Cemented and Cementless Knee Replacement

Cemented and Cementless Knee Replacement 

In a normal knee, four ligaments help hold the bones in place so that the joint works properly. When a knee becomes arthritic, these ligaments can become scarred or damaged. During knee replacement surgery, some of these ligaments, as well as the joint surfaces, are substituted or replaced by the new artificial prostheses. Two types of fixation are used to hold the prostheses in place. Cemented fixation uses a fast-curing bone cement (polymethylmethacrylate) to hold the prostheses in place. Cementless fixation relies on bone growing into the surface of the implant for fixation.

Cemented Fixation

Most knee replacements done today are cemented into place. Cemented fixation has a generally excellent track record and may last more than 20 years. The longevity and performance of a knee replacement depends on several factors, including activity level, weight, and general health.

Cemented fixation relies on a stable interface between the prosthesis and the cement as well as a solid mechanical bond between the cement and the bone. Metal alloy components rarely break, but they can occasionally come loose from the bone. Two processes, one mechanical and one biological, can contribute to loosening.

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Cementless Fixation

In the 1980s, implants were introduced that were intended to attach directly to bone without the use of cement. These implants have a surface topography that is conducive to attracting new bone growth. Most are textured or coated so that the new bone actually grows into the surface of the implant. They may also use screws or pegs to stabilize the implant until bone ingrowth occurs. Because they depend on new bone growth for stability, cementless implants require a longer healing time than cemented replacements. Some cementless total knee replacement implants have been as successful as cemented implants in relieving pain and restoring function.

Cementless implants, however, have not solved the problems of wear and bone loss. In all knee replacement implants, metal (usually a titanium- or cobalt/chromium-based alloy) rubs against ultra-high-density polyethylene. Even though the metal is polished smooth and the polyethylene is treated to resist wear, the loads and stresses of daily movements will generate microscopic particulate debris. This debris, in turn, can trigger the inflammatory response that results in osteolysis. 

Hybrid Fixation

In a hybrid fixation for total knee replacement, the femoral component is inserted without cement, and the tibial and patellar components are inserted with cement. This technique was introduced in the early 1980s; long-term results are just now being measured and are generally positive. 
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Knee replacement operations, whether they use cemented or cementless fixation, are highly successful in relieving pain and restoring movement. However, the ongoing problems with wear and particulate debris may eventually necessitate further surgery, including replacing one or more parts of the knee replacement (revision surgery).