What is the role of Lenke classification in treating adolescent idiopathic scoliosis?

Role of Lenke Classification in Treating Adolescent Idiopathic Scoliosis

The Lenke classification system is the gold standard for surgical planning in adolescent idiopathic scoliosis (AIS), providing a comprehensive framework to determine which spinal curves require fusion and which can be left unfused, ultimately guiding surgeons to achieve optimal correction while preserving spinal mobility. 1, 2

Understanding the Lenke Classification System

The Lenke classification is a triad system that categorizes AIS into:

1. Curve Type (1-6): Identifies the major curve and structural characteristics
2. Lumbar Spine Modifier (A, B, C): Describes the position of the lumbar curve relative to the center sacral vertical line
3. Sagittal Thoracic Modifier (-, N, +): Characterizes the thoracic kyphosis

This system requires analysis of:

• Upright coronal radiographs
• Upright sagittal radiographs
• Supine side bending radiographs 1

Clinical Application in Surgical Decision-Making

The Lenke classification directly guides surgical treatment by:

• Identifying structural curves: Both major and structural minor curves should be included in instrumentation and fusion
• Identifying non-structural curves: These can be excluded from fusion, preserving mobility 1
• Enabling selective fusion: When appropriate, allows fusion of only the major curve while leaving minor curves unfused 3

Selective Fusion Guidelines Based on Lenke Classification:

• Selective thoracic fusions: Potentially indicated for:

  • Type 1C patterns (major main thoracic/minor lumbar)
  • Some Type 2C and 3C patterns
  • When lumbar apex deviates from center sacral vertical line 3

• Selective thoracolumbar/lumbar fusions: Potentially indicated for:

  • Type 5C patterns (major thoracolumbar/lumbar-minor main thoracic)
  • Some Type 6C patterns
  • When thoracic apex lies off the C7 plumbline 3

Importance in Preoperative Planning

The Lenke classification is crucial for:

• Standardizing curve description: Creates a common language for surgeons to communicate about AIS patterns 2
• Surgical approach selection: Guides decisions between anterior and posterior approaches 4
• Fusion level selection: Determines which vertebral levels should be included in the fusion 5
• Maximizing correction: Helps achieve optimal correction in coronal, sagittal, and axial planes 4

Radiographic Evaluation Requirements

Proper application of the Lenke classification requires:

• Standing full-spine radiographs (posteroanterior and lateral views) to evaluate curve severity, pattern, and sagittal balance 6
• PA technique rather than AP views to reduce breast radiation exposure 6
• Supine side bending radiographs to assess curve flexibility 1

Common Pitfalls and Considerations

• Complexity in daily practice: Despite reliability and reproducibility, the classification can be complex to apply 2
• Additional factors beyond classification: Clinical appearance of the patient's trunk alignment and structural characteristics ratios between curves are essential to confirm appropriate selective fusion plans 3
• Potential for curve progression: Careful monitoring is needed after selective fusion, as unfused curves may progress in some cases 3
• Inadequate imaging: Separate cervical, thoracic, and lumbar X-rays (instead of full-spine images) prevent accurate Cobb angle measurement and proper classification 6

Treatment Outcomes

When properly applied, the Lenke classification helps achieve:

• Prevention of curve progression
• Correction of existing deformity
• Improved trunk balance and cosmesis
• Prevention of long-term complications
• Improved pain and self-image 6

For surgical cases guided by Lenke classification, studies have shown successful outcomes:

• In selective thoracic fusions: Average thoracic curve correction from 61° to 39°, with spontaneous lumbar curve improvement from 48° to 32° 3
• In selective thoracolumbar/lumbar fusions: Average curve correction from 56° to 22°, with spontaneous thoracic curve improvement from 38° to 28° 3