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Child Orthopedics
Spine - Cervical
Spine - Lumbar
Spine - Thoracic

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I think I'm going to have a knee replacement soon but I'm still just a little bit cautious about something this major. And my sister had a knee job done and ended up having it removed and another one put in. She had something they called osteolysis. She was osteoporotic and I'm not but I'm still not sure I won't get this problem. What do you think?

Knee replacements have been around long enough now that their track record is clear. Ninety per cent of these implants last 15 to 20 years without problems. Patients experience a pain free return to normal function. Reports of patient satisfaction are high. But that doesn't mean problems can't or don't occur -- they can and they do. One of those common problems is osteolysis (bone resorption). It might help you make the decision if you have a little more information about this problem. First, what really causes osteolysis after a knee replacement? The main reason osteolysis occurs is because tiny particles flake off from the polyethylene (plastic) portion of the implant. The body responds to this debris as it would any "foreign invader." It sets up an inflammatory response to destroy the particles. In the process, bone is destroyed as well. Studies show the debris can be made up of different sized flakes of material. The smaller pieces are the ones that seem to trigger the inflammation. Larger particles aren't as likely to start a foreign-body cellular response, but instead delaminate or wear away the smooth surface of the implant. Either way, the end-result can be osteolysis and implant failure. The implant itself can be a source of problems. Different design features have advantages but also disadvantages. For example, efforts have been made to shape the implant so that it conforms better to the bone. Implants with small contact areas have less surface area to spread the force and load placed on the knee. The increased stress on the implant also increases the risk of wear and osteolysis. A second design feature is the placement of holes in the baseplate of the implant. The holes actually gave particles of debris a way to migrate or move into the joint. Screws used to hold the tibial portion of the implant in place did the same thing. The locking mechanism on the implant is another design feature that is intended to hold the implant steady. But even the tiniest movement or slippage of that locking feature and the backside of the tibial implant starts to wear. Over time, the finish on the surface of the implant wears away resulting in delamination, greater stress on the implant, and resulting implant failure. Not only is the implant itself a potential source of problems, but the way the implant is manufactured has actually been identified as a factor. Off-the-shelf implants that are machined to finish them (rather than compression molded) are more likely to have surface irregularities that lead to delamination. And one final manufacturing factor that affects how well implants hold up is the method of sterilization used. Of course the sterilization process is important and must be done but the way in which it is done can contribute to oxidation (breakdown) of the polyethylene. When that happens, the same results occur: debris formation, bone osteolysis, and implant failure. Scientists are studying ways to prevent this oxidation. Additives such as vitamin E have been added to the polyethylene in an effort to maintain the stable properties of the plastic. The hope is that by stabilizing the plastic portion of the implant, there will be less uneven load and better resistance to wear and tear. Until the problem of osteolysis is solved following a knee joint replacement, there is always a risk of this occurring. There's no evidence that we know of to suggest the problem is hereditary (i.e., no proof that if your sister developed osteolysis, you will too). It's common to have questions and doubts about any major surgery. Be sure and talk with your surgeon about this and any other concerns you may have.


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