Type 4 curves have structural proximal thoracic, main thoracic, and thoracolumbar/lumbar curves (triple major).
A minor curve is defined as structural if at least one of the two below criteria are met:
The left X-rays show a 15 year old female with Lenke 4C curve consisting of a:
Both the PT and the TL/L curves are structural.
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 lumbar modifier is determined by drawing a vertical line from the center of the sacrum.
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 "+".