is the plastic used in knee and hip implants safe
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KNEE AND HIP JOINTTRANSCRIPT
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Knee Implant with Polyethylene
Is the Plastic Used in Knee and Hip Implants Safe?31 Shares
Every total knee replacement implant and many total hip replacement implants utilize ultra-high molecular-weightpolyethylene (UHMWPE), a plastic, in their components. In knee implants, the tibial component is a flat metal platform with apolyethylene cushion and the patellar component, if used, is a dome-shaped piece of polyethylene. In hip implants, the acetabularsocket is often polyethylene, or a combination of polyethylene backed by metal.
But what happens to that plastic once it has been implanted in your body? Plastics and their effect on the human body and theenvironment get quite a bit of negative press these days. Its not surprising that patients are concerned about the polyethylenecomponents of knee and hip implants.
Bisphenol A (BPA)
The health concern with other plastics, such as those used in baby bottles, sippy cups, water bottles and plastic dishware relates toa chemical called bisphenol A (BPA), which is used in the manufacture of polycarbonate to improve the strength and appearanceof the plastic. Several years ago, scientists determined that BPA can have a negative impact on humans, especially on babies andchildren.
In general, plastics that are marked with recycle codes 1, 2, 4, 5, and 6 are very unlikely to contain BPA. Some, but not all, plasticsthat are marked with recycle codes 3 or 7 may be made with BPA. Polyethylene like that used in knee implants and hip implants is avery different polymer than the polycarbonate used in some of those other products.
Ultra-High Molecular-Weight Polyethylene (UHMWPE)UHMWPE has over 40 years of clinical history as a successful biomaterial for use in hip and kneeimplants. In the late 1990s, highly-crosslinked UHMWPE materials were introduced and have rapidlybecome the standard of care for total hip replacements. The new material very successfully resistsoxidation, not breaking down at a molecular level with time.
What Happens When the Plastic Breaks Down?
BPA is not used in polyethylene and is, therefore, not contained in any hip implants or kneeimplants. When the polycarbonate containing BPA breaks down, the BPA is ultimately released asindividual molecules, which may act like the female hormone estrogen in the body. This is thoughtto lead to various health problems.
When polyethylene (including the UHMWPE in joint implants) breaks down, it breaks down intosmaller pieces of polyethylene, all of which are substantially larger than BPA molecules. The bodywill create inflammation to try to protect itself from these pieces of plastic after time.
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Liner (MicroPort Orthopedics)The new highly cross-linked polyethylene was developed to be more wear-resistant. Slowerbreakdown means fewer and smaller polyethylene particles are generated. This means less risk ofinflammation that can lead to bone damage and failure of the prosthesis.
Polyethylene has been in use in hip and knee prostheses since the 1960s, with the only long-term complaint being the inflammationresulting from breakdown. For almost 15 years now, the improved polyethylene has greatly reduced even that complaint due toimproved wear-resistance.
image credit: ConforMIS
Filed Under: Joint Replacement Hip Implants Knee Implants
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Is the Plastic Used in Knee and Hip Implants Safe?Bisphenol A (BPA)What Happens When the Plastic Breaks Down?Related Articles & FAQsRecent Forum Discussions