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What Happens During a Knee or Hip Replacement?

By Christina2 - May 29, 2014

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For most seniors, joints are something that wear away to the point that they may need to be replaced. This can often be a scary proposition, because it means acknowledging that your body doesn't work the way it used to. There's also the fear that something could go wrong and leave you worse off than before, or not fix the problem at all. It's a lot easier to keep going with the status quo instead of trying to forge a new path, even if that change could prove to be much more beneficial than the previous state. However, knee and hip replacements are really commonplace now, and performed with more regularity than ever before. Let's take a quick look at what you could potentially be preparing for.

Knee Replacement

You can essentially get one type of knee replacement (or athroplasty, which means "joint replacement") depending on the severity of the problem: partial, or total. And if you guessed that total knee replacements — or TKR — are the more common option, you'd be absolutely right. They account for about 90% of all knee replacement surgeries in the United States.

Total knee replacement: What happens is the doctor will take out all of the bone that's been damaged, and replace it with an implant, taking time to shape it so it fits snugly like a knee should. There are four main parts to the surgery:

  • 1. Slicing off the damaged cartilage from both the femur and tibia ends, plus a tiny bit of the bone underneath to prepare the area for the new joint.
  • 2. The surgeon will then put the new implant on. One option is with a press-fit where the implant has a rough surface so the bone can grow into it, while the other option is to cement-attach it on.
  • 3. A plastic button is placed under the patella to mimic the action of it (remember, that bony part has been cut off).
  • 4. The last step is to recreate a smooth, glide-y surface just like your old knee, and this is done with a medical grade plastic spacer between the tibia and femur (where there's now metal).
  • This type of surgery works splendidly well for about 90% of recipients, with a near-perfect feel-good rate of 90-95% after 10 years, and 85% after 20 years. Infection is always a risk, but a lesser one is the implant not being properly aligned, which would mean a trip back to the O.R. for a new implant. Rehab is super important to ensure the new knee works well right off the bat, and you'll likely be back on your feet that day or the day after. You need to get it moving right away to make sure that the joint doesn't "freeze".

    Partial knee replacement: This isn't a very common kind of surgery at all, and is usually performed when there's healthy tissue worth salvaging. There's really only three spots where PKR is performed: inside the knee, outside the knee, or the front of the knee between the femur and patella.

    Hip Replacement

    This type of surgery is a much more serious option to consider, because the ball-and-socket hip joint is one of the largest in the body, and situated near the femoral arteries. Many more things can go wrong, such as fracturing the hip, nicking an artery, or causing severe pain if the joint is misaligned. However, when done correctly, hip replacement surgery can mean a huge relief from near-constant pain. New hip joints are attached with either cement or a porous coating.

    Cement: Just as with TKR, the bone has to be prepared first and the surgeon will cut away a portion of it so the implant can fit neatly on. If it's being attached with cement, the new joint will be "glued" onto the existing bone.

    Porous coating: The main benefit of this is to allow the existing bone to fuse into the replacement, and so no cement is used. The idea is to stimulate bone growth through this coating so that the body can form its own bond.

    Whether the new joint is used with cement or not, they both follow the same basic four-step process:

  • 1. The damaged bone is cleaned off to present a working space for the new joint, which is a metal stem that slides into the center of the femur.
  • 2. A ball head goes on the top of the stem to complete the ball-and-socket joint.
  • 3. The joint needs a metal socket to hold it in place because the surgeon will remove the bad cartilage from the joint.
  • 4. The surgery is finished off by putting in a spacer so the joint can glide around easily, and is made from either plastic, ceramic or metal.
  • Unlike a knee replacement, hip replacements aren't restricted by age or weight. They do necessitate a lot more care during the rehabilitation process, though, because it's a much more delicate area than the knee. Whatever pain and disability you had before the surgery can be compounded if anything goes wrong, and the recovery process (such as for a fractured hip) is longer and more touch-and-go. Common complications from a hip replacement include blood clots, infection, leg-length inequality, dislocation, or loosening.

    Some of the things to follow really closely after the surgery include not crossing your legs, not bending your hips at a greater than right angle, and sleeping with a pillow between your legs to avoid the previous two.

    For many seniors, getting a joint replacement is the last available option after others have been exhausted and proved fruitless. Your doctor will be the one to best determine how appropriate a joint replacement surgery is for you, refer you to a surgeon, and answer any basic questions you may have.