THE EFFECT OF TIBIAL STEM DESIGN ON COMPONENT MICROMOTION IN KNEE ARTHROPLASTY

Rigid body mechanics with computer data acquisition and analysis techn iques were used to determine the three-dimensional motions of any poin t on the tibial component of a total knee arthroplasty, Three stem con figurations were compared: (1) no stem; (2) short stem (40 mm); and (3 ) long stem (75 mm), In addition, three loading conditions were analyz ed for each stem configuration: (1) central loading; (2) posterior loa ding; and (3) medial loading, The longer stem implants were associated with increased micromotion, especially under eccentric loading, Cemen ted implants seemed to have more stable fixation, compared with noncem ented implants, It was thought that the increased motion was secondary to a toggling of the implant under load, secondary to uneven medullar y cortical contact, Overall, the results indicated that short and long stems do not enhance initial fixation with cemented or cementless imp lantation in routine knee arthroplasty.