Why does your body not attack metal plates and screws after surgeries?
In: Biology
It does if you use the wrong materials. You need to use biologically inert material. Non-reactive metals don’t give your immune system much to work against (your immune system is all based on chemistry). Hence a lot of stainless steel. Your body will try to grow over/on/around metal plates and screws…that’s a good thing, that’s part of how they bond securely with bone.
We carefully chose the metals used, it’s usually titanium because it’s basically invisible to your immune system. Even then cases of it being rejected happen. So most things surgically installed in your body are at least coated with a biocompatible material.
Your body doesn’t attack metal plates and screws because they are typically made of materials like titanium or stainless steel, which are biocompatible. This means they are unlikely to cause an immune response or be rejected by your body. Plus, the surgery process usually involves cleaning and sterilizing the area to reduce the risk of infection. So, your body sees them as part of the healing process rather than a threat. Hope that helps.
It does. Or at least, it *tries*. Those metal parts are made out of metals that are particularly difficult to attack because they are very nonreactive.
Almost all metals react with oxygen. With iron, we call this *rust*. When iron rusts, the resulting iron oxide expands and doesn’t stick well to the iron underneath, so it flakes off and the iron underneath is exposed to oxygen and then *it* rusts. The oxides of a lot of metals, though, sticks quite well to the metal underneath. Once the metal is oxidized, it’s *really* hard for anything else to get to it. Oxygen really does not like to share. So, that oxidized layer forms a kind of armor, where the metal is “pre-reacted” and won’t react well to anything else.
Titanium is one such metal. Titanium oxide is tough stuff. Add a little of some other metals and you make something that your body just doesn’t have any tools to break apart.
Being non-reactive also helps hide it from your immune system. Your immune system doesn’t have eyes – it can only “see” what reacts to the antigen receptors on the outside of immune cells. Immune cells learn that certain antigens indicate *you* and shouldn’t be attacked, and antigens that *aren’t you* are foreign and should be attacked. All the bacteria living in your body have adapted to hide their bacterial antigens and give off fake “I’m part of you, don’t attack me” antigens. But something that doesn’t react *at all* doesn’t have antigens. Your immune cells just bounce off of it and never really notice that it’s there.
Since it “isn’t there” your immune system doesn’t try very hard to get rid of it, and since your immune system doesn’t have any tools that can get through that protective oxide layer anyway, the metal is fine.
It *is* possible, though, for a body to notice and try to reject the metal part. That usually doesn’t do anything to the metal, but the inflammation can be dangerous for the cells around the metal part and cause problems for your body. In that case, anti-rejection drugs that suppress your immune system will *hopefully* get your body to stop attacking until it gets used to the part being there and “forgets” to attack it. Or, they have to try a different alloy.
This is also why your body doesn’t attack medical plastics. The plastic is very nonreactive. And, it’s why bullets are usually left inside the patient. Elemental lead is pretty nonreactive so although your body will try to attack it, which will put some lead into your blood to spread through your body, it’s such a slow process that it isn’t going to hurt you. The surgery to remove the bullet will cause more damage. (Unless the bullet is like, right next to your heart and you really need to get it out.)
Through research and experiments and past experiences in science, we’ve discovered materials that the body does not react to.
We then make surgical implants and instruments out of these materials.
It’s not “why does the body not attack implants” – it is “we found materials that the body doesn’t attack and therefore we use these materials to make implants”.
If these materials didn’t exist, then we either won’t be able to make implants or we will make implants that the body does attack. There’s old implants from decades ago that does break down in the body and cause heavy metal poisoning etc. before we made scientific advances that allow us to have safe implants now.
Lots of folks explaining what happens with the right metals, but if you’re curious about what happens when you use the *wrong* metals you can do some research on what it’s like to have a “gold allergy.” Many of the women in my family can’t wear gold because their body has an autoimmune response and they get a reaction. Obviously, if you were to use gold as a surgical implant they would have a *very* bad time.
Last time I checked – no one knows why titanium doesn’t elicit an immune response in most patients. Free TiO can even bioaccumlate in the event of mechanical stress ablating some surface oxidation. Anyhow, specifically why that material is ignored by the body is largely unknown.
It was observed by chance that it doesn’t and so we use that and ultra high weight polyethylene (high tensile strength, low surface deformation after casting, and oxidative resistance if mixed with antioxidants, eg. Vitamin e) – the latter not as good, but better at bone interface admittedly at the cost of oxidative stress susceptibility – but other answers already covered that
Some of the plastic materials used in early joint replacements had a problem of creating small particles as they wore down. These particles inside the joint caused an immune response where the implants were attacked by the body and loosened up. Luckily, doctors learned and changed these. I have had both knees and both hips replaced all with different materials because of insurance coverage. My right hip is the oldest at 20 years old. It is part ceramic.
I had a friend with a screw loose. He fell off a ladder. He had a metal screw in his foot from a previous injury, when he fell it pulled that screw loose.
Most surgical implants are made of titanium which is biologically inert. As far as your immune system is concerned titanium doesn’t exist and it wont reject it if used in place of bone.
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