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Fixation of the components of the TKR
The implants may be cemented in place using a special bone cement, or the surgeon may elect to put a "cementless" prosthesis in place that allows the bone to grow into it over a period of time.
The prosthesis has a rough surface into which the bone can grow. This is called porous coating. The roughen surface can be also sprayed with a coating of hydroxyapatite. This material is the same as the mineral content of bone. The body therefore recognises the prostheses as bony and bonds to it as bone bonds together at a fracture site. It is hoped that this bond will be more durable than cement fixation.
The ingrowth of bone into the component takes at least 4 to 6 weeks to occur.
It has been found that the part of the knee replacement which attaches to the femur more readily bonds to the bone without cement than do the parts on the tibia and patella. For this reason, some surgeons use a conventional cementless component on the femur but uses porous coating with a coating of hydroxyapatite. Some surgeons continue to cement the tibial and patellar components or . This mixture of cemented and uncemented parts is known as a "hybrid" (mixed) total knee replacement.
I rarely use cement in primary knee replacements but need to use it routinely in some revision knee replacements.
The successful ingrowth and fixation of the components can be checked with an x-ray. See The Components on X-Ray
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