Lenke 1 curves are one where the major curve (the curve with the largest Cobb angle) is in the main thoracic region while the proximal thoracic and thoracolumbar are non-structural.
A minor curve is defined as structural if at least one of the two below criteria are met:
The left X-rays show a 13 year old female with Lenke 1A curve consisting of a:
As the residual PT and TL/L curves are less than 25° in bending radiographs they are non-structural.
The lumbar modifier is determined by drawing a vertical line from the center of the sacrum.
Lumbar modifier A is designated if this line lies between the pedicles at the apical level of the lumbar curve.
Lumbar modifier B is designated if this line touches the apical vertebral pedicle.
Lumbar modifier C is designated if this line does not touch any part of the vertebral body or pedicle at the apex.
The sagittal modifiers are determined from the lateral radiograph from T5-T12. A measurement less than 10° is designated as "-".
Measurements between 10°- 40° is designated as "N".
A measurement larger than 40° is designated as "+".