Abstract
Introduction
Alignment and positioning of implants is important in total knee arthroplasty (TKA). Identifying the femoral hip center (FHC) without fluoroscopy or computer navigation is considered difficult. The Complete Compass system (CoCo) is a femoral extramedullary guidance system designed to identify the FHC. This apparatus provides an accurate representation of the femoral functional axis in the coronal plane without a computer navigation system. We compared postoperative implant alignment of patients undergoing total knee arthroplasty between CoCo and intraoperative computer navigation.
Materials and Methods
Twenty-five consecutive TKAs using CoCo were analyzed. CoCo has a pivotal arm with a pivotal shaft arranged to extend perpendicular to the coronal plane. A marker is attached to the pivotal arm to depict a circular arc on the marking plate with rotation of the pivotal arm. The pivotal shaft is placed at the intercondylar notch of the femur. The distance from the pivotal shaft to the marker is equal to the distance from the intercondylar notch of the femur to the FHC of the patient based on preoperative measurements in the coronal plane. This apparatus has a level of the horizontal plane and the condition of the pivotal shaft is able to match neutral positions in the sagittal and axial planes. The intersection of two arcs drawn by using CoCo with the hip joint in abduction and adduction indicates the FHC position. Postoperative coronal and sagittal views radiographs were obtained. Twenty-five TKAs implanted using computer navigation were also analyzed for postoperative alignment. For two groups, targeted implant position was 90° in both planes for the femoral functional axis.
Results
In the CoCo group, mean absolute difference between planned and actual femoral placement was 0.5° (standard deviation (SD), 0.7) in the coronal plane and 2.8° (SD, 1.3) in the sagittal plane. For the computer navigation group, mean difference from ideal placement for the femur was 0.6° (SD, 0.7) in the coronal plane and 2.2° (SD, 1.4) in the sagittal plane. In all comparisons, no significant differences were seen between CoCo and computer navigation.
Conclusion
In this study, the Coco group achieved accurate alignment and implant positioning without computer navigation, and results were comparable to computer navigation TKA. CoCo is a simple system, and has the possibility to take the place of expensive computer navigation systems.
