ABGII both gained FDA clearance through
a process known as the 510(k). To gain this type of clearance a medical device
must only show it is substantially equivalent to a similar device. The problem
with this type of clearance is that many times the device the new application
is claiming to be similar to may have had its own share of safety issues.
There is a much more stringent
type of FDA approval known as Premarket Approval or PMA. This approval requires
the company to conduct clinical trials and safety testing—essentially to prove
the device is safe and effective prior to marketing it to consumers. The 510(k)
process requires little in the way of scientific research to prove safety.
Further, at the time the Rejuvenate gained its 510(k) approval the neck was not
constructed of cobalt and chromium, rather was changed later in 2009 without
benefit of further FDA approval. The FDA did ask that Stryker conduct a study
known as the Rejuvenate Modular Outcome Study which would follow patients for
five and ten years to determine whether they had revision-free wear with no
serious issues. At present this study shows it is ongoing, but not recruiting
new participants.
Did the Design of the Rejuvenate and ABGII Contribute to Cobalt Hip
Poisoning?
At the time the two Stryker
designs were released, they were considered cutting edge as far as the
innovation of the design. Offering a variety of necks and stems allowed
surgeons to more closely match the implant to the patient’s individual size as
well as their activity level. The titanium stem was believed to be more flexible
than the much harder cobalt and chromium, adding a little “give” at the joint,
while the cobalt and chromium neck were believed to be more durable. The
Rejuvenate and ABGII were believed to be more stable and were advertised as
being extremely long-lasting—maybe even up to twenty years. Because the two
models were covered with a proprietary blend of titanium, molybdenum, zirconium
and iron mixed with plasma spray, Stryker claimed there would be no corrosion
from the dissimilar metals of the titanium stem and cobalt/chromium neck to
worry about.
This coating failed to offer
the resistance to corrosion Stryker expected, and, in fact, corrosion and
fretting were occurring at significantly higher rates at the neck and stem
junction. This corrosion caused microscopic metal ions to shear away from the
hip implant, entering the bloodstream or the hip tissues. When the cobalt ions
entered the hip region, pain as well as destruction and death of the tissue,
muscle and bone could occur. Cobalt ions which entered the bloodstream caused
metal toxicity among many Stryker patients. Symptoms of cobalt poisoning
included: Gastrointestinal, renal, thyroid, cardiovascular and neurological
damage, loss of vision and hearing, vertigo, DNA disruption, the formation of
pseudo-tumors and issues such as irritability, depression and anxiety.
What did Stryker Know Prior to the Recall of the Rejuvenate and ABGII?
An “Urgent Field Safety
Notice” was issued by Stryker in April prior to the recall in July of 2012.
This safety notice went to doctors and hospitals—but not to recipients of the
implants or consumers considering a Stryker hip implant. The notice admitted to
certain flaws, claiming there was a higher-than-normal risk of fretting,
corrosion and metal debris. Stryker went on to say that such things as the
patient’s weight, whether the patient suffered from diabetes or had an
infection, and the patient’s sensitivity to metals could all be responsible for
a failed hip implant. They further stated that in some
cases the neck pieces had not been adequately cleaned and that there were
deficiencies in the locking and assembly of the tapers. It is unclear at this
point exactly how much Stryker knew regarding the dangers of the Rejuvenate and
ABGII prior to the recall. It is expected that this will be an issue in the
pending Stryker Rejuvenate hip recall lawsuits as well as future lawsuits which
are filed against Stryker.
