According to a Canadian orthopedic research team who performed a 2014 comprehensive literature review on side effects from non-metal-on-metal hip prosthetics for the Bulletin of the NYU Hospital for Joint Diseases, one of the best ways to accurately diagnose a failing hip prosthetic is to use imaging techniques, such as computed tomography (CT) or magnetic resonance imaging (MRI) scans, as well as visualization through ultrasound.
Local Side Effects From Metal Buildup
Adverse local tissue reaction (ALTR) is a general term for inflammation or other conditions arising in close proximity to the source of metal ion release in the body, and the side effect most commonly associated with malfunctioning or failing metal-on-metal or metal-on-polyethylene hip devices.
When metal debris from faulty hip implants builds up in the blood stream, a patient may develop a condition called metallosis, a type of metal poisoning. It can be hard to diagnose metallosis because it has a wide range of symptoms, many of which are nonspecific. Furthermore, some patients, even those exhibiting high levels of metal in blood serum or joint fluid, may not exhibit any discernible symptoms even after an extended period of time, or at all.
One common local tissue reaction to metal ion buildup is the formation of “pseudotumors,” fleshy or fluid-filled masses surrounding the infected area. These bulky growths can cause discomfort and even pain, especially when many of them are clumped together and / or reach very large sizes. They can also interfere with digestion, urination, and excretion, depending on where the pseudotumors are located.
Necrosis & Osteolysis
The toxic effects of high metal serum levels can cause tissue and even bone cells to die. This can cause pain and joint instability. Over time, loosening and / or breakage of the hip replacement device can occur, which generally calls for immediate revision surgery. The degree of risk in a revision surgery depending on how much of the implant needs to be replaced, Revision surgery can be especially invasive and risky if the patient is elderly or overweight / obese.
Implant Fracture Or Other Failure
When the trunnion interface corrodes and weakens the bond between the femoral stem and the femoral head, the two parts can break apart, with disastrous effects for the victim. Patients who’ve experienced hip implant failure of this type often describe hearing a sudden snapping sound, followed by intense pain and discomfort. Broken hip implants must be removed and replaced via invasive surgery.
Potentially Life-Threatening Systemic Effects
As explained in a two-part literature review from Rubin Institute for Advanced Orthopedics in Baltimore, Maryland, in addition to the local side effects described above, an overabundance of cobalt and chromium ions can also lead to adverse effects that cause damage throughout the patient’s entire body:
Although researchers are still trying to establish exactly how cobalt toxicity can affect the heart, one leading theory says that cobalt ions affect the transport of oxygen to the heart.
Symptoms commonly experienced by patients suffering from cardiac issues from high cobalt levels are sensations of chest tightness during physical exertion, difficulty breathing, and heart palpitations. Recorded cases of patients with suspected cobalt toxicity from hip implant debris were found to have extremely high cobalt levels (over 100 μg/L)
Excess cobalt can interfere with the body’s absorption of iodine and also prevent the thyroid gland from making enough thyroxine, a key hormone that helps regulate the normal functioning of the heart, metabolism, and digestive system.
Patients with cobalt-related thyroid problems often exhibit symptoms similar to those of hypothyroidism, such as difficulty concentrating, feeling physically weak and lethargic, and poor reflexes. Again, patients with malfunctioning artificial hip devices found to have thyroid issues tested with extremely high cobalt levels, and in at least one case, thyroid function markedly improved after the patient underwent hip revision surgery that halted metal ion buildup.
Cobalt toxicity can lead to depleted levels of crucial neurotransmitters such as dopamine and serotonin, as well an increase in free radicals that can cause damage to neurologically sensitive areas that are vulnerable to oxidative stress , such as the sheath protecting the nerve fibers of the brain and spinal cord.
Some common adverse neurological effects of excess cobalt in the bloodstream are short-term memory loss, fatigue, headaches, blurred vision,and increasing loss of hearing. Cases of patients with hip device-related cobalt toxicity also reported tinnitus and unexplained paraesthesia (“pins and needles” sensation), and most tested with moderately high cobalt levels (between 20 and 100 μg/L).
Though all of these patients saw their symptoms improve after hip revision surgery, the degree of improvement varied. Furthermore, researchers haven’t firmly established whether or not neurological damage from cobalt toxicity is completely reversible after cobalt levels return to normal, and so,we may later discover that patients can develop lifelong problems.
Though hepatotoxicity from excess cobalt is thought to be rare because the liver has a high toxicity threshold for cobalt uptake, it can prove fatal. At least one recorded patient, who exhibited a shockingly-high serum cobalt level of 6521μg/L after implantation with a cobalt-chromium hip device, was diagnosed with hepatotoxicity and eventually died from multiple organ failure.
Are Modern Hip Device Designs To Blame?
Many researchers, including Philip Pastides and his colleagues in the UK, believe that they are.
In an extensive editorial on recent metal-on-metal hip implant research in the World Journal of Orthopedics, Pastides explains that even though the total metal debris contributed from the stem-trunnion interface is less than the amount that comes off from the main articulating surfaces (that is, the ball and the cup rubbing against each other during normal movement) – which was one of the major design aims of modern hip devices – this particular type of debris may actually be more biologically active and therefore potentially more harmful.
A “Modern Orthopedic Failure”
This means that the particles released from stem-trunnion friction may cause more adverse tissue reactions, including osteolysis, and can contribute more to disastrous loosening. Though Pastides and his team reviewed mainly literature on metal-on-metal hips, they believe similar issues are at play in non-MoM hip implants as well. Particularly convincing were measurement comparisons between various ion levels from patients suffering complications from modular THR replacements and those having similar issues from hip resurfacing (in which there is no stem-trunnion junction to speak of).
The authors denounce metal-on-metal hip implants in no uncertain terms, calling them a “modern orthopedic failure” that promise better fit but at the expense of much higher wear rates than expected. Such wear, they say, causes destruction of surrounding bone and tissue that often proves “devastating” to hip replacement patients, who are still mostly unaware of the potential risks of their hip implants.
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