Geometry of Deformities

The knowledge of the parameters and limits of physiological alignment is the first step to understand both simple and complex deformities of the upper and lower limbs. Representing and reducing alignment, joint orientation, and the three-dimensional shape of bones and joints to plain lines can simplify the comprehension of the physiological and pathological anatomy. X-ray examination with standard views is the first diagnostic exam. CT is considered the gold standard for the assessment of the rotation of the proximal and of the distal epiphysis of long bones. In the chapter, the anatomical and mechanical axes of the long bones and the joint orientation angle are described. X-ray in anteroposterior and lateral view and CT images are used to explain and visualize the main lines of physiological alignment. Some of the most important parameters for the evaluation and the correction of the deformity are shown and illustrated using representations on X-ray images.