TY - JOUR T1 - Optimizing Limb Position for Measuring Knee Anatomical Axis Alignment from Standing Knee Radiographs JF - The Journal of Rheumatology JO - J Rheumatol SP - 472 LP - 477 DO - 10.3899/jrheum.080732 VL - 36 IS - 3 AU - T. DEREK V. COOKE AU - ELIZABETH A. SLED Y1 - 2009/03/01 UR - http://www.jrheum.org/content/36/3/472.abstract N2 - There is abundant literature describing approaches to radiographic measurement of alignment of the lower limb and the knee. This is timely in the context of the current transition to digital imaging applications and software for taking and recording measurements1–9. It is obviously beneficial to move toward uniformity of methods for defining alignment, and we have supported approaches toward this end10. Yet, while touched on in these and other accounts10–13, limited emphasis has been placed on the importance of limb positioning for radiographic measurements.Limb positioning is prone to errors that often arise from a lack of standardization, most notably the poor control of limb rotation during patient set-up for imaging. These errors may be exacerbated in the presence of limb deformities, especially those that obscure reference bone landmarks useful in the control of rotation. Therefore, recognition of deformities and control of rotation in the context of both health and disease are important goals for reproducible radiography. Certainly, variations of limb position, especially rotation, significantly influence the alignment measures14,15. The purpose of our editorial is to discuss practical ways to minimize positional errors. This arises from our experience of measurements using a supporting frame to limit positioning variations, thereby improving imaging reliability. Using a positioning frame can limit measurement errors for angles, such as the hip-knee-ankle (HKA) angle, to less than 2° and, with parallax corrected, leg-length distances within 2 mm14. Long radiographic views of the whole limb in stance are ideal for measuring alignment of the knee, in terms of both the HKA angle and the other joint angles that may contribute to any deformity (Figure 1). In practice, femorotibial alignment is commonly assessed from short views of the knee (Figure 1, hatched … Address reprint requests to Dr. T.D.V. Cooke, 797 Princess Street, Suite 404, Kingston, Ontario K7L 1G1. E-mail: derek{at}cookes.ca ER -