Metallosis: A Risk For Patients Implanted With Defective Depuy Mom Hip Devices

Metallosis is one of the complications that were reported among the thousands of

complaints received by the US Food and Drug Administration (FDA) concerning metal-on-metal (MoM) hip implants. The New York Times published an article reporting that nearly 4,000 of the about 5,000 complaints received involved the Articular Surface Replacement (ASR) hip systems which has been recalled by the DePuy Orthopaedics Inc., a subsidiary of the Johnson & Johnson, in August 2010. As the FDA continues to receive complaints, the U.S. House of Representatives committee members asked for an investigationof metal-on-metal hip replacements.

When metal particles build up in the tissue surrounding the implanted joint, the condition is called metallosis. Metal debris is released into the body as a result of the friction when the metal ball on the femur moves on the metal liner in the acetabular cup in the hip. The scavenger cells attack the metal debris, being a foreign substance, and in the process the metal fragments are broken down into ions which are positively electrically charged. Positively charged ions have been known to cause chemical changes in the human tissue which could trigger an immune response called metallosis.

Symptoms of metallosis include:

Rash that is a sign of dying tissue

Swelling around the implant area

Difficulty walking

Pain around the hip joint

Those symptoms may indicate these severe problems:

Loosening, when the implant does not stay attached to the bone in the right position.

Fracture, where the bone around the implant may have broken.

Dislocation, where the two parts of the implant that move against each other are no longer aligned. This happens because tissue around the joint becomes inflamed and weakened, and cant hold it in place.

Damage to the nerves, tissues and muscles near the implant area

A revision surgery is required to correct the defective hip replacement surgery among affected patients, a surgery that includes the removal of the failing metal-on-metal hip implant and replacing it with another model preferred by the patient. However, it is often during the revision surgery when doctors discover more problems associated with metallosis. Doctors find a dense black staining of the synovial membrane and surrounding muscles in most revision surgeries.

The membrane is a sac filled with fluid that helps certain joints move freely. In patients with DePuy hip implants, it appears that the immune system inflames cells in the synovial membrane, causing synovitis. Synovitis is painful because the swelling prevents the joint from rotating properly.

Aside from synovitis, surgeons also often find pseudotumors or masses of inflamed cells that look like tumors. Found more commonly in women and persons of small stature, these pseudotumors can either be solid or fluid-filled. Patients with pseudotumors usually experienced gradually increasing pain. Greatly elevated levels of cobalt and chromium are also found in the blood stream of patients who had undergone hip revision. Cobalt and chromium have been linked to cancer. Cobalt poisoning and cobaltism, on the other hand, has serious side effects including neurological (brain) damage, heart irregularities, and seizures.

It is then understandable why the DePuy hip replacement recall is inadequate compensation for affected patients. Johnson & Johnsons offer of handling the revision surgery of affected patients is allegedly not enough to meet all the expenses that arise from addressing the complications of the defective implant. Affected patients also deserved to be fairly compensated for the anguish that they had gone through with having the defective implants.

by: Katherine Russel

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