Type 3 curves are double major curves where the thoracic curve is major and the lumbar curve is structural. They are distinct from type 6 curves because the main thoracic curve is always larger than the thoracolumbar/lumbar curve.
A minor curve is defined as structural if at least one of the two below criteria are met:
Residual curve greater than or equal to 25 ° on supine bending radiograph
T2 – T5, T10-L2 kyphosis greater than or equal to 20 ° (regardless of coronal flexibility)
The left X-rays show a 16 year old male with Lenke 3C curve consisting of a:
15° minor PT curve, correcting to 2° on side bending
95° major MT curve, correcting to 62° on side bending
85° minor TL/L curve, correcting to 62° on side bending
The PT curve is here non-structural and the TL/L curve 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 "+".