Modern Management of Spinal Deformities by Robert A. Dickson Jürgen Harms

Author:Robert A. Dickson,Jürgen Harms
Language: eng
Format: epub
Publisher: Thieme Medical Publishing Inc.
Published: 2017-12-02T00:00:00+00:00

Fig. 6.14 PA radiograph showing that, from T11 to L1 on the left side, a posterior plaque is seen. Note there is no rib fusion that would occur with a vertebral body failure of segmentation, because ribs are derived from the costal processes of the vertebrae.

Conversely, failures of formation tend not to have the same “tethering” effect posteriorly and, thus, while the deformity may progress in the coronal plane, it is less often associated with rotation and so progression potential tends to be less marked. However, when a failure of segmentation is sited opposite to a failure of formation (▶ Fig. 6.13)—a notoriously progressive situation 37,​ 39,​ 41—then the biplanar asymmetry so produced facilitates a marked degree of rotational progression.

It has also been stated that a bilateral failure of segmentation should theoretically not produce a scoliosis 37 and yet sometimes, apparently surprisingly, a curvature is seen. This is due entirely to the sagittal plane. Two, or more, vertebrae that are fused together before birth do not develop a normal sagittal shape and this area also represents a region of stiffness. In the thoracic region a normal kyphotic shape is essential so that the axis of spinal rotation is anterior to the vertebral bodies in order to protect them from rotation. 36 With block vertebrae the axis is now sited more posteriorly and, as the block is not always symmetrical in the coronal plane, this latter provides directional instability to the block and thus a rotational lordoscoliosis is produced in exactly the same fashion as with idiopathic scoliosis. It is therefore not uncommon to encounter an apparently idiopathic deformity with a disk space that is absent or difficult to visualize to which the semantically incorrect term congenital idiopathic scoliosis would appear very appropriate (▶ Fig. 6.15). As we have seen, if the area of congenital fusion is cervicothoracic and resists rotation locally, then rotation can be translated lower down the spine, as not uncommonly occurs with the Klippel Feil syndrome.

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