Neurosurgery notes/Spine/Deformity/Classification-Spinal deformity/Global Alignment Proportion (GAP) scoring system

Global Alignment Proportion (GAP) scoring system

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Classification-Spinal deformity

General

  • As a predictor of failure based on ratios of sagittal radiographic parameters in relation to the individual PI
  • Increasing postoperative GAP score and the risk of mechanical failure.
  • However, subsequent attempts at external validation have been conflicting and the reproducibility of the GAP score is yet to be determined.
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Components

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Outcome:

Calculating the risk of mechanical complications:
  • GAP-P = balance
    • 0-2
  • GAP-MD = moderate imbalance
    • 3-6
  • GAP-SD = severe imbalance
    • 7-13
 
  • Performance of GAP score:
    • Sensitivity: 93.8%
    • Specificity: 73.8%
    • + Predictive value: 73.9%
    • - Predictive value: 93.9%
    • Accuracy: 82.4%
Postoperative mechanical complication rates according to the GAP scores (P = proportioned, MD = moderately disproportioned, and SD = severely disproportioned) in the derivation cohort.
Postoperative mechanical complication rates according to the GAP scores (P = proportioned, MD = moderately disproportioned, and SD = severely disproportioned) in the derivation cohort.

Weakness

  • External validation studies have shown mixed results, indicating a moderate predictive accuracy (global AUC of 0.68 ± 0.2) for mechanical complications
  • It dismisses the thoracic region and does not take TK or C2 Tilt into account

Strengths:

  • The GAP score reflects ideal shape and distribution in a quantitative, individualized fashion.
  • LDI, paired with RLL, is asserted to be associated with mechanical failure.
  • It has been shown to better correlate with HRQL scores and predict mechanical complications