Impact of surgical alignment, bone properties, AP translation, and implant design factors on fixation in cementless unicompartmental knee arthroplasty.

Micromotion exceeding 150μm at the implant-bone interface may prevent bone formation and limit fixation after cementless knee arthroplasty. Understanding the critical parameters impacting micromotion is required for optimal implant design and clinical performance. However, few studies have focused on UKA. This study assessed the impacts of alignment, surgical, and design factors on implant-bone micromotions for a novel cementless UKA design during a series of simulated daily activities. Three validated finite element knee models for predicting cementless micromotions were loaded with design-specific kinematics/loading to simulate gait, deep knee bending, and stair descent. The implant-bone micromotion and the porous surface area ideal for bone ingrowth were estimated and compared. Overall, the peak tray-bone micromotions were consistently found at the lateral aspect of the tibial baseplate and were consistently higher than the femoral micromotions. The femoral micromotion was insensitive to almost all the factors studied, and the porous area favorable for bone ingrowth was no less than 93%. For a medial uni, implanting the tray 1mm medially or the femoral component 1mm laterally reduced the tibial micromotion by 19.3% and 26.3% respectively. A 5 mm more posterior femoral translation increased the tibial micromotion by 35.8%. The presence of the tray keel prevented the spread of the micromotion and increased the overall porous surface area. In conclusion, centralizing the load transfer to minimize tibial tray applied moment and optimizing the fixation features to minimize micromotion are consistent themes for improving cementless fixation in UKA.