Measurement of Metal Ion Levels in Your Blood
Your artificial joint is made of two metal surfaces rubbing together (metal-on-metal joint). The metal is an alloy of cobalt and chromium, which is harder and smoother than titanium. Any artificial joint that has surfaces that rub together will produce friction, and therefore, create wear particles. With a metal-on-metal joint, the wear particles are microscopic and will dissolve into your joint fluid and get absorbed into the bloodstream. Thus, the metal wear particles can be measured in the bloodstream in ionic form. The kidneys filter the majority of the metal particles out of the body, and the amount left is usually in the 3-4 parts per billion (ppb) range. Therefore, it is expected that a single metal-on-metal joint will produce 3-4 ppb of cobalt and chromium in your bloodstream. If you have bilateral implants, then the amount will be doubled.
I recommend that we measure your metal levels starting at 1 year postoperative, which gives the body time to reach steady-state with regard to wear production and kidney filtration. Then, I like to measure the metal ion levels on an annual basis. When the metal levels are stable, then I may suggest that we start skipping some years of measurement.
The "normal" values for cobalt and chromium in the bloodstream are less than 1ppb for people without a joint replacement implant. For a well-functioning joint replacement, we expect the values to be less than 7 ppb. If the values are less than 7 ppb, there is no cause for concern. Systemic health issues have been reported when cobalt or chromium levels are above approximately 50 ppb, though different people may have different responses to metals.
If your values are abnormal, we will need to repeat the blood test to ensure that the high values were not a laboratory error. It is best to be well-hydrated and to avoid any vitamins or supplements for 2 weeks prior to the test. If the repeat lab test confirms the elevated values, then we must investigate other causes. Other reasons for having high metal levels include activities or movements of the hip that create friction or edge-loading. Examples of activities that can produce metal wear include deep squats (beyond 90 degrees) with weights. Other reasons that the metal levels may be higher than expected is if the kidneys are not filtering out the metal ions sufficiently. Finally, there can be greater than expected production of metal wear debris from the implant because of loss of fluid film lubrication, because the interaction of movement, your body, and implant position are not working well together.
Cross-sectional imaging such as an MRI or ultrasound may be helpful in evaluating the tissues around hip to see if they are being affected by the higher than expected amount of metallic wear debris. If there is any evidence of bone, muscle, or tissue damage from these metallic particles, then it may be necessary to revise your implant.
FAQ regarding metal ion measurement:
Do I have to come to your office for metal ion measurement?
No, it isn't necessary, but I do recommend you go to a reputable laboratory that uses Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to get the most accurate results. Furthermore, it can be difficult to compare results across different labs, so please stay with the same laboratory once you have begun.
Why are you measuring my metal ion levels? My other doctors have not recommended that I have this performed?
It is true that measuring metal ion levels goes above and beyond the recommended followup after a joint replacement. However, Dr. Su finds it can help detect problems at an earlier stage, and helps him intervene if necessary so that the end result will be optimal. Furthermore, having repeated metal ion levels over time can help predict the longevity of an implant.
Does my activity influence my metal ion levels?It does not appear that the amount of activity you perform has an influence on your metal ion level metal ions have been measured before and after extreme activity (such as an Ironman triathlon), and other than being affected by dehydration, the metal ion levels did not change.
Some surgeons actually believe that activity helps promote the lubrication of your joint by bringing fluid in between the implant surfaces.
What kind of symptoms would I have if my metal ion levels are high?
This can be different for everyone, but the most common symptoms of high metal ion levels are pain and swelling around the hip joint.
What about chelation - are there ways to reduce my metal levels?
As of right now, I am not aware of any methods to safely reduce your metal ion levels other than to keep well-hydrated. I have spoken to many toxicologists and they have informed me that chelation would remove more "good" metals from the body before being able to remove the "bad".
Are chromium and cobalt harmful to the body?
Both cobalt and chromium are elements that naturally occur in foods, and are essential ingredients for many physiologic processes. For example, chromium is an essential element utilized in the metabolism of sugar. Cobalt is part of vitamin B12, also known as cobalamin.
Therefore, we believe that if the levels of chromium and cobalt stay at the levels that we typically see after a hip resurfacing, that there would not be any deleterious health consequences
Will these elevations in metal levels cause cancer?
There has been extensive research on this topic, since cobalt and chromium have been used in total hip replacements since the 1970's. A scientist from Finland, Tuomo Visuri, examined his national joint registry and identified the total hip replacements that used cobalt and chromium metal-on-metal surfaces. He then cross-referenced this database with the national cancer registry, examining over 38000 person years of exposure. Fortunately Dr. Visuri and colleagues did not find any increased risk of any type of cancer, in the patients who had metal-on-metal hip replacements when compared to THR made from other materials.