A very good question and one that hasn’t been addressed until recently.
Several studies have been done that show elevated levels of metals in the blood of patients with metal-on-metal total hip replacements. This led scientists to wonder about toxic levels of metals in children undergoing spinal fusion with rods, screws, and/or hooks.
A recent study from the Children’s Hospital in Boston showed elevated levels of nickel and chromium after spinal fusion. The metals were seen early after the operation and remained elevated even years later.
It’s not clear if the metals are actually toxic to the body. It’s possible that long-term exposure can lead to a depressed immune system. Any time the immune system is affected, other problems such as cancer can occur.
More studies are needed to answer your question fully. For now nothing will change in terms of the use of metal rods and implants for spinal fusion or joint replacement.