Lenke Classification System for Scoliosis

Lenke classification is a comprehensive radiographic classification of Adolescent Idiopathic Scoliosis named after Dr Lawrence Lenke who was instrumental in devising it.

Adolescent idiopathic scoliosis is the most common types of scoliosis encountered.

Though originally intended to be include factors in 3 planes, it eventually included two saggital and coronal plane.

The classification was published in 2001 and is being widely used.

The Lenke Classification System provides surgeons with a simple, accurate and reproducible way to measure and communicate about scoliosis.

It evaluates the x-rays used in different positions [the front, side, and in bending positions.]

For classification, the following things are used

• By the curve type
• Lumbar spine modifier
• Sagittal thoracic modifier.

The Lenke Classification System recognizes and measures scoliosis as a multi-dimensional problem. It thus helps to devise a focused treatment.

Details of The Lenke Classification System

The Lenke classification is a triad classification system consisting  of:

1. curve type (1-6)
2. lumbar spine modifier (A, B, C)
3. sagittal thoracic modifier (-, N, +)

X-rays Required

The final classification mentions all three factors. Thus an example of the classification may be Lenke 2A-

To determine the components of the triad the following radiographs of the spine are required:

• Upright AP view
• Upright lateral view
• Left supine bending
• Right supine bending

Step 1 – Determination of curve type

The spine is divided into 3 regions.

• Proximal thoracic – Apex at T3, T4 or T5
• Main thoracic – Apex between T6 and the T11-T12 disc
• Thoracolumbar/Lumbar – Thoracolumbar apex between T12 and L1, and lumbar apex between the L1-L2 disc and L4

Proceed as follows

Measure regional curves

• Proximal thoracic (PT)
• Main thoracic (MT)
• Thoracolumbar/lumbar (TL/L)

Identify major curve

Cobb angles are measured from cranial end vertebra to caudal end vertebra. End vertebra is the vertebra that is most tilted from the horizontal apical vertebra. For a given curve the cranial end plate is used for the proximal end vertebra while the caudal end-plate is used for the distal end-vertebra.

The curve with the largest cobb angle is by definition the major curve.

Other curves are by definition minor curves.

A major curve is

• The biggest curve
• Has largest cobb angle and is always structural.
• Always either
  • MT (Type 1-4)
  • MT/L (Type 4,5,6)

[If PT is the largest curve, then by default major curve is assigned to MT]

Determine if a minor curve is structural or not

This is done by evaluating the left and right supine bending and lateral x-rays. Following criteria are used for marking the curves structural. Only one of the two criteria needs to be met

• Minor Proximal thoracic
  • Residual coronal curve greater than or equal to 25 ° on supine bending radiograph
  • Kyphosis T2 – T5 of greater than or equal to 20 °
• Minor main thoracic curve
  • Residual coronal curve greater than or equal to 25 ° on supine bending radiograph
  • Kyphosis T10 – L2 greater than or equal to  20 ° (regardless of coronal flexibility)
• Minor thoracolumbar/lumbar curve
  • Residual coronal curve greater than or equal to 25 ° on supine bending radiograph
  • Kyphosis T10 – L2 greater than or equal to  20 ° (regardless of coronal flexibility)

Assign Type 1-6 based on the chart below

Step 2 – Assignment of Lumbar modifiers (A,B,C)

• Identify apical lumbar vertebrae (ALV)
  • Inferior lumbar body that falls outside of the curve
• Draw  vertical line from the center of the sacrum [Centeral sacral vertical line (CSVL)]
• See its relationship to pedicles of apical lumbar vertebra
• Assign modifier
  • A –  CSVL passes between pedicles of apical lumbar vertebrae
  • B –  CSVL touches pedicle of apical lumbar vertebrae
  • C –  CSVL does not touch apical lumbar vertebrae

Step 3: Assignment of Sagittal thoracic modifier (-, N, +)

• Measure sagital Cobb from T5 to T12
• Assign modifier
  • hypokyphotic (-) if < 10°
  • normal if 10-40°
  • hyperkyphotic (+) if >40°

Combine the three values to provide final triad.

References

• Lenke Classification of AIS
• Lenke Classification