Differing prosthetic alignment and femoral component sizing between 2 computer-assisted CT-free navigation systems in TKA.

We adopted a new computed tomography (CT)-free navigation system and noticed that, compared with our previous experience using a different type of CT-free navigation system that led to oversized and extended femoral component implanted compared with the conventional implantation, the femoral components were similarly implanted to the conventional method. The purpose of our study was to compare alignment and sizing with these 2 image-free systems and determine whether the method to determine the knee center could explain these differences in femoral component size and flexion of the component. Thirty posterior-stabilized total knee prostheses were implanted using the OrthoPilot CT-free navigation system (B. Braun-Aesculap, Tuttlingen, Germany). Postoperative coronal and sagittal long leg radiographs were retrospectively compared with those of a control group of 30 matched-paired total knee prostheses previously implanted using the VectorVision CT-free navigation system (Depuy-BrainLAB, Heimstetten, Germany). Sagittal alignment of the femoral component in the VectorVision group showed a significantly extended position compared with that in the OrthoPilot group. In addition, the size of the selected femoral component in the Vector Vision group was significantly larger than that in the OrthoPilot group. This discrepancy may be explained by the differences in the determined knee center, which influenced the postoperative implantation. When surgeons select a navigation system, the characteristics of each system should be taken into consideration.