Questioning the Location and Amount of Cement in a Total Knee Implant
Total knee joint replacements have two parts: the femoral component and the tibial component. The femoral part fits up into the thighbone and forms the upper half of the new joint. The tibial implant has a plate that meets the femoral side and a stem to hold it into the tibia (lower leg bone).
This study compared the use of full versus partial cement on the tibial component. Just the underside of the plate is covered with cement in a partial, or surface, cement approach. Full cement covers the plate and the stem as it fits into the long shaft of the tibia.
One other variable was added in this study. Two different shapes of tibial stems were compared using just surface cement. Some of the tibial stems cemented in place were I-shaped, while others were more rectanglular, or cruciate, in shape.
Tibial bones from cadavers (human bodies preserved for study) were used. Today's modern equipment and computer systems make it possible to measure the effect of stress on the implant. The bone and tibial implant were exposed to 6000 cycles of stress. The machines put three times the average body weight on the implant, as if the person were standing on the leg during walking.
The authors found that the location of the cement isn't as important as the amount of cement used. Tiny motion sensors measured any movement of the implant inside the tibia. There is no difference in implant motion when the depth of cement is 3 to 5 mm. There was also no difference in motion between the I-beam and cruciate stem with surface cement.
The authors conclude that since knee joint replacements may have to be revised or replaced, surface cement should be used. With less cement, the implant may come out more easily if it needs to be removed. Less bone damage improves the chances of success for a second implant.
References: Christopher L. Peters, MD, et al. Tibial Component Fixation with Cement. In Clinical Orthopaedics and Related Research. April 2003. Vol. 409. Pp. 158-168.
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