Hindfoot coronal alignment: a modified radiographic method

Accurate clinical evaluation of the alignment of the calcaneus relative to the tibia in the coronal plane is essential in the evaluation and treatment of hindfoot pathologic condition. Previously described radiographic views of the foot and ankle do not demonstrate the true coronal alignment of the calcaneus relative to the tibia. Some of these views impose on the patient an unnatural posture that itself changes hindfoot alignment, whereas other methods distort the coronal alignment by the angle of the x-ray beam. Our purpose was to develop a modified radiographic view and measurement method for determining an angular measurement of hindfoot coronal alignment based on a cadaver study of the radiographic characteristics of the calcaneus and motion analysis of standing subjects. The view was obtained by having the subject stand on a piece of cardboard to create a foot template. The template was then positioned so that each foot was x-rayed perpendicular to the cassette while still maintaining the natural base of support. A method using multiple ellipses was developed to determine more accurately the coronal axis of the posterior calcaneus. A study using cadavers was performed in which radio-opaque markers were placed on multiple bony landmarks on the calcaneus. The tibia was held fixed in a vertical position, and the foot was x-rayed using the above techniques in different degrees of rotation without changing the relation of the calcaneus to the tibia. The radiographs of the modified Cobey and our view were examined to verify which markers were visible at different angles of rotation and how the hindfoot alignment measurements changed with foot rotation. To define further the differences between the views, an analysis of postural stability was conducted while the subjects were standing with the feet in the positions for imaging both the Buck modification of the Cobey view and our hindfoot alignment view. The combined results of the cadaver, radiographic measurement, and postural stability segments of the study reveal that this coronal hindfoot alignment view and measurement method is reproducible, more closely measures "true" coronal hindfoot alignment, and is more clinically applicable because the alignment is measured while the patient is standing with a normal angle and base of stance. The modified radiographic measurement method relies on posterior calcaneal anatomic landmarks, is less affected by rotation of the foot and ankle, and is reproducible between observers.