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Validation of the SRS Adult Deformity Radiographic Classfiication

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Written by Thomas G. Lowe, MD, Sigurd H. Berven, M.D., Keith Bridwell, MD and Frank J. Schwab, MD

Introduction: The adult with spinal deformity presents with clinical symptoms and radiographic findings that are distinct from that of the adolescent with spinal deformity. Important differences include primary curve patterns, coronal and sagittal imbalance, degenerative components within and outside the primary curve and regional sagittal abnormalities. Existing classification systems have not dealt with the various components of the adult deformity. The Adult Deformity Committee of the SRS has developed a radiographic classification specifically for adult deformity.

Purpose: This classification system is designed to provide a radiographic framework for categorizing adults with complex spinal deformities, which will be helpful in predicting treatment strategies.

Methods: Seven primary curve types were developed: 1) Single Thoracic, 2) Double Thoracic, 3) Double Major, 4) Triple Major, 5) Thoracolumbar, 6) Lumbar, and 7) Primary Sagittal Deformity. Three modifiers were developed, which include a Regional Sagittal modifier (upper thoracic, main thoracic, thoracolumbar, and lumbar), a Lumbar Degenerative modifier (degenerative disc disease, listhesis, and fractional lumbosacral curve), and a Global Balance modifier (sagittal and coronal). Erect long AP and Lateral radiographs of 25 adult spinal deformity cases were reviewed by 17 SRS surgeons (including members of the SRS Adult Deformity Committee) for validation of the system and prediction of instrumentation levels based purely on radiographic data.

Results: Kappa scores were calculated for the primary curve type (k=0.64), regional sagittal modifier (k=0.73), degenerative lumbar modifier (k=0.65), global balance modifier (k=0.92), upper instrumented level (k=0.56), and the lower instrumented level (k=0.77). See table 1 for the Kappa value scale.

Summary: Substantial interobserver reliability was noted when classifying complex adult deformities radiographically by SRS surgeons. Clinical modifiers are currently being developed to help further define treatment strategies in adult deformity patients.

Table 1 - Kappa value scale