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Using 3-D Views of the Spine to Classify and Treat Scoliosis

Posted on: 04/16/2009
Scoliosis (curvature of the spine) is managed based on the type and severity of curve. A smaller curve (mild scoliosis) can be treated conservatively without surgery. A larger curve (moderate to severe scoliosis) often requires fusion to straighten it as much as possible and keep it from getting worse. X-rays are used to determine the degree of the main curve. An angle called the Cobb angle is measured and used as a guide to conservative versus surgical treatment.

In this study, curve shape is determined using three-dimensional views of the spine. The data collected on 110 patients was used to see if a different classification scheme could further define treatment. The authors set out to classify patients seen at a scoliosis clinic into distinct groups based on a three-dimensional curve shape. The goal was to help plan when to do surgery.

The patients all had idiopathic scoliosis. Idiopathic means the cause of the curvature is unknown. In all cases, there were two scoliosis curves located between T4 of the thoracic spine and L3 of the lumbar spine. But the patients' curves were considered very diverse in their characteristics. By diverse, we mean there were a wide range of Cobb angle measurements as well as a wide range of curve locations between those two segments.

Classifying scoliosis patients based on curve regions and spinal shape is a complex task. Whatever approach is used must include everyone who has scoliosis without overlap (placing patients in more than one group). The method used should be quick and easy. The same results should be obtained for each patient no matter who is doing the measuring.

Other classification methods (e.g., King, Lenke) have been studied with a specific question in mind. For example, how long (how many vertebral segments) should the surgical fusion be? What levels of the spine should be fused? Maybe by looking at this from a broader perspective (based on patterns of curvature), it will be possible to find a classification scheme that could be used for all patients.

Stereoradiography was performed on each patient in the standing position. Stereoradiography is a technique for producing X-rays that give a three-dimensional view of an internal body structure (in this case, the spine). The stereoradiographs are produced by combining two separate X-ray films. Each X-ray is taken from a slightly different angle. The developed films are then viewed through a device that allows the two images to be seen as one three-dimensional object.

Measurements of spinal shape including curvature and rotation were made from all angles (side, front, top). The spinal axis system technology was advanced enough to make all of the spinal shape measurements digitally by using physical landmarks and three-dimensional coordinates.

The data showed four basic groups based on the plane of maximum curvature (PMC). Group 1 had the standard (most common) right upper curve and left lower curve. Rotation of the vertebrae was counterclockwise (as seen from above) for both curves. Group 2 had the same curve direction but with a clockwise rotation of the PMC in the lower curve.

Group 3 was the opposite of group 1 with a left upper curve and right lower curve and both curves going in a clockwise direction. And group 4 (smallest group) had a mix of right upper/left lower curve pattern or left upper/right lower curve pattern. But the rotational direction was clockwise in all cases.

What does this all mean? Well, it means that it is possible to group patients seen in a scoliosis clinic according to curve region and direction of rotation. The cluster analysis showed a natural division at T10 defining patients with curves above T10 as having an upper curve and patients with curves below T10 with a lower curve. This is the first study to use the direction of rotation as a guiding factor when planning treatment.

It appears that the rotation of the plane of maximum curvature (PMC) increases with even small changes in the spinal curvature. That's one reason why the authors think this measurement is more important than previously thought. In fact, other classification methods don't even use the PMC to divide patients into groups.

Up until now, the main way to view treatment was based on size of the curve (small versus large). Small curves can be treated conservatively with bracing when needed. Large curves are more likely to require surgery. Although rotation of the curve can't be used as the only guiding factor, size shouldn't be the only determining point either. The authors suggest that treatment or management decisions for all patients with scoliosis must be made on a case-by-case basis using both methods of classification (curvature size and pattern).

References:
Ian A. F. Stokes, PhD, et al. Classification of Scoliosis Deformity Three-Dimensional Spinal Shape by Cluster Analysis. In Spine. April 2009. Vol. 34. No. 6. Pp. 584-590.

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