Abstract
Introduction: Using navigation the AP alignment of a total knee arthroplasty (TKA) improves. However, much less is known on the influence of navigation on the rotation of the femoral component.
The rotation of the femoral component is of high importance considering the balancing of the knee and the patellofemoral joint. The aim of our study was to evaluate the accuracy of the femoral component rotation when using navigation.
Materials and Methods: We evaluated twenty navigated TKA’s. The Vector Vision system of Brainlab was used during surgery. The preoperative data considering the rotation were stored. On postoperative CT scans the rotation of the femoral component was measured twice at different times by two observers. The posterior condylar angle (the angle between the posterior condylar line and the epicondylar line) was used to define the rotation. The definite position was compared to the per-operative data. The difference between the preoperative determined rotation and the postoperative rotational position was analyzed. The Cohen’s kappa coefficient was used to compare the agreement of results.
Results: The postoperative CT scan showed an average measured rotation of the femoral component (posterior condylar angle) of 3,8 degrees. The average rotation based on the navigation data was 5.8 degrees. The difference between the preoperative data and the definite position measured on the CT was 2,8 degrees with a large range. We found a moderate agreement between the two observers and a good agreement within the two observers.
Conclusion: The rotation of the femoral component is important in the knee kinematics and patellofemoral joint. Using navigation, it is (yet) not possible to accurately determine or improve the rotational position of the femoral component. Further development of the software and method of determining the epicondylar axis during surgery is needed to be able to improve the rotational position of the femoral component.
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