PRESSURIZATION AND CENTRALIZATION ENHANCE THE QUALITY AND REPRODUCIBILITY OF CEMENT MANTLES

Cementing technique has a profound influence on the incidence of asept ic loosening of total hip replacements. Two specific measures that see m to have the greatest impact on the longevity of cemented femoral ste ms are pressurization of cement and control of mantle thickness, typic ally through the use of modular centralizing devices attached to the t ip of the prosthesis. Two laboratory studies are presented that examin e the success of these measures in clinical practice. In the first stu dy, the performance of five designs of intramedullary plugs in resisti ng migration during pressurization of cement was evaluated in human an atomic specimen femurs. Profound differences were observed between the performance of the different plug designs. In canals larger than 12 t o 14 mm, most commercial devices failed to resist pressures greater th an 30 to 40 pounds per square inch. Overall, it was estimated that bet ween 6% to 76% of these devices would fail to resist cement pressures of 50 pounds per square inch in clinical practice. The second study ex amined the role of distal centralizers in the accumulation of air bubb les around the distal tip of the prosthesis during insertion of the st em into the femur. Acrylic replicas of a femoral stem were implanted i n cavities simulating the femoral canal. Colored dyes, present within the cement, revealed the complex patterns of cement flow. It was shown that cement, dragged from the top of the femur, forms a thin layer th at covers the entire surface of the prosthesis and the distal centrali zer. Significant voids were present behind the trailing edges of the d istal centralizer in 42% of the cases examined. These studies show tha t improvements in intramedullary plugs and stem centralizers are neede d to increase the reproducibility of cement technique in total hip rep lacement.