Polyethelene safety factors - an explanation

[alexthecat]

In my real life, I hold a PhD in chemistry from a well-known American university and I think I can explain a little about plastic.

The hard plastic that is (or I should say "was" as many manufacturers are moving away from it) used in water bottles is called polycarbonate. This is a very different polymer than the polyethylene that is used in hip replacements.

The health concern with water bottles is not from the polycarbonate itself, but from a chemical called bis-phenol A (or BPA for short), which is used in the manufacture of polycarbonate to improve the strength of the plastic and make it look prettier. BPA was used for a long time before scientists figured out that it can act like a hormone in our bodies and cause all kinds of problems for us and, more importantly, our kids.

The good news is that BPA is not used in polyethylene and it is not in any components of prosthetic hips. There has been a lot of research done on polyethylene in human bodies. It's not just in hips either. Polyethylene has been used for all kinds of things for a really long time and it's very, very safe. Especially this new generation of highly cross-linked polyethylene, which is very stable and doesn't seem to break down much at all.

 

[alexthecat]

The breakdown of polyethylene that is talked about is different than the leaching of BPA from polycarbonate.

BPA is released as individual molecules and, in the body, those molecules may act like the female hormone estrogen. This is thought to lead to various health problems, including cancer, diabetes, and birth defects.

Polyethylene breaks down into smaller pieces of polyethylene. Those pieces are hundreds or thousands of times larger than the BPA molecules that I discussed above. They don't cause any sort of disease, but the body sees them as foreign invaders and creates inflammation to try to protect itself from them.

This inflammatatory response causes tissue to become swollen and perhaps, with time, the tissue begins to break down. If the bone around the prosthesis is affected, there is a risk the prosthesis can become loose and fail.

That has been a big problem with polyethylene in hip replacements, but the new highly cross-linked polyethylene was developed to solve that problem. This new polyethylene is a lot more rugged and wear resistant. Fewer polyethylene particles are generated and the ones that are generated are a lot smaller. That means that there is less risk of inflammation that can lead to bone damage and prosthesis failure.