Fig. 4From: Spinal mobility in radiographic axial spondyloarthritis: criterion concurrent validity of classic and novel measurementsThe radiographic method of calculating the lumbar spine angle from a lateral projection radiograph film. Horizontal lines are drawn parallel and through the superior endplate of L1 and the superior endplate of S1. Perpendicular lines are drawn from the two original lines and the large angle at their intersection is measuredBack to article page