The Lenke classification system was devised as a project by Lawrence Lenke, MD and the Harms Study Group (HSG) to enhance the ability to accurately compare similar types of spinal curves among different treatment centers. The classification system was devised from the beginning to be descriptive, comprehensive, and reproducible with excellent inter- and intraobserver reliability. It sought to accomplish this goal by devising objective criteria for each type of curve, incorporating data on coronal deformity, flexibility, and sagittal alignment toward the goal of consistently classifying patterns of deformity and developing standardized treatment protocols for them, with reliable outcomes.

The Lenke Classification System provides surgeons with a simple, accurate and reproducible way to communicate about scoliosis. It relies on measurements taken from standard radiographs (x-rays). The surgeon evaluates x-rays of the patient from the front, side, and in bending positions. Each scoliosis curve is then classified in three ways:

  • By the curve type based on which of the three regions of the spine; the proximal thoracic, main thoracic and thoracolumbar/lumbar is structural or non-structural

  • A lumbar spine modifier based on the distance of the center of the lumbar spine to the midline

  • A sagittal thoracic modifier based on the amount of side (lateral) curvature to the thoracic region

Every aspect of the curve is also evaluated for its relative stiffness or flexibility on side bending x-rays. The triad system, therefore, combines the curve type (1-6) with the lumbar modifier (A, B, C) and the sagittal thoracic modifier (-, N, +) to form the complete classification. For example, the most common type is a 1AN curve classification.

Why use the Lenke Classification System?

The Lenke Classification System helps surgeons acquire a complete picture of a patient’s condition by understanding scoliosis as a multi-dimensional problem, and considering it from more than one view. This enables surgeons to focus treatment where it is needed and optimize the patient’s curve correction and balance.

Dr. Lenke’s method provides a type of detailed shorthand that improves surgeon-to-surgeon communication using a widely understood set of criteria. This helps surgeons participate in and convey their research, as well as exchange diagnoses and treatment plans.

How to Measure Lenke Classifications

The Lenke classification for adolescent idiopathic scoliosis has gained popularity and consists of three steps:


Identification of Major Curve (Type 1-6)


Assignment of Lumbar modifiers (A,B,C)


Assignment of Sagittal thoracic modifier (-, N, +)

    1. Measure regional curves
      • proximal thoracic (PT)
      • main thoracic (MT)
      • thoracolumbar/lumbar (TL/L)
    2. Identify major curve (biggest curve)
      • always either MT (Type 1-4) or .MT/L (Type 4*,5,6)
    3. Determine if minor curve is structural or not
      • definition of structural
      • > 25° in coronal plane on standing AP and do not bend out to < 25° on bending films
      • OR > 20° in sagital plane
    4. Assign Type 1-6 based on this chart
      • Identify apical lumbar vertebrae (ALV)
        • is the inferior lumbar body that falls outside of the curve
      • Draw centeral sacral vertical line (CSVL) and see where it sits in relationship to pedicles of ALV
      • Assign modifer
        • A if CSVL passes between pedicles of apical lumbar vertebrae (ALV)
          • CSVL falls between pedicles of the lumbar spine up to stable vertebra
        • B modifier if CSVL touches pedicle of apical lumbar vertebrae (ALV)
        • C modifier if CSVL does not touch apical lumbar vertebrae (ALV)
          • apex of lumbar curve falls completely off the midline depicting a curve with complete apical translation off the CSVL
      • Measure sagital Cobb from T5 to T12
      • Assign modifier
        • hypokyphotic (-) if < 10°
        • normal if 10-40°
        • hyperkyphotic (+) if >40°

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