Lenke classification of adolescent idiopathic scoliosis

The Lenke classification sorts the curve pattern of adolescent idiopathic scoliosis into one of six types, with a lumbar modifier (A, B or C) and a sagittal modifier (−, N or +). It was published in 2001 as a classification “to determine extent of spinal arthrodesis”. (Lenke 2001)

The curve type, 1 to 6

The six types are: 1 main thoracic, 2 double thoracic, 3 double major, 4 triple major, 5 thoracolumbar/lumbar, and 6 thoracolumbar/lumbar – main thoracic. (Lenke 2001)

• The major curve is always structural. It is the one with the largest Cobb angle; if the main thoracic and the thoracolumbar/lumbar curves measure the same, the thoracic one.
• A thoracolumbar/lumbar curve leads a type 6 only if it measures at least 5° more than a structural main thoracic curve. With less than 5° between them the two are a double major, type 3 (type 4 if the proximal thoracic curve is structural too).

Structural minor curves

A minor curve is structural if its angle on the bending film is 25° or more, or if its regional kyphosis is +20° or more. The kyphosis is measured T2–T5 for the proximal thoracic curve and T10–L2 for the others. (Lenke 2001)

This is why the bending films matter: without a bending, a minor curve can only be judged on its standing angle.

The lumbar modifier: A, B or C

The modifier comes from the position of the central sacral vertical line against the apex of the lumbar curve. As the paper defines it on the film: C when the sacral vertical falls beyond the lateral margin of the apical body, B when it touches the apex between the medial border of the pedicle and that margin, and A while it runs between the pedicles. (Lenke 2001)

The sagittal modifier: T5–T12

The thoracic kyphosis from T5 to T12 gives the sagittal modifier: under +10° is hypo (−), +10° to +40° is normal (N), over +40° is hyper (+). (Lenke 2001)

How ScolioSim classifies

1. Load the standing frontal film and the side-bending films, and fit the model to them in Guide, Fitting. Cobb angles can also be drawn by hand with the Cobb tool in Simulate, 2D: click the two ends of a line along the endplate of each end vertebra.
2. ScolioSim reads the angle of each segment standing and on each bending, and applies the criteria above: the major curve structural by definition, minor curves structural by bending angle or regional kyphosis, and the 5° rule for type 6.
3. The lumbar modifier is worked out on the 3D model as the paper defines it on the film.
4. The type appears in the Coronal curves block of the 3D model panel and in the PDF report.

ScolioSim classifies the curves; it does not choose the levels of a fusion, and it does not forecast how a patient will stand afterward. The choice stays with the surgeon.