Effect of a distal centralizer on the positioning of an anatomical stem.

Femoral stem centralizers were originally designed for double tapered, straight stems. In a slightly modified configuration, the PMMA centralizer is plugged in a hole in the tip of the ABG II femoral prosthesis. The purpose of this study was to determine the effect of the centralizer on the position of the anatomical ABG II stem. Thirty-nine cemented ABG II stems with a centralizer were compared with thirty-nine stems without a centralizer. We evaluated positioning of the tip of the stem according to a standard selection of criteria, using conventional AP and lateral X-ray imaging. The centralizer supplied with the ABG II was found to have no additional value in guaranteeing optimal varus-valgus positioning. If a stem was not placed neutral, generally it was placed in a slight valgus position. The number of deficient cement mantles was not influenced by the three-fin centralizer. Furthermore, the distal centralizer of the ABG II prosthesis adds a length of 27 mm to the stem, and the distal cement plug found in stems with centralizer was almost twice as long on average. The ABG II centralizer was found in this study to provide insufficient guiding of this anatomical stem and to add excessive length to the distal cement plug.