3-DIMENSIONAL PRIMARY STABILITY OF CEMENTLESS FEMORAL STEMS

Objective. This study investigates by means of a new bone-prosthesis i nterface motion detector whether conceptual design differences of femo ral stems are reflected in their primary stability pattern. Design. An in vitro experiment using a biaxial materials testing machine in comb ination with three-dimensional motion measurement devices was performe d. Background. Primary stability of uncemented total hip replacements is considered to be a prerequisite for the quality of bony ongrowth to the femoral stem. Dynamic motion as a response to loading as well as total motion of the prosthesis have to be considered under quasi-physi ological cyclic loading conditions.Methods. Seven paired fresh cadaver ic femora were used for the testing of two types of uncemented femoral stems with different anchoring concepts: CLS stem (Spotorno) and Cone Prosthesis (Wagner). Under sinusoidal cyclic loading mimicking in viv o hip joint forces a new measurement technique was applied allowing fo r the analysis of the three-dimensional interface motion. Results. Con siderable differences between the two prostheses could be detected bot h in their dynamic motion and total motion behaviour. Whereas the CLS stem, due to the wedge-shaped concept, provides smaller total motions, the longitudinal ribs of the Cone prostheses result in a substantiall y smaller dynamic motion. Conclusions. The measuring technique provide d reliable and accurate data illustrating the three-dimensional interf ace motion of uncemented femoral stems. Relevance Analysis of differen t concepts of prosthetic stems with the presented standardized approac h may contribute to future design improvements of hip replacement. Wit h respect to the clinical outcome the role of primary stability for th e long-term success will furthermore be elucidated. (C) 1997 Elsevier Science Ltd.