Artificial Knee and Hip Replacement Implant Info

During joint replacement surgery, the implants can be fixated (held in place) two ways. They may be press-fit implants that allow the body to form new bone connections to it. Or, they may be cemented in place. For some joints, hybrid fixation is used, with cement on one component and press-fit on the other.

Press-Fit or Cementless Implants

Press-fit implants have a rough surface on which the surrounding bone can grow. Bone is living tissue, and the new joint can stimulate it to grow into the new surface, which becomes more secure if there are indentations for it to grow onto for a strong connection.

The surface of the implant either has a dimpled surface (grit blasted) or a rough surface (porous coated). This surface roughness allows the bone to grow onto the implant to hold it in place. A smooth surface would not have the same effect.

• Advantages: 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.
• Disadvantages: 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.

Even with normal bone, certain implants, such as knee replacements, cannot typically 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. It usually is polymethylmethacrylate, a fast-curing bone cement. This hard substance acts as a space-filler or grout and holds the implant solidly in position.

• Advantages: 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 the less-supportive bone.
• Disadvantages: Over time, cemented implants have a tendency to become loose. Because cement is not a living substance, once it begins to come loose, it is likely to continue to looosen over time.

Type of Fixation Most Commonly Used

• Knee replacement: Different types of implants may be used for a knee replacement. 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, for certain procedures. Foley cementless knee implants have been designed and are being used most commonly for younger people because they may last for a longer time.
• Hip replacement: Hip replacement implants are usually press-fit on the pelvis (socket) side. The femur (stem) 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. A longer stem might be needed and they may use metal augment pieces.

A Word From Verywell

Many joint replacement surgeries are routine, but some situations that may require specialized implants or a particular type of implant.

Both cement and cementless joint replacement implants can be used effectively, but there may be certain situations where one is preferred over the other. Talk to your surgeon about the method that they intend to use to hold your joint replacement implant in the bone.