Description:
Measurement accuracy is easily confounded by radiographic magnification, patient rotation away from the true frontal plane, innominate rotation in the sagittal plane, and non-rigorous measurement technique that fails to precisely identify the same bony landmarks as the measurement points on each view. The best technique therefore requires minimisation of magnification, minimisation of patient rotation, all dynamic stabilisers truly switched off on the hanging side, and a meticulous choice of measurement landmarks. The author advocates using the two most closely spaced and reliably identified landmarks on either side of the joint for measurement, usually at the upper end of the joint rather than the inferior margin (panel D in the illustration).
