Individuals with rigid scoliosis have a lateral deviation and a vertebral rotation that can be appreciated in the frontal plane by a rib hump on the convex side. The spinal rotation causes the rib on the convex side to be pushed posteriorly and the concave side to be pushed anteriorly during the forward bending test.
With secondary or supple scoliosis (eg. leg length inequality), the scoliosis will be visible while the patient is standing but will resolve (not show a rib hump) with lumbar flexion.