Initial stability of fully and partially cemented femoral stems

Objective. To test the initial stability of a newly designed partially ceme nted 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 sl im prosthesis stem in the distal region. Before a clinical study can be sta rted, the new stem has to show an initial stability comparable to that of f ully cemented prostheses. Method Six paired fresh cadaveric femora were used for the testing of the n ew partially cemented stem (Option 3000, Mathys Orthopaedics, Bettlach, Swi tzerland) and a fully cemented stein (Weber Shaft, AlloPro, Baar, Swizerlan d). Under cyclic loading up to 1600 N hip joint forces, the interface motio n between implants and bone was measured at six locations. Results. Bath stems showed uncritical interface motions below 43 mum. Howev er, the Option 3000 stem exhibited significantly smaller motions in the pro ximal region and slightly larger movements in the distal regions than the W eber prosthesis. Conclusions. The new type of partially cemented stem provided a comparable initial stability to the fully cemented Weber prosthesis.