Prosthetic Problems

Eric Lis

If you think that video games are unhealthy, wait until you get your first bionic limb.

Some months ago, I wrote a few words about the impracticality of cybernetic enhancements in light of the simple fact that metal is heavy. The topic came back to me recently while I was evaluating a young woman in the emergency department. She'd come to the hospital because she suspected that she was showing signs of lead poisoning. On taking her history, it turned out that she'd been shot about twenty years previously, and for various reasons, the bullet had never been removed. A chest x-ray proved that the story was true; there were metal fragments in her chest wall, which weren't dangerous in and of themselves but which happened to be in one of those spots that are really difficult to reach surgically. In the decades since, her body's defences had been very slowly wearing away at the bullet, and lead had been leeching into her system, resulting in chronic lead poisoning, and now she presented with hearing loss, abdominal pain, numb fingers, and symptoms of depression.

Research has been done on survivors of gunshots, and we know that it's actually rare for this to be a cause of metal poisoning, with one exception: bullets near joints. For various reasons, metal fragments in joints leech more and are more likely to cause poisoning over time. Fortunately, there aren't that many people walking around today with bullets in their bodies, but there's one particular form of metal that's actually commonly placed into people's joints: prosthetics. Unsurprisingly, it therefore turns out that some people do react to their prosthetic limbs, which I have to imagine is an increasingly common and vastly under-diagnosed health problem in most medieval fantasy settings.

In one respect, I'm actually being a little bit disingenuous. We know that lead and many other metals are potentially toxic, so they don't tend to be used to manufacture any device that's intended to be implanted in a human body. Medical prosthetics (and presumably also military prosthetics, in settings where they exist) are built out of materials which we hope aren't dangerous in the same way. The fact is, however, that any implant is going to be worn away over time, molecule by molecule, particularly if it has any moving parts that rub against each other. The result is two potential complications: toxicity, or a related problem, allergic reaction.

A lot of the data on real-world prostheses comes from studies of hip replacement patients. Hip replacements are very common, and they're a better model for cybernetics than many prosthetic limbs because they go inside of, rather than strap on to, the body. A hip prosthesis generally consists of two pieces: a socket, which gets attached to the pelvic bone, and a rod which gets attached to the leg bone. At this joint, the bar rubs against the socket, slowly wearing away both. There's been increasing awareness that this can lead to patients being exposed to toxic ions, and with the current devices used, particularly cobalt, which is a component of many steel alloys. Like poisoning with other heavy metals, slow cobalt poisoning damages several body systems, including the thyroid gland (slowing metabolism and making the creature more easily fatigued and more sensitive to cold), the heart (reduced contractility of the muscle resulting in poor pumping), and the nervous system (hearing loss, vision loss, poor concentration, tingling and numbness). The overall picture would be a gradual loss of strength, energy, and sensory acuity over the course of years, probably accompanied by slowly increasing irritability and depression.

Independent of toxicity, some people eventually prove to be allergic to metals. You probably know someone whose skin is especially sensitive to some metals; they may get rashes or blemishes from wearing silver jewelry, for example. While you can take out an earring, it isn't so easy to detach an implanted prosthesis. Prostheses are generally made from the least allergic substances possible, but the current thinking is that over time the metal begins to corrode, and the corrosion products may trigger a reaction. Allergic reactions to a prosthetic device may be limited to the skin or may have systemic effects. Either way, as the body reacts, the skin over the area can become red, itchy, and allergic looking, much as if the person was wiping themselves with poison ivy once or twice a day. The allergic reaction can spread to nearby blood vessels, causing swelling and pain, and bone may start to degrade near the implant.

With cybernetics and bionics, we can't really know if these problems will be bigger or smaller. On the one hand, we presume that by the time we're giving people functional robotic arms with built-in grappling hooks, we'll have advanced enough to build them out of a truly non-reactive substance. On the other hand, as near as we know at this time, there's no such thing as a truly non-reactive substance. Furthermore, when you put a new hip into an octogenarian, you don't have to worry too much about whether it will still be strong and stable in twenty years. In contrast, when you attach a forearm-mounted laser cannon to a healthy twenty year-old, or graft a living wooden hand to an elf who's going to live another four hundred years, there's a very real question of how long such an implant will last before causing problems. None of this is to say that giving your characters augmetic enhancements is impossible, but rather to say that, like anything worth doing in life, it's never as easy as it looks. 

More than four years ago, Dr. Eris Lis, M.D., began writing a series of brilliant and informative posts on RPGs through the eyes of a medical professional, and this is the one that appeared here on November 2, 2014. Lis is a physician, gamer, and author of the Skirmisher Publishing LLC OGL sourcebook Insults & Injuries, which is also available for the Pathfinder RPG system