Vertebral rotation is measured by following methods
- Nash and Moe
- Perdriolle and Vidal.
Nash and Moe
In this method the distance of the pedicle is noted from the sides of vertebral bodies.Vertebral body is divided into six segments and grades 0 to 4+ are assigned, depending on location of pedicle within segments. Because pedicle on concave side disappears early in rotation, pedicle on convex side, easily visible through wide range of rotation, is used as standard.
The rotation by this method is calculated by analyzing the AP radiograph.
Stage 0 Rotation – Both the pedicles are at equidistant and there is no asymmetry
Stage I Rotation – The pedicle on the convex side migrates within first segment and the pedicle on the concave side may start disppearring.
Stage II Rotation – The pedicle on the convex side moves to second segment and the other pedicle disappears.
Stage III Rotation – The pedicle on the convex side migrates to third segment and other pedicle is not visible
Stage IV Rotation – The pedicle on the convex side moves past the midline
Perdriolle method uses a template called torsion meter that measures the amount of vertebral rotation on a spinal radiograph.
CT scan is also a good and reliable method to measure rotation but is not don on routine basis.
If a plumb line is dropped from the dens, it usually falls anterior to the thoracic spine, posterior to the lumbar spine, and through the posterior superior corner of S1. However because on the standing long lateral films, the dens is not easily seen and therefore, the plumb line is dropped from the middle of the C7 vertebral body. This plumb line is called the saggittal vertebral axis.
A positive sagittal vertebral axis is considered present when the plumb line is anterior to the anterior aspect of S1. A negative sagittal vertebral axis occurs when this plumb line passes posterior to the anterior body of S1.
For sagittal balance to be maintained, lumbar lordosis should measure 20 to 30 degrees more than the kyphosis.
In the thoracic spine, the normal sagittal curvature is kyphotic and the normal regional lumbar sagittal alignment is lordotic.
The thoracolumbar junction is the transition area from a relatively rigid kyphotic thoracic spine to a relatively mobile lordotic lumbar spine. Bernhardt and Bridwell showed that the thoracolumbar junction is nearly straight. This relationship must be maintained during reconstructive procedures to prevent a junctional kyphosis.
If there exists sagittal plane imbalance, it must also be corrected so that there is no undue stress on unfused vertebrae when the segments are fused.
Classification of Scoliosis Curves
Ponseti and Friedman Classification
1. Single major lumbar curve.
2. Single major thoracolumbar curve.
The thoracolumbar curve apex is at T12 or L1 and tends to produce more trunk imbalance than other curves. It often produces a severe cosmetic deformity.
3. Combined thoracic and lumbar curves (double major curves).
Cause less visible deformities because the the trunk usually is well balanced.
4. Single major thoracic curve.
Generally is a convex right pattern. The curve produces prominence of the ribs on the convex side, depression of the ribs on the concave side, and elevation of one shoulder.
5. Single major high thoracic curve.
The apex of the curve usually is at T3, and the curve extending from C7 or T1 to T4 or T5.
6. Double major thoracic curve.
There is a short upper thoracic curve, often extending from T1 to T5 or T6, with considerable rotation of the vertebrae and other structural changes and a lower thoracic curve extending from T6 to T12 or L1.
The upper curve usually is convex to the left, and the lower usually is convex to the right.
This classification system is used to describe thoracic curves.
1. Type I curve
Lumbar curve is larger than the thoracic curve or nearly equal, but the lumbar curve is less flexible on side bending.
2. Type II curves
A combined thoracic and lumbar curve and thoracic curve is larger than or equal to the lumbar. On supine side-bending radiographs, the lumbar curve is more flexible than the thoracic curve.
3. Type III curve
Thoracic scoliosis with the lumbar curve not crossing the midline.
4. Type IV curve
Single long thoracic curve, with L4 tilted into the curve and L5 balanced over the pelvis.
5. Type V curve
A double structural thoracic curve. The first thoracic vertebra is tilted into the concavity of the upper curve, which is structural. An elevation of the left shoulder is a frequent finding. There is an upper left thoracic rib hump and a lower right thoracic rib prominence.
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