"Because we thought they have no pain, normal x-rays, we thought we would find a bit of fluid and a bit of metal. But quite the opposite. We found a horrendous amount of metal debris and the cups often have sort of been loosened by the metal and the metal gets behind the cup—the metal debris—and gets into the bone and goes deep into the pelvis and blown holes in the pelvis, we're almost at the bladder. It's just unbelievable and the unbelievable fact is that the patients have no pain."
- Orthopaedic Surgeon, Dr. Antoni Nargol
Even DePuy ASR recipients who feel great, have positive Harris Hip Scores (above 80), and clean x-rays are finding out they have astonishing internal injuries caused by metal particles worn off their implant. Referrred to under a variety of names, the severe inflammatory reaction to this metal debris can destroy the muscles, tendons, and other soft tissues around the femur, sometimes killing off the blood supply to the femur.
Some patients have even had to go through reconstructive surgery involving bone grafts to repair the extensive damage done to the pelvis by this reaction to metal debris. The taper, or stem, of the ASR XL (full hip replacement device) is especially guilty of releasing metal particles.
Because patients may lack any outward symptoms, blood ion levels (specifcally, cobalt) should be measured in all patients regardless of symptoms (see "Blood Ion Levels: Cobalt" at right). Needle aspiration of the joint may also be performed to remove the accumulated fluid.
This destructive process has been cited under the following terms (some formally, some informally):
In the late 19th and early 20th century, the first attempts and artificial hips used materials such as ivory and glass. These were eventually replaced by a cobalt-chromium alloy known as Vitallium that was considered better than other metals because of its resistance to corrosion and light weight. Other materials were eventually incorporated into various hip replacements so there are now five different types—based on material used—of replacement hips currently used in the US:
Both DePuy hip replacement systems being recalled are metal-on-metal hip replacements.
Replacement hips made from a metal ball and metal socket were originally designed to last longer than their counterparts that use polyethylene (plastic) or cermic parts. However, despite the increased durabilty provided by metal, these joints will also wear down during regular use.
As the metal ball slides against the metal cup, the metal is worn away. If the placement is good, and the design is effective, this wear should be minimal. In an ideal scenario, the metal cup and the metal ball actually do no touch, as the naturally occuring lubricating fluid in joint would be pulled between the two surfaces, allowing them to slide against one another.
In the real world, however, rarely does this occur, no matter the material used in the hip device. However, the ASR has proven extremely susceptible to edge-loading, where too much pressure is put on the cup's edge by the ball, dramatically increasing the speed at which material is worn off the replacement joint.
The tiny metal particles that wear off the joint through regular use, edge-loading, and/or corrosion can inflame surrounding flesh, lead to the joint or components loosening, and enter the bloodstream, causing illness or injuries elsewhere in the body.
In addition to the immediate injuries of tissue and bone, there are growing concerns about the effect elevated cobalt and chromium will have in patients.
According to a May 2010 study titled "Cobalt Toxicity in Two Hip Replacement Patients," two patients reported suffering rashes, tinnitus (ringing in the ears), hearing loss (confirmed by testing), headaches irritability, shortness of breath, tremors, memory loss, a loss of coordination, and/or vertigo. After revision surgeries, both patients reported an improvement in nearly all their symptoms.
The effects of metal ions throughout the rest of the body are not totally known, but according to the FDA, patients should be aware of "changes in their general health or new symptoms outside their hip including symptoms related to":
Dr. Nargol talks to Deborah Cohen for the British Medical Journal about the ASR, metal ion injuries, and metal-on-metal hip implants.
The two metals that can leach off ASR implants into the bloodstream are cobalt and chromium. Cobalt levels are considered a more accurate measure than chromium so blood cobalt levels are what orthopaedic surgeons are currently measuring in the interest of finding these metal debris injuries.
What should blood cobalt levels be at? At what blood cobalt level are you at risk? Blood cobalt levels by the numbers:
The long-term systemic effects of elevated blood cobalt and chromium levels are unknown.
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