Knees for You Guide to Knee ReplacementServing the Patient Community since 12/18/2006 Patricia Walter Owner/Webmaster |
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Cemented, Cementless and Hybrid Fixation Total Knee Replacement OptionsFour ligaments hold the bones of the knee in place. These ligaments can become scarred or damaged with a person develops arthritis in their knees. Some of these ligaments are replaced by new artificial prostheses during surgery. Also the joint surfaces are replaced by a knee replacement device. There are two type of fixation to hold the knee device in place - Cemented and Cementless. Cemented uses a fast-curing bone cement to hold the device in place. Cementless devices rely on new bone growth into the surface of the knee device for permanent fixation. Cemented FixationThe majority of knee replacements are cemented. Cemented fixation has been used for years and some have lasted more than 20 years. A patient's activity level, weight and general health affect the longevity and performance of their knee replacement. 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.
Cementless FixationIn 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. Because cementless implants have not been used as long as cemented implants, comparisons of long-term use is not possible. However, short-term outcome studies have shown that cementless fixation has success rates comparable to those of cemented fixation. Hybrid FixationIn 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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