Fig. 29

The so-called B2 type is a 4C compatible curve pattern defined by a high main thoracic structural curve combined with a long-high thoracolumbar curve, with the apex at T12. The second and third radiological criteria for 4C are also accomplished (TP offset to the concave thoracic side and L4–L5 positive counter-tilting). Very rarely it can be also combined with a short structural proximal thoracic curve (mostly iatrogenic)