All artificial implants will wear at the moving bearing surface. A low level of any type of wear particle is usually well tolerated. Excessive wear of any artificial bearing can lead to failure and may require revision surgery.
Plastic bearings release plastic particles that mostly accumulate around the local implant area and can cause bone destruction called osteolysis. These particles cannot be measured in the blood. Wear is best assessed by appearance on routine follow-up x-rays.
Ceramic bearings exhibiting abnormal wear chiefly fail by causing loud squeaking. Soft tissue or bone reaction is rare.
Metal bearings release cobalt and chromium particles that are deposited in the local tissues. They are absorbed in the blood and excreted in the urine. Wear cannot be determined from x-rays. The wear rate can be gauged very reliably from blood ion measurements.
We have learned that implant design flaws (DePuy ASR recall) and certain implant positions can cause abnormally high wear rates. High wear rates result in larger particle overload of the local tissues that causes pain and swelling. We call this an Adverse Wear Related Failure (AWRF). It is diagnosed by a triad of findings: high ion level above 15ug/L, a steep cup position (acetabular inclination angle AIA), fluid collection or inflammatory mass on MRI/CT, and extensive metal debris in the tissues (metalosis) seen at the time of revision surgery. We can screen for this problem by checking ion levels in the blood.
Extensive scientific studies of this problem have allowed us to determine safe implant positions to prevent this problem. We have had only 9 AWRF in over 4500 cases (0.2% incidence, or Kaplan-Meier (time adjusted) 1% rate of failure by 10 years) and have not had a single case in surgeries performed since 2007. But we still advocate a monitoring protocol for early detection.
There is a period of run-in wear that lasts from 1-2 years, thereafter levels steadily decline in most patients, except those that have AWRF. Systemic harm such as cancer has been disproven in multiple studies. Heart, kidney or nerve damage has been rarely anecdotally reported at extreme levels.