An alternative but less used method of assessing limb length is the block or board technique, using different height lifts under the shorter limb until the pelvis is level in the frontal plane. Visual correction, as described by Rene Cailliet, uses three anatomical references points to establish this: a) iliac crest levelness, b) vertical appraisal of the spine from the sacral promontory (the lumbar spine should be perpendicular to the sacral base, and c) the posterior superior iliac spines (PSIS’s) at the dimples of Venus should also be level.
In a study by Aspegren and colleagues using lifts of varying thicknesses were placed under the shorter limb and assessed for levelness using both visual and established radiographic techniques. This study found that the visual method of assessing limb length with board correction did not differ significantly from the X-ray method to measure the magnitude of limb length insufficiency. With a strong correlation ration (eta 2) this technique demonstrates that there is a strong relationship between visual and X-ray assessment methods (Aspegren, et al., 1987).