Optimizing Limb Position for Measuring Knee Anatomical Axis Alignment from Standing Knee Radiographs

Standard, accurate, and reliable measurements of knee alignment, while desirable, are too frequently unavailable. The main drawbacks are the diversity of methods for imaging measurements and the variety of imaging set-ups in which imaging error is unknown or not well defined. It is obviously desirable to work toward uniformity in these areas. Regarding radiographic configurations, short views are commonly used, but fail to locate the mechanical axes (at least directly), which is a limitation that becomes serious in the presence of many limb deformities. Long views overcome these limitations, providing locations for the hip, knee, and ankle centers from which the limb mechanical axes, along with the orientations of the knee's articulating surfaces, may be computed. Whatever methods are used, there is a universal requirement to reduce errors by control of positioning, and we have described our use of a special frame to this end. The basic approach to positioning is important and we have outlined a procedure where the knee's plane of flexion is the common reference for positioning, specifically to align it within the sagittal plane. We have discussed our reasons, notably heightened risk of error in the presence of deformities, for distrusting the use of other positioning guides that include positioning the limbs according to the orientation of the patella, tibial tubercle, foot, and condylar outlines. Finally, the importance of technologist training has been emphasized, in the context of correct positioning of patients, and in identification of (and compensation for) mal-rotation errors in the radiographic images. Thus, as in every field, training and experience are both critical elements of good radiography. The Journal of Rheumatology Copyright © 2009. All rights reserved.