a. Hemiveebrai. Most common type of failure of formation anomaly.ii. This is where a poion of the veebra is missing resulting in a small, triangularshaped "half veebra" or hemiveebra.iii. Hemiveebrae can be subclassified based on their relationship to the adjacentspine (segmented, semisegmented, nonsegmented).b. Block veebrai. When several veebral segments fail to separate bilaterally, a block veebra resultsproducing fused veebral bones.c. Unilateral unsegmented veebral barsi. are caused by the failure of segmentation only on the left or right side of the spine.The thoracic curves have the poorest prognosis, with the worst anomaly being aunilateral unsegmented bar combined with single or multiple convex hemiveebrae,followed by a unilateral unsegmented bar, double convex hemiveebrae, and a singleconvex hemiveebra, with the bloc veebra having the best prognosis.Classification of Congenital Scoliosisa. Failure of formation (see Fig. 38-120)i. Paial failure of formation (wedge veebra)ii. Complete failure of formation (hemiveebra)b. Failure of segmentationi. Unilateral failure of segmentation (unilateral unsegmented bar)ii. Bilateral failure of segmentation (block veebra)c. Miscellaneous