Classification of Congenital Scoliosis and Kyphosis: A New Approach to the Three-dimensional Classification for Progressive Vertebral Anomalies Requiring Operative Treatment

Noriaki Kawakami, MD; Taichi Tsuji, MD; Shiro Imagama, MD; Lawrence G. Lenke, MD; Rolando M. Puno, MD; Timothy R. Kuklo, MD


Spine. 2009;34(17):1756-1765. 

In This Article

The Problems of 2D Classifications

Although the quality of the plain x-ray images has improved significantly through the development of computerized digital radiographic technique, it still has limitations in resolution. Furthermore, plain x-ray images are not 3D and cannot demonstrate the spatial relationship of the structure of each vertebra. In particular, as long as we evaluate congenital spinal deformities with such a variety in curve types and morphologies, it is clearly impossible to understand the 3D structure of each abnormal vertebra using only plain x-ray.

The vertebral body is relatively easier to evaluate in plain x-ray images compared with the posterior components. Thus, it can be said that 2D classifications using plain x-ray images were comprised mainly of vertebral bodies. A solitary hemivertebra can be easily diagnosed by every spine surgeon using only plain x-ray images. By contrast, it is very difficult to judge the type of multiple complex vertebral anomalies using plain x-ray images (Figure 1). Some may recognize it as a unilateral unsegmented bar. However, 3D images have shown this deformity as a combination of slight wedged vertebral body of the anterior structure and contralateral 3 hemilaminae skipping every normal-shaped lamina on the posterior structure (Figure 1). This vertebral anomaly exhibits a difference in type between anterior and posterior structures. Complicated mixtures of anomalous vertebrae like this case with a combination of the different abnormalities of the anterior structure and the posterior structure would be only classified into mixed type, according to the Winter's classification. It is too simple to put all these types into the mixed type together with the multiple of other possible spine abnormalities.

Figure 1.

Complicated Case of Congenital Scoliosis.
A Unilateral Unsegmented Bar may be Diagnosed With a Plain X-ray Image (A,B).However, 3D CT shows a combination of slight wedged vertebral bodies of the anterior structure and contralateral 3 hemilaminae skipping 1 normal-shaped lamina each on the posterior structure (C,D).

Severe curvature of the spinal column is another example that is difficult to evaluate by plain x-ray images. It can be very difficult to classify even a single malformed vertebra once the spinal column becomes so twisted so much that it develops into an imbalanced severe 3D kyphoscoliotic deformity (Figure 2).

Figure 2.

Severe Curve of Congenital Kyphoscoliosis.
A 12-year-old boy exhibiting 97 ° of scoliosis and 81° of kyphosis in the thoracolumbar segment. It is almost impossible to determine the type of congenital scoliosis according to Winter's classification. Three-dimensional CT shows a combination of hemivertebra of T11 and wedge vertebra of T10.

Failure of segmentation is one of 3 major categories in 2D classification in congenital scoliosis and kyphosis. However, even anomalous vertebrae that are classified as due to failure of formation sometimes exhibit different types of synostosis to the adjacent vertebrae. A semisegmented hemivertebra is 1 example and these anomalous vertebrae have 2 different characters: one is nature of formation failure and the other is of segmentation failure. Although this type of anomalous vertebrae has been classified into failure of formation, according to the Winter's classification to date, should this type be classified as the mixed type? A nonsegmented hemivertebra is another example and can also be regarded as a hemivertebra that has a character of segmentation failure both caudally and cranially. From the viewpoint of synostosis with cranial and caudal adjacent vertebrae, both a nonsegmented hemivertebra and a block vertebra should belong to the same group, segmentation failure. However, the former is recognized as a vertebral anomaly of failure of formation and a latter is one of the failure of segmentation, according to the Winter's classification (Figure 3).

Figure 3.

Ambiguous Border of Segmentation Failure.
Failure of formation in the Winter's classification includes fully segmented, semisegmented, and nonsegmented hemivertebrae. However, semisegmented and nonsegmented vertebrae have the same characteristics of segmentation failure as a block vertebra that belongs to segmentation failure.

When we consider the natural history of each type of congenital vertebral anomaly, it is uncertain without considering the type of anterior and posterior abnormalities, including segmentation abnormalities. The presence of hemivertebrae makes it very difficult to predict progression. Some of hemivertebrae cause severe progression, and others do not progress at all.[2,3,8] Although McMaster and Ohtsuka[3] reported the natural history of each types of congenital vertebral anomalies, it is not rare that some of them unexpectedly progress or not. Of course, many factors influence the progression. As long as we are evaluating hemivertebrae using plain x-ray images, our abilities to predict the natural history and prognosis are limited.


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