Initial mechanical stability of cementless porous titanium patellar components

Cementless fixation in total knee replacement has enjoyed limited success in the past; however, there is a renewed interest in cementless fixation, which has the potential to increase operative efficiency and to improve the strength of the bone-implant interface. The initial mechanical stability of cementless implants is critical to minimizing micromotion between the bone and the porous-coated surface, thus providing the necessary conditions for successful osseointegration (long-term bonding between the bone and implant). A critical element to any total knee replacement system is a durable and well-functioning patellar component. The first purpose of this study is to assess whether vibration analysis techniques can be used to evaluate and characterize initial mechanical stability of cementless implants as accurately as the traditional method of micromotion measurement using LVDTs, which have significant experimental limitations. The second purpose is to evaluate and determine the comparative mechanical stability of various designs of cementless patella components under mechanical loading designed to simulate in vivo forces. The various designs included two control groups of cemented patella designs; a "cementless control" of a currently accepted cementless design; a group of newly-developed, cementless, porous titanium designs; and a cementless design with oversized peg holes. The LVDT data showed no statistical difference between the two cemented groups, nor between the press-fit cementless groups, although the cemented groups had less micromotion than the uncemented groups. Vibration analysis techniques were not able to accurately assess mechanical stability.