Dynamics constrained by the brace geometry. On the convex side, the superior margin ends under the apex vertebra, allowing the lateral flexion movement to induce the deflection of the curve and the realignment of the spine under the apex vertebra. The posterior edge is modeled with a central active prominence which is uncomfortable and compels the patient to perform an anterior translation that allows the hyperlordosis correction (A). Such a profile imposes a particular dynamics, for which the anterior flection movements can be performed only together with a lateral flexion and a rotation in the direction of the correction of the curve. The bending X-ray exam at the convexity side without (B) and with the brace (C) confirms the theoretical assumptions, showing a remarkable difference between the dynamics of the free and the constrained spine.