Micromotion of cementless tibial baseplates under physiological loading conditions.

Initial implant stability is crucial to cementless knee arthroplasty success. The objective of this study was to develop a physiological relevant methodology that incorporates torsion, shear, and compression forces to evaluate two tibial component designs that feature either a keel or cylindrical porous metal pegs. The data were compared with a simplified compression loading scenario. Results show a loading profile that combines compressive, shear, and torsional loads results in significantly larger motions than occur when loading in compression only. When comparing between a keeled and a pegged device, the new method shows significant differences in tibial component subsidence/liftoff at the anterior and posterior locations, which were lacking in the simplified test model. To accurately assess implant stability, studies should use physiological relevant loading.