Updated September 11, 2014.

Question: How are joint replacement implants held in the bone?

Answer: Joint replacement implants can be held in place in one of two ways:

Press-Fit Implants

Press-fit implants have a rough surface in which the surrounding bone can grow. The surface of the implant either has a dimpled surface (grit blasted) or a rough surface (porous coated). This surface roughness allows bone to grow into the implant to hold it in place.
What are the advantages of press-fit implants?
The advantage of a press fit implant is that over time, the bone holds solidly to the implant, lessening the chance of the implant becoming loose.

What are the disadvantages of press-fit implants?
Press-fit implants require solid bone for fixation, and must be fit very snug into the bone at the time of surgery. Therefore, weak, osteoporotic bone, will often not tolerate a press-fit implant. Press-fit implants also require time for the bone to grow into the implant.

Additionally, even with normal bone, certain implants, such as knee replacements, cannot be held in place adequately without cement to hold the implant in position.

Cemented Implants

Cemented implants also fit tightly into the bone. Around the implant is a hard substance often referred to as cement or glue. This hard substance acts as a space-filler or grout, and holds the implant solidly in position.
What are the advantages of cemented implant?
Cemented implants are as solid the day they are put into place as they will ever be. These implants can be placed more delicately, therefore they can be placed in less-supportive bone.

What type of fixation is most commonly used?

Knee Replacements
Knee replacements are most often cemented into position.

Some surgeons may opt to place press-fit implants, usually on the end of the thigh bone, in some patients. However, most commonly the knee implanted are cemented.
Hip Replacements
Hip replacement implants are usually press-fit on the socket (pelvis) side. The stem (femur) can be either press-fit or cemented. Most surgeons press-fit the implant in patients who have stronger bone, and cement if there is a concern about bone quality.

Revision Implants
In cases of revision joint replacement (replacement of a joint replacement) other options than those listed above may be suggested.