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Knee Replacement

How Is The Artificial Implant Fixed To Bone?

Wednesday, April 18, 2012 - 16:58

Contributing Author: Guy Slowik FRCS

Options available that hold the knee replacement into position:

With a cemented procedure the components of the implant are fixed to the bone with a grout-like cement known as polymethyl-methacrylate. This cement allows the implants to perfectly fit to the irregularities of the bone.

A cemented knee is a very reliable procedure with approximately 90to 95 percent expected to enjoy pain-free activities for at least ten years beyond surgery. The advantage is that this type of knee replacement is immediately stable and one can walk fully bearing weight immediately following surgery. The disadvantages are that if it should become loose, some bone may be ground away by the loosened cement potentially making revision more difficult.

In a non-cemented procedure, components of the implant have a roughened porous surface designed to allow bone to grow into it, eliminating the need for cement.

The implants are "press fit" against the bony surfaces that are precisely cut through the use of multiple cutting jigs. Faultless positioning is necessary for bony attachment to occur with initial fixation by metal pegs and screws of the implant to bone. Since this implant relies on the bone to hold it in place, this procedure requires good bone to be successful

Since the non-cemented procedure is relatively new, years of experience and studies are not available regarding this type of implant as compared to the cemented implant. Therefore, at this time it is not yet known if a non-cemented implant will be as successful or will last as long as the cemented type.

One potentially positive aspect is that if this implant should become loose, less bone loss may occur due to the lack of the irritant cement. After surgery the individual with this type of implant is usually instructed to be toe-touch only until a follow-up x-ray usually done by the fifth or sixth week after surgery. The weight-bearing status following non-cemented knee replacement will be determined by the surgeon.

Occasionally a hybrid fixation is used which consists of a combination of the cemented and non-cemented technique. In this method the femoral component is not cemented and the tibia component is cemented.

At present, cemented knee replacements are most commonly used, representing 90% of knee replacement surgery. Non-cemented replacements are much less common, as are hybrid replacements.

Knee Replacement