Initial stability of fully and partially cemented femoral stems

Objective. To test the initial stability of a newly designed partially cemented femoral stem in comparison with a fully cemented conventional stem. Design. An in vitro study to determine the interface motion between femoral stem and bone as a response to loading. Background. The aim of the new prosthesis design is a proximal load transfer by a defined partial cement fixation in the proximal femur region and a slim prosthesis stem in the distal region. Before a clinical study can be started, the new stem has to show an initial stability comparable to that of fully cemented prostheses. Method. Six paired fresh cadaveric femora were used for the testing of the new partially cemented stem (Option 3000, Mathys Orthopaedics, Bettlach, Switzerland) and a fully cemented stem (Weber Shaft, AlloPro, Baar, Swizerland). Under cyclic loading up to 1600 N hip joint forces, the interface motion between implants and bone was measured at six locations. Results. Both stems showed uncritical interface motions below 43 μm. However, the Option 3000 stem exhibited significantly smaller motions in the proximal region and slightly larger movements in the distal regions than the Weber prosthesis. Conclusions. The new type of partially cemented stem provided a comparable initial stability to the fully cemented Weber prosthesis.